Superabsorbent polymer material comprising cross-linked polyacrylic acid polymer

Abstract

The present invention provides a superabsorbent polymer material comprising cross-linked polyacrylic acid and salts thereof. The superabsorbent polymer material further comprises at least 3.0 wt. % of a soluble polyacrylic acid polymer, based on the total weight of the superabsorbent polymer material. A method for preparing such a superabsorbent polymer material is also disclosed.

Description

Technical Field

[0001] The present invention relates to a superabsorbent polymer material comprising a non-crosslinked polyacrylic acid polymer. The non-crosslinked polyacrylic acid polymer is obtainable from (partially) degraded recycled superabsorbent polymer particles. Background Art

[0002] The use of superabsorbent polymer materials (hereinafter referred to as "SAP materials"), usually in the form of particles (hereinafter referred to as "SAP particles"), in particular in disposable absorbent articles is well known in the art. In view of the large number of used and discarded absorbent articles, there is a need to find methods for recycling the materials contained in the absorbent articles. SAP materials form a significant part of the materials contained in absorbent articles. Therefore, recycling SAP materials from used and discarded absorbent articles is important for the recycling of absorbent articles. SAP materials originating from used absorbent articles cannot usually be recycled as such, but need to be degraded in order to be recycled. Recently, various methods for the degradation of SAP materials have been developed, including chemical degradation, degradation via UV radiation, ultrasonic treatment, microwave radiation or mechanochemical degradation.

[0003] However, there is a need to recycle and reuse materials derived from the degradation of SAP materials. Summary of the Invention

[0004] SAP materials, such as SAP particles used in absorbent articles, are most commonly made from cross-linked polyacrylic acid polymers. Degrading cross-linked polyacrylic acid polymers into acrylic acid monomers is typically very energy-intensive and / or time-consuming. Depending on the SAP material degradation method, and also depending on how much time and / or energy is provided during the SAP material degradation method, such methods may not necessarily result in complete degradation, i.e., they do not produce acrylic acid monomers. Instead, such methods favor degradation into soluble polyacrylic acid polymers. As a result, the cross-links of the insoluble superabsorbent polymer material are disrupted, generating polyacrylic acid polymers (hereinafter also referred to as "s-PAA polymers") that are soluble in aqueous solutions.

[0005] It is known to use polyacrylic acid oligomers in the preparation of SAP materials, for example in combination with acrylic acid monomers. These oligomers generally polymerize into the cross-linked acrylic acid network of the SAP material. In contrast, it is believed that acrylic acid polymers (i.e., molecules with a much higher molecular weight than the oligomers) do not readily polymerize or only polymerize to a small extent into the cross-linked acrylic acid network of the SAP.

[0006] For absorbent articles containing SAP particles that exhibit good absorption and containment functions, the SAP particles need to meet specific technical requirements, such as sufficient capacity and permeability of the SAP particles. Generally, high capacity and high permeability are desired. Another important parameter is the amount of extractables in the SAP material. High levels of extractables are generally undesirable for SAP particles because they negatively affect the performance of the SAP particles. Once the superabsorbent polymer material swells, the extractables tend to leach out from the cross-linked polymer network, thereby affecting the superabsorbent performance through both the loss of superabsorbent material and the competition of the extractables for penetration into the insoluble polymer matrix.

[0007] It has been found that when certain s-PAA polymers are introduced into SAP particles, the amount of extractables can undesirably increase. Following detailed analysis, the inventors have also discovered that s-PAA polymers can be included in SAP materials (such as SAP particles) if certain requirements regarding the cross-linked polymer network and configuration of the s-PAA polymer are met. In this case, the amount of extractables can be kept low, and parameters reflecting capacity and permeability are not adversely affected compared to SAP materials that do not include soluble PAA polymers. This has been demonstrated even for SAP materials that include relatively high amounts of soluble PAA polymers.

[0008] In the cross-linked polymer network of SAP material, the adjacent cross-links of the polymer chains contained in the network are at a certain average distance R xl The distance between adjacent crosslinks is determined by the amount of crosslinking agent used to form the SAP material. The distance increases when the SAP material swells, as the polymer chains in the crosslinked network unravel and expand. The inventors have calculated the average distance R between adjacent crosslinks at a SAP material loading of 20 g / g. xl (Details are given below).

[0009] Furthermore, in order to define the spherical characteristics of s-PAA polymers, the gyration diameter 2*R of s-PAA polymers has been calculated. g (Details are also given below.) If the total mass of the object is concentrated, then the radius of gyration (= 1 / 2) or the radius of gyration of an object about its axis of rotation is defined as the radial distance to a point at which the moment of inertia is the same as the actual mass distribution of the object.

[0010] Mathematically, the radius of gyration R g The radius of gyration is the root mean square distance of each part of an object from its center of mass. It is effectively the perpendicular distance from the mass to the axis of rotation. One can represent the trajectory of a moving point as an object. The radius of gyration can then be used to characterize the typical distance traveled by that point.

[0011] It has been found that if the rotation diameter 2*Rg The average distance R between adjacent cross-linking points in the polymer network xl A ratio of at least 1.1 effectively reduces the amount of extractables. This is because the soluble PAA polymers are inhibited from escaping from the cross-linked network of polyacrylic acid because they are "trapped" in the interstices of the cross-linked network.

[0012] The rotation diameter of the s-PAA polymer contained in the SAP material is 2*R g The average distance R between adjacent cross-linking points in the polymer network xl The ratio of 2*R may be at least 1.2, or at least 1.25, or at least 1.3, or at least 1.4, or at least 1.5. g With R xl The ratio may be no greater than 5.0, or no greater than 4.5, or no greater than 4.0, or no greater than 3.5, or no greater than 3.0, or no greater than 2.5.

[0013] For the present invention, the R values ​​for a 20 g / g SAP material loading (ie, a SAP material absorbing 20 g of saline containing 0.9% w NaCl per gram of dry SAP material) are used. xl The gyration diameter 2*R of the s-PAA polymer contained in the SAP material is calculated by g The average distance R between adjacent cross-linking points in the polymer network xl ratio.

[0014] Furthermore, when R is calculated for a SAP material loading of 25 g / g (ie, for a SAP material that absorbs 25 g of saline containing 0.9% wNaCl per gram of dry SAP material), xl When the value of , the gyration diameter of the s-PAA polymer contained in the SAP material is 2*R g The average distance R between adjacent cross-linking points in the polymer network xl The ratio may also be at least 1.1, or at least 1.2, or at least 1.25, or at least 1.3, or at least 1.4, or at least 1.5.

[0015] The average distance R between adjacent crosslinks in a polymer network xl The average distance R between adjacent crosslinks in the polymer network may be at least 10 nm, or at least 12 nm, or at least 15 nm, or at least 20 nm, or at least 25 nm. xl It may be no greater than 100 nm, or no greater than 70 nm, or no greater than 50 nm, or no greater than 40 nm, or no greater than 35 nm.

[0016] The average distance R between adjacent crosslinks in the polymer network was calculated for a SAP material loading of 20 g / g (ie, for a SAP material that absorbed 20 g of saline containing 0.9% w NaCl per gram of dry SAP material). xl .

[0017] If we consider the gyration diameter 2*R of the s-PAA polymer contained in the SAP material at a SAP material loading of 25 g / g, g The average distance R between adjacent cross-linking points in the polymer network xl The average distance R between adjacent crosslinks in the polymer network is calculated for a SAP material loading of 25 g / g (i.e., for a SAP material that has absorbed 25 g of saline containing 0.9% w NaCl per gram of dry SAP material). xl (Except calculations under 20g / g).

[0018] The gyration diameter of s-PAA polymer is 2*R g The diameter of gyration 2*R of the s-PAA polymer may be at least 15 nm, or at least 20 nm, or at least 25 nm, or at least 30 nm, or at least 35 nm, or at least 40 nm. g It may be no greater than 200 nm, or no greater than 150 nm, or no greater than 100 nm, or no greater than 80 nm, or no greater than 70 nm.

[0019] The present invention relates to a superabsorbent polymer material comprising crosslinked polyacrylic acid and its salts. The superabsorbent polymer material further comprises at least 3.0 wt. % of a soluble polyacrylic acid polymer, based on the total weight of the superabsorbent polymer material. The crosslinked polyacrylic acid and its salts have an average distance R between adjacent crosslinking points of xl At least 3% by weight of the soluble acrylic acid polymer has 2*R g Average diameter of gyration. 2*R g With R xl The ratio is at least 1.1.

[0020] The soluble polyacrylic acid polymer may have a weight average molecular weight M of 250 kDa to 3 MDa. w .

[0021] The average distance R between adjacent crosslinks in a polymer network xl The average distance R between adjacent crosslinks in the polymer network may be at least 10 nm, or at least 12 nm, or at least 15 nm, or at least 20 nm, or at least 25 nm. xl It may be no greater than 100 nm, or no greater than 70 nm, or no greater than 50 nm, or no greater than 40 nm, or no greater than 35 nm.

[0022] The average distance R between adjacent crosslinks in the polymer network was calculated for a SAP material loading of 20 g / g (ie, for a SAP material that absorbed 20 g of saline containing 0.9% w NaCl per gram of dry SAP material). xl .

[0023] If we consider the gyration diameter 2*R of the s-PAA polymer contained in the SAP material at a SAP material loading of 25 g / g, g The average distance R between adjacent cross-linking points in the polymer network xl The average distance R between adjacent crosslinks in the polymer network is calculated for a SAP material loading of 25 g / g (i.e., for a SAP material that has absorbed 25 g of saline containing 0.9% w NaCl per gram of dry SAP material). xl (Except for calculations under 20 g / g) Gyration diameter of soluble acrylic acid polymer 2*R g It may be at least 20 nm and not greater than 100 nm, preferably not greater than 80 nm.

[0024] The ratio of extractables [wt%] to capacity (in g / g, measured as CRC according to the test method described herein) of the superabsorbent polymer material may be less than 0.30, or less than 0.28, or less than 0.26.

[0025] The superabsorbent polymer material may be at least partially neutralized, preferably 50% to 95% neutralized.

[0026] The superabsorbent polymer material may have an EFFC of at least 25 g / g.

[0027] The present invention also relates to a method for producing the superabsorbent polymer material described herein. The method comprises the following steps:

[0028] The above-mentioned SAP material can be prepared by a method in which the SAP material is obtained by polymerizing an aqueous solution, the method comprising the following steps:

[0029] a) providing an aqueous solution of polymerizable acrylic monomers and / or polymerizable acrylic oligomers, optionally neutralizing at least some of the polymerizable acrylic monomers and / or the polymerizable acrylic oligomers;

[0030] b) optionally providing one or more ethylenically unsaturated comonomers, optionally neutralizing at least some of the ethylenically unsaturated comonomers of step b);

[0031] c) providing one or more cross-linking agents;

[0032] d) providing one or more initiators;

[0033] e) providing at least 3 wt% of a soluble polyacrylic acid polymer based on the total weight of the soluble polyacrylic acid polymer provided in step e) and the monomers, oligomers, comonomers, crosslinkers and initiators provided in steps a) to d)

[0034] f) mixing the aqueous solutions of the monomers, oligomers, comonomers, crosslinking agents and initiators provided in steps a) to e) with the soluble polyacrylic acid polymer; and

[0035] g) polymerizing the mixture obtained in step f) to obtain a superabsorbent polymer material.

[0036] The monomers and / or oligomers provided in process step a) may be neutralized with a degree of neutralization of 40 mol % to 95 mol %.

[0037] The optional comonomer may be provided at less than 25 wt%, or less than 15 wt%, or less than 10 wt%, or less than 5 wt%, or even less than 2 wt%, based on the total weight of the polymerizable acrylic monomer and / or polymerizable acrylic oligomer. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a top view of an exemplary absorbent article in the form of a diaper that may contain the agglomerated superabsorbent polymer particles of the present invention with some layers partially removed.

[0039] Figure 2 for Figure 1 A transverse cross-sectional view of a diaper.

[0040] Figure 3 A partial cross-sectional side view of a suitable permeability measurement system for performing a urine permeability measurement test.

[0041] Figure 4 A cross-sectional side view of a piston / cylinder assembly used to perform a urine permeability measurement test.

[0042] Figure 5 For Figure 4 Top view of the piston head of the piston / cylinder assembly shown in .

[0043] Figure 6 For the sintered plate placed on the swelling phase Figure 4 Cross-sectional side view of the piston / cylinder assembly. DETAILED DESCRIPTION

[0044] definition

[0045] "Absorbent article" refers to a device that absorbs and contains body exudates, especially urine and other aqueous liquids, and more specifically refers to a device that is placed against or adjacent to the wearer's body to absorb and contain various exudates discharged from the body. Absorbent articles may include diapers (both for infants and for adults with incontinence), pants (both for infants and for adults with incontinence), disposable absorbent inserts for diapers and pants with reusable outer covers, feminine care absorbent products such as sanitary napkins or pantiliners, breast pads, nursing pads, bibs, wipes, etc. As used herein, the term "exudates" includes, but is not limited to, urine, blood, vaginal discharge, breast milk, sweat, and feces. Preferred absorbent articles of the present invention are disposable absorbent articles, more preferably disposable diapers, disposable pants, and disposable absorbent inserts.

[0046] As used herein, "absorbent core" refers to a structure positioned between the topsheet and the backsheet of an absorbent article for absorbing and containing liquids received by the absorbent article.

[0047] As used herein, "airfelt" refers to comminuted wood pulp in the form of cellulose fibers.

[0048] As used herein, "base polymer particles" refer to SAP particles that have not undergone any surface treatment (such as surface cross-linking and / or surface coating) after having been polymerized and comminuted into superabsorbent polymer particles.

[0049] Typically, matrix polymer particles have higher capacity and lower permeability than surface treated SAP particles.

[0050] As used herein, the term "degradation" refers to the conversion of SAP into soluble PAA polymers via depolymerization, decrosslinking, molecular backbone scission, or any combination thereof.

[0051] "Disposable" is used in its ordinary sense to mean an article that is disposed of or discarded after a limited number of use events of varying lengths (e.g., less than 10 events, less than 5 events, or less than 2 events). If the disposable absorbent article is a diaper, pant, absorbent insert, sanitary napkin, catamenial pad, or wet wipe for personal hygiene, the disposable absorbent article is generally intended to be discarded after a single use.

[0052] "Diapers" and "pants" refer to absorbent articles that are generally worn by infants and incontinent patients around the lower torso so as to surround the wearer's waist and legs and are particularly suitable for receiving and containing urine and feces. In pants, as used herein, the longitudinal edges of the first waist region and the second waist region are attached to each other to pre-form a waist opening and leg openings. The pants are put on the wearer by inserting the wearer's legs into the leg openings and pulling the pants absorbent article into a position near the wearer's lower torso. Pants can be pre-formed using any suitable method, including but not limited to joining the parts of the absorbent article together using refastenable and / or non-refastenable bonding (e.g., stitching, welding, adhesives, cohesive bonding, fasteners, etc.). Pants can be pre-formed at any position along the periphery of the article (e.g., side fastening, front waist region fastening). In diapers, the waist opening and leg openings are only formed when the diaper is put on the wearer by attaching the longitudinal edges of the first waist region and the second waist region to each other (releasably) on both sides using a suitable fastening system.

[0053] "Superabsorbent polymer" ("SAP") is used herein to refer to cross-linked polymeric materials that are capable of absorbing at least 10 times their weight in an aqueous 0.9% saline solution when measured using the Centrifuge Retention Capacity (CRC) test described below. The superabsorbent polymer material of the present invention is made from polyacrylic acid polymers.

[0054] "Superabsorbent polymer particles" ("SAP" particles) are used herein to refer to superabsorbent polymer materials that are in particulate form so as to be flowable when dry.

[0055] "Pre-existing superabsorbent polymer material" ("pre-existing SAP material") is used herein to refer to SAP material that is not within the scope of the present invention, but is material that has been degraded to obtain the s-PAA polymer useful in the present invention.

[0056] "Soluble polyacrylic acid polymers" (hereinafter referred to as "s-PAA polymers") are polypropylene polymers that are soluble in aqueous solution. They are not crosslinked above the gel point. The "gel point" is the abrupt change in viscosity of a solution containing the polymer. At the gel point, the solution undergoes gelation, as reflected by a loss of fluidity and the formation of a 3D network (i.e., crosslinked polymer chains), resulting in gel formation.

[0057] "% wt," "%w," "weight-%," and "wt%" are used interchangeably herein and all refer to "percent by weight."

[0058] Superabsorbent polymer materials comprising soluble polyacrylic acid polymers

[0059] The superabsorbent polymer material of the present invention comprises cross-linked poly(meth)acrylic acid and its salt (hereinafter referred to as "polyacrylic acid") and further comprises s-PAA polymer. The cross-linked polyacrylic acid has an average distance R between adjacent cross-linking points of xl , and the soluble acrylic acid polymer has an average diameter of gyration 2*R g 2*R g With R xl The ratio of 2*R is at least 1.1, or at least 1.2, or at least 1.25, or at least 1.3, or at least 1.4, or at least 1.5. g With R xl The ratio may be no greater than 5.0, or no greater than 4.5, or no greater than 4.0, or no greater than 3.5, or no greater than 3.0, or no greater than 2.5.

[0060] The s-PAA polymer may have a weight average molecular weight M of 250 kDa to 3 MDa, or 300 kDa to 2 MDa, or 300 kDa to 1 MDa. w .

[0061] Weight average molecular weight M w Especially affects the gyration diameter of s-PAA polymer. Higher weight average molecular weight M w This generally results in a higher diameter of gyration. However, there are other factors that also influence the diameter of gyration of an s-PAA polymer, particularly whether the s-PAA polymer is linear or branched, and if the s-PAA polymer is branched, the degree of branching (the number of branches and the length of the polymer chains within the branches). In general, branched polymers have lower diameters of gyration than linear polymers, and polymers with a higher degree of branching have lower diameters of gyration than polymers with a relatively lower degree of branching.

[0062] S-PAA polymers with a weight-average molecular weight below 250 kDa may negatively impact the amount of extractables and reduce SAP material properties such as capacity (defined by CRC) and permeability (defined by UPM). A lower weight-average molecular weight means a smaller molecular size, which increases the risk of s-PAA polymers leaking out of the SAP material as it absorbs liquid and swells the material.

[0063] By choosing the weight average molecular weight M wAbove 3 MDa of s-PAA polymer, the viscosity of the polyacrylic acid polymer in solution increases, which negatively impacts processability. Furthermore, an excessively high weight-average molecular weight means the SAP material contains very large polymers, which can negatively impact the performance of the SAP material because the polyacrylic acid polymer does not polymerize into the cross-linked polyacrylic acid network of the SAP material, or does so only to a very small extent. Consequently, a relatively large proportion of the total weight of the SAP material fails to contribute meaningfully to absorbent properties, such as those of CRC and UPM.

[0064] Interestingly, it has been found that when s-PAA polymers obtained by degradation of pre-existing SAP materials are used for incorporation into (new) SAP materials, it is possible to use s-PAA polymers with lower weight average molecular weights M compared to s-PAA polymers prepared from pure acrylic acid monomers. w s-PAA polymer.

