Recycling of superabsorbent fibers using an extended flow device

Abstract

Superabsorbent fibers (SAF) in the feed stream are converted to soluble polymers in an extended flow device. The total energy used to break down the SAF into soluble polymers is less than about 50 MJ / kg SAF.

Description

[Technical Field]

[0001] The present invention generally relates to the recycling of superabsorbent fiber (SAF) using an extended flow device with optional and additional cavitation at short residence times. More specifically, a feed stream containing SAF is fed to the extended flow device, and a product stream containing essentially soluble polymer is produced. The concentration of SAF in the feed stream is greater than about 1 wt. % and the total energy used to convert the SAF to soluble polymer is less than about 50 MJ / kg SAF. [Background technology]

[0002] Recycling absorbent hygiene products (AHPs) (i.e., baby diapers, feminine protective pads, and adult incontinence pads) is good for the environment and is required to meet the sustainability goals of many consumer companies. These goals include using 100% recycled materials and zero consumer and manufacturing waste to landfills. In addition to these goals, successful recycling helps the environment, stimulates economies, improves human health and water quality, and generates energy needed by consumers in developing regions of the world.

[0003] The primary component of AHPs is typically superabsorbent polymer (SAP), with other components being adhesives, cellulose fibers, polyethylene, polypropylene, and polyester. SAPs are absorbent, water-swellable, and water-insoluble powdery solids that are crosslinked, partially neutralized homopolymers of glacial acrylic acid. SAPs have an exceptionally high capacity to absorb aqueous liquids, such as contaminated water or urine. An alternative to poly(acrylic acid)-based SAPs is superabsorbent fiber (SAF). These fibers generally contain relatively high amounts of comonomers (compared to superabsorbent polymer particles). Therefore, like SAFs, there is also a need to recycle SAFs used in AHPs.

[0004] Recycling of AHPs involves cleaning them from soils accumulated during their use and separating the various components into a recycled material stream. More specifically, the recycled SAF material stream can be used in less demanding applications than AHPs (since recycled SAF has inferior properties compared to virgin SAF; for example, agricultural or horticultural water retention agents and industrial waterproofing agents) and / or converted into essentially non-crosslinked, slightly branched or linear soluble polymers. These soluble polymers can be used as feedstock for various applications. For example, the soluble polymers can be 1) used as is in applications such as water treatment or corrosion protection, or 2) esterified and then used in adhesives, coatings, etc., or 3) used as is in SAF fabrication, such as SAF fiber spinning, or 4) converted to SAF (see item 3) and blended with virgin SAF. The first two sets of applications are part of an attempt to recycle SAF into other products by replacing virgin compounds with compounds derived from recycled SAF, while the last two sets of applications are part of a circular economy for SAF, i.e., recycling SAF back into SAF. In all cases, the aim is to achieve the same properties as virgin material.

[0005] Although no references have been identified addressing the decomposition of SAFs that are not based purely on acrylic acid, non-limiting examples of processes for the purification of spent SAF from recycled AHPs and producing a separated material stream are disclosed and claimed in U.S. Patent Nos. 9,095,853(B2), issued August 4, 2015, and 9,156,034(B2), issued October 13, 2015, both of which were assigned to Fater SpA (Pescara, Italy).

[0006] Most SAPs are based on poly(acrylic acid) and are crosslinked network materials. Non-limiting examples of procedures used to prepare SAPs from glacial acrylic acid and a crosslinker are disclosed in U.S. Pat. No. 8,383,746 (B2), issued February 26, 2013, and assigned to Nippon Shokubai Co., Ltd. (Osaka, Japan), and U.S. Pat. No. 9,822,203 (B2), issued November 21, 2017, and assigned to BASF SE (Ludwigshafen, Germany).

[0007] The ultrasonic decomposition of SAP has been described in (1) Ebrahimi, R., et al., Organic Chemistry Intl, 2012 (Reference ID 343768, page 5), and (2) Shukla, N.B., and Madras, G., J. Appl. Polym. Sci., 125 (2012), 630-639. The ultrasonic decomposition of PAA has been described in (1) Shukla, N.B., et al., J. Appl. Polym. Sci., 112 (2009), 991-997, and (2) Prajapat, A.L., and Gogate, P.R., Ultrason. Sonochem., 32 (2016), 290-299. A general description of the ultrasonic degradation of polymers in solution is also given in Basedow, AM, and Ebert, KH, Adv. Polym. Sci., 22 (1977), 83-148.

[0008] Regarding the degradation of SAP, both references use viscosity as a measure of degradation level and find that it takes approximately 5–10 minutes to reduce the viscosity by one order of magnitude, e.g., from 10 Pa·s to 1 Pa·s, indicating that a lot of energy is required to achieve that level of degradation. Regarding the degradation of linear polymers, the main themes from these references (as well as others reporting on the use of UV, thermal, and other forms of energy) are that (1) preferential scission occurs at the midpoint of the polymer chain, (2) high molecular weight chains degrade at a faster rate than low molecular weight chains, and (3) there is a minimum molecular weight below which degradation or depolymerization does not occur. In all cases, ultrasonic degradation of polymers results from cavitation and the rapid growth and collapse of the resulting microbubbles. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent No. 9,095,853(B2) [Patent Document 2] U.S. Patent No. 9,156,034(B2) [Patent Document 3] U.S. Patent No. 8,383,746 (B2) [Patent Document 4] U.S. Patent No. 9,822,203(B2) [Non-patent literature]

[0010] [Non-Patent Document 1] Ebrahimi, R., et al., Organic Chemistry Intl, 2012 (Reference ID 343768, page 5) [Non-patent document 2] Shukla, N.B., and Madras, G., J.Appl.Polym.Sci., 125(2012), 630-639 [Non-patent document 3] Shukla, NB, et al., J. Appl. Polym. Sci., 112 (2009), 991-997 [Non-patent document 4] Prajapat,AL,and Gogate,PR,Ultrason.Sonochem.,32(2016),290-299 [Non-Patent Document 5] Basedow, AM, and Ebert, KH, Adv. Polym. Sci., 22 (1977), 83-148 Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, there is a need to recycle AHPs and their main component (which may be SAF). Recycling SAF requires that the SAF be decomposed into soluble polymers on a short-term scale, with low energy and power per unit mass of SAF, and under mild conditions, such as room temperature, thus avoiding chemical degradation, such as decarboxylation, of the decomposed SAF. The requirement for low energy per unit mass of SAF arises from the fact that recycling used SAF and its decomposition into soluble polymers is only beneficial if the energy consumed during its conversion to soluble polymers is less than, for example, the energy used to make the same fossil-derived soluble polymer. In the case of acrylic acid from propylene (petro-AA), the energy required is approximately 50 MJ / kg AA. The soluble polymers produced from SAF can then be incorporated back into virgin SAF (thus increasing its recycled content and supporting a circular economy for SAF) and / or derivatized into materials for other applications, such as adhesives, coatings, water treatment, and fabric care. [Means for solving the problem]

[0012] In one embodiment of the present invention, a method is provided for degrading superabsorbent fiber (SAF) into a soluble polymer, the soluble polymer comprising 5% to 75%, preferably 10% to 75%, or 10% to 70% by weight of polymerized acrylic acid monomer units, based on the total weight of the soluble polymer. As used herein, the term "acrylic acid monomer units" excludes derivatives of acrylic acid monomers, such as esters and amides, and also excludes methacrylic acid monomer units and salts thereof.