[0065] It is believed that s-PAA polymers obtained by degrading pre-existing SAP materials (such as pre-existing SAP particles) have a higher degree of branching, that is, there are more crossover points at which the polymer chain branches into two polymer chains (not to be confused with crosslinks, which bind two pre-existing polymer chains to each other to form a crosslink). In contrast, s-PAA polymers polymerized from original acrylic acid polymers are linear or at least branched to a very small extent. S-PAA polymers with a higher degree of branching will adopt different three-dimensional configurations within the SAP material, especially when the SAP material begins to swell.

[0066] If the s-PAA polymer included in the SAP material of the present invention is derived from the degradation of a pre-existing SAP material (such as pre-existing SAP particles), the pre-existing SAP material can be a pre-existing virgin SAP material, a pre-existing post-consumer recycled SAP material, a pre-existing post-industrial recycled SAP material, or a combination of these materials. As used herein, "post-consumer recycled SAP material" refers to a pre-existing SAP material that has been included in an absorbent article and the absorbent article has been used by a consumer (e.g., worn by an incontinent user). After use, the absorbent article is recycled, and the pre-existing post-consumer recycled SAP material is separated from the absorbent article and degraded into s-PAA polymer. As used herein, "post-industrial recycled SAP material" refers to a pre-existing SAP material that may or may not be included in an absorbent article. Post-industrial recycled SAP has not been previously used, for example, it is not included in an absorbent article that has been used by a consumer. In contrast, post-industrial recycled SAP material may be derived from absorbent articles that have been sorted out during production, for example, because they have defects. Post-industrial recycled SAP material that is not contained within an absorbent article may have been selected during the production of a previous SAP material, for example, because it did not meet desired performance targets (such as capacity, whiteness, etc.).

[0067] The s-PAA polymer may be present throughout the SAP material, i.e., the presence of the s-PAA polymer may not be limited to the surface of the SAP material (e.g., not limited to the surface of the SAP particles). Thus, the s-PAA polymer is not intended for use as a surface treatment for SAP materials or the like.

[0068] If the SAP material is in the form of SAP particles, the SAP particles can have a variety of shapes. The term "particles" refers to granules, fibers, flakes, spheres, powders, thin plates, and other shapes and forms known to those skilled in the art of SAP particles. In some embodiments, the SAP particles can be in the shape of fibers, i.e., elongated needle-shaped superabsorbent polymer particles. In those embodiments, the SAP particle fibers have a small scale (i.e., the diameter of the fiber) of less than about 1 mm, typically less than about 500 μm, and preferably less than 250 μm down to 50 μm. The length of the fiber is preferably from about 3 mm to about 100 mm. The fiber can also be in the form of a long, braided filament.

[0069] Alternatively, the SAP particles of the present invention are spherical particles. According to the present invention and in contrast to fibers, "spherical particles" have a longest and a smallest dimension, and the ratio of the longest and smallest particle dimensions of the particles is in the range of 1-5, where a value of 1 would be equivalent to a perfectly spherical particle, while a value of 5 would account for some deviation from such a spherical particle. In this embodiment, the SAP particles may have a particle size of less than 850 μm, or from 50 μm to 850 μm, preferably from 100 μm to 500 μm, and more preferably from 150 μm to 300 μm, as measured according to EDANA method WSP 220.2-05. SAP particles with a relatively low particle size help increase the surface area in contact with liquid exudates and, therefore, support rapid absorption of liquid exudates.

[0070] The superabsorbent polymer material may be partially neutralized, for example by polymerizing acrylic acid monomers at 40 to 95 mol% neutralization, or 50 to 80 mol% neutralization, or 55 to 75 mol% neutralization. Alternatively or in addition, the superabsorbent polymer material may be neutralized after polymerization so that the total degree of neutralization is 40-95 mol%, or 50-80 mol%, or 55-75 mol%.

[0071] The term "surface" describes the outward-facing boundary of a particle. For porous SAP particles, the exposed interior surface can also be considered a surface. The term "surface-crosslinked SAP particle" refers to SAP particles whose molecular chains are crosslinked near the particle surface by a compound called a surface crosslinker. The surface crosslinker is applied to the surface of the particle. In surface-crosslinked SAP particles, the level of crosslinking near the SAP particle surface is generally higher than the level of crosslinking within the SAP interior.

[0072] Commonly used surface crosslinkers are heat-activatable. The term "heat-activatable surface crosslinker" refers to a surface crosslinker that reacts only upon exposure to elevated temperatures, typically around 150°C. Heat-activatable surface crosslinkers known in the art are, for example, difunctional or multifunctional agents capable of establishing additional crosslinks between the polymer chains of the SAP. Examples of heat-activatable surface crosslinkers include, but are not limited to, diols or polyols or derivatives thereof capable of forming diols or polyols, alkylene carbonates, ketals and diglycidyl or polyglycidyl ethers, halogenated epoxides, polyaldehydes, polyols, and polyamines. Crosslinking is based on reactions between functional groups contained in the polymer, such as esterification reactions between carboxyl groups (contained in the polymer) and hydroxyl groups (contained in the surface crosslinker). Because a relatively large fraction of the carboxyl groups of the polymer chains are typically neutralized prior to the polymerization step, only a small number of carboxyl groups are available for such surface crosslinking processes known in the art. For example, in a 70% neutralized polymer, only 3 out of 10 carboxyl groups are available for covalent surface crosslinking.

[0073] The surfaces of the SAP particles can be coated, either instead of surface crosslinking, or more preferably in addition to surface crosslinking (where coating is performed after surface crosslinking). Coating makes the surface tacky so that the SAP particles cannot easily rearrange themselves when wetted (so they cannot block interstices).

[0074] For example, the SAP particles may be coated with a cationic polymer. Preferred cationic polymers may include polyamine or polyimine materials that react with at least one component contained in body fluids, particularly urine. Preferred polyamine materials are selected from (1) polymers having primary amine groups (e.g., polyethyleneamine, polyallylamine); (2) polymers having secondary amine groups (e.g., polyethyleneimine); and (3) polymers having tertiary amine groups (e.g., poly-N,N-dimethylalkylamine). Specific examples of cationic polymers include polyethyleneimine, modified polyethyleneimine cross-linked by epihalohydrin within the water-soluble range, polyamines, modified polyamidoamines grafted by ethyleneimine, polyetheramines, polyethyleneamines, polyalkylamines, polyamidopolyamines, and polyallylamines.

[0075] The cationic polymer coated on the surface of the SAP particles may have a weight average molecular weight M of at least 500 Da, more preferably 5000 Da, and most preferably 10,000 Da or more. w The cationic polymer having a weight average molecular weight of 500 or more is not limited to polymers showing a single maximum value (peak) in molecular weight analysis by gel permeation chromatography, and even if it shows a plurality of maximum values ​​(peaks), a polymer having a weight average molecular weight of 500 or more can be used.

[0076] The amount of the cationic polymer is preferably about 0.05 to 20 parts by weight, more preferably about 0.3 to 10 parts by weight, and most preferably about 0.5 to 5 parts by weight, relative to 100 parts by weight of the superabsorbent polymer particles.

[0077] The s-PAA polymer may be included in the SAP material in an amount of up to 50.0 wt%, or up to 40.0 wt%, or up to 30.0 wt%, or up to 25.0 wt%, or up to 20.0 wt%, based on the total weight of the SAP material. Such amounts have been found to not negatively impact the properties of the SAP material, such as capacity (measured as CRC) and permeability (measured as permeability).

[0078] The s-PAA polymer may be included in the SAP material in an amount of at least 3.0 wt%, or at least 5.0 wt%, or at least 7.5 wt%, or at least 10.0 wt%, based on the total weight of the SAP material.

[0079] It has been found that the SAP materials of the present invention comprising s-PAA polymers having a weight average molecular weight of 250 kDa to 3 MDa have good properties, which make them useful for incorporation into absorbent articles.

[0080] The SAP material of the present invention may have an amount of extractables of less than 15 wt%, or less than 12 wt%, or less than 11 wt%. If the capacity of the SAP material increases, the amount of extractables generally increases. The SAP material of the present invention may have a ratio of the amount of extractables (wt%) to the capacity (g / g) of less than 0.30 or less than 0.25.

[0081] The SAP materials of the present invention may have a capacity of at least 25 g / g as measured according to the Centrifuge Retention Capacity (CRC) method described below.

[0082] The SAP material of the present invention may have an EFFC value of at least 25 g / g or at least 25 g / g. The EFFC value combines the capacity (CRC) and absorption under pressure (AAP) properties of the SAP material into

[0083] EFFC=(CRC+AAP) / 2.

[0084] Method for preparing SAP material containing s-PAA polymer

[0085] The above-mentioned SAP material can be prepared by a method in which the SAP material is obtained by polymerizing an aqueous solution, the method comprising the following steps:

[0086] a) providing an aqueous solution of polymerizable acrylic monomers and / or polymerizable acrylic oligomers, optionally neutralizing at least some of the polymerizable acrylic monomers and / or the polymerizable acrylic oligomers;

[0087] b) optionally providing one or more ethylenically unsaturated comonomers, optionally neutralizing at least some of the ethylenically unsaturated comonomers of step b);

[0088] c) providing one or more cross-linking agents;

[0089] d) providing one or more initiators;

[0090] e) providing at least 3 wt% of a soluble polyacrylic acid polymer based on the total weight of the soluble polyacrylic acid polymer provided in step e) and the monomers, oligomers, comonomers, crosslinkers and initiators provided in steps a) to d)

[0091] f) mixing the aqueous solutions of the monomers, oligomers, comonomers, crosslinking agents and initiators provided in steps a) to e) with the soluble polyacrylic acid polymer; and

[0092] g) polymerizing the mixture obtained in step f) to obtain a superabsorbent polymer material.

[0093] Since it can be assumed that all components provided in steps a) to e) react in the polymerisation reaction, the weight % of step e) is the same as the weight % of s-PAA polymer in the superabsorbent polymer material obtained by the process.

[0094] When providing the s-PAA polymer in process step e), the s-PAA polymer can be provided in dry form (as a powder) into an aqueous solution, or it can be provided as an aqueous solution. Since s-PAA polymers are generally difficult to dissolve, providing the s-PAA polymer as an aqueous solution is advantageous. Furthermore, if the s-PAA polymer is obtained from the degradation of pre-existing post-consumer recycled SAP material, the degradation product (i.e., the s-PAA polymer) will most likely be an aqueous solution, and thus drying and re-dissolving the s-PAA polymer will be time-consuming and energy-intensive.

[0095] The s-PAA polymer may be provided in a weight percentage of up to 50.0%, or up to 40.0%, or up to 30.0%, or up to 25.0%, or up to 20.0%, based on the total weight of the soluble polyacrylic acid polymer provided in step e) and the monomers and oligomers provided in process step a).

[0096] The SAP material may be dried after polymerization. The SAP material may also be comminuted to obtain SAP particles. Comminution may be performed after drying or may be performed before drying (e.g. by so-called wet grinding).

[0097] The ethylenically unsaturated comonomers provided in process step b) may be water-soluble, i.e. their solubility in water at 23° C. is typically at least 1 g / 100 g water, preferably at least 5 g / 100 g water, more preferably at least 25 g / 100 g water and most preferably at least 35 g / 100 g water.

[0098] Suitable ethylenically unsaturated comonomers provided in process step b) are, for example, ethylenically unsaturated carboxylic acids, such as methacrylic acid and itaconic acid.

[0099] Further suitable monomeric ethylenically unsaturated comonomers provided in process step b) are, for example, ethylenically unsaturated sulfonic acids, such as styrenesulfonic acid.

[0100] Further ethylenically unsaturated comonomers which can be added in combination with acrylic acid, methacrylic acid, itaconic acid or ethylenically unsaturated sulfonic acids are styrenesulfonic acid which is copolymerizable with the ethylenically unsaturated monomers provided in process step a), for example acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminoethyl methacrylate and / or diethylaminoethyl methacrylate.

[0101] The acid groups of monomer a) and / or comonomer b) may be partially neutralized. Neutralization can be carried out at the monomer stage. This is usually accomplished by incorporating a neutralizing agent in the form of an aqueous solution or preferably a solid. The degree of neutralization is preferably 40 to 95 mol%, more preferably 40 to 80 mol%, and most preferably 50 to 75 mol%. Conventional neutralizing agents can be used, preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or alkali metal bicarbonates, and mixtures thereof. Ammonium salts may also be used instead of alkali metal salts. Particularly preferred alkali metals are sodium and potassium, but very particularly preferred are sodium hydroxide, sodium carbonate or sodium bicarbonate, and mixtures thereof.

[0102] Suitable crosslinking agents provided in process step b) are compounds having at least two groups suitable for crosslinking. Such groups are, for example, ethylenically unsaturated groups that can be free-radically polymerized into the polymer chain, and functional groups that can form covalent bonds with the acid groups of the monomers provided in process step a) and / or with the comonomers provided in process step b). Furthermore, polyvalent metal salts that can form coordinate bonds with at least two acid groups of the monomers provided in process step a) are also suitable crosslinking agents.

[0103] The crosslinker provided in process step c) is preferably a compound having at least two polymerizable groups which can be free-radically polymerized into the polymer network. Suitable crosslinkers provided in process step b) are, for example, methylenebisacrylamide, ethylene glycol dimethacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, allyl methacrylate, trimethylolpropane triacrylate, triallylamine, tetraallylammonium chloride, tetraallyloxyethane or mixed acrylates which, in addition to acrylate groups, contain further ethylenically unsaturated groups.

[0104] The amount of crosslinker provided in process step c) is preferably from 0.0001 to 0.5% by weight, more preferably from 0.001 to 0.2% by weight, most preferably from 0.01 to 0.1% by weight, based on the total weight of the unneutralized monomer provided in process step a) and the unneutralized comonomer provided in process step b).

[0105] The initiators provided in process step d) may be all compounds which generate free radicals under the polymerization conditions, for example thermal initiators, redox initiators or photoinitiators.

[0106] Suitable redox initiators are potassium or sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascorbic acid, potassium or sodium peroxodisulfate / sodium bisulfite and hydrogen peroxide / sodium bisulfite. Preference is given to using mixtures of thermal initiators and redox initiators, such as potassium or sodium peroxodisulfate / hydrogen peroxide / ascorbic acid. However, the reducing component used is preferably a mixture of the sodium salt of 2-hydroxy-2-sulfinatoacetic acid, the disodium salt of 2-hydroxy-2-sulfinatoacetic acid and sodium bisulfite. This mixture can be used as Brühl FF6 and Brü FF7 (Brüggemann Chemicals; Heilbronn; Germany) was obtained.

[0107] Suitable thermal initiators are especially azo initiators, for example 2,2′-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride and 2,2′-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2′-azobis(2-amidinopropane) dihydrochloride, 4,4″-azobis(4-cyanovaleric acid), 4,4′ and its sodium salt, 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and 2,2′-azobis(imino-1-pyrrolidinyl-2-ethylpropane) dihydrochloride.

[0108] Suitable photoinitiators are, for example, 2-hydroxy-2-methylpropiophenone and 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one.

[0109] The mixing and polymerization in process steps f) and g) can be carried out in a kneading reactor or a belt reactor. In a kneading reactor, the polymer gel formed during polymerization is continuously comminuted, for example, by counter-rotating agitator shafts. Polymerization in belt reactors is also well known in the art. Polymerization in a belt reactor forms a polymer gel, which must be comminuted in a further process step, for example, in an extruder or kneader.

[0110] Surface crosslinking can be performed by spraying a solution of the surface crosslinking agent (such as an aqueous solution) onto the dried SAP particles. After spray application, the surface crosslinking agent-coated polymer particles are thermally surface crosslinked.

[0111] The spray application of the surface crosslinker solution onto the SAP particles is preferably carried out in mixers with moving mixing tools, such as screw mixers, disk mixers and paddle mixers.

[0112] absorbent products

[0113] Typical disposable absorbent articles (in which the SAP materials of the present invention may be used) are placed against or adjacent to the wearer's body to absorb and contain the various exudates discharged from the body and are in the form of diapers 20. Figure 1 and Figure 2 Indicated in.

[0114] In more detail, Figure 1 is a plan view of an exemplary diaper 20 in a flattened position with portions of the diaper cut away to more clearly illustrate the construction of the diaper 20. The diaper 20 is shown for illustrative purposes only, as the SAP material of the present invention may be included in a wide variety of diapers or other absorbent articles.

[0115] like Figure 1 and Figure 2 As shown, absorbent article (here is diaper) can comprise liquid-permeable top sheet 24, liquid-impermeable back sheet 26, absorbent core 28 positioned between top sheet 24 and back sheet 26.Absorbent core 28 can absorb and hold the liquid received by described absorbent article, and can comprise absorbent material 60, other absorbent material commonly used in such as SAP material 66 of the present invention and / or cellulose fiber and absorbent article and non-absorbent material (for example thermoplastic adhesive fixing SAP particles).Absorbent material and non-absorbent material can be wrapped in substrate (for example one or more nonwovens, tissue), such as by facing the upper core cover layer 56 of top sheet and facing the lower core cover layer 58 of back sheet.Such upper core cover layer and lower core cover layer can be made by nonwoven, tissue etc. and can for example be attached to each other continuously or discontinuously along its periphery.

[0116] Absorbent cores may include one or more substrates (such as nonwoven webs or tissue paper), a SAP material (such as SAP particles) arranged on one or more substrates, and a thermoplastic composition generally arranged on a SAP material (such as SAP particles). Typically, the thermoplastic composition is a thermoplastic adhesive material. In one embodiment, the thermoplastic adhesive material forms a fiber layer that is at least partially in contact with the SAP material (such as SAP particles) on one or more substrates and partially in contact with one or more substrates. In order to enhance the adhesion of SAP material (such as SAP particles) and / or thermoplastic adhesive material to the corresponding substrate, an auxiliary adhesive may be deposited on one or more substrates before applying the SAP material (such as SAP particles). Absorbent cores may also include one or more cover layers so that the SAP material (such as SAP particles) is contained between one or more substrates and one or more cover layers. The one or more substrates and one or more cover layers may include or be composed of a nonwoven web. Absorbent cores may also include an odor control compound.

[0117] The absorbent core may consist essentially of one or more substrate layers, SAP material (eg, SAP particles), a thermoplastic composition, optionally an auxiliary binder, optionally a cover layer, and optionally an odor control compound.

[0118] The absorbent core may also comprise a mixture of SAP particles and airfelt, which may be embedded in one or more substrate layers such as a nonwoven web or tissue paper. Such absorbent cores may comprise 30% to 95%, or 50% to 95%, of SAP particles by weight of the absorbent material and may comprise 5% to 70%, or 5% to 50%, of airfelt by weight of the absorbent material (for these percentages, any embedded substrate layer is not considered absorbent material). The absorbent core may also be free of airfelt and may comprise 100% SAP particles by weight of the absorbent material.

[0119] The absorbent core may comprise a mixture or combination of the SAP material of the present invention and other SAP materials (such as other SAP particles and / or SAP foams). For example, the absorbent core may comprise at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or 100% SAP material by weight of the absorbent material, wherein the SAP material comprises at least 10%, or at least 20%, or at least 30%, or at least 50%, or at least 75%, or at least 90%, or 100% SAP material of the present invention based on the total weight of the SAP material in the absorbent core.

[0120] The absorbent articles of the present invention, particularly diapers and pants, may include an acquisition layer 52, a distribution layer 54, or a combination of the two (collectively referred to herein as an acquisition-distribution system "ADS" 50). The function of the ADS 50 is generally to quickly acquire the fluid and distribute it to the absorbent core in an efficient manner. The ADS may include one, two, or more layers. In the following example, the ADS 50 includes two layers: a distribution layer 54 and an acquisition layer 52 disposed between the absorbent core and the topsheet.

[0121] The ADS may not contain SAP materials. The prior art discloses various types of acquisition-dispensing systems, see for example WO2000 / 59430, WO95 / 10996, US5700254, WO02 / 067809. However, the SAP material of the present invention may also be contained in the ADS.

[0122] The function of the distribution layer 54 is to distribute the incoming fluid liquid over a larger surface area within the article, enabling a more efficient use of the absorbent capacity of the absorbent core. The distribution layer can be made of a nonwoven material based on synthetic or cellulosic fibers and having a relatively low density. The distribution layer can typically have a density of 30 g / m 2 Up to 400g / m 2, specifically 80g / m 2 Up to 300g / m 2 The average basis weight of

[0123] The distribution layer may, for example, comprise at least 50%, or 60%, or 70%, or 80%, or 90%, or 100% cross-linked cellulose fibers by weight. The cross-linked cellulose fibers may be wrinkled, twisted, or curled, or combinations thereof (including wrinkled, twisted, and curled). The cross-linked cellulose fibers provide higher elasticity and, therefore, higher resistance to compression of the first absorbent layer under product packaging or use conditions (e.g., under the weight of an infant). This provides the core with relatively high void volume, permeability, and liquid absorption, thereby reducing leakage and improving dryness.

[0124] The absorbent article 20 may also include an acquisition layer 52, the function of which is to quickly acquire the fluid away from the top sheet in order to provide good dryness for the wearer. The acquisition layer 52 is typically placed directly below the top sheet and below the distribution layer. The acquisition layer can typically be or include a nonwoven material, such as an SMS or SMMS material, which includes a spunbond layer, a meltblown layer, and other spunbond layers or alternatively a carded chemically bonded nonwoven material. The nonwoven material can specifically be latex bonded. An exemplary upper acquisition layer 52 is disclosed in US7786341. Carded resin-bonded nonwoven materials can be used, especially when the fibers used are solid round or round and hollow PET staple fibers (e.g., a 50 / 50 or 40 / 60 mixture of 6 denier fibers and 9 denier fibers). An exemplary binder is butadiene / styrene latex.

[0125] The acquisition layer 52 may be stabilized by a latex binder, such as a styrene-butadiene latex binder (SB latex). Methods for obtaining such a lattice are known, for example, from EP 149 880 (Kwok) and US 2003 / 0105190 (Diehl et al.). The binder may be present in the acquisition layer 52 in excess of 12%, 14% or 16% by weight, but may be present in no more than 30%, or no more than 25% by weight of the acquisition layer. SB latex is available under the trade name GENFLO TM 3160 (OMNOVA Solutions Inc.; Akron, Ohio).

[0126] The diaper may also include elasticized leg cuffs 32 and barrier cuffs 34 that improve the containment of liquids and other body exudates, particularly in the leg opening areas. Typically, each leg cuff 32 and barrier cuff 34 will include one or more elastic threads 33 and 35, which are shown in enlarged form in FIG. Figure 1 and Figure 2In addition, the diaper 20 may include other features such as rear ears 40, front ears 46, and / or attached barrier cuffs 34 to form a composite diaper structure. The diaper may also include a fastening system, such as an adhesive fastening system or a mechanical fastening system (e.g., a hook-and-loop fastening system), which may include tape tabs 42, such as adhesive tape tabs or tape tabs including hook elements that cooperate with landing zones 44 (e.g., a nonwoven web that provides the loops in the hook-and-loop fastening system). In addition, the diaper may include other elements, such as a rear elastic waist structure and a front elastic waist structure, side panels, or a lotion application.

[0127] like Figure 1 and 2 As shown, the diaper 20 can be imaginary divided into a first waist region 36, a second waist region 38 opposite the first waist region 36, and a crotch region 37 located between the first waist region 36 and the second waist region 38. The longitudinal centerline 80 is an imaginary line that separates the diaper into two equal halves along its length. The transverse centerline 90 is an imaginary line that is perpendicular to the longitudinal centerline 80 in the plane of the diaper when flattened and passes through the middle of the length of the diaper. The perimeter of the diaper 20 is defined by the outer edges of the diaper 20. The longitudinal edges of the diaper can extend generally parallel to the longitudinal centerline 80 of the diaper 20, and the end edges extend generally parallel to the transverse centerline 90 of the diaper 20 between the longitudinal edges.

[0128] Bio-based materials

[0129] Using ASTM D6866-10, Method B, absorbent articles comprising the SAP material of the present invention may comprise a biobased content value of from about 10% to about 100%, or from about 25% to about 75%, or from about 50% to about 60%.

[0130] Using Method B of ASTM D6866-10, various components of the absorbent article, such as the topsheet, backsheet, fasteners, ADS, back ears, outer cover nonwoven material, elastic laminate (such as the elastic laminate forming the belt of the absorbent article), or any other component may contain a biobased content value of about 10% to about 100%, or about 25% to about 75%, or about 50% to about 60%.

[0131] In order to determine the bio-based content of a single component material (i.e., nonwoven) using the method of ASTM D6866-10, the material is separated and cleaned so that the resulting sample reflects the composition starting material as closely as possible. For example, if a component needs to be deconstructed (e.g., elastic strands are removed from a laminate formed by one or more nonwovens and elastic strands), the nonwoven is washed with a suitable solvent to remove any residual adhesive present. In order to apply the method of ASTM D6866-10 to a sample assembly of two or more materials having different or unknown compositions, the sample is homogenized by grinding the material into a particle form (particle size of about 20 meshes or less) using a known grinding method (such as using a Wiley grinder). A representative sample of suitable quality is then taken out from the sample of the resulting randomly mixed particles.

[0132] Verification of polymers derived from renewable resources

[0133] A suitable verification technique is by 14C analysis. Small amounts of carbon dioxide in the atmosphere are radioactive. 14C carbon dioxide is produced when nitrogen is attacked by neutrons produced by ultraviolet light, causing it to lose a proton and form carbon with a molecular weight of 14, which is immediately oxidized to carbon dioxide. This radioactive isotope represents a small but measurable fraction of atmospheric carbon. Atmospheric carbon dioxide is recycled by green plants to produce organic molecules during photosynthesis. When green plants or other forms of life metabolize organic molecules to produce carbon dioxide, the cycle ends and the carbon dioxide is released back into the atmosphere. Almost all forms of life on Earth rely on green plants to produce organic molecules to grow and reproduce. Therefore, the 14C present in the atmosphere becomes part of all life forms and their biological products. In contrast, fossil fuel-based carbon does not have the labeled radiocarbon ratio of atmospheric carbon dioxide.

[0134] The assessment of renewable carbon in materials can be performed using standard test methods. By using radiocarbon and isotope ratio mass spectrometry, the biobased content of a material can be determined. ASTM International (formally known as the American Society for Testing and Materials) has established a standard method for assessing the biobased content of a material. The ASTM method is designated ASTM D6866-10.

[0135] The application of ASTM D6866-10 to derive "biobased content" is based on the same concepts as radiocarbon dating, but without the use of an age equation. The analysis is performed by deriving the ratio of the amount of organic radiocarbon (14C) in the unknown sample to the amount of radiocarbon in a modern reference standard. This ratio is reported as a percentage, using the unit "pMC" (percent modern carbon).

[0136] The modern reference standard used in radiocarbon dating is the NIST (National Institute of Standards and Technology) standard, which has a known radiocarbon content corresponding to approximately 1950 AD. 1950 AD was chosen because it represents a time before thermonuclear weapons testing, which introduced large amounts of excess radiocarbon into the atmosphere with each explosion (the term "carbon explosion"). The 1950 AD reference is expressed as 100 pM C.

[0137] Tests show that atmospheric radiocarbon levels peaked in 1963, nearly double normal levels, due to a "carbon explosion" before the end of thermonuclear weapons testing. The distribution of atmospheric radiocarbon levels remained roughly constant after reaching this peak, resulting in biological radiocarbon concentrations exceeding 100 pMc in both plants and animals after 1950 AD. This concentration has gradually decreased over time, reaching current values ​​closer to 107.5 pMc. This means that fresh biomass materials, such as corn, can produce radiocarbon signatures close to 107.5 pMc.

[0138] Combining fossil carbon with contemporary carbon in a material will result in a dilution of the contemporary pMC content. Assuming 107.5 pMC represents a contemporary biomass material and 0 pMC represents a petroleum derivative, the pMC value measured for that material will reflect the proportions of the two component types. A material derived 100% from contemporary soybeans should give a radiocarbon signature close to 107.5 pMC. If that material were diluted with, for example, 50% petroleum derivatives, it would give a radiocarbon signature close to 54 pMC (assuming petroleum derivatives have the same carbon percentage as soybeans).

[0139] The results for biomass content were derived by setting 100% equal to 107.5 pMC and 0% equal to 0 pMC. In this regard, a sample measuring 99 pMC would give an equivalent biobased content value of 92%.

[0140] The materials described herein can be evaluated according to ASTM D6866. The average values ​​quoted in this report cover an absolute range of 6% (±3% on either side of the biobased content value) to account for variations in the radiocarbon signature of the final components. It is assumed that all materials are modern or fossil in their original state, and that the desired result is the amount of biobased components "present" in the material, not the amount of biobased materials "used" in the manufacturing process.

[0141] Test Method

[0142] Gel Permeation Chromatography with Multi-Angle Light Scattering and Refractive Index Detection for Polymer Molecular Weight Distribution Measurements Method (GPC-MALS / RI)

[0143] Gel Permeation Chromatography with Multi-Angle Light Scattering (MALS) and Refractive Index (RI) detection (GPC-MALS / RI) allows the determination of the absolute weight-average molecular weight, M, of polymers. w No column calibration methods or standards are required. GPC systems allow molecules to be separated as a function of their molecular size. MALS and RI allow information on number average (Mn) and weight average (Mw) molecular weights to be obtained.

[0144] M of water-soluble polymers such as s-PAA polymers w The distribution is typically measured by using a liquid chromatography system, which typically consists of a pump system, an autosampler (e.g., an Agilent 1260 Infinity pump system with OpenLab Chemstation software, Agilent Technology, Santa Clara, CA, USA), and an appropriately sized column set (e.g., a Waters Super Hydrogel guard column, 6 mm ID x 40 mm long, two Super Hydrogel linear columns, 7.8 mm ID x 300 mm long, Waters Corporation of Milford, MA, USA) typically operated at 40°C.

[0145] A column set comprises one or typically a plurality of subsequently connected columns having different pore sizes graded for polymers of different molecular weights, and the columns are generally selected to provide resolution over a broad and relevant molecular weight range.

[0146] Typically, the mobile phase is, for example, 0.1 M sodium nitrate in water containing 0.02% sodium azide and is pumped isocratically at a flow rate of about 1 mL / min. ) controlled multi-angle light scattering (MALS) detector (e.g. ) and a differential refractive index (RI) detector (e.g., Wyatt Technology of Santa Barbara, California, USA).

[0147] The samples were typically prepared by dissolving the polymer material (such as s-PAA polymer) at approximately 1 mg / ml in the mobile phase and hydrating the solution by mixing overnight at room temperature. Prior to GPC analysis, the samples were filtered through a membrane filter (e.g., 0.8 μm Versapor filter, PALL, Life Sciences, NY, USA) using a syringe into an LC autosampler vial.

[0148] Dn / dc (differential change of refractive index with concentration) values ​​are typically measured on the polymeric material of interest and used to determine the number average molecular weight and weight average molecular weight by the respective detector software.

[0149] Urine Permeability Measurement (UPM) Test Method

[0150] Laboratory conditions :

[0151] The test must be carried out in a climate-conditioned room under standard conditions of 23°C ± 2°C temperature and 45% ± 10% relative humidity.

[0152] Urine osmotic pressure measurement system

[0153] This method measures the permeability of the swollen hydrogel layer 1318. The apparatus used for this method is described below. This method is closely related to the prior art SFC (Saline Flow Conductivity) test method.

[0154] Figure 3 Shown is a permeability measurement system 1000 equipped with a constant hydrostatic head reservoir 1014, an open-ended tube 1010 for air entry, a plug 1012 for refilling, a test stand 1016, a transfer tube 1018 having a flexible tube 1045 with a Tygon tubular nozzle 1044, a stopcock 1020, a cover plate 1047 and a support ring 1040, a receiving container 1024, a balance 1026, and a piston / cylinder assembly 1028.

[0155] Figure 4 The piston / cylinder assembly 1028 is shown including a metal weight 1112, a piston shaft 1114, a piston head 1118, a cover 1116, and a cylinder 1120. The cylinder 1120 is made of a transparent polycarbonate (e.g., ) and has an inner diameter p of 6.00 cm, (area = 28.27 cm 2 ), wherein the inner cylindrical wall 1150 is smooth. The bottom 1148 of the cylinder 1120 is covered with a stainless steel mesh (ISO 9044 material 1.4401, mesh size 0.038 mm, wire diameter 0.025 mm) (not shown), which is biaxially stretched to a taut state before being connected to the bottom 1148 of the cylinder 1120. The piston shaft 1114 is made of a transparent polycarbonate (e.g., ) and has an overall length q of approximately 127 mm. The middle portion 1126 of the piston shaft 1114 has a diameter r of 22.15 (± 0.02) mm. The upper portion 1128 of the piston shaft 1114 has a diameter s of 15.8 mm, thereby forming the shoulder 1124. The lower portion 1146 of the piston shaft 1114 has a diameter t of approximately 5 / 8 inches (15.9 mm) and is threaded to be tightly screwed into the central hole 1218 of the piston head 1118 (see Figure 5 The piston head 1118 is perforated and made of a transparent polycarbonate (e.g., ) and is also screened with stretched stainless steel mesh (ISO 9044 material 1.4401, mesh size 0.038 mm, wire diameter 0.025 mm) (not shown). Weight 1112 is stainless steel with a central hole 1130, slides onto the upper portion 1128 of the piston shaft 1114 and rests on the shoulder 1124. The combined weight of the piston head 1118, piston shaft 1114, and weight 1112 is 596 g (± 6 g), which is equivalent to 0.30 psi on the inner area of ​​the cylinder 1120. The combined weight can be adjusted by drilling a blind hole down the central axis 1132 of the piston shaft 1114 to remove material and / or provide a cavity for adding weights. The cylinder cover 1116 has a first cover opening 1134 at its center for vertical alignment of the piston shaft 1114 and a second cover opening 1136 near the edge 1138 for introducing fluid from the constant static head reservoir 1014 into the cylinder 1120 .

[0156] A first linear indicator mark (not shown) is radially marked along the upper surface 1152 of the weight 1112, the first linear indicator mark being transverse to the central axis 1132 of the piston shaft 1114. A corresponding second linear indicator mark (not shown) is radially marked along the top surface 1160 of the piston shaft 1114, the second linear indicator mark being transverse to the central axis 1132 of the piston shaft 1114. A corresponding third linear indicator mark (not shown) is radially marked along the middle portion 1126 of the piston shaft 1114, the third linear indicator mark being parallel to the central axis 1132 of the piston shaft 1114. A corresponding fourth linear indicator mark (not shown) is radially marked along the upper surface 1140 of the cylinder cover 1116, the fourth linear indicator mark being transverse to the central axis 1132 of the piston shaft 1114. Furthermore, a corresponding fifth linear indicator mark (not shown) is marked along the lip 1154 of the cylinder cover 1116, the fifth linear indicator mark being parallel to the central axis 1132 of the piston shaft 1114. A corresponding sixth linear indicator mark (not shown) is scored along outer cylinder wall 1142 and is parallel to central axis 1132 of piston shaft 1114. Aligning the first, second, third, fourth, fifth, and sixth linear indicator marks allows weight 1112, piston shaft 1114, cylinder cover 1116, and cylinder 1120 to be repositioned with the same orientation relative to one another for each measurement.

[0157] Cylinder 1120 specification details are:

[0158] Outer diameter u of cylinder 1120: 70.35 mm (± 0.05 mm)

[0159] Inner diameter p of cylinder 1120: 60.0 mm (± 0.05 mm)

[0160] The height ν of the cylinder 1120 is 60.5 mm. The cylinder height must not be less than 55.0 mm!

[0161] The specifications of cylinder cap 1116 are as follows:

[0162] Outer diameter w of cylindrical cover 1116: 76.05 mm (± 0.05 mm)

[0163] Inner diameter x of cylindrical cover 1116: 70.5 mm (± 0.05 mm)

[0164] Thickness y of the cylindrical cover 1116 including the lip 1154: 12.7 mm

[0165] Thickness z of the drum cover 1116 without the lip 1154: 6.35 mm

[0166] Diameter a of the first cover opening 1134: 22.25 mm (± 0.02 mm)

[0167] Diameter b of the second cover opening 1136: 12.7 mm (± 0.1 mm)

[0168] Distance between the centers of the first cover opening 1134 and the second cover opening 1136: 23.5 mm

[0169] The specifications of weight 1112 are as follows:

[0170] Outer diameter c: 50.0mm

[0171] Diameter d of center hole 1130: 16.0 mm

[0172] Height e: 39.0mm

[0173] The specifications of piston head 1118 are as follows:

[0174] Diameter f: 59.7mm (±0.05mm)

[0175] Height g: 16.5mm. The piston head height must be no less than 15.0mm.

[0176] The outer holes 1214 (14 in total) have a diameter h of 9.30 (±0.25) mm and are equally spaced with the center being 23.9 mm from the center of the center hole 1218 .

[0177] The inner holes 1216 (7 in total) have a diameter i of 9.30 (±0.25) mm, and the inner holes 1216 are equally spaced, with their centers being 13.4 mm from the center of the center hole 1218.

[0178] The central bore 1218 has a diameter j of approximately 5 / 8 inch (15.9 mm) and is threaded to receive the lower portion 1146 of the piston shaft 1114 .

[0179] Before use, the stainless steel screens (not shown) of the piston head 1118 and cylinder 1120 should be checked for blockage, holes, or excessive stretching and replaced if necessary. A urine osmotic pressure measuring device with a damaged screen may output erroneous UPM results and should not be used until the screen is replaced.

[0180] A 5.00 cm mark 1156 is made on the cylinder 1120 at a height k of 5.00 cm (±0.05 cm) above the screen (not shown) attached to the bottom 1148 of the cylinder 1120. This marks the fluid level to be maintained during analysis. Maintaining a correct and constant fluid level (hydrostatic pressure) is critical to measurement accuracy.