[0013] The method includes flowing a feed stream containing the SAF to an inlet of an extended flow device and producing a product stream at an outlet of the extended flow device comprising the soluble polymer, wherein the feed stream comprises the SAF at a concentration greater than about 1 wt %, the feed stream has a residence time in the extended flow device of less than about 120 seconds, and the decomposition of the SAF to the soluble polymer requires a total energy of less than about 50 MJ / kg SAF.

[0014] Also provided is a method for degrading superabsorbent fibers (SAF) into soluble polymers, the soluble polymers comprising 5% to 75%, preferably 10% to 75%, or 10% to 70% by weight of polymerized acrylic acid monomer units, based on the total weight of the soluble polymer. The method includes flowing a feed stream containing the SAF through an inlet of an extended flow device and producing a product stream containing the soluble polymer at an outlet of the extended flow device, the feed stream comprising water and the SAF at a concentration greater than about 1% by weight, the feed stream having a residence time in the extended flow device of less than about 120 seconds, the decomposition of the SAF into the soluble polymer requiring a total energy of less than about 16 MJ / kg SAF, and the soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol.

[0015] Still further, a method is presented for degrading superabsorbent fibers (SAF) into soluble polymers, the soluble polymers comprising 5% to 75% by weight, preferably 10% to 70% by weight, of polymerized acrylic acid monomer units, based on the total weight of the soluble polymer. The method includes flowing a feed stream comprising the SAF through an inlet of an extended flow device and producing a product stream comprising the soluble polymer at an outlet of the extended flow device, the feed stream comprising water and the SAF at a concentration greater than about 5% by weight, the feed stream having a residence time in the extended flow device of less than about 120 seconds, the decomposition of the SAF into the soluble polymer requiring a total energy of less than about 16 MJ / kg SAF, and the soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol.

[0016] The soluble polymer may be water-soluble. The soluble polymer preferably has a solubility in water at 25° C. of more than 5 g of soluble polymer per 100 g of water, or more than 15 g of soluble polymer per 100 g of water, or from 20 g to 120 g of soluble polymer per 100 g of water, or from 35 g to 100 g of soluble polymer per 100 g of water.

[0017] The soluble polymer obtained by the method of the present invention can be subjected to the NMR content method described below. The NMR content method can be used to determine the molar ratio of protons of functional groups with different NMR signals, such as alkene terminal moieties, alkoxy groups (-O-CHR1-, where R1 is one of H, alkyl, aryl, heteroaryl, alkoxy, or halogen groups), aliphatic groups (-CHR1-, where R1 is one of H, alkyl, aryl, heteroaryl, or halogen groups), and / or other 1H-NMR active groups. Considering that the spectrum obtained by the NMR content method allows the determination of various functional groups by their different NMR signals, the NMR content method also allows the determination of many monomer units other than acrylic acid monomer units contained in the soluble polymer.

[0018] The soluble polymers obtained by the methods of the present invention may have a 3.6:CH ratio of at least 0.04, as measured by the NMR content method described herein. The soluble polymers may have a 3.6:CH ratio of at least 0.1, or at least 0.2, as measured by the NMR content method described herein. The soluble polymers may have a 3.6:CH ratio of 0.7 or less, as measured by the NMR content method described herein.

[0019] The soluble polymers obtained by the present invention may have a content of "%3.6 ppm" of at least 5% as measured by the NMR content method described herein. The soluble polymers may have a content of "%3.6 ppm" of at least 10%, or at least 15%, as measured by the NMR content method described herein. The soluble polymers may have a content of "%3.6 ppm" of 75% or less as measured by the NMR content method described herein.

[0020] The soluble polymers obtained by the methods of the present invention may have an alkene content "% Alkene" of 0.31% or less, as measured by the NMR content method described herein. DETAILED DESCRIPTION OF THE INVENTION

[0021] I definition As used herein, the term "SAF" refers to superabsorbent fibers. The SAF of the present invention can absorb at least 7 times their dry weight, preferably at least 10 times their dry weight, of 0.9% by weight saline solution at 25°C, as measured using the Centrifuge Retention Capacity (CRC) test method described herein. The typical absorption mechanism is osmotic pressure. SAF that absorbs water or aqueous solutions becomes softer and gel-like.

[0022] "Superabsorbent fiber" ("SAF") is used herein to refer to a superabsorbent polymer material in fiber form. Superabsorbent fibers have a length and a cross-section. The length is the maximum dimension of the fiber when it is, or would be, laid flat and straight on a surface so that any curvature or crimp in the fiber disappears and the fiber assumes a generally rod-like configuration. The cross-section is perpendicular to the length. For purposes of this specification, a fiber is a material having a maximum and a minimum dimension, the ratio of the maximum to the minimum dimension being at least 10:1, preferably at least 15:1, and even more preferably at least 20:1; i.e., the maximum dimension (also referred to as the length) of a superabsorbent fiber is at least 10 times, or at least 15 times, or at least 20 times the minimum dimension (also referred to as the width) of the fiber. When a superabsorbent fiber has a cross-section that varies along the length of the fiber, the maximum dimension of the cross-section (determined by the length of the fiber) is taken as the width of the fiber when calculating the ratio of the maximum to the minimum dimension. As used herein, the term "soluble polymer" refers to an essentially non-crosslinked, either slightly branched or linear polymer, which comprises 5% to 75%, or 10% to 75%, or 10% to 70% by weight of acrylic acid as monomer units, and which may have a degree of polymerization of 2 or higher. For the purposes of the present invention, there is no distinction between a polymer and an oligomer when it comes to a soluble polymer.