[0181] The constant static head reservoir 1014 is used to deliver the saline solution 1032 to the cylinder 1120 and maintain the level of the saline solution 1032 at a height k of 5.00 cm above a screen (not shown) attached to the bottom 1148 of the cylinder 1120. The bottom 1034 of the inlet tube is positioned so as to maintain the level of the saline solution 1032 in the cylinder 1120 at the desired height k of 5.00 cm during measurement, i.e., the bottom 1034 of the inlet tube is located in approximately the same plane 1038 as the 5.00 cm mark 1156 on the cylinder 1120 when the cylinder is positioned on the cover plate 1047 and support ring 1040 (having a circular inner opening having a diameter of not less than 64 mm) above the receiving container 1024.

[0182] The cover plate 1047 and the support ring 1040 are components used in an apparatus for the method "K(t) test method (dynamic effective permeability and absorption kinetics measurement test method)" as described in EP 2 535 027 A1 and are referred to as " "üfstand" or "Time Dependent Permeability Tester", device number 03-080578 and commercially available at BRAUN GmbH, Frankfurter Str. 145, 61476 Kronberg, Germany). Detailed technical drawings are also available upon request.

[0183] The proper height alignment of the air inlet tube with the 5.00 cm mark 1156 on the cylinder 1120 is critical for analysis. A suitable reservoir 1014 consists of a wide-mouth bottle 1030 containing a horizontally oriented L-shaped transfer tube 1018 connected to a flexible tube 1045 (e.g., Tygon tubing, capable of connecting the nozzle to the reservoir outlet) and a Tygon tubular nozzle 1044 (at least 6.0 mm inner diameter and approximately 5.0 cm long) for fluid transfer, a vertically oriented open-ended tube at a fixed height within the constant hydrostatic head reservoir 1014 for admitting air, and a stopcock 1012 for refilling the constant hydrostatic head reservoir 1014. The tube has an inner diameter of approximately 12 mm, but not less than 10.5 mm. The transfer tube 1018, located near the bottom 1042 of the constant hydrostatic head reservoir 1014, houses a stopcock 1020 for starting / stopping saline solution 1032 delivery. The outlet of the delivery flexible tube 1045 is sized (e.g., 10 mm outer diameter) to be inserted through the second cover opening 1136 on the cylinder cover 1116, with its end positioned below the surface of the saline solution 1032 in the cylinder 1120 (after the saline solution 1032 reaches a height of 5.00 cm in the cylinder 1120). The inlet tube is held in place by an O-ring gasket 1049. The constant static head reservoir 1014 can be positioned on the test stand 1016 at an appropriate height relative to the cylinder 1120. The components of the constant static head reservoir 1014 are sized to quickly fill the cylinder 1120 to the desired height (i.e., static head) and maintain that height throughout the measurement. The constant static head reservoir 1014 must be capable of delivering saline solution 1032 at a flow rate of at least 2.6 g / s for at least 10 minutes.

[0184] The piston / cylinder assembly 1028 is positioned on a support ring 1040 or a suitable alternative rigid support in the cover plate 1047. The saline solution 1032 that passes through the piston / cylinder assembly 1028, including the swollen hydrogel layer 1318, is collected in a receiving container 1024, which is positioned below (but not in contact with) the piston / cylinder assembly 1028.

[0185] The receiving container 1024 is placed on a balance 1026 accurate to at least 0.001 g. The digital output of the balance 1026 is connected to a computerized data acquisition system 1048.

[0186] Preparation of reagents (not shown)

[0187] Jayco Synthetic Urine (JSU) 1312 (See Figure 6) was used as the swelling phase (see UPM procedure below), and 1032 of a 0.118 M sodium chloride (NaCl) solution was used as the mobile phase (see UPM procedure below). The following preparations are based on a standard 1 liter volume. If preparing a volume other than 1 liter, all amounts were weighed accordingly.

[0188] JSU: Fill a 1 L volumetric flask to 80% of its volume with distilled water and place a magnetic stir bar inside the flask. Using an analytical balance, weigh the following dry ingredients to the nearest ±0.01 g using weighing paper or a beaker. Add them quantitatively to the flask in the same order listed below. Stir the solution on a suitable stir plate until all solids have dissolved. Remove the stir bar and dilute the solution to 1 L with distilled water. Replace the stir bar and continue stirring the solution for several minutes.

[0189] Amount of salt to prepare 1 liter of Jayco synthetic urine:

[0190] Potassium chloride (KCl) 2.00g

[0191] Sodium sulfate (Na2SO4) 2.00g

[0192] Ammonium dihydrogen phosphate (NH4H2PO4) 0.85g

[0193] Diammonium hydrogen phosphate ((NH4)2HPO4) 0.15g

[0194] Calcium chloride (CaCl2) 0.19g-[or calcium chloride hydrate (CaCl2·2H2O) 0.25g]

[0195] Magnesium chloride (MgCl2) 0.23g-[or hydrated magnesium chloride (MgCl2·6H2O) 0.50g]

[0196] To prepare more quickly, in a 1 L volumetric flask, potassium chloride, sodium sulfate, ammonium dihydrogen phosphate, ammonium phosphate (dibasic) and magnesium chloride (or hydrous magnesium chloride) are mixed and dissolved in 80% distilled water. Calcium chloride (or hydrous calcium chloride) is dissolved separately in approximately 50 ml of distilled water (e.g., in a glass beaker), and after the other salts are completely dissolved therein, the calcium chloride solution is transferred to a 1 L volumetric flask. Then, distilled water is added to 1 L (1000 ml ± 0.4 ml) and the solution is stirred for a few more minutes. Jayco synthetic urine can be stored in a clean plastic container for 10 days. If the solution becomes cloudy, it should not be used.

[0197] 0.118 M Sodium Chloride (NaCl) Solution: Use 0.118 M sodium chloride as salt solution 1032. Using weighing paper or a beaker, weigh 6.90 g (± 0.01 g) of sodium chloride and quantitatively transfer it to a 1 L volumetric flask (1000 ml ± 0.4 ml). Fill the flask to volume with distilled water. Add a stir bar and stir the solution on a stir plate until all solids have dissolved.

[0198] The conductivity of the prepared Jayco solution must be in the range of about 7.48-7.72 mS / cm, and the conductivity of the prepared 0.118 M sodium chloride (NaCl) solution must be in the range of about 12.34 mS / cm to 12.66 mS / cm (e.g., measured via a COND 70 instrument (#50010522) without CELL, equipped with a Cell VPT51-01 C=0.1 from xs instruments, or via a LF 320 / Set, #300243, equipped with a TetraCon 325 from WTW, or via a COND 330i, #02420059, equipped with a TetraCon 325 from WTW). The surface tension of each solution must be in the range of 71-75 mN / m (measured, for example, via a tensiometer K100 from Kruess with a Pt plate).

[0199] Test Preparation

[0200] Using a solid reference cylindrical weight (not shown) (50 mm diameter, 128 mm height), set a caliper (not shown) (measuring range 25 mm, accurate to 0.01 mm, piston pressure maximum 0.50 g; e.g., a Mitutoyo digital height gauge) to read zero. This operation is conveniently performed on a smooth, level work surface (not shown) that is at least approximately 11.5 cm x 15 cm. Position the piston / cylinder assembly 1028, without superabsorbent polymer particles, under the caliper (not shown) and record the reading L1 to the nearest 0.01 mm.

[0201] The constant static head reservoir 1014 is filled with saline solution 1032. The bottom 1034 of the inlet tube is positioned so as to maintain the top (not shown) of the liquid meniscus (not shown) in the cylinder 1120 at the 5.00 cm mark 1156 during the measurement. Proper height alignment of the inlet tube at the 5.00 cm mark 1156 on the cylinder 1120 is critical to the analysis.

[0202] The receiving container 1024 is placed on a balance 1026, and the digital output of the balance 1026 is connected to a computerized data acquisition system 1048. A cover plate 1047 having a support ring 1040 is positioned over the receiving container 1024.

[0203] UPM Program

[0204] 1.5 g (± 0.05 g) of superabsorbent polymer particles are weighed onto a suitable weighing paper or weighing aid using an analytical balance. The moisture content of the superabsorbent polymer particles is measured according to the EDANA moisture content test method NWSP 230.0.R2 (15) or via a moisture analyzer (HX204, from Mettler Toledo, drying temperature 130° C., starting superabsorbent polymer particle weight 3.0 g (± 0.5 g), stop standard 1 mg / 140 s). If the moisture content of the superabsorbent polymer particles is greater than 3% by weight, the superabsorbent polymer particles are dried to a moisture content of <3% by weight, for example in an oven at 105° C. for 3 h or, for example, at 120° C. for 2 h. If the moisture content is greater than 5% by weight, the agglomerated superabsorbent polymer particles are dried, for example, in an oven at 105° C. for 3 h or, for example, at 120° C. for 2 h.

[0205] Empty cylinder 1120 is placed on horizontal workbench 1046 (not shown), and superabsorbent polymer particles are quantitatively transferred into cylinder 1120. Superabsorbent polymer particles are evenly dispersed on the screen (not shown) of the bottom 1148 attached to cylinder 1120, while cylinder 1120 is rotated, for example, via (manual or electric) turntable (for example, petriturn-E or petriturn-M, deriving from Schuett) assistance. The uniform distribution of particles on the screen (not shown) of the bottom 1148 connected to cylinder 1120 is very important, to obtain the highest precision result. After superabsorbent polymer particles have been evenly distributed on the screen (not shown) of the bottom 1148 attached to cylinder 1120, particles must not adhere to inner cylinder wall 1150. Insert piston shaft 1114 through first cover opening 1134, wherein the lip 1154 of cover 1116 faces piston head 1118. Carefully insert piston head 1118 into cylinder 1120 to a depth of several centimeters. Then place cap 1116 on the upper edge 1144 of cylinder 1120, while carefully keeping piston head 1118 away from superabsorbent polymer particles. Weight 1112 is placed on the top 1128 of piston shaft 1114 so that it rests on shoulder 1124 so that the first and second linear indicator marks are aligned. Then carefully rotate cap 1116 and piston shaft so that the third, fourth, fifth and sixth linear indicator marks are aligned and then aligned with the first and second linear indicator marks. Then gently lower piston head 1118 (by piston shaft 1114) to rest on dry superabsorbent polymer particles. The proper position of cap 1116 prevents the adhesion of weights on hydrogel layer 1318 and ensures uniform distribution.

[0206] Swelling phase :

[0207] A fritted disk 1310 of at least 8 cm in diameter (e.g., 8-9 cm in diameter) and at least 5.0 mm thick (e.g., 5-7 mm thick) with a "coarse" or "extra-coarse" porosity (e.g., Chemglass Inc. #CG 201-51, coarse porosity; or, e.g., Robu 1680, porosity 0) is placed in a wide, flat-bottomed petri dish 1314 and JSU 1312 is added by pouring it into the center of the fritted disk 1310 until the JSU 1312 reaches the top surface 1316 of the fritted disk 1310. The height of the JSU must not be greater than the height of the fritted disk 1310. It is important to avoid any air or bubbles being trapped in the fritted disk 1310 or the bottom layer.

[0208] The entire piston / cylinder assembly 1028 is lifted and placed on the fritted disk 1310 in the culture dish 1314. The JSU 1312 from the culture dish 1314 passes through the fritted disk 1310 and is absorbed by the superabsorbent polymer particles (not shown) to form a hydrogel layer 1318. The JSU 1312 available in the culture dish 1314 should be sufficient for all swelling phases. If necessary, more JSU 1312 can be added to the culture dish 1314 during hydration to maintain the JSU 1312 level at the top surface 1316 of the fritted disk 1310. After a period of 60 minutes, the piston / cylinder assembly 1028 is removed from the fritted disk 1310, taking care to ensure that the hydrogel layer 1318 does not lose JSU 1312 or absorb air during this step. The piston / cylinder assembly 1028 is placed under a calliper (not shown) and the reading L2 is recorded to the nearest 0.01 mm. If the reading changes over time, only the initial value is recorded. The thickness L0 of the hydrogel layer 1318 is determined by L2-L1, with an accuracy of 0.1 mm.

[0209] Transfer the piston / cylinder assembly 1028 to the support ring 1040 in the cover plate 1047. Position the constant static head reservoir 1014 so that the Tygon tubular nozzle 1044 is placed through the second cover opening 1136. Begin the measurement in the following order:

[0210] a) Open the stopcock 1020 of the constant hydrostatic head reservoir 1014 to allow the saline solution 1032 to reach the 5.00 cm mark 1156 on the cylinder 1120. This saline solution 1032 level should be achieved within 10 seconds of opening the stopcock 1020.

[0211] b) Once 5.00 cm of saline solution 1032 is obtained, the data collection procedure is initiated.

[0212] The mass of saline solution 1032 (in grams, to 0.001 grams) that passed through the hydrogel layer 1318 was recorded at 20-second intervals for 10 minutes using a computer 1048 attached to a balance 1026. At the end of the 10 minutes, the stopcock 1020 on the constant hydrostatic head reservoir 1014 was closed.

[0213] The UPM calculation uses data from 60 seconds to the end of the experiment. Data collected before 60 seconds are not included in the calculation.

[0214] For each 20-second period after the initial 60 seconds of the experiment (time t (i-1) to t i ), the corresponding flow rate Fs (t) (in g / s) and the corresponding midpoint in time t (1 / 2)t (in s) is calculated according to the following formula:

[0215] and

[0216] Each time interval (t (i-1) to t i ) flow rate Fs (t) Relative to each time interval (t (i-1) to t i ) at the midpoint of time t (1 / 2) The intercept was calculated as Fs(t=0).

[0217] Calculation of the intercept :

[0218] The intercept is calculated by the best fit regression line, for example as follows: The formula for the regression line intercept a is:

[0219] a=y 平均 -b·x 平均 (XIII)

[0220] The slope b is calculated as:

[0221]

[0222] And where x 平均 and y 平均 are the sample means, i.e. the average of known_x and the average of known_y.

[0223] Calculation of urine osmotic pressure Q :

[0224] The intercept Fs(t=0) is used to calculate Q according to the following formula:

[0225]

[0226] where the flow rate Fs (t=0) is given in g / s, L0 is the initial thickness of the hydrogel layer 1318 in cm, and ρ is the density of the saline solution 1032 in g / cm 3 A (derived from the above formula) is expressed in cm 2 The area of ​​the hydrogel layer 1318 (e.g., 28.27 cm 2 ), ΔP is in dynes / cm 2 The hydrostatic pressure of the gauge (e.g. 4920 dynes / cm 2 ), and urine osmotic pressure Q is measured in cm 3 The unit is sec / g. The average value of three measurements should be recorded.

[0227]

[0228] Capacity as described in EDANA NWSP 241.0.R2(15) Centrifuge retention capacity (CRC) Test Method Determination: Unlike EDANA NWSP 241.0.R2 (15), the CRC measurement starts at a lower limit of 24.2 g / g (instead of 27.19 g / g as stated in EDANA NWSP 241.0.R2 (15)).

[0229] In EDANA method NWSP 242.0.R2 (15) Absorption Against Pressure (AAP) Test Method: Unlike the EDANA method, a pressure of 0.7 psi was applied (instead of the 0.3 psi pressure provided in EDANA method NWSP 242.0.R2 (15)).

[0230] Amount of extractables Measured according to EDANA test method NWSP 270.0.R2(15). The following differences from EDANA test method NWSP 270.0.R2(15) apply to this article:

[0231] 9. Procedure (Procedural steps not described below are to be performed without deviating from EDANA test method NWSP 270.0.R2 (15)):

[0232] 9.2 Add exactly 200.0 ± 0.1 ml of saline solution to a 200 ml dispenser (not to a 250 ml beaker or Erlenmeyer flask as described in EDANA test method NWSP 270.0.R2 (15)).

[0233] 9.4 The saline solution was added to the 250 ml Erlenmeyer flask by weighing 0.95-1.05 g of the SAP granules sample directly into the flask and adding a magnetic coin (rather than adding the sample to a weighing container or laboratory paper and weighing the balance again as described in EDANA test method NWSP 270.0.R2 (15)). The flask was filled with saline solution only at the beginning of the extraction time.

[0234] 9.7 Stopper / lid / closure for beaker or Erlenmeyer flask, and at 250 ±

[0235] 50r.min -1 The solution was stirred at a rate of 100 μg / min for 16 hours (instead of 1 hour as described in EDANA test method NWSP 270.0.R2 (15)).

[0236] 9.8 Prepare a titration blank by treating 200.0 ± 0.1 ml of the same batch of saline solution as used for sample preparation in the same manner. Differences from EDANA test method NWSP 270.0.R2 (15): n = 2.

[0237] 9.9 Stop stirring the solution and filter the extracted sample directly through the flask covered with mesh (CCRC flask) with no downtime (instead of allowing the gel to completely settle to the bottom of the flask as described in EDANA test method NWSP 270.0.R2 (15)).

[0238] Calculation of the average distance Rxl between adjacent crosslinking points and the average gyration diameter 2*Rg

[0239] The SAP material is synthesized via polymerization of acrylic acid and an internal crosslinking agent comonomer with at least two reactive polymerizable groups (the number of polymerizable groups of each crosslinking agent comonomer is generally referred to as functionality and represented by f). The network polymer obtained has an average crosslink density (expressed as CXL%, in %mol relative to %mol of acrylic acid monomer) that depends on the addition level of the crosslinking agent monomer. Copolymerization is a random free radical reaction, and the average crosslinking distribution in the polymer can be calculated according to the average number of acrylic acid (AA) monomer units (also including sodium acrylate units, because acrylic acid can be neutralized to a certain extent in situ) between the crosslinking monomers. Due to the assumption that most of the crosslinking agent monomers have reacted all of their available polymerizable groups, the average number of AA units between two adjacent crosslinked molecules will be N xl (See Formula 1). Therefore:

[0240]

[0241] It is recognized that during synthesis, chains grow and crosslink randomly in an unstressed state (without external force fields), so the chain size obeys a random conformation that can be described to a first approximation by the Flory equation, which converts the average end-to-end geometric distance in space of self-avoiding polymer chains (R ee ) (i.e., taking into account the excluded volume of the chains, but neglecting in this case concentration and ionic interaction factors since all the gels considered have similar polymer solids content and ionic charge) is related to the number (N) and individual sizes of the monomer units (b) of which it is composed (see also PJ Flory, Principles of Polymer Chemistry, Cornell University Press, Ithaca (1953)):

[0242] R ee =b·N 3 / 5 (2)

[0243] For the case of the random infinite network mentioned above, the R synthesized in the solution under the stress-free condition (natural condition) of the network is ee The value can be used to evaluate the distance between two adjacent cross-linking points. For the natural state, R xl(n) represents. Therefore, R xl (n) will depend on the number of AA units between these crosslinks (N xl ) and the size of the monomer unit b (for acrylic acid AA, ):

[0244]

[0245] Therefore, substituting (1) into (3), we obtain:

[0246]

[0247] As a characteristic of SAP materials, after preparation, the polymer can be swollen with a liquid (e.g., urine, saline, or pure water), which results in a large volume expansion of the network up to the equilibrium capacity, as measured, for example, by centrifuge retention capacity (CRC). xl The distance will increase accordingly to accommodate the volume expansion of the network. At a certain level of swelling, whether balanced or not (expressed as x-loading, xL, in grams liquid / gram dry SAP material), the cross-link-cross-link distance increases from R xl (n) changes to R xl (xL). Most typically, modern SAP materials used in absorbent articles swell (CRC) to about 30 g of urine (or saline containing 0.9% wNaCl) per g of dry SAP material at equilibrium (if their capacity (CRC) is less than 30 g / g, they will of course absorb less than 30 g / g). On average, during use of a diaper or pants, the SAP material swells to about 20 g / g before the caregiver changes the diaper or pants (i.e., diaper changes are typically performed before the SAP material has absorbed the maximum possible amount of urine), or to about 25 g / g during nighttime or other extended use. Therefore, for the present invention, the ratios claimed herein refer to a SAP material loading of 20 g / g, i.e., R xl The calculation is for a load of 20 g / g. In addition, the following examples also provide R for a load of 25 g / g. xl Since x-load is defined as liquid mass / SAP material dry mass, the volume expansion of the network under a given x-load (xL) is calculated (with R xl The increase is proportional to the amount of increase in the cubic power of isotropic swelling), the density of the dry SAP material (r d ) and the density of the swelling liquid (r liq ).