[0023] As used herein, the term "degradation" refers to the conversion of SAF into a soluble polymer through partial depolymerization, decrosslinking, molecular backbone disruption, or any combination of the above. For purposes of the present invention, the terms degrading, recycling, and conversion are used interchangeably, as long as they refer to the conversion of SAF into a soluble polymer. Degradation also essentially preserves the carboxyl groups of SAF, and therefore, the product soluble polymer contains these carboxyl groups. Note that complete depolymerization of SAF should yield the monomers originally contained in the SAF.

[0024] As used herein, the term "virgin SAF" refers to SAF made from virgin monomers, which are the feedstocks used today to make SAF. Virgin monomers can be produced from either fossil-derived or biologically derived materials (non-limiting examples of biological materials are lactic acid, 3-hydroxypropionic acid, glycerin, biopropylene, carbon dioxide, and sugars). Virgin SAF does not contain more than about 1% by weight of any recycled SAF.

[0025] As used herein, the term "used SAF" refers to SAF that has already been industrially manufactured and / or used commercially, for example, in baby diapers, feminine pads, adult incontinence pads, or other articles and / or applications. Used SAF can be post-consumer SAF (after consumer use), post-industrial SAF (from the manufacturing process), or a combination of both. Unless otherwise specified in this invention, SAF refers to either "used SAF" or "virgin SAF."

[0026] As used herein, the term "degraded SAF" refers to SAF that has been degraded into soluble polymers. For purposes of the present invention, the terms "degraded SAF" and "soluble polymers" are used interchangeably.

[0027] As used herein, the term "recycled SAF" refers to SAF that contains at least 1 wt. % degraded SAF (or equivalent soluble polymer) that was incorporated into the SAF while it was being manufactured from acrylic acid and comonomers using typical manufacturing methods. Thus, recycled SAF is a blend of virgin SAF and at least 1 wt. % degraded SAF.

[0028] As used herein, the term "feed stream" refers to a body of fluid that flows in a particular direction and is supplied to the inlet of an extended flow device.

[0029] As used herein, the term "product stream" refers to the body of fluid that is produced at the outlet of an extended flow device when a feed stream is fed into the inlet of the same device.

[0030] As used herein, the term "liquid whistle" refers to a Sonolator-type device (manufactured by Sonic Corporation, Stratford, CT) that uses a mixing chamber with an inlet chamber, an orifice, and a blade in front of the orifice in the direction of flow. As material flows through the orifice, the resulting jet strikes the blade, which is then vibrated at its resonant frequency, further enhancing the cavitation field when the blade is located away from the orifice within 7-8 hydraulic diameters of the orifice (i.e., when the blade is engaged). When the blade is located away from the orifice outside the range of 7-8 hydraulic diameters, the blade is considered disengaged. The closer the blade is to the orifice and the lower the viscosity of the feed stream, the stronger the cavitation. The main applications of Liquid Whistle (LW) are mixing, emulsifying, deagglomerating, and disinfecting in the household, personal care, and fine chemical industries (U.S. Patent No. 8,517,595 (B2) and Ryan, DJ et al., Chem. Engng Sci., 189 (2018), 369-379). For the purposes of this invention, LW is one of the extended flow devices that can be used.

[0031] As used herein, the term "extensional flow device" refers to a flow device that generates extensional flow, strain, and stress. Non-limiting examples of extensional flow devices are devices having converging and / or diverging channels, orifices, impingement jets, four-roll mills, screens, dies, etc. The terms "extensional" and "elongational" are used interchangeably for purposes of the present invention.

[0032] As used herein, the term "viscosity ratio" or "viscosity reduction ratio" refers to the ratio of the viscosity of the product stream to the viscosity of the feed stream. The viscosity of the feed stream is typically measured using a parallel plate fixture in oscillatory mode, and the reported complex viscosity typically corresponds to a frequency of 1 rad / sec. The real and imaginary parts of the complex viscosity represent the dynamic viscosity and storage viscosity, respectively. To calculate the viscosity ratio, applicants use the dynamic viscosity, i.e., the real part of the complex viscosity. The viscosity of the product stream is measured using either a cup-and-bob fixture in steady mode or a parallel plate fixture in oscillatory mode. When the viscosity is measured in steady mode using a cup-and-bob fixture, the reported viscosity is typically 4 s -1 These viscosity measurement techniques are well known to those skilled in the art. For purposes of this invention, the negative decimal logarithm of the viscosity ratio indicates, by several orders of magnitude, the extent of SAF decomposition into soluble polymer, as it is accepted by those skilled in the art that the lower the viscosity of a soluble polymer solution, the lower the molecular weight of the soluble polymer at a given concentration.

[0033] As used herein, M n is the number average molecular weight expressed in g / mol or equivalently in Da, and M w is the weight average molecular weight expressed in g / mol or equivalently in Da, and M z is the z-average molecular weight expressed in g / mol or equivalently Da, and PDI is M w / M n is the polydispersity index, defined as

[0034] "Disposable" is used in its ordinary sense to mean an article that is disposed of or discarded after a limited number of uses over different periods of time, for example, less than 20 uses, less than 10 uses, less than 5 uses, or less than 2 uses. Where the disposable absorbent article is a diaper, pants, sanitary napkin, sanitary pad, or wet wipe for personal hygiene use, the disposable absorbent article may (in most cases) be intended to be disposed of after a single use.

[0035] II Feed stream It has been unexpectedly discovered that when an SAF feed stream (in the form of a gel) flows through an extensional flow device (e.g., LW) and experiences extensional flow with short residence times, the SAF decomposes into soluble polymers (i.e., essentially without decarboxylation). Without wishing to be bound by any theory, Applicants believe that extensional stresses generated in the SAF feed stream / gel as it flows through the orifice cause the crosslinker, its attachment to the backbone, and the backbone bonds to stretch and break. Applicants expected the gel to develop slip at the walls of the inlet chamber and orifice, and therefore not develop extensional stresses when the gel flows in plug flow within the inlet chamber and orifice (as is well known to those skilled in the art).