[0248] Scheme 1. Schematic diagram of the network structure in its natural state and after swelling with fluid:

[0249]

[0250] R xl Calculation of (xL)

[0251] First, assume that the swelling (represented by the exponent (n)) from native to any other xL different from native is isotropic, i.e., uniform and equal in all directions, so that the volume ratio at a given xL to that at native is equal to the cross-link-cross-link distance R at a given xL to that at native. xl The cubic ratio of:

[0252]

[0253] Recognize that the volume from natural swelling to a given xL is additive (i.e., there is no expansion or contraction):

[0254] V (xL) =V (n) +V liq (6)

[0255] And by definition, xL is defined as the mass of the swelling liquid m liq / Mass of dry SAP material (m d ):

[0256]

[0257] And the volume of the swelling liquid is only m liq Its corresponding density (r liq ) ratio:

[0258]

[0259] Swelling liquid V liq The volume of can be expressed by substituting (7) into (8), then into (6), and finally into (5), obtaining:

[0260]

[0261] Next, the natural volume V of SAP can be expressed as n , assuming the colligative nature of volume when synthesizing SAP in aqueous solution, where V d is the dynamic volume of dry SAP material, V w is the volume of water from the polymerization solution remaining in the native SAP material:

[0262] V (n) =V d +V w (10)

[0263] The dry polymer (m d and r d ) and water (m w and rw ) by substituting the corresponding mass density ratio (by definition) for the volume yields:

[0264]

[0265] An important parameter when synthesizing SAP materials is the solids content at synthesis, which is the amount of dry SAP material relative to the total weight of the native SAP material (where the sum of dry polymer and water is the native gel weight). By definition, the solids content w under native conditions can be expressed as:

[0266]

[0267] Therefore, m in natural gel w So it can be expressed as:

[0268]

[0269] Substitute (13) into (11) and realize that r w =1g / ccm to obtain:

[0270]

[0271] Substituting (14) into (9) and simplifying, we obtain:

[0272]

[0273] Therefore, R xl (xL) can be expressed as natural R xl (n) (derived from (4)) times the cube root of the volume expansion coefficient (a function of xL, the densities of the dry SAP material and the swelling liquid, and the solids content w of the native gel):

[0274]

[0275] For the most common type of urine-swellable SAP used in diapers, which is based on AA monomers and internally cross-linked by a bifunctional cross-linker such as PEG-diacrylate (PEGDA), the following constants are appropriate (approximately):

[0276] parameter value b 0.27nm f 2 <![CDATA[ρ d ]]> <![CDATA[1.6g / cm 3 ]]> <![CDATA[ρ liq ]]> <![CDATA[1.004g / cm 3 ]]>

[0277] If the SAP material contains comonomers, the value of b must be adjusted accordingly. For mixtures of monomers and comonomers, a weighted average of b must be calculated based on the individual sizes of the different monomers and their proportions in the monomer / comonomer mixture. The same applies to calculating the number of polymerizable groups f per crosslinker comonomer if a mixture or combination of different crosslinker molecules is used.

[0278] For this article's R xl The calculation of R for a possible surface crosslinking of the SAP particles is not considered. Surface crosslinking affects only a negligible mass fraction of the crosslinked polyacrylic acid network of the SAP particles, since only very thin areas on the surface undergo additional crosslinking. Furthermore, for the present invention, R for a 20 g / g SAP particle loading is calculated. xl Under such loads, the SAP particles have undergone considerable expansion and swelling, which leads to significant breaking of the surface crosslinks. Therefore, the Rxl values ​​calculated for the matrix polymer particles as provided herein are also applicable to SAP particles that have been surface crosslinked.

[0279] Because the s-PAA polymer is introduced during the synthesis of the SAP material, its chains are unreactive during the polymerization of the AA monomers (except for minimal chain transfer to free radicals). Consequently, when the SAP material network forms around these s-PAA polymer chains, the latter can be much larger than the network pores between crosslinks due to the high solids content during synthesis (natural conditions). This results in significant interpenetration of the s-PAA polymer chains into the network, leading to entanglement between s-PAA polymer chains from the free polymer and those from the network. Upon swelling in a large amount of liquid (e.g., 20 g / g or higher), the volume expansion of the network leads to a significant increase and stretching of the polyacrylic acid chains contained within and polymerized into the network. The dilution effect helps the free s-PAA polymer chains transition from an entangled, semi-dilute or concentrated state to a more relaxed conformation in the dilute state. Because these free s-PAA polymer chains form a less entangled or even unentangled chain conformation in the dilute state, their characteristic size is determined by the radius of gyration R, which is proportional to their molecular weight. g Described by (see formula (17)), their molecules can move within the network, which depends on their size and the size of the network pores. When the size of the free s-PAA polymer chain is relatively larger than the pores of the network, it will be more difficult for the free s-PAA polymer chain to migrate within the network, especially to reach the surface of the SAP particles in excess swelling liquid and leave the surface, thus becoming an extractable polymer. When the mobile s-PAA polymer chain has an R smaller than the network pores, the free s-PAA polymer chain will be more difficult to migrate within the network, especially to reach the surface of the SAP particles in excess swelling liquid and leave the surface, thus becoming an extractable polymer. g When the SAP particles are of a certain size (as shown in Scheme 2), they are able to move more freely within the pores of the gel network and eventually leave the surface of the SAP particles as extractable polymer. As mentioned above, absorbent articles such as diapers and pants are usually changed well before the SAP particles reach their maximum capacity (i.e., the SAP particles only load up to about 20 g / g). Therefore, for the present invention, when calculating 2*R g / R xl We focus on the 20g / g loading of R xlThe s-PAA polymers comprised by the SAP particles of the present invention are readily prevented from migrating under the SAP particle load, which is typical under the use conditions of the absorbent article.

[0280] Scheme 2. Incorporation of non-crosslinked s-PAA polymer into SAP polymer. Note that the chemical nature of the incorporated polymer and network is the same (e.g., typically partially neutralized polyacrylic acid-based) and are shown in different colors to indicate their different connectivity:

[0281]

[0282] The dashed lines in Scheme 2 represent polymer chains. The dashed lines are not intended to show breaks in the chains, but rather to make it easier to distinguish between lines showing the cross-linked polymer network and lines showing sPAA polymers.

[0283] As mentioned above, the conformation and chain size of an s-PAA polymer can be expressed by its radius of gyration. Thus, a sphere of the same radius will approximate the folded chain, which will therefore have a size of 2*Rg(diameter). The radius of gyration of a free chain, including the excluded volume, can be conveniently approximated by the relationship obtained from renormalization group theory (J. des Cloizeaux, G. Jannink, Polymers in Solution: Their Modelling and Structure, Oxford Univ. Press: Clarendon (1990)) and (2):

[0284]

[0285] Here the value N is the average number of monomer units (in this case partially neutralized acrylic acid). It can be determined from the weight average molecular weight M of the polymer chain. w The average molecular weight of the partially neutralized acrylic acid monomer is calculated, where the neutralization degree of acrylic acid is 68% mol, so M m ≈87g / mol:

[0286]

[0287] Substituting (18) into (17) gives the estimated R of the incorporated s-PAA polymer g The easy way:

[0288]

[0289] 68% mole of acrylic acid neutralization produces M mThe average monomer molecular weight is ≈87 g / mol and the value of b is about 0.27 nm. Therefore, the R of all incorporated s-PAA polymers can be easily calculated. g value, and compared with R when xL=20g / g xl Compare distances, etc.

[0290] The average or effective molecular weight of the monomers of the partially neutralized acrylic acid-based SAP material can be calculated from the molar weight of the acrylic acid monomers. The soluble PAA polymer will have the same degree of neutralization as the remaining SAP material because the counterions such as Na + The effective molar weight of the s-PAA polymer monomer at a given degree of neutralization (DN, % mol) will be the molar weight of the pure acrylic acid monomer (M AA =72.06 g / mol) and the molar weight of sodium acrylate monomer (M NaAA =94.04 g / mol) (see Equation 20). Therefore, at DN = 68% mol, the effective monomer molar weight will be 87.02 g / mol≈87 g / mol

[0291] Equation 20. Determination of the effective molar weight of a PAA monomer MWm unit at a specific DN % mol:

[0292] MW m =DN%·MW NaAA +(100-DN ％ )·MW AA (20)

[0293] Extractable polymers in SAP materials are a major challenge in SAP material technology because they represent polymers that are mobile and not part of the network. Since extractable polymers contain partially neutralized polyacrylic acid chemicals with the same charge, the extractable polymers contribute to capacity through osmotic pressure only when they are within the SAP network structure. Once they leave the network and SAP particles respectively during swelling, the extractable polymers will have a negative impact on capacity. This happens for two reasons. First, by migrating out of the SAP particles, the extractable polymers reduce the active mass of the swellable polymer. Second, the extractable polymers are also charged polymers, increasing the osmotic pressure outside the SAP particles, which further reduces their capacity. It was found that the negative impact on absorption against pressure (AAP) is particularly large, and it is even more sensitive to the osmotic pressure gradient outside and inside the SAP particles. At the same time, in essence, because they are not connected to the network, the extractable polymers do not contribute to the mechanical strength of the SAP material network. Therefore, the extractable polymers negatively affect both the capacity and mechanical strength (related to flow permeability (SFC / UPM)) of the SAP material. As is well known in the art, these two performance parameters are inversely correlated, and therefore extractable polymer is undesirable in SAP materials. Typically, the amount of extractable polymer in commercially relevant SAP materials varies between 4%w and 15%w for surface-crosslinked materials and between 8%w and 17%w for matrix polymer SAPs. Because extractable polymer is inversely correlated with capacity in a trade-off relationship, SAP materials with higher capacity are expected to exhibit higher extractables, and vice versa.

[0294] Example

[0295] Various examples of the present invention as well as comparative examples have been prepared and evaluated.

[0296] The difference of the embodiment of the present invention is that a) the weight average molecular weight M of the s-PAA polymer is w , b) the amount of s-PAA polymer contained in the SAP particles, and c) the source of the s-PAA polymer (different commercially available s-PAA polymers and s-PAA polymers obtained from different SAP particle degradation methods).

[0297] The comparative example is a SAP material in which no s-PAA polymer is added during the preparation of the SAP material, and a SAP material with a relatively low mass average molecular weight M is used. w An embodiment of an s-PAA polymer having a low mass average molecular weight M w The embodiment has a 2*R below 1.0 g With R xl ratio.

[0298] Table 1: Overview of Examples A1 to A7 and Comparative Examples C1 to C8

[0299]

[0300] *) The molecular weights of the s-PAA polymers of Example A6 and Comparative Examples C6 and C8 were not determined by the test method described herein. Instead, the molecular weights are given on the labels of the commercially available s-PAA polymers.

[0301] Table 2: Summary II of Examples A1 to A7 and Comparative Examples C1 to C8

[0302]

[0303]

[0304] 1) The calculations were performed for a loading of 20 g of SAP particles with 0.9%w NaCl in brine per gram of dry SAP material.

[0305] 2) The calculations were performed for a loading of 25 g of SAP particles with 0.9%w NaCl in brine per gram of dry SAP material.

[0306] Preparation of base polymer BP C1 of Comparative Example C1 and Comparative Example C2:

[0307] A 20,000 mL resin kettle (equipped with a four-necked glass stopper sealed with a septum, suitable for accommodating a thermometer and a syringe needle) was charged with approximately 5097.0 g of ice (approximately 50% of the total ice volume: 9676.1 g of ice prepared from deionized water). A magnetic stirrer capable of mixing the entire contents (when liquid) was added and stirring was initiated.

[0308] Take about 200.0 g of deionized water to dissolve 5.181 g of "KPS" (=potassium peroxodisulfate, obtained from Sigma Aldrich) in, for example, a 250 mL glass beaker. Close the container containing the "KPS" solution and set aside.

[0309] Take about 10.0 g of deionized water to dissolve 0.112 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0310] Take 200.0 g of deionized water to dissolve 33.589 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn of about 700 Da, obtained from Sigma Aldrich) in, for example, a glass beaker. Cover the beaker containing the "PEG700-DA" solution with parafilm and set aside.

[0311] The entire amount of 4600.3 g of glacial AA (=acrylic acid) was added to the ice in the resin kettle while continuing to stir.

[0312] A thermometer was inserted and a total of 3472.6 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) and the remaining amount of ice (prepared from deionized water) were subsequently added portionwise, bringing the temperature below 30°C.

[0313] While continuing to stir, add the PEG700-DA solution to the mixture of AA, NaOH solution, and ice at approximately 30°C. Wash the beaker containing the PEG700-DA solution twice with deionized water, using approximately 10% of the volume of the PEG700-DA solution for each wash. Add the wash water from both washes to the stirred mixture.

[0314] Deionized water (the remaining amount required to achieve a total of 11888.3 g (ice + water)) was added to the stirred mixture.

[0315] The resin kettle is then closed and the pressure is released, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar through an 80 cm syringe needle while stirring at approximately 400-600 RPM. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0316] After about 1 hour of argon purging and stirring, the "ASC" solution was added to the reaction mixture at a temperature of about 20° C. via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge. Then, about 0.022 g of a 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and the latter was then added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge.

[0317] After the initiator solutions "KPS" and "ASC" were mixed with the reaction mixture, stirring and argon purging were continued, but the argon needle was held a few centimeters above the liquid. Within 5 minutes of adding the "KPS" solution, the solution characteristically began to become cloudy or a sudden increase in viscosity was observed. The "gel point" was observed and recorded when the stir bar could no longer rotate freely at the bottom of the resin pot and stirring was therefore stopped. The argon purge was continued at a reduced flow rate (0.2 bar).

[0318] The temperature is monitored; typically it rises from about 20° C. to about 80° C. within 60 minutes. Once the temperature begins to drop from the maximum, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0319] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0320] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0321] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, and a rotation speed of 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 10 minutes) into the following particle size fractions with the following yields:

[0322] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield 4500g

[0323] The fractions "fines" and "crude" were discarded and not used further.

[0324] Preparation of Base Polymer BP C3 of Comparative Example C3

[0325] A 20,000 mL resin kettle (equipped with a four-necked glass stopper sealed with a septum, suitable for accommodating a thermometer and a syringe needle) was charged with approximately 4528.9 g of ice (approximately 50% of the total ice volume: 8941.1 g of ice prepared from deionized water). A magnetic stirrer capable of mixing the entire contents (when liquid) was added and stirring was initiated.

[0326] Take about 200.0 g of deionized water to dissolve 5.177 g of "KPS" (=potassium peroxodisulfate, obtained from Sigma Aldrich) in a glass beaker of, for example, 250 mL volume. Close the container containing the "KPS" solution and set aside.

[0327] Take about 10.0 g of deionized water to dissolve 1.124 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0328] Take 200.0 g of deionized water to dissolve 80.44 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn of about 700 Da, obtained from Sigma Aldrich) in, for example, a glass beaker. Cover the beaker containing the "PEG700-DA" solution with parafilm and set aside.

[0329] The entire amount of 4600.0 g of glacial AA (=acrylic acid) was added to the ice in the resin kettle while continuing to stir.

[0330] A thermometer was inserted and a total of 3472.7 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) and the remaining amount of ice (prepared from deionized water) were subsequently added portionwise, bringing the temperature below 30°C.

[0331] While continuing to stir, add the PEG700-DA solution to the mixture of AA, NaOH solution, and ice at approximately 30°C. Wash the beaker containing the PEG700-DA solution twice with deionized water, using approximately 10% of the volume of the PEG700-DA solution for each wash. Add the wash water from both washes to the stirred mixture.

[0332] The remainder of the deionized water required to achieve a total amount of 11838.6 g (ice + water) was added to the stirred mixture.

[0333] The resin kettle is then closed and the pressure is released, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at about 0.4 bar through an 80 cm syringe needle while stirring at about 400°C. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0334] After about 1 hour of argon purging and stirring, the "ASC" solution was added to the reaction mixture at a temperature of about 20° C. via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing the argon purge. Then, about 0.25 g of a 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and the latter was then added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing the argon purge.

[0335] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is pulled a few centimeters above the liquid. Typically, within 2 minutes of adding the "KPS" solution, typically at a temperature of about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. When the stirring rod cannot rotate freely at the bottom of the resin pot and stirring is therefore stopped, the "gel point" is observed and recorded. The argon purge is continued at a reduced flow rate (0.2 bar).

[0336] The temperature is monitored; typically it rises from about 20° C. to about 80° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0337] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0338] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0339] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0340] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 4200g

[0341] The fractions "fines" and "crude" were discarded and not used further.

[0342] Preparation of Base Polymer BP C4 of Comparative Example C4

[0343] A 10,000 mL resin kettle (equipped with a four-necked glass stopper sealed with a septum, suitable for accommodating a thermometer and a syringe needle) was charged with approximately 2258.0 g of ice (approximately 60% of the total ice volume: 3882.7 g of ice prepared from deionized water). A magnetic stirrer capable of mixing the entire contents (when liquid) was added and stirring was initiated.

[0344] Take about 100.0 g of deionized water to dissolve 2.276 g of "KPS" (=potassium peroxodisulfate, obtained from Sigma Aldrich) in, for example, a 250 mL glass beaker. Close the container containing the "KPS" solution and set aside.

[0345] Take about 10.0 g of deionized water to dissolve 0.493 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0346] Take 200.0 g of deionized water to dissolve 16.78 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn of about 700 Da, obtained from Sigma Aldrich) in, for example, a glass beaker. Cover the beaker containing the "PEG700-DA" solution with parafilm and set aside.

[0347] The entire amount of 2020.6 g of glacial AA (=acrylic acid) was added to the ice in the resin kettle while continuing to stir.

[0348] An amount of 799.2 g of an aqueous solution of polyacrylic acid having a concentration of about 35% w PA 110S (BASF) was added to the mixture in the resin kettle while stirring was continued, with a weight average molecular weight Mw of 223 kDa as determined by gel permeation chromatography and reported by size exclusion chromatography (test method as described above).

[0349] A thermometer was inserted and a total of 1736.3 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) and the remaining amount of ice (prepared from deionized water) were subsequently added portionwise, bringing the temperature below 30°C.