[0036] Typical properties of SAF are mechanical properties, swelling capacity, and centrifuge retention capacity (CRC) measured according to the test methods set forth herein. SAF also contains more than 25% by weight and less than 95% by weight of other comonomers (i.e., other than acrylic acid). Suitable comonomers are, for example, methyl acrylate, methyl methacrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, or monomer groups including / consisting of polymers and copolymers such as polyacrylamide, polyvinyl alcohol, ethylene-maleic anhydride copolymers, polyvinyl ethers, hydroxypropyl cellulose, polyvinyl morpholinone, and vinyl sulfonic acid, polyvinylamine, polyallylamine, and polyvinylpyridine. Other suitable polymers in SAF include hydrolyzed acrylonitrile-grafted starch, acrylic acid-grafted starch, and isobutylene-maleic anhydride copolymers, and mixtures thereof. SAF is crosslinked to render the material substantially water-insoluble. Preferred monomers are methyl (meth)acrylate and / or monomers containing hydroxyl groups, such as hydroxyalkyl (meth)acrylates, e.g., hydroxyethyl methacrylate, tripropylene glycol monoacrylate, 5 glyceryl monoacrylate, etc. The SAF may comprise / consist of polymers formed from two types of monomers (including acrylic acid) or, more preferably, three or more types of monomers.

[0037] The SAF may have a sodium level greater than about 8 wt% Na, or a sodium level of 10-20 wt%, or 15-18 wt% Na. In yet another embodiment of the invention, the SAF has a sodium level of less than 12 wt% Na.

[0038] The SAF provided by the method can be i) in the form of loose fibers, or ii) in the form of a nonwoven web, or a combination of i) and ii). When the SAF is in the form of a nonwoven web, the nonwoven web can consist of or include the SAF. Nonwoven webs comprising SAF and provided by the method can include at least 50% by weight of SAF, based on the total weight of the nonwoven web, or at least 60% by weight, or at least 70% by weight, or at least 80% by weight, or at least 90% by weight of SAF, based on the total weight of the nonwoven web.

[0039] The nonwoven web may further comprise additional components such as synthetic fibers, natural fibers (e.g., cellulose fibers), or combinations thereof. The synthetic fibers that may be included in such nonwoven webs may be polyolefin fibers (e.g., polyethylene, polypropylene, or combinations thereof), or PET fibers, or a combination of polyolefin and PET fibers.

[0040] The non-SAF components of the nonwoven web can be, but need not be, removed before subjecting the SAF to the process of the present invention. Alternatively, the nonwoven web containing the SAF can be subjected to the process of the present invention (as an intact nonwoven web, cut, shredded, or comminuted) along with the non-SAF components of the nonwoven web.

[0041] Prior to or during the process of the present invention, the nonwoven web may be cut into small pieces or ground or otherwise shredded to make the SAF more accessible to the oxidized water-soluble salt. Alternatively, the nonwoven web may be subjected to the process "as is."

[0042] The non-SAF components of the nonwoven web can be, but need not be, removed before subjecting the SAF to the process of the present invention. Alternatively, the nonwoven web containing the SAF can be subjected to the process of the present invention (as an intact nonwoven web, cut, shredded, or comminuted) along with the non-SAF components of the nonwoven web.

[0043] In one embodiment of the present invention, the feed stream comprises SAF. In another embodiment of the present invention, the feed stream comprises SAF and water. In yet another embodiment of the present invention, the feed stream comprises SAF and ethylene glycol (EG). In yet another embodiment of the present invention, the feed stream comprises SAF, water, and ethylene glycol. The water in the feed stream can be RO water, regular tap water, or water containing dissolved inorganic salts at various salt concentrations. A non-limiting example of water containing salt is a 0.9 wt% solution of sodium chloride. Other salts with monovalent cations but higher ionic strength can be used to reduce the viscosity of the feed stream or, alternatively, allow for the use of higher SAF concentrations. A non-limiting example of a viscosity-reducing salt is sodium sulfate.

[0044] The feed stream may also contain any free radical-generating compound, non-limiting examples of which include hydrogen peroxide (HO), persulfates (e.g., sodium or potassium persulfate), perborates, perphosphates, percarbonates, diazo compounds, ozone, organic free radical initiators (e.g., di-tert-butyl peroxide (DTBP)), combinations thereof, and the like.

[0045] In one embodiment of the invention, the feed stream comprises SAF and H2O2. In another embodiment of the invention, the feed stream comprises SAF and H2O2 solution.

[0046] In one embodiment of the invention, the feed stream comprises SAF at a concentration greater than about 1 wt%. In another embodiment of the invention, the feed stream comprises SAF at a concentration greater than about 5 wt%. In yet another embodiment of the invention, the feed stream comprises SAF at a concentration greater than about 10 wt%. In yet another embodiment of the invention, the feed stream comprises SAF at a concentration of about 2.5 wt%. In one embodiment of the invention, the feed stream comprises SAF at a concentration of about 5 wt%.

[0047] In one embodiment of the present invention, the feed comprises SAF and an HO solution, wherein the concentration of SAF is about 2.5 wt %, the concentration of the HO solution is 97.5 wt %, and the concentration of HO in the HO solution is less than about 3 wt %. In another embodiment of the present invention, the feed comprises SAF and HO, wherein the concentration of SAF is about 5 wt %, the concentration of the HO solution is about 95 wt %, and the concentration of HO in the HO solution is less than about 3 wt %. In yet another embodiment of the present invention, the feed comprises SAF and an HO solution, wherein the concentration of SAF is about 2.5 wt %, the concentration of the HO solution is 97.5 wt %, and the concentration of HO in the HO solution is about 3 wt %. In another embodiment of the invention, the feed comprises SAF and H2O2, wherein the concentration of SAF is about 5 wt%, the concentration of the H2O2 solution is about 95 wt%, and the concentration of H2O2 in the H2O2 solution is about 3 wt%.

[0048] In one embodiment of the present invention, the feed comprises SAF and an HO solution, wherein the concentration of SAF is about 2.5 wt %, the concentration of the HO solution is 97.5 wt %, and the concentration of HO in the HO solution is about 0.3 wt %. In another embodiment of the present invention, the feed comprises SAF and HO, wherein the concentration of SAF is about 5 wt %, the concentration of the HO solution is about 95 wt %, and the concentration of HO in the HO solution is about 0.3 wt %. In yet another embodiment of the present invention, the feed comprises SAF and an HO solution, wherein the concentration of SAF is about 2.5 wt %, the concentration of the HO solution is 97.5 wt %, and the concentration of HO in the HO solution is about 0.03 wt %. In another embodiment of the invention, the feed comprises SAF and H2O2, wherein the concentration of SAF is about 5 wt%, the concentration of the H2O2 solution is about 95 wt%, and the concentration of H2O2 in the H2O2 solution is about 0.03 wt%.

[0049] In one embodiment of the invention, the feed comprises SAF and an HO solution, wherein the concentration of HO in the HO solution is less than about 3 wt %. In another embodiment of the invention, the feed comprises SAF and an HO solution, wherein the concentration of HO in the HO solution is less than about 0.3 wt %. In yet another embodiment of the invention, the feed comprises SAF and an HO solution, wherein the concentration of HO in the HO solution is less than about 0.03 wt %.

[0050] The viscosity of the feed stream is typically measured using a parallel plate fixture in oscillatory mode, and the reported complex viscosity typically corresponds to a frequency of 1 rad / sec. Depending on the SAF concentration, the complex viscosity of the feed stream can be higher than 200 Pa.s (or equivalently, 200,000 cP). The feed stream can be in the form of a solution or a gel, depending on the concentration of the SAF.

[0051] The non-renewable energy use (NREU) for producing acrylic acid (AA) from fossil-derived propylene is estimated to be approximately 50 MJ / kg AA. Therefore, any successful recycling attempt of SAF desirably consumes less energy than NREU to produce AA, i.e., less than approximately 50 MJ / kg SAF, to be environmentally and commercially competitive with fossil-derived virgin materials. For purposes of NREU, SAF is assumed to be fully unneutralized (DN=0).

[0052] III. Extended Flow Devices and Cavitation Typically, the feed stream is in fluid communication with the expansion flow device via a tube or channel and a pump. Non-limiting examples of the tube or channel include glass tubes, metal tubes, alloy tubes (such as stainless steel tubes), and polymer tubes. The tubes or channels can have any cross-sectional shape, such as circular, rectangular, oval, or diamond-shaped. The cross-sectional area of ​​the tubes or channels can be the same or can vary in size depending on the flow direction. A non-limiting example of a different cross-sectional shape of the tube is a corrugated tube, which can subject the feed stream to expansion stresses as it flows down the tube. These expansion stresses can be beneficial to the decomposition of SAF, which is part of the feed stream. The feed stream can also pass through a static mixer or other mixing element located inside the tube and / or channel through which the feed stream flows.

[0053] Non-limiting examples of pumps include centrifugal pumps (such as axial, radial, and mixed flow pumps) and positive displacement pumps (such as reciprocating, rotary, piston, diaphragm, gear, peristaltic, screw, and vane pumps). An extended flow device can use one or more pumps.

[0054] In one embodiment of the present invention, the extended flow device is a liquid whistle (LW). Typically, the LW includes, in the flow direction, an inlet chamber, an orifice, and a mixing chamber, where a blade is located in front of and at a distance from the orifice. The extended flow device also typically includes an inlet and an outlet. A feed stream enters the extended flow device at the inlet, and a product stream exits the extended flow device at the outlet. Non-limiting examples of extended flow devices are the SONOLATOR® manufactured by Sonic Corp. and the MICROFLUIDIZER® manufactured by Microfluidics Corp (Newton, MA). In one embodiment of the present invention, there are no blades downstream of the orifice in the LW.

[0055] Non-limiting configurations of the orifice include slot-shaped, eye-shaped, oval-shaped, circular, triangular, square, rectangular, and polygonal. The width of the orifice can be up to 1 inch (2.541 cm) or greater. The height of the orifice can be up to 0.5 inches (1.27 cm) or greater. In another embodiment of the present invention, the orifice is oval-shaped. In yet another embodiment of the present invention, the width of the orifice is about 1.9 mm and the height of the orifice is about 0.6 mm. Non-limiting examples of materials used to fabricate the orifice housing include stainless steel, titanium, ceramic, cemented tungsten, various borides, various carbons, various carbides, and various diborides. The land length of the orifice can be up to 10 mm. In one embodiment of the present invention, the land length of the orifice is about 0.5 mm to about 5 mm. In another embodiment of the present invention, the land length of the orifice is about 1 mm.

[0056] When the LW blade vibrates at its natural frequency, it generates strong cavitation, and the formed bubbles grow and collapse very quickly. Non-limiting examples of materials used to fabricate the blade include stainless steel, titanium, ceramic, cemented tungsten, various borides, various carbons, various carbides, and various diborides. The LW blade can have any suitable configuration, including, but not limited to, a tapered shape, a sharp edge, a rectangular or square cross section, and the like. The LW blade can have any suitable dimensions. In one embodiment of the present invention, the length of the LW blade is about 1 mm to about 100 mm. In another embodiment of the present invention, the length of the LW blade is about 10 mm to about 50 mm. In yet another embodiment of the present invention, the thickness of the LW blade is about 7 μm to about 100 mm. In another embodiment of the present invention, the thickness of the LW blade is about 0.2 mm to about 50 mm.

[0057] The cavitation induced by the vibrating blade of the LW can be hydrodynamic, acoustic (e.g., 20 Hz to 20 kHz), or ultrasonic (e.g., greater than 20 kHz). In one embodiment of the present invention, the blade of the LW is subjected to ultrasonic vibrations at frequencies from about 20 kHz to about 100 kHz.

[0058] The distance between the blade and the LW orifice can vary from about 0.1 mm to about 25 mm. In one embodiment of the present invention, the distance between the blade and the LW orifice is about 0.5 mm. In another embodiment of the present invention, the distance between the blade and the LW orifice is about 0.5 mm to about 13 mm. In yet another embodiment of the present invention, the distance between the blade and the LW orifice is about 1 mm to about 10 mm. In yet another embodiment of the present invention, the distance between the blade and the LW orifice is about 3 mm to about 6 mm.

[0059] In one embodiment of the present invention, the blade is a distance from the LW orifice such that cavitation is not achieved when the fluid jet exits the orifice and impacts the blade. In another embodiment of the present invention, the blade is a distance from the LW orifice such that cavitation is achieved when the fluid jet exits the orifice and impacts the blade. In yet another embodiment of the present invention, the cavitation achieved in the extended flow device is hydrodynamic. In yet another embodiment of the present invention, the cavitation achieved in the extended flow device is ultrasonic. In one embodiment of the present invention, the cavitation achieved in the extended flow device is acoustic.

[0060] In one embodiment of the invention, the distance of the blade from the orifice in the LW is at least about 7 times the hydraulic diameter of the orifice. In another embodiment of the invention, the distance of the blade from the orifice in the LW is less than about 7 times the hydraulic diameter of the orifice. In yet another embodiment of the invention, the distance of the blade from the orifice in the LW is about 6 times the hydraulic diameter of the orifice. In yet another embodiment of the invention, the distance of the blade from the orifice in the LW is about 0.3 times the hydraulic diameter of the orifice.