[0350] While continuing to stir, add the PEG700-DA solution to the mixture of AA, NaOH solution, and ice at approximately 30°C. Wash the beaker containing the PEG700-DA solution twice with deionized water, using approximately 10% of the volume of the PEG700-DA solution for each wash. Add the wash water from both washes to the stirred mixture.

[0351] Deionized water (the remaining amount required to achieve a total of 5422.6 g (ice + water)) was added to the stirred mixture.

[0352] The resin kettle is then closed and the pressure is released, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar through an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0353] After about 1 hour of argon purging and stirring, the "ASC" solution was added to the reaction mixture at a temperature of about 20° C. via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing the argon purge. Then, about 1.00 g of a 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and the latter was then also added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing the argon purge.

[0354] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is pulled a few centimeters above the liquid. Typically, within 2 minutes of adding the "KPS" solution, typically at a temperature of about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. When the stirring rod cannot rotate freely at the bottom of the resin pot and stirring is therefore stopped, the "gel point" is observed and recorded. The argon purge is continued at a reduced flow rate (0.2 bar).

[0355] The temperature is monitored; typically it rises from about 20° C. to about 80° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0356] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0357] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0358] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0359] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 2100g

[0360] The fractions "fines" and "crude" were discarded and not used further.

[0361] Preparation of base polymer BP C5 of comparative example C5

[0362] A 10,000 mL resin kettle (equipped with a four-necked glass stopper sealed with a septum, suitable for accommodating a thermometer and a syringe needle) was charged with approximately 2536.1 g of ice (approximately 60% of the total ice volume: 3050.3 g of ice prepared from deionized water). A magnetic stirrer capable of mixing the entire contents (when liquid) was added and stirring was initiated.

[0363] Take about 100.0 g of deionized water to dissolve 2.599 g of "KPS" (=potassium peroxodisulfate, from Sigma Aldrich) in a glass beaker of, for example, 250 mL volume. Close the container containing the "KPS" solution and set aside.

[0364] Take about 10.0 g of deionized water to dissolve 0.566 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0365] Take 200.0 g of deionized water to dissolve 16.76 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn of about 700 Da, from Sigma Aldrich) in, for example, a glass beaker. Cover the beaker with the "PEG700-DA" solution with parafilm and set aside.

[0366] The entire amount of 2300.1 g of glacial AA (=acrylic acid) was added to the ice in the resin kettle while continuing to stir.

[0367] An amount of 908.7 g of an aqueous solution of polyacrylic acid having a concentration of about 35% w PA 110S (BASF) was added to the mixture in the resin kettle while stirring was continued, with a weight average molecular weight Mw of 223 kDa as determined by gel permeation chromatography and reported by size exclusion chromatography (test method as described above).

[0368] A thermometer was inserted and a total of 1975.4 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) and the remaining amount of ice (prepared from deionized water) were subsequently added portionwise, bringing the temperature below 30°C.

[0369] While continuing to stir, add the PEG700-DA solution to the mixture of AA, NaOH solution, and ice at approximately 30°C. Wash the beaker containing the PEG700-DA solution twice with deionized water, using approximately 10% of the volume of the PEG700-DA solution for each wash. Add the wash water from both washes to the stirred mixture.

[0370] Deionized water (the remaining amount needed to achieve a total amount of 4795.0 g (ice + water)) was added to the stirred mixture.

[0371] The resin kettle is then closed and the pressure is released, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar through an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0372] After about 1 hour of argon purging and stirring, the "ASC" solution was added to the reaction mixture at a temperature of about 20° C. via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing the argon purge. Then, about 1.90 g of a 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and the latter was then also added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing the argon purge.

[0373] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is pulled a few centimeters above the liquid. Typically, within 2 minutes of adding the "KPS" solution, typically at a temperature of about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. When the stirring rod cannot rotate freely at the bottom of the resin pot and stirring is therefore stopped, the "gel point" is observed and recorded. The argon purge is continued at a reduced flow rate (0.2 bar).

[0374] The temperature is monitored; typically it rises from about 20° C. to about 80° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0375] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0376] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0377] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0378] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 2100g

[0379] The fractions "fines" and "crude" were discarded and not used further.

[0380] Preparation of base polymer BP C6 of comparative example C6

[0381] A 10,000 mL resin kettle (equipped with a four-necked glass stopper sealed with a septum, suitable for accommodating a thermometer and a syringe needle) was charged with approximately 2392.1 g of ice (approximately 60% of the total ice volume: 3622.5 g of ice prepared from deionized water). A magnetic stirrer capable of mixing the entire contents (when liquid) was added and stirring was initiated.

[0382] Take about 100.0 g of deionized water to dissolve 2.296 g of "KPS" (=potassium peroxodisulfate, obtained from Sigma Aldrich) in, for example, a 250 mL glass beaker. Close the container containing the "KPS" solution and set aside.

[0383] Take about 10.0 g of deionized water to dissolve 0.492 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0384] Take 200.0 g of deionized water to dissolve 14.71 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn of about 700 Da, obtained from Sigma Aldrich) in, for example, a glass beaker. Cover the beaker containing the "PEG700-DA" solution with parafilm and set aside.

[0385] The entire amount of 2020.3 g of glacial AA (=acrylic acid) was added to the ice in the resin kettle while continuing to stir.

[0386] An amount of 798.5 g of a solution comprising polyacrylic acid in water at a concentration of about 35%w (Sigma Aldrich), with a weight average molecular weight Mw of 100,000 Da as reported by the supplier Sigma Aldrich, was added to the mixture in the resin kettle while continuing to stir.

[0387] A thermometer was inserted and a total of 1735.5 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) and the remaining amount of ice (prepared from deionized water) were subsequently added portionwise, bringing the temperature below 30°C.

[0388] While continuing to stir, add the PEG700-DA solution to the mixture of AA, NaOH solution, and ice at approximately 30°C. Wash the beaker containing the PEG700-DA solution twice with deionized water, using approximately 10% of the volume of the PEG700-DA solution for each wash. Add the wash water from both washes to the stirred mixture.

[0389] Deionized water (the remaining amount required to achieve a total of 5429.5 g (ice + water)) was added to the stirred mixture.

[0390] The resin kettle is then closed and the pressure is released, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar through an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0391] After about 1 hour of argon purging and stirring, the "ASC" solution was added to the reaction mixture at a temperature of about 20° C. via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing the argon purge. Then, about 0.99 g of a 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and the latter was then added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing the argon purge.

[0392] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is pulled a few centimeters above the liquid. Typically, within 2 minutes of adding the "KPS" solution, typically at a temperature of about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. When the stirring rod cannot rotate freely at the bottom of the resin pot and stirring is therefore stopped, the "gel point" is observed and recorded. The argon purge is continued at a reduced flow rate (0.2 bar).

[0393] The temperature is monitored; typically it rises from about 20° C. to about 80° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0394] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0395] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0396] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0397] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 2100g

[0398] The fractions "fines" and "crude" were discarded and not used further.

[0399] Preparation of Base Polymer BP C7 of Comparative Example C7

[0400] A 2,000 ml resin kettle (equipped with a four-necked glass lid closed with a septum, suitable for accommodating a thermometer and syringe needle) was placed in an ice bath containing approximately 1 liter of water, 100 g of sodium chloride, and approximately 200 g of ice, such that the mixture covered approximately half the height of the kettle. Approximately 80.0 g of a solution comprising an aqueous solution of polyacrylic acid (PAA) at a concentration of approximately 35% w / w, with a weight average molecular weight (Mw) of 223 kDa as determined by gel permeation chromatography and size exclusion chromatography (test method as described above) was added to the kettle. Approximately 496.6 g of water was added as ice prepared from DI water, and approximately 497.5 g of DI water was also added to the mixture. A magnetic stirrer capable of mixing the entire contents was added and stirring was initiated.

[0401] When the PAA is completely dispersed, the entire amount of 432.5 g of glacial AA (=acrylic acid) is added to the PAA solution in the resin kettle while continuing to stir.

[0402] Take about 13.6 g of deionized water to dissolve 0.4874 g of "KPS" (=potassium peroxodisulfate, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. Close the container with the "KPS" solution with a plastic snap cap and set aside.

[0403] Take about 10.0 g of deionized water to dissolve 0.0529 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0404] Take about 115 g of deionized water to dissolve 3.15 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn about 700 Da, from Sigma Aldrich) in, for example, a 250 mL glass beaker. Cover the beaker with the "PEG700-DA" solution with parafilm and set aside.

[0405] The remaining 3.60 g of water for a final weight of 1136.3 g was added to the resin kettle and stirring was continued to obtain a homogeneous solution within 1-5 minutes.

[0406] A thermometer was inserted and a total of 347.6 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) were subsequently added portionwise, bringing the temperature below 30°C.

[0407] While continuing to stir, the "PEG700-DA" solution was added to the mixture of AA, NaOH solution and ice at a temperature of about 30°C.

[0408] The resin kettle is then closed, the ice bath below is removed and the pressure is relieved, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar via an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0409] Then, after about a minimum of 10 minutes to 1 hour of argon purging and stirring, about 0.03 g (about 1-2 drops) of a 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and then the latter was added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge. Thereafter, the "ASC" solution was added to the reaction mixture at a temperature of about 20°C via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge.

[0410] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is held a few centimeters above the liquid. Typically, within 3 minutes of the "ASC" solution, typically at about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. The "gel point" is observed and recorded when the stir bar no longer rotates freely at the bottom of the resin pot and stirring is therefore stopped. The argon purge is continued at a reduced flow rate (0.2 bar).

[0411] The temperature is monitored; typically it rises from about 20° C. to about 70° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0412] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0413] The residual moisture content of the dried gel is less than about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0414] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0415] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 350g

[0416] The fractions "fines" and "crude" were discarded and not used further.

[0417] Preparation of base polymer BP C8 of comparative example C8

[0418] A 2,000 ml resin kettle (fitted with a four-necked glass lid sealed with a septum, suitable for accommodating a thermometer and syringe needle) was placed in an ice bath containing approximately 1 liter of water, 100 g of sodium chloride, and approximately 200 g of ice, such that the mixture covered approximately half the kettle's height. Approximately 80.0 g of a solution containing approximately 35% w / w aqueous polyacrylic acid (PAA), with a weight average molecular weight (Mw) of 100,000 Da as reported by the supplier, Sigma Aldrich, was added to the kettle. Approximately 591.4 g of water was added as ice prepared from DI water, and approximately 443.6 g of DI water was also added to the mixture. A magnetic stirrer capable of mixing the entire contents was added and stirring was initiated.

[0419] When the PAA is completely dispersed, the entire amount of 432.5 g of glacial AA (=acrylic acid) is added to the PAA solution in the resin kettle while continuing to stir.

[0420] Take about 20.0 g of deionized water to dissolve 0.4870 g of "KPS" (=potassium peroxodisulfate, from Sigma Aldrich) in, for example, a 40 mL volume glass vial. The container with the "KPS" solution is closed with a plastic snap cap and set aside.

[0421] Take about 10.0 g of deionized water to dissolve 0.053 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0422] Take about 70 g of deionized water to dissolve 3.15 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn about 700 Da, from Sigma Aldrich) in, for example, a 100 mL glass beaker. Cover the beaker with the "PEG700-DA" solution with parafilm and set aside.

[0423] The remaining water, to a final weight of 1136.3 g, was added to the resin kettle and stirring was continued to obtain a homogeneous solution within 1-5 minutes.

[0424] A thermometer was inserted and a total of 347.5 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) were subsequently added portionwise, bringing the temperature below 30°C.

[0425] While continuing to stir, the "PEG700-DA" solution was added to the mixture of AA, NaOH solution and ice at a temperature of about 30°C.

[0426] The resin kettle is then closed, the ice bath below is removed and the pressure is relieved, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar via an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0427] Then, after about 1 hour of argon purging and stirring, about 0.026 g (about 1-2 drops) of a 1% w aqueous hydrogen peroxide solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and then the latter was added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge. Thereafter, the "ASC" solution was added to the reaction mixture at a temperature of about 20° C. via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge.

[0428] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is held a few centimeters above the liquid. Typically, within 3 minutes of adding the "ASC" solution, typically at about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. The "gel point" is observed and recorded when the stir bar no longer rotates freely at the bottom of the resin pot and stirring is therefore stopped. Argon purging is continued at a reduced flow rate (0.2 bar).

[0429] The temperature is monitored; typically it rises from about 20° C. to about 70° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0430] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0431] The residual moisture content of the dried gel is less than about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0432] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0433] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 350g

[0434] The fractions "fines" and "crude" were discarded and not used further.

[0435] Preparation of base polymer BP A1 of Example A1

[0436] A 2,000 ml resin kettle (equipped with a four-necked glass lid closed with a septum, suitable for accommodating a thermometer and a syringe needle) was placed in an ice bath containing about 1 liter of water, 100 g of sodium chloride, and about 200 g of ice, so that the mixture covered about half the height of the resin kettle. About 1017.0 g of a solution containing about 5.5% w aqueous polyacrylic acid (PAA) with a viscosity average molecular weight Mv of 450,000 Da reported by the supplier Sigma Aldrich was charged to the resin kettle. The 5.5% w aqueous solution was prepared by

[0437] 110.0 g of dry PAA polymer (Sigma-Aldrich) with a reported viscosity average molar weight Mv of 450,000 Da was mixed into 1890.0 g of DI water in a 3 L glass beaker and stirred overnight to prepare a stock solution earlier. A magnetic stirrer capable of mixing the entire contents (when liquid) was added and stirring was started.

[0438] The entire amount of 404.4 g of glacial AA (=acrylic acid) was added to the PAA solution in the resin kettle while continuing to stir.

[0439] Take about 20.0 g of deionized water to dissolve 0.444 g of "KPS" (=potassium peroxodisulfate, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "KPS" solution is closed with a plastic snap cap and set aside.

[0440] Take about 10.0 g of deionized water to dissolve 0.015 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0441] Take about 30 g of deionized water to dissolve 2.974 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn about 700 Da, from Sigma Aldrich) in, for example, a 50 mL glass beaker. Cover the beaker with the "PEG700-DA" solution with parafilm and set aside.

[0442] The remaining amount of water to a final weight of 232.2 g was added to the resin kettle and stirring was continued to obtain a homogeneous solution within 1-5 minutes.

[0443] A thermometer was inserted and a total of 345.9 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) were subsequently added portionwise, bringing the temperature below 30°C.

[0444] While continuing to stir, the "PEG700-DA" solution was added to the mixture of AA, NaOH solution and ice at a temperature of about 30°C.

[0445] The resin kettle is then closed, the ice bath below is removed and the pressure is relieved, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar via an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0446] Then, after about a minimum of 10 minutes to 1 hour of argon purging and stirring, about 0.005 g (about 1 drop) of a 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and then the latter was added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing the argon purge. Thereafter, the "ASC" solution was added to the reaction mixture at a temperature of about 20°C via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing the argon purge.

[0447] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is held a few centimeters above the liquid. Typically, within 3 minutes of adding the "ASC" solution, typically at about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. The "gel point" is observed and recorded when the stir bar no longer rotates freely at the bottom of the resin pot and stirring is therefore stopped. Argon purging is continued at a reduced flow rate (0.2 bar).

[0448] The temperature is monitored; typically it rises from about 20° C. to about 70° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0449] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0450] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0451] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0452]

[0453]

[0454] The fractions "fines" and "crude" were discarded and not used further.

[0455] Preparation of base polymer BP A2 of Example A2

[0456] A 2,000 ml resin kettle (fitted with a four-necked glass lid closed with a septum, suitable for accommodating a thermometer and syringe needle) was placed in an ice bath containing approximately 1 liter of water, 100 g of sodium chloride, and approximately 200 g of ice, so that the mixture covered approximately half the kettle's height. Approximately 1118.0 g of a solution containing approximately 2.5% w aqueous polyacrylic acid (PAA) with a reported viscosity-average molecular weight (Mv) of 450,000 Da, as reported by the supplier, Sigma-Aldrich, was charged to the kettle. The 2.5% w aqueous solution was prepared earlier as a stock solution by mixing 50.0 g of dry PAA polymer (Sigma-Aldrich), with a reported viscosity-average molecular weight (Mv) of 450,000 Da, into 1950.0 g of DI water in a 3 L glass beaker and stirring overnight. A magnetic stirrer capable of mixing the entire contents (when liquid) was added and stirring was initiated.

[0457] The entire amount of 431.9 g glacial AA (=acrylic acid) was added to the PAA solution in the resin kettle while continuing to stir.

[0458] Take about 20.0 g of deionized water to dissolve 0.487 g of "KPS" (=potassium peroxodisulfate, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "KPS" solution is closed with a plastic snap cap and set aside.

[0459] Take about 10.0 g of deionized water to dissolve 0.011 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0460] Take about 30 g of deionized water to dissolve 3.14 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn about 700 Da, from Sigma Aldrich) in, for example, a 50 mL glass beaker. Cover the beaker with the "PEG700-DA" solution with parafilm and set aside.

[0461] The remaining amount of water to a final weight of 99.1 g was added to the resin kettle and stirring was continued to obtain a homogeneous solution within 1-5 minutes.

[0462] A thermometer was inserted and a total of 347.1 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) were subsequently added portionwise, bringing the temperature below 30°C.

[0463] While continuing to stir, the "PEG700-DA" solution was added to the mixture of AA, NaOH solution and ice at a temperature of about 30°C.

[0464] The resin kettle is then closed, the ice bath below is removed and the pressure is relieved, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar via an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0465] Then, after about a minimum of 10 minutes to 1 hour of argon purging and stirring, about 0.017 g (about 1 drop) of a 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and then the latter was added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge. Thereafter, the "ASC" solution was added to the reaction mixture at a temperature of about 20°C via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge.

[0466] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is held a few centimeters above the liquid. Typically, within 3 minutes of the "ASC" solution, typically at about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. The "gel point" is observed and recorded when the stir bar no longer rotates freely at the bottom of the resin pot and stirring is therefore stopped. The argon purge is continued at a reduced flow rate (0.2 bar).

[0467] The temperature is monitored; typically it rises from about 20° C. to about 70° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0468] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0469] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0470] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0471] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 350g

[0472] The fractions "fines" and "crude" were discarded and not used further.

[0473] Procedure for obtaining the PAA used in Example A3 (=PAA A3) from the degradation of pre-existing SAP material: Persulfate Salt-mediated degradation of pre-existing SAP materials

[0474] Pre-existing SAP materials :

[0475] The pre-existing SAP material used for degradation (in the form of pre-existing SAP particles) is commercially available in Pampers Baby Dry sold in Germany in 2020. The same pre-existing SAP material was used in the degradation procedure to obtain PAA A4 and PAA A5 as described below. Generally, any other commercially available acrylic-based pre-existing SAP material (in the form of pre-existing SAP particles) is suitable for the degradation method described below.

[0476] The acrylic-based pre-existing SAP material had a capacity (CRC) of 27.6 g / g and a moisture content of 0.4% (see UPM test method for a description of how to determine the moisture content). The D50 average particle size measured according to ISO method 13322-2 was 398 μm (particle size distribution PSD of 63 μm to 710 μm). The absorption against pressure (AAP) of the pre-existing SAP material was 25.5 g / g, as determined by EDANA method NWSP 242.0.R2 (15). In a deviation from EDANA NWSP 242.0.R2 (15), a pressure of 0.7 psi was applied (whereas the EDANA method specifies a pressure of only 0.3 psi).