[0061] The process can be carried out at any suitable pressure as measured upstream of the feed stream and orifice. In one embodiment of the invention, the pressure is from about 500 psi (34.5 bar) to about 20,000 psi (1379 bar). In another embodiment of the invention, the pressure is greater than about 20,000 psi (1379 bar). In yet another embodiment of the invention, the pressure is from about 1000 psi (68.9 bar) to about 10,000 psi (689.5 bar). In yet another embodiment of the invention, the pressure is from about 2,000 psi (137.9 bar) to about 7,000 psi (482.6 bar). In one embodiment of the invention, the pressure is about 5,000 psi (344.7 bar).

[0062] The flow rate of the feed stream to the extended flow device can be any suitable value. In one embodiment of the present invention, the flow rate of the feed stream to the extended flow device is between about 1 L / min and about 1,000 L / min. In another embodiment of the present invention, the flow rate of the feed stream to the extended flow device is between about 2 L / min and about 500 L / min. In yet another embodiment of the present invention, the flow rate of the feed stream to the extended flow device is between about 3 L / min and about 200 L / min. In yet another embodiment of the present invention, the flow rate of the feed stream to the extended flow device is between about 4 L / min and about 100 L / min. In one embodiment of the present invention, the flow rate of the feed stream to the extended flow device is about 5 L / min.

[0063] The residence time of the feed stream in the extended flow device can be any suitable value. Residence time is defined as the average time the feed stream spends throughout the extended flow device, not just in the orifices, but also in the inlets and mixing chambers. In one embodiment of the invention, the residence time of the feed stream in the extended flow device is less than about 120 seconds. In another embodiment of the invention, the residence time of the feed stream in the extended flow device is less than about 60 seconds. In yet another embodiment of the invention, the residence time of the feed stream in the extended flow device is less than about 15 seconds. In one embodiment of the invention, the residence time of the feed stream in the extended flow device is between about 1.5 seconds and about 50 seconds. In another embodiment of the invention, the residence time of the feed stream in the extended flow device is between about 2 seconds and about 20 seconds. In yet another embodiment of the invention, the residence time of the feed stream in the extended flow device is between about 2.5 seconds and about 10 seconds. In yet another embodiment of the invention, the residence time of the feed stream in the extended flow device is between about 3 seconds and about 5 seconds.

[0064] The residence time of the supply stream in the orifice of the extended flow device can be any suitable value. In one embodiment of the present invention, the residence time of the supply stream in the orifice is from about 1 ms to about 100 ms. In another embodiment of the present invention, the residence time of the supply stream in the orifice is from about 2 ms to about 50 ms. In yet another embodiment of the present invention, the residence time of the supply stream in the orifice is from about 5 ms to about 20 ms. In yet another embodiment of the present invention, the residence time of the supply stream in the orifice is from about 7 ms to about 15 ms. In one embodiment of the present invention, the residence time of the supply stream in the orifice is about 11 ms.

[0065] Total energy is the electrical energy supplied to the extended flow device and is based on the voltage and amperage of the device and the residence time of the feed stream. Specific energy is the energy dissipated in the feed stream inside the extended flow device, which is used to convert the SAF to soluble polymer, and is based on the pressure drop in the feed stream as it flows through the extended flow system. Calculations of total energy and specific energy are exemplified in Methods Section VII (and are well known to those skilled in the art).

[0066] In one embodiment of the invention, the specific energy used to convert SAF to a soluble polymer is less than about 30 MJ / kg SAF. In another embodiment of the invention, the specific energy used to convert SAF to a soluble polymer is less than about 20 MJ / kg SAF. In yet another embodiment of the invention, the specific energy used to convert SAF to a soluble polymer is less than about 10 MJ / kg SAF. In yet another embodiment of the invention, the specific energy used to convert SAF to a soluble polymer is less than about 5 MJ / kg SAF. In one embodiment of the invention, the specific energy used to convert SAF to a soluble polymer is less than about 1 MJ / kg SAF.

[0067] In one embodiment of the invention, the total energy used to convert SAF to a soluble polymer is less than about 50 MJ / kg SAF. In another embodiment of the invention, the total energy used to convert SAF to a soluble polymer is less than about 32 MJ / kg SAF. In yet another embodiment of the invention, the total energy used to convert SAF to a soluble polymer is less than about 16 MJ / kg SAF. In yet another embodiment of the invention, the total energy used to convert SAF to a soluble polymer is less than about 10 MJ / kg SAF. In one embodiment of the invention, the total energy used to convert SAF to a soluble polymer is less than about 2 MJ / kg SAF.

[0068] The extensional flow can occur at room temperature or any other temperature. Additionally, the extensional flow can occur before or after other processes, such as microwave heating, UV irradiation, IR heating, ultrasound / cavitation, extrusion, extensional drawing, etc.

[0069] Enhanced flow can also occur simultaneously with oxidative, enzymatic, or biological degradation.

[0070] Oxidative decomposition method It has been unexpectedly discovered that SAF can be decomposed into soluble polymers, particularly in the form of polymers containing acrylic acid, by mixing the SAF with an oxidizing water-soluble salt (hereinafter referred to as "salt"). The salt contains at least one cation and at least one anion. The SAF and salt are mixed with an aqueous carrier, such as water or saline.

[0071] Heating the mixture to a temperature between 30°C and 200°C initiates decomposition of the SAF, likely via radical decomposition caused by decomposition of the oxidizing salts into radicals and / or radical ions. The elevated temperature can be at least 35°C, or at least 40°C, or at least 50°C, or at least 60°C, or at least 70°C, or at least 80°C. The elevated temperature can be less than 190°C, or less than 180°C, or less than 150°C. Generally, at elevated temperatures above 200°C, the SAF begins to decompose and break down in an uncontrolled manner, which is undesirable for the present invention.

[0072] Without wishing to be bound by theory, it is believed that upon heating, the oxidizing salt forms radicals or radical ions via decomposition. The radicals or radical ions result in hydrogen abstraction from water or the aqueous carrier, generating hydroxyl radicals, or directly from the SAF. The hydroxyl radicals can abstract hydrogen from the SAF. After abstracting hydrogen from the SAF, the polymer network of the SAF can be scissioned by chain scission. An exemplary mechanism is shown in the following schematic diagram: The elevated temperature to which the mixture is heated can be at least 10° C. below the decomposition temperature of the salt (leading to radical or radical ion formation, or radical ion formation), or the mixture can be heated to an elevated temperature that is at least the decomposition temperature, or at least 10° C. above the decomposition temperature of the salt.

[0073] As used herein, "decomposition temperature" refers to the 10 hour half-life temperature in water, e.g., 69°C for ammonium persulfate and 60°C for potassium persulfate.

[0074] Therefore, different salts (specifically, different anions) have different decomposition temperatures, and therefore the selection of the optimal temperature range depends, inter alia, on the salt selection. The formed radicals or radical ions can react with the SAF, for example, by reacting with aliphatic C—H groups contained in the polymer chain of the SAF. As a result of this radical reaction, the polymer chain of the SAF is decomposed, and carbon-centered radicals are formed in the decomposed SAF polymer chain. Reactions can also occur at carboxyl groups of the SAF, resulting in carbon-centered radicals. Alternatively or additionally, reactions can occur at nitrogen atoms, which may be involved by the crosslinking agent used to initially prepare the SAF. When reactions occur at nitrogen atoms, nitrogen-centered radicals are formed instead of carbon-centered radicals.

[0075] Without wishing to be bound by theory, the following reaction scheme is believed to illustratively illustrate the decomposition process of SAF into soluble polymers (i.e., the "decrosslinked polymer products" below):

[0076] [ka] where R is H, or an alkali cation, an ammonium cation, or a bridging residue, or other derivative of a carboxyl group, such as an ester, a hydroxyester, etc.

[0077] The mixture can be maintained at elevated temperature for 10 minutes to 10 hours, preferably 10 minutes to 5 hours, and more preferably 10 minutes to 4 hours. From an economical point of view, shorter times are preferred. A shorter process time can be obtained, for example, by using a higher salt concentration, a higher temperature (but below 200°C), and / or an optimized blend of SAF and salt. The time the mixture is maintained at elevated temperature also depends on the desired degree of decomposition (i.e., the average molecular weight of the soluble polymer obtained by the process). Generally, once the SAF has been degraded to the point where no or only a small amount of insoluble SAF is present, indicating that most of the SAF has been decomposed into soluble polymer, the mixture no longer needs to be maintained at elevated temperature, and the temperature can be reduced to room temperature (25°C) or below.

[0078] The SAF, salt, and aqueous carrier can be mixed, for example, by premixing the salt with the aqueous carrier, so that the salt is partially or completely dissolved in the aqueous carrier. The aqueous carrier with the dissolved salt therein can then be mixed with the SAF, for example, by spraying the aqueous carrier with the dissolved salt onto the SAF. After spraying the aqueous carrier with the dissolved salt onto the SAF, the mixture may or may not be further mixed, depending, for example, on the amount of SAF, i.e., the thickness of the layer of SAF. If the aqueous carrier with the dissolved salt is sprayed onto a thin layer of SAF so that the SAF is in adequate contact with the aqueous carrier and dissolved salt, further mixing may not be necessary.

[0079] As an alternative to premixing the aqueous carrier with the salt and dissolving the salt in the aqueous carrier, the aqueous carrier and salt can be provided separately to the SAF, with the salt dissolving in the aqueous carrier only after being mixed with the SAF. Importantly, the salt must be capable of dissolving in the aqueous carrier either after contact with the SAF, or preferably before contact with the SAF.

[0080] The aqueous carrier may be preheated to an elevated temperature before mixing the aqueous carrier with the salt and SAF. Such preheating may accelerate the decomposition process. Alternatively, the aqueous carrier may be preheated to a temperature less than the elevated temperature before mixing the salt and SAF. Still further alternatively, the aqueous carrier may not be preheated before mixing with the salt and SAF, and heating to the elevated temperature occurs after the aqueous carrier, salt, and SAF are mixed.

[0081] The SAF can be mixed with the aqueous carrier and salt using, for example, a paddle mixer, a plowshare mixer or kneader, or a static rotor mixer. Preferably, the mixture of SAF, aqueous carrier, and salt is mixed via high shear mixing.

[0082] If the salt is dissolved in the aqueous carrier before mixing with the SAF, the aqueous carrier may be preheated to a temperature below an elevated temperature to avoid premature formation of radicals or radical ions by the anions, which would result in the oxidizing salt decomposing by autolysis and then no longer being available to decompose the SAF after mixing with the SAF. However, if the salt is dissolved in the aqueous carrier only for a short time, or is dissolved immediately before mixing with the SAF, the aqueous carrier may be preheated to an elevated temperature before mixing with the SAF. Preheating may speed up the time it takes for the salt to dissolve in the aqueous carrier.

[0083] Alternatively or additionally, the SAF can be preheated to an elevated or lesser temperature before mixing with the aqueous carrier and salt. Preheating the SAF can result in a shorter swelling time for the SAF, thus facilitating absorption of the aqueous carrier and dissolved salt into the SAF and enabling faster decomposition. Faster absorption of the dissolved salt into the SAF can also improve the uniform distribution of the dissolved salt within the SAF, which can aid in more uniform decomposition and thus avoid leaving undecomposed pieces of SAF in the mixture.

[0084] Further alternatively, the mixture obtained in process step d) can be heated to an elevated temperature only after at least 50 wt. %, or at least 70 wt. %, or at least 90 wt. %, or all, of the aqueous carrier with the salt dissolved therein has been absorbed into the SAF, although some preheating to a temperature below the elevated temperature may already have taken place.

[0085] The ratio of salt to SAF can be from 0.001g to 0.05g salt per 1g SAF, or from 0.005g to 0.03g salt per 1g SAF, or from 0.01g to 0.03g salt per 1g SAF.

[0086] The ratio of aqueous carrier to SAF can be 2 g to 30 g of aqueous carrier per 1 g of SAF, or 2 g to 20 g of aqueous carrier per 1 g of SAF, or 5 g to 15 g of aqueous carrier per 1 g of SAF. The SAF can be provided in process step a) in a dry state or swollen with less than 20 g, or less than 15 g, or less than 10 g, or less than 5 g of liquid (such as water or saline) per 1 g of SAF.

[0087] The total amount of liquid absorbed (i.e., contained) in the SAF in process step e), including the liquid contained in the swollen SAF as provided in process step a), and the amount of aqueous carrier absorbed in and thus contained by the SAF in process step e) can be from 2 g to 25 g per gram of SAF, or from 2 g to 20 g per gram of SAF, or from 5 g to 15 g per gram of SAF, or from 8 g to 13 g per gram of SAF. As used herein, "dry SAF" means that the SAF has a liquid content (referred to as "moisture content") of less than 0.20 g per gram of SAF, preferably less than 0.15 g per gram of SAF. The moisture content of the SAF is measured according to EDANA Moisture Content Test Method NWSP 230.0.R2(15).