[0477] The deionized water used below was Millipore Q. The conductivity was measured using a laboratory conductivity meter COND 70 instrument (without CELL, #50010522, equipped with Cell VPT51-01 C=0.1, obtained from XS Instruments) or via LF 320 / Set (#300243, equipped with The conductivity was measured with WTW (TESTEL® 325, obtained from WTW) and was <160 μS / cm at 0° C. Therefore, similar equipment for measuring conductivity can be used.

[0478] Unless otherwise stated, experimental procedures were performed in a climate-conditioned room under standard conditions of 23°C ± 2°C temperature and 45% ± 10% relative humidity.

[0479] program :

[0480] 1. Prepare 2100 g of KPS by completely dissolving 3.003 g of dry KPS (Sigma-Aldrich, >= 99.0% purity, stock number 216224-500G) in 2097.0 g of deionized water by stirring.

[0481] A 0.143% w solution of potassium persulfate (KPS) in deionized water is placed in, for example, a 3 L glass beaker equipped with a stir bar of appropriate size so that the entire volume of the solution can be thoroughly mixed using magnetic stirring at approximately 400 rpm. Complete dissolution of the KPS salt is observed when no visible salt crystals remain in the solution.

[0482] 2. A 300.0 g quantity of dry pre-existing SAP material was weighed onto a balance into a 500 mL glass beaker and placed into a 2.5 L glass reactor for AGM synthesis (obtained from Normag GmbH). Magnetic stirring was initiated at 500 rpm, wherein 2100 g of a 0.143% w KPS stock solution was then quickly added to the reactor along with the pre-existing SAP material to achieve a final x loading of approximately 7 g / g of KPS solution. After swelling, the viscosity of the mixture of pre-existing SAP material and KPS solution increased until stirring was no longer possible. The stirring bar was removed from the bottom of the reactor.

[0483] 3. Close the reactor with a cap (standard cap with four openings). Place a syringe into the opening with the rubber stopper. Preheat a circulating oven (Binder FED720 model from Binder GmbH) to 100°C. When the set temperature is reached, place the closed reactor in the oven for 9 hours.

[0484] 4. Remove the reactor from the oven and cool to below approximately 40°C. The mixture obtained from the reaction vessel, containing the solution and some soft, swollen gel particles, is filtered through a 500 μm mesh (240 mm, obtained from Retsch GmbH) metal sieve placed on top of a 2 L plastic beaker. The apparatus is placed in a fume hood and left for 3 hours to allow the liquid to enter the beaker. Mix the sample with a plastic spoon to increase the filtration rate. The yield after filtration is 1280 g of a clear, light yellow solution with a viscosity similar to that of sunflower oil. The solution is transferred to a 2 L plastic bottle.

[0485] 5. Measure an aliquot of 2.0644 g of the filtered clear solution into a pre-weighed 20 mL glass vial (without a snap cap) via a 5 mL plastic syringe. The 20 ml vial with the clear solution was then placed in a vacuum oven (Heraeus Vacutherm, Thermo Scientific) at 40° C. and a pressure of 5 to 50 mbar. TM) for 4 hours to ensure significant evaporation of the water. The dried polymer residue weighed 0.28 g, which was used to calculate the solids content of the filtered PAA solution to be 13.6% w. This value, multiplied by the 1280 g total solution collected after filtration, yielded a total of 175.36 g of soluble, dry PAA polymer obtained as a SAP degradation product. Dividing this latter value by the starting 300 g SAP, the yield of the degradation reaction was calculated to be approximately 58.4% w.

[0486] Thus, the yield represents the ratio of the amount of extracted soluble polymer as a product of the SAP degradation solution to the amount of the initially dried pre-existing SAP material. Considering that the pre-existing SAP material is a cross-linked network of polyacrylic acid, the extracted soluble polymer is substantially soluble polyacrylic acid.

[0487] Preparation of the base polymer BP A3 containing PAA A3 of Example A3

[0488] A 2,000 ml resin kettle (fitted with a four-necked glass lid sealed with a septum, suitable for accommodating a thermometer and syringe needle) was placed in an ice bath containing approximately 1 liter of water, 100 g of sodium chloride, and approximately 200 g of ice, so that the mixture covered approximately half the kettle's height. Approximately 811.0 g of a solution containing an approximately 6.67% w aqueous solution of polyacrylic acid PAA A3, obtained as described above, with a weight-average molecular weight (Mw) of 517,500 Da as determined by gel permeation chromatography (as described above) was added to the kettle. A 6.67% w aqueous solution of PAA A3 was prepared as a stock solution by diluting the 13.6% w solution with an appropriate amount of DI water and stirring overnight. A magnetic stirrer capable of mixing the entire contents (when liquid) was added to the kettle and stirring was initiated.

[0489] The entire amount of 405.9 g of glacial AA (=acrylic acid) was added to the PAA solution in the resin kettle while continuing to stir.

[0490] Take about 20.0 g of deionized water to dissolve 0.455 g of "KPS" (=potassium peroxodisulfate, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. Close the container with the "KPS" solution with a plastic snap cap and set aside.

[0491] Take about 10.0 g of deionized water to dissolve 0.011 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0492] Take about 30 g of deionized water to dissolve 2.95 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn about 700 Da, from Sigma Aldrich) in, for example, a 50 mL glass beaker. Cover the beaker with the "PEG700-DA" solution with parafilm and set aside.

[0493] The remaining amount of water to a final weight of 497.7 g was added to the resin kettle and stirring was continued to obtain a homogeneous solution within 1-5 minutes.

[0494] A thermometer was inserted and a total of 281.8 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) were subsequently added portionwise, bringing the temperature below 30°C.

[0495] While continuing to stir, the "PEG700-DA" solution was added to the mixture of AA, NaOH solution and ice at a temperature of about 30°C.

[0496] The resin kettle is then closed, the ice bath below is removed and the pressure is relieved, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar via an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0497] Then, after about a minimum of 10 minutes or a maximum of 1 hour of argon purging and stirring, about 0.025 g (about 1-2 drops) of a 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and then the latter was added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge. Thereafter, the "ASC" solution was added to the reaction mixture at a temperature of about 20°C via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge.

[0498] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is held a few centimeters above the liquid. Typically, within 4 minutes of adding the "ASC" solution, typically at about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. The "gel point" is observed and recorded when the stir bar no longer rotates freely at the bottom of the resin pot and stirring is therefore stopped. Argon purging is continued at a reduced flow rate (0.2 bar).

[0499] The temperature is monitored; typically it rises from about 20° C. to about 70° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0500] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0501] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0502] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0503] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 350g

[0504] The fractions "fines" and "crude" were discarded and not used further.

[0505] Procedure for obtaining the PAA used in Example A4 (=PAA A4) from the degradation of pre-existing SAP material: UV Thread-mediated degradation of pre-existing SAP materials

[0506] Pre-existing SAP material for degradation (in the form of pre-existing SAP particles) is commercially available in Pampers Baby Dry sold in Germany in 2020.

[0507] The pre-existing SAP material was mixed with RO (reverse osmosis) water in a Quadro mixer to produce a feed stream (in gel form) having 2.5 wt% SAP and 97.5 wt% RO water. The starting viscosity of the gel was about 840 Pa.s. Approximately 140 mL of the feed stream was loaded into a syringe and fed to a Fusion UV curing system (FUSION UV SYSTEMS, Inc., Maryland, USA; Hg lamp (H-bulb) with a UV curing rate of 6 mL / min using a syringe pump (New Era Pump Systems, Inc., Farmdale, NY; Model NE-1000 Single Syringe Pump) through a 6 mm outer diameter (OD) (3.68 mm inner diameter (ID)) quartz tube. The feed stream was exposed to UV radiation at 300 W / in. and 2.74 W / cm² (measured using a UV lamp #20082105 A / B / C / V (EIT, Inc.; Sterling, VA). The UV lamp was positioned perpendicular to the quartz tube. The length of the quartz tube exposed to UV radiation was estimated to be 15 cm, with the longitudinal axis of the tube approximately 8 mm above the focal point of the UV lamp. The residence time of the feed stream in the irradiation zone was 16 s, and the UV radiation energy was calculated to be 1.4 MJ / kg SAP. The viscosity of the product stream was measured using a cup and swing fixture in steady-state mode and was found to be 155 mPa.s at 4 s².

[0508] Preparation of the base polymer BP A4 containing PAA A4 of Example A4

[0509] A 2,000 ml resin kettle (equipped with a four-necked glass lid closed with a septum, suitable for accommodating a thermometer and syringe needle) was placed in an ice bath containing approximately 1 liter of water, 100 g of sodium chloride, and approximately 200 g of ice, such that the mixture covered approximately half the kettle's height. Approximately 1043.1 g of a solution comprising an approximately 2.68% w aqueous solution of PAA-A4 obtained as described above, having a weight-average molecular weight (Mw) of 1,080 kDa as determined by gel permeation chromatography (testing method as described above), was added to the kettle. A magnetic stirrer capable of mixing the entire contents (when liquid) was added to the kettle and stirring was initiated.

[0510] The entire amount of 432.1 g of glacial AA (=acrylic acid) was added to the PAA solution in the resin kettle while continuing to stir.

[0511] Take about 20.0 g of deionized water to dissolve 0.483 g of "KPS" (=potassium peroxodisulfate, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "KPS" solution is closed with a plastic snap cap and set aside.

[0512] Take about 10.0 g of deionized water to dissolve 0.011 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0513] Take about 30 g of deionized water to dissolve 3.22 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn about 700 Da, from Sigma Aldrich) in, for example, a 50 mL glass beaker. Cover the beaker with the "PEG700-DA" solution with parafilm and set aside.

[0514] The remaining amount of water to a final weight of 174.0 g was added to the resin kettle and stirring was continued to obtain a homogeneous solution within 1-5 minutes.

[0515] A thermometer was inserted and a total of 347.2 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) were subsequently added portionwise, bringing the temperature below 30°C.

[0516] While continuing to stir, the "PEG700-DA" solution was added to the mixture of AA, NaOH solution and ice at a temperature of about 30°C.

[0517] The resin kettle is then closed, the ice bath below is removed and the pressure is relieved, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar via an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0518] Then, after about 1 hour of argon purging and stirring, about 0.020 g (about 1-2 drops) of a 1% w aqueous hydrogen peroxide solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and then the latter was added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge. Thereafter, the "ASC" solution was added to the reaction mixture at a temperature of about 20° C. via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge.

[0519] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is held a few centimeters above the liquid. Typically, within 4 minutes of adding the "ASC" solution, typically at about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. The "gel point" is observed and recorded when the stir bar no longer rotates freely at the bottom of the resin pot and stirring is therefore stopped. Argon purging is continued at a reduced flow rate (0.2 bar).

[0520] The temperature is monitored; typically it rises from about 20° C. to about 80° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0521] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0522] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0523] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0524] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 350g

[0525] The fractions "fines" and "crude" were discarded and not used further.

[0526] Procedure for obtaining the PAA used in Example A5 (=PAA A5) from the degradation of pre-existing SAP material: Liquid Whistle (LW)-mediated mechanical energy degradation

[0527] Pre-existing SAP material for degradation (in the form of pre-existing SAP particles) is commercially available in Pampers Baby Dry sold in Germany in 2020.

[0528] The pre-existing SAP material was mixed with RO (= reverse osmosis) water in a stirred tank system similar to the EnSight Solutions Likwifier LORSS series equipped with an approximately 20-gallon working capacity tank, a top-mounted waste surface agitator, and a bottom 6-hole / 3-wing rotor-stator high shear impeller to produce a feed stream (in gel form) having 2.5 wt% SAP and 97.5 wt% RO water. The gel had a viscosity of 841 Pa.s. The feed stream was fed into a liquid whistle device (LW; Sonolator Model A; Sonic Corp., Stratford, CT); the oval orifice dimensions were: width 2×0.0375 inches = 1.9 mm, height 2×0.012 inches = 0.6 mm (calculated hydraulic diameter 1.7 mm), segment length 1 mm, and volume V = π×(width)×(height)×(segment length) / 4 = 0.9 mm 3 ) (The oval orifice has a diameter of approximately 1.3 mm 2 The LW device was operated at a flow rate of about 8 L / min and a pressure of about 4,500 psi (about 310 bar), with the product stream being recycled back into the stirred tank system. The tank volume was passed through the LW device about 8 times, representing a total residence time in the LW chamber area of ​​about 40 ms (about 5 ms per pass). The energy density achieved by the mixing device was about 62 MJ / m 3 (approximately 2.48 MJ / kg SAP).

[0529] The actual final solids content of the product was determined to be 2.73 wt% by placing 3.00 g of product in a pre-weighed glass vial of 40 mL volume and placing the vial, uncovered, in a vacuum oven.

[0530] Preparation of the base polymer BP A5 containing PAA A5 of Example A5

[0531] A 2,000 ml resin kettle (equipped with a four-necked glass lid closed with a septum, suitable for accommodating a thermometer and a syringe needle) was placed in an ice bath containing about 1 liter of water, 100 g of sodium chloride, and about 200 g of ice, so that the mixture covered about half the height of the resin kettle. About 1024.0 g of a solution comprising an aqueous solution of PAA A5 obtained as described above with a concentration of about 2.73% w was charged to the resin kettle, wherein the mixture was stirred for 1 minute. Gel permeation chromatographyThe weight average molecular weight Mw was determined to be 418 kDa (test method as described above). A magnetic stirrer capable of mixing the entire contents (when liquid) was added to the resin kettle and stirring was started.

[0532] The entire amount of 432.1 g of glacial AA (=acrylic acid) was added to the PAA solution in the resin kettle while continuing to stir.

[0533] Take about 20.0 g of deionized water to dissolve 0.484 g of "KPS" (=potassium peroxodisulfate, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "KPS" solution is closed with a plastic snap cap and set aside.

[0534] Take about 10.0 g of deionized water to dissolve 0.012 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0535] Take about 30 g of deionized water to dissolve 3.14 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn about 700 Da, from Sigma Aldrich) in, for example, a 50 mL glass beaker. Cover the beaker with the "PEG700-DA" solution with parafilm and set aside.

[0536] The remaining amount of water to a final weight of 193.0 g was added to the resin kettle and stirring was continued to obtain a homogeneous solution within 1-5 minutes.

[0537] A thermometer was inserted and a total of 347.4 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) were subsequently added portionwise, bringing the temperature below 30°C.

[0538] While continuing to stir, the "PEG700-DA" solution was added to the mixture of AA, NaOH solution and ice at a temperature of about 30°C.

[0539] The resin kettle is then closed, the ice bath below is removed and the pressure is relieved, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar via an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0540] Then, after about 1 hour of argon purging and stirring, about 0.025 g (about 1-2 drops) of 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and then the latter was added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge. Thereafter, the "ASC" solution was added to the reaction mixture at a temperature of about 20°C via a plastic funnel temporarily inserted into one of the necks of the resin pot lid while stirring and continuing the argon purge.

[0541] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is held a few centimeters above the liquid. Typically, within 3 minutes of adding the "ASC" solution, typically at about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. The "gel point" is observed and recorded when the stir bar no longer rotates freely at the bottom of the resin pot and stirring is therefore stopped. Argon purging is continued at a reduced flow rate (0.2 bar).

[0542] The temperature is monitored; typically it rises from about 20° C. to about 80° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0543] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0544] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0545] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0546] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 350g

[0547] The fractions "fines" and "crude" were discarded and not used further.

[0548] Preparation of base polymer BP A6 of Example A6

[0549] A 2,000 ml resin kettle (fitted with a four-necked glass lid closed with a septum, suitable for accommodating a thermometer and syringe needle) was placed in an ice bath containing approximately 1 liter of water, 100 g of sodium chloride, and approximately 200 g of ice, so that the mixture covered approximately half the kettle's height. Approximately 447.0 g of a solution containing approximately 2.5% w aqueous polyacrylic acid (PAA) with a reported weight average molecular weight (Mw) of 1,000 kDa, as reported by the supplier, Sigma-Aldrich, was charged to the kettle. A 2.5% w aqueous solution was prepared earlier as a stock solution by mixing 50.0 g of dry PAA polymer (Sigma-Aldrich), with a reported Mw of approximately 1,000 kDa, into 1950.0 g of DI water in a 3 L glass beaker and stirring overnight. A magnetic stirrer capable of mixing the entire contents (when liquid) was added and stirring was initiated.

[0550] The entire amount of 218.3 g of glacial AA (=acrylic acid) was added to the PAA solution in the resin kettle while continuing to stir.

[0551] Take about 20.0 g of deionized water to dissolve 0.246 g of "KPS" (=potassium peroxodisulfate, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "KPS" solution is closed with a plastic snap cap and set aside.

[0552] Take about 10.0 g of deionized water to dissolve 0.055 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0553] Take about 30 g of deionized water to dissolve 1.59 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn about 700 Da, from Sigma Aldrich) in, for example, a 50 mL glass beaker. Cover the beaker with the "PEG700-DA" solution with parafilm and set aside.

[0554] The remaining amount of water to a final weight of 159.9 g was added to the resin kettle and stirring was continued to obtain a homogeneous solution within 1-5 minutes.

[0555] A thermometer was inserted and a total of 173.2 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) were subsequently added portionwise, bringing the temperature below 30°C.

[0556] While continuing to stir, the "PEG700-DA" solution was added to the mixture of AA, NaOH solution and ice at a temperature of about 30°C.

[0557] The resin kettle is then closed, the ice bath below is removed and the pressure is relieved, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar via an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0558] After about 30 minutes of argon purging and stirring, about 1.015 g of a 1% w aqueous hydrogen peroxide solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and then the latter was added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while continuing to stir and purge with argon. Thereafter, the "ASC" solution was added to the reaction mixture at a temperature of about 20° C. via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing to purge with argon.

[0559] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is held a few centimeters above the liquid. Typically, within 15 minutes of adding the "ASC" solution, typically at about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. The "gel point" is observed and recorded when the stir bar no longer rotates freely at the bottom of the resin pot and stirring is therefore stopped. Argon purging is continued at a reduced flow rate (0.2 bar).

[0560] The temperature is monitored; typically it rises from about 20° C. to about 70° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 20 hours.

[0561] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0562] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0563] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0564] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 200g

[0565] The fractions "fines" and "crude" were discarded and not used further.

[0566] Preparation of base polymer BP A7 of Example A7

[0567] A 2,000 ml resin kettle (fitted with a four-necked glass lid closed with a septum, suitable for accommodating a thermometer and syringe needle) was placed in an ice bath containing approximately 1 liter of water, 100 g of sodium chloride, and approximately 200 g of ice, so that the mixture covered approximately half the kettle's height. Approximately 1240.8 g of a solution containing aqueous polyacrylic acid (PAA) at a concentration of approximately 9.0% w, with a viscosity-average molecular weight (Mw) reported by the supplier, Sigma-Aldrich, of 450,000 Da, was charged to the kettle. The 9.0% w aqueous solution was prepared earlier as a stock solution by mixing 135 g of dry PAA polymer (Sigma-Aldrich), with a reported Mv of 450,000 Da, into 1365.0 g of DI water in a 3 L glass beaker and stirring overnight. A magnetic stirrer capable of mixing the entire contents (when liquid) was added and stirring was initiated.