[0088] To ensure that the salt can be used to efficiently decompose the SAF, it is desirable that a significant amount of the aqueous carrier having the salt dissolved therein be absorbed by the SAF in process steps d) and e). At least 50 wt. %, or at least 60 wt. %, or at least 75 wt. %, or at least 90 wt. %, or 100 wt. % of the aqueous carrier having the salt dissolved therein provided in step c) can be absorbed by the SAF. Absorption of the aqueous carrier having the salt dissolved therein in process steps d) and e) means that the aqueous carrier having the salt dissolved therein can be absorbed only in process step d) (this is particularly the case when 100 wt. % is absorbed), or can be absorbed predominantly in process step e) (this can be the case when heating has already begun while the SAF, salt, and aqueous carrier are being mixed), or that a portion of the aqueous carrier having the salt dissolved therein is absorbed by the SAF in process step d), and another portion of the aqueous carrier having the salt dissolved therein is absorbed by the SAF in process step e).

[0089] The SAF provided in process step a) may have a centrifuge retention capacity (CRC) value of 7 g / g to 40 g / g, or 10 g / g to 35 g / g, or 15 g / g to 35 g / g. In the case of recycled SAF, after drying, the CRC should be measured, measured according to the CRC test method described herein.

[0090] If the SAF provided in method step a) is post-consumer recycled SAF, the CRC of the SAF has to be determined by first drying (a sample of) the SAF and then measuring the CRC on this sample.

[0091] At least one anion of the salt may be selected from the group consisting of peroxydisulfate, peroxymonosulfate, peroxydicarbonate, peroxydiphosphate, peroxydiborate, or mixtures thereof.

[0092] The at least one cation of the salt is typically not critical in that the cation does not dissociate into radicals. The at least one cation can be selected to have sufficient solubility in the aqueous carrier and should be available at a relatively low cost. The at least one cation is typically Li + , Na + , K. + , Rb + , Cs + , NH4 + , organic substituted ammonium, Ca2+, Mg2+, Sr2+, Ba2+, Al3+, transition metal cations in the oxidation states 1+ to 3+, or mixtures thereof (e.g., combinations of different salts with different cations). Most preferred are salts of one or more alkaline cations and NH4 + It is a cation.

[0093] At least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or 100% by weight of the total salt may be alkaline persulfate.

[0094] Hydrogen peroxide can be added in this method. Hydrogen peroxide can help increase the time yield of the soluble polymer, i.e., the decomposition rate. Hydrogen peroxide can also help decolorize decomposed contaminants. Hydrogen peroxide can be added to the SAF as a separate aqueous solution, with or without the salt dissolved in the aqueous carrier, or can be added to the aqueous carrier before mixing with the SAF. The amount of hydrogen peroxide used in the method of the present invention can be 10% to 200% by weight based on the weight of the salt, or 20% to 100% by weight ...

[0095] Process step e) can be carried out at a pH of 3 to 7. Typically, no further special measures are necessary to obtain a pH in this range. Persulfate radicals, for example, are less stable at pHs above 7.

[0096] Additives may be used in the method of the present invention. For example, low molecular weight alcohols such as methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, propylene glycol, glycerin, or mixtures thereof may be added to the aqueous carrier provided in method step c) or to the mixture in method step d). These additives, together with the aqueous carrier and the salts dissolved therein, may support the initial wettability of the SAF. They may also improve the stability of the aqueous carrier against bacterial contamination. Other additives, such as antimicrobial additives, may also be added. The total amount of additives may be 10% by weight or less, or 8% by weight or less, or 5% by weight or less, or 3% by weight or less, based on the weight of the aqueous carrier. In another embodiment, the decomposition mixture in method step d) does not contain additives and does not contain low molecular weight alcohols such as methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, propylene glycol, glycerin, or mixtures thereof.

[0097] The method of the present invention can be carried out in a continuous process or as a batch process. Generally, continuous processes are often preferred from a commercial / cost perspective. In a continuous process, the SAF can be provided, for example, in a continuous flow, such as, for example, a carrier belt, and the aqueous carrier and salt are mixed with the SAF, for example, by spraying the aqueous carrier and salt (and optionally hydrogen peroxide) onto the SAF. The mixture of SAF, salt, and aqueous carrier can be transferred onto the belt after process step d) (e.g., after the aqueous carrier with the salt dissolved therein has been partially or completely absorbed into the SAF) and heated in a continuous or batch manner.

[0098] Alternatively, the aqueous carrier (with the salt dissolved therein) can be provided in a batch tank or similar vessel before or after providing the aqueous carrier in the tank. The SAF can then be added to the tank already filled with the aqueous carrier and dissolved salt, and the SAF can be allowed to absorb the aqueous carrier and the salt dissolved therein, and simultaneously or subsequently, the mixture can be heated to an elevated temperature.

[0099] In the case of SAF, especially when provided as dry SAF, air tends to become "trapped" between the SAF, i.e., in the gaps between the SAF as it absorbs liquid and swells. Thus, the swollen SAF tends to "float" in the liquid. As the SAF decomposes, the soluble polymer may sink in the tank, where it can be (continuously) removed. To prevent undecomposed or partially decomposed SAF from being removed along with the soluble polymer (because some SAF may sink in the tank), a mesh or the like may be placed in the tank to prevent undecomposed or fully decomposed SAF from sinking further to the bottom of the tank, because the SAF will be trapped in the mesh until it is more completely decomposed and able to pass through the mesh.

[0100] Alternatively, the mixture of SAF, salt, and aqueous carrier can also be agitated so that the swollen SAF sinks toward the bottom of the vessel and the soluble polymer, i.e., the product of the process, can be removed from the top of the vessel.

[0101] The resulting solution containing the solubilized soluble polymer therein can be transferred, for example, via a pump, to a different tank, a pipe, or any other suitable device for any post-treatment that may be desired for the solution. Possible post-treatments are filtration, desalting, concentration by evaporation, or a number of other treatments.

[0102] The energy consumption of the decomposition process depends, inter alia, on the high temperature. The higher the temperature, the higher the energy consumption per hour (i.e., a short process time at a higher temperature may require less energy overall than a lower high temperature with a longer process time). For example, the energy consumption is about 3.5 MJ / kg dry SAF at a high temperature of about 100°C for a batch process in an insulated tank, i.e., a process in which heating to high temperature is performed only once.

[0103] The SAF provided in process step a) can