[0568] The entire amount of 348.3 g of glacial AA (=acrylic acid) was added to the PAA solution in the resin kettle while continuing to stir.

[0569] Take about 20.0 g of deionized water to dissolve 0.393 g of "KPS" (=potassium peroxodisulfate, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "KPS" solution is closed with a plastic snap cap and set aside.

[0570] Take about 10.0 g of deionized water to dissolve 0.009 g of "ASC" (=ascorbic acid, from Sigma Aldrich) in a glass vial of, for example, 40 mL volume. The container with the "ASC" solution is closed with a plastic snap cap and set aside.

[0571] Take about 25 g of deionized water to dissolve 2.54 g of "PEG700-DA" (= polyethylene glycol diacrylate with Mn about 700 Da, from Sigma Aldrich) in, for example, a 50 mL glass beaker. Cover the beaker with the "PEG700-DA" solution with parafilm and set aside.

[0572] The remaining amount of water to a final weight of 60.3 g was added to the resin kettle and stirring was continued to obtain a homogeneous solution within 5 minutes.

[0573] A thermometer was inserted and a total of 347.3 g of 50%w NaOH (sodium hydroxide) solution (for analysis, from Merck KGaA) were subsequently added portionwise, bringing the temperature below 30°C.

[0574] While continuing to stir, the "PEG700-DA" solution was added to the mixture of AA, NaOH solution and ice at a temperature of about 30°C.

[0575] The resin kettle is then closed, the ice bath below is removed and the pressure is relieved, for example, by piercing the septum with two syringe needles. The solution is then vigorously purged with argon at approximately 0.4 bar via an 80 cm syringe needle while stirring at approximately 400 rpm. The argon stream is placed close to the stirrer to effectively and quickly remove dissolved oxygen.

[0576] After about 30 minutes of argon purging and stirring, about 0.2 g (about 10 drops) of a 1% w aqueous hydrogen peroxide H2O2 solution (Sigma-Aldrich) was added to the "KPS" solution via a 1 mL plastic pipette, and then the latter was added to the reaction mixture via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while continuing to stir and purge with argon. Thereafter, the "ASC" solution was added to the reaction mixture at a temperature of about 20°C via a plastic funnel temporarily inserted into one of the necks of the resin pot lid, while stirring and continuing to purge with argon.

[0577] After the initiator solutions "KPS" and "ASC" are mixed with the reaction mixture, stirring and argon purging are continued, but the argon needle is held a few centimeters above the liquid. Typically, within 3 minutes of adding the "ASC" solution, typically at about room temperature, the solution characteristically begins to become cloudy or a sudden increase in viscosity is observed. The "gel point" is observed and recorded when the stir bar no longer rotates freely at the bottom of the resin pot and stirring is therefore stopped. Argon purging is continued at a reduced flow rate (0.2 bar).

[0578] The temperature is monitored; typically it rises from about 20° C. to about 70° C. within 60 minutes. Once the temperature begins to drop from the maximum value, the resin kettle is transferred to a circulation oven (e.g., Binder FED 720 from Binder GmbH) and maintained at about 60° C. for about 18 hours.

[0579] The resin kettle of 100mg / ml is cooled to 400 DEG C and is kept in the baking oven for 2 hours.After this, close baking oven and make the resin kettle cool to approximately 2 hours simultaneously and remain in the baking oven.After this, take out gel, and manually fragment or be cut into smaller piece with scissors.Gel is ground with grinder (X70G from Scharfen Slicing Machines GmbH, it has Unger R70 plate system: 3 band diameters are the pre-cutter kidney-shaped plates of the straight hole of 17mm) grind, be placed on perforated stainless steel dish (aperture 4.8mm, 50cm * 50cm, 0.55mm caliper, 50% open area, from RS; The maximum height of gel before drying: approximately 3cm) and transfer in approximately 120 ℃ circulating oven (from the Binder FED720 of Binder GmbH) for approximately 20 hours.

[0580] The residual moisture content of the dried gel was about 3% by weight (see UPM test method for a description of how to determine the moisture content).

[0581] The dry gel was then ground using a centrifugal mill (Retsch ZM 200 from Retsch GmbH with a vibrating feeder DR 100 (setting 50-60), interchangeable sieves with a 1.5 mm opening setting, at 8000 rpm). The ground polymer was then sieved via a sieving machine (AS 400 control from Retsch with sieve DIN / ISO 3310-1, at about 250 rpm for about 5-10 minutes) into the following particle size fractions with the following yields:

[0582] powder Collected fractions Crude product Screening and classification <150μm 150-710μm >710μm Yield About 350g

[0583] The fractions "fines" and "crude" were discarded and not used further.

[0584] Surface crosslinking treatment of base polymer particles BP A1 to BP A7 and BP C1 to BP C8 (hereinafter referred to as "SXL") to obtain Examples A1 to A7 and Comparative Examples C1 to C8

[0585] equipment List:

[0586] Glassware, one-way pipettes, spatulas, and spoons for preparing solutions and weighing absorbent materials

[0587] Glass beaker: 250ml opening

[0588] Balance: Sartorius or equivalent; accuracy 0.01g

[0589] Analytical balance: Mettler or equivalent; accuracy 0.0001g

[0590] Electric stand mixer: IKA Eurostar power control (range 50 rpm-2000 rpm)

[0591] or equivalent

[0592] ·With stirrer: PTFE Propeller stirrer 4 blades

[0593] Pipette: Eppendorf Multi stream or equivalent

[0594] Aluminum foil for covering

[0595] Circulation oven: Binder FD 240 or equivalent

[0596] Moisture measuring device: Halogen Moisture Balance Mettler or equivalent

[0597] Screening machine: Retch AS200control "g" or equivalent

[0598] With screen: stainless steel: DIN / ISO 3310-1

[0599] solution Preparation ：

[0600] Aluminum lactate solution

[0601] A 1 kg 15 w% aluminum lactate solution in deionized water (Millipore Q, conductivity <1.6 μS / cm) was prepared by adding 850 g deionized water to 150 g aluminum lactate.

[0602] Surface cross-linking solution (SXL solution) (see Table A):

[0603] The Denacol concentrations used were prepared according to Table 3 and each was contained in a snap-top jar of approximately 50 ml volume.

[0604] To prepare solutions, remove the Denacol bottle or container (approximately 1 L) from the refrigerator and allow to thermally equilibrate for approximately 30 minutes before preparing solutions.

[0605] The solution was prepared as follows :

[0606] For a given example, different corresponding concentrations of Denacol EX-810, DN-810ex Nagase Co. Ltd) were prepared by adding the amounts shown in Table 3 to snap-top plastic jars, which were then filled to 20 g with 1,2-propylene glycol (Merck KGaA).

[0607] Table 3 :

[0608]

[0609] Implementation of the SXL process:

[0610] Each of the dry base polymer particles BP A1 to BP A7 and BP C1 to BP C8 was weighed to 20-30 g and recorded to ±0.1 g and placed in a separate 250 ml glass beaker so that the filling height was ≤25% of the total height. The exact amounts are shown in Table 5.

[0611] The matrix polymer particles were mixed in a beaker using a PTFE stirrer at 600 + / - 50 rpm. The stirrer only touched the bottom of the beaker. The matrix polymer particles needed to be stirred until a good fluidization of the bed was achieved.

[0612] The required amount of solution was added using an Eppendorf pipette, proceeding step by step as described below, and the actual amounts are given in Table B. (Speed ​​setting of the Eppendorf pipette: medium speed)

[0613] Step 1:

[0614] Add a certain amount of aluminum lactate solution to the center of the stirring beaker. Then, increase the stirring speed to 2000 + / - 50 rpm. Stir for about 15 seconds and continue with step 2. If necessary, cover the beaker with aluminum foil, for example, to prevent the material from popping out.

[0615] Step 2:

[0616] Add a certain amount of SXL solution to the center of the stirring tube. Stir for about 15 seconds and continue with step 3.

[0617] Step 3:

[0618] A certain amount of deionized water (3% by weight based on sample weight) is added to the center of the stirring. Stir for about 15 seconds. After the agitator stops, the material is transferred to a heat-resistant wide-mouthed glass bottle (such as a crystallizing dish) and evenly distributed. Only loose material is taken out, and the wall of the beaker leaves a strongly stacked material. Remove the loose material by gently tapping on the beaker wall or using a spatula. Avoid scratching. Cover the wide-mouthed glass bottle with aluminum foil and store it in a fume hood at room temperature for about 16h to 18h (recommended overnight), then heat the material in an oven at the required temperature and time (for example, except for the 3h heating time, the surface cross-linked Denacol is warmed up to 120°C from room temperature for 20min).

[0619] After a heating time of 2 h 20 min, the aluminum foil was half-opened and remained like this for the remaining 1 h of heating in order to drive the moisture content below 1 %w.

[0620] After the heating time, the container was removed from the oven and the material was placed in a fume hood to cool to room temperature for approximately 15 min.

[0621] The final polymer was tested for moisture and the results are shown in Table 4.

[0622] Table 4 :

[0623]

[0624]

[0625] Table 5

[0626]

[0627] The amount of Denacol Ex 810 was chosen such that the resulting Examples and Comparative Examples exhibited a CRC above 25 g / g and an EFFC between 23 g / g and 29 g / g (see Table 6).

[0628] Table 6: Properties of Examples A1 to A7 and Comparative Examples C1 to C8

[0629]

[0630]

[0631] 1) The value of the matrix polymer particles

[0632] 2) The value of SAP particles after surface cross-linking

[0633] Examples A1 to A7 all have an average gyration diameter 2*R much higher than 1.1 g The average distance R between adjacent cross-linking points xl Comparative Examples C4 to C8 have an average gyration diameter 2*R much lower than 1.0. g The average distance R between adjacent cross-linking points xl (Comparative Examples C1 to C3 did not contain any s-PAA polymer, so this ratio is not applicable.) As reflected in the results, when comparing Examples and Comparative Examples having similar amounts of s-PAA polymer (i.e., similar percentages of s-PAA polymer based on the total weight of the SAP particles), SAP particles having a ratio higher than 1.1 have improved performance properties, particularly an improved extractables to capacity (CRC) ratio, compared to the Comparative Examples.

[0634] As can be seen from the results, the extractables to capacity (CRC) ratios of Examples A1 to A6 are as good as or even better than the results of Comparative Examples C1 to C3 without the addition of s-PAA polymer.

[0635] Despite containing a relatively high amount of s-PAA polymer (20 wt%), Example A7 exhibits good performance characteristics. For the base polymer, i.e., before surface crosslinking, the amount of extractables is 16.6%. The amount of extractables generally decreases after surface crosslinking (due to a higher crosslink density between polymer chains on the particle surface), so for Example A7 after surface crosslinking, the amount of extractables is even lower than 16.6%.

[0636] Comparative Examples C4 to C6 exhibit high extractables to capacity (CRC) ratios. Comparative Examples C7 and C8 have ratios similar to those of Example A7. However, Example A7 has an s-PAA polymer content of 20 wt%, while Comparative Examples C7 and C8 only have an s-PAA polymer content of 5 wt%.

[0637] Comparative Examples C5 and C6 differ from Comparative Examples C7 and C8 only in the amount of s-PAA polymer. The results show that increasing the amount of s-PAA polymer from 5 wt% (C7 and C8) to 10 wt% (C5 and C6) has a significant negative impact on the extractables to capacity (CRC) ratio. In contrast, the use of s-PAA polymers with relatively high weight-average molecular weights in Examples A1 to A7 significantly improves the extractables to capacity (CRC) ratio, resulting in significantly lower amounts of extractables relative to capacity.

[0638] The dimensions and values ​​disclosed herein are not to be construed as being strictly limited to the exact numerical values ​​recited. Instead, unless otherwise indicated, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm." Furthermore, every numerical range given throughout this specification includes every narrower numerical range falling within such broader numerical range.

[0639] Unless expressly excluded or otherwise limited, each document cited herein, including any cross-referenced or related patent or application, is hereby incorporated by reference in its entirety. The citation of any document is not an admission that it is prior art with respect to any of the present inventions disclosed or claimed herein, or that it, by itself or in combination with any one or more of the references, proposes, suggests, or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

[0640] Although specific embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various other changes and modifications may be made without departing from the spirit and scope of the present invention. It is therefore intended that all such changes and modifications within the scope of the present invention be encompassed in the appended claims.

Claims

1. A superabsorbent polymer material comprising cross-linked polyacrylic acid and salts thereof, said superabsorbent polymer material further comprising at least 3.0% by weight, based on the total weight of said superabsorbent polymer material, of a soluble polyacrylic acid polymer, The cross-linked polyacrylic acid and its salt have an average distance R between adjacent cross-linking points. xl , the average distance R xl is calculated for a superabsorbent polymer material loaded with 20 g of saline containing 0.9% w NaCl per gram of dry superabsorbent polymer material and wherein at least 3 wt. % of the soluble polyacrylic acid polymer has 2*R g The average diameter of gyration, and Where 2*R g With R xl The ratio is at least 1.1, The soluble polyacrylic acid polymer is a polypropylene polymer that is soluble in aqueous solution and is not crosslinked above the gel point, which is the abrupt change in viscosity of a solution containing the polymer.

2. The superabsorbent polymer material according to claim 1, wherein the soluble polyacrylic acid polymer has a weight average molecular weight M of 250 kDa to 3 MDa. w .

3. The superabsorbent polymer material according to claim 1 or 2, wherein the average distance R between adjacent crosslinking points in the polymer network is xl is at least 15 nm and not greater than 50 nm.

4. The superabsorbent polymer material according to claim 3, wherein the average distance R between adjacent crosslinking points in the polymer network is xl Not greater than 40nm.

5. The superabsorbent polymer material according to claim 1 or 2, wherein the diameter of gyration 2*R of the soluble polyacrylic acid polymer is g is at least 20 nm and not greater than 100 nm.

6. The superabsorbent polymer material according to claim 5, wherein the diameter of gyration 2*R of the soluble polyacrylic acid polymer is g Not larger than 80nm.

7. The superabsorbent polymer material according to claim 1 or 2, wherein the soluble polyacrylic acid polymer is contained in the superabsorbent polymer material in an amount of at most 50.0 wt.-%, based on the total weight of the superabsorbent polymer material.

8. The superabsorbent polymer material according to claim 7, wherein the soluble polyacrylic acid polymer is contained in the superabsorbent polymer material in an amount of at most 30.0 wt.-%, based on the total weight of the superabsorbent polymer material.

9. The superabsorbent polymer material according to the preceding claim 7, wherein the soluble polyacrylic acid polymer is contained in the superabsorbent polymer material in an amount of at most 25 wt.-%, based on the total weight of the superabsorbent polymer material.

10. The superabsorbent polymer material according to claim 1 or 2, wherein the superabsorbent polymer material is in the form of superabsorbent polymer particles.

11. Superabsorbent polymer material according to the preceding claim 1 or 2, wherein the superabsorbent polymer particles are surface cross-linked.

12. The superabsorbent polymer material according to claim 1 or 2, wherein the superabsorbent polymer material has an amount of extractables of less than 15.0 wt. %, the amount of extractables being measured according to EDANA test method NWSP 270.0.R2 (15).

13. The superabsorbent polymer material according to claim 1 or 2, wherein the superabsorbent polymer material has a capacity measured as Centrifuge Retention Capacity (CRC) of at least 20 g / g, the capacity being determined according to the Centrifuge Retention Capacity (CRC) test method described in EDANA NWSP 241.0.R2 (15), except that according to EDANA NWSP 241.0.R2 (15), the CRC measurement starts at a lower limit of 24.2 g / g.

14. The superabsorbent polymer material according to claim 1 or 2, wherein the soluble polyacrylic acid polymer is obtained from pre-existing recycled post-consumer superabsorbent polymer material, and / or from pre-existing recycled post-industrial superabsorbent polymer material.

15. An absorbent article comprising the superabsorbent polymer material according to any one of the preceding claims.

16. A method for preparing a superabsorbent polymer material, said method comprising the steps of a) providing an aqueous solution of polymerizable acrylic monomers and / or polymerizable acrylic oligomers, optionally neutralizing at least some of the polymerizable acrylic monomers and / or the polymerizable acrylic oligomers; b) optionally providing one or more ethylenically unsaturated comonomers, optionally a neutralization step b) at least some of the ethylenically unsaturated comonomers; c) providing one or more cross-linking agents; d) providing one or more initiators; e) providing at least 3 wt% of the soluble polyacrylic acid polymer provided in step e) based on the total weight of the monomers, oligomers, comonomers, crosslinkers and initiators provided in steps a) to d); f) mixing the aqueous solutions of the monomers, oligomers, comonomers, crosslinking agents and initiators provided in steps a) to e) with the soluble polyacrylic acid polymer; and g) polymerizing said mixture obtained in step f) to obtain a superabsorbent polymer material, The superabsorbent polymer material obtained comprises cross-linked polyacrylic acid having an average distance R between adjacent cross-linking points of xl , the average distance R xl is calculated for a loading of said superabsorbent polymer material with 20 g of saline containing 0.9% w NaCl per gram of dry superabsorbent polymer material, and wherein at least 3% by weight of the soluble polyacrylic acid polymer has a mean diameter of gyration of 2*Rg, and Where 2*R g With R xl The ratio is at least 1.1, The soluble polyacrylic acid polymer is a polypropylene polymer that is soluble in aqueous solution and is not crosslinked above the gel point, which is the abrupt change in viscosity of a solution containing the polymer.

17. The method according to claim 16, wherein the method further comprises the step h) of drying the superabsorbent polymer material.

18. The method according to claim 16 or 17, further comprising the step i) of comminuting the superabsorbent polymer material to obtain superabsorbent polymer particles.

19. The method according to claim 18, further comprising the step of surface cross-linking the superabsorbent polymer particles.

20. The method of claim 16 or 17, wherein the soluble polyacrylic acid polymer is obtained from pre-existing recycled post-consumer superabsorbent polymer material, and / or from pre-existing recycled post-industrial superabsorbent polymer material.

21. The method according to claim 16 or 17, wherein the average distance R between adjacent crosslinking points in the polymer network of the obtained superabsorbent polymer material is xl is at least 15 nm and not greater than 50 nm.

22. The method according to claim 21, wherein the average distance R between adjacent crosslinking points in the polymer network of the obtained superabsorbent polymer material is xl Not greater than 40nm.

23. The method according to claim 16 or 17, wherein the diameter of gyration 2*R of the soluble polyacrylic acid polymer is g is at least 20 nm and not greater than 100 nm.

24. The method of claim 23, wherein the diameter of gyration 2*R of the soluble polyacrylic acid polymer is g Not larger than 80nm.

25. The method of claim 16 or 17, wherein the soluble polyacrylic acid polymer has a weight average molecular weight Mw of 250 kDa to 3 MDa.

26. The process according to claim 16 or 17, wherein the superabsorbent polymer material obtained by the process is a superabsorbent polymer material according to any one of claims 1 to 10.

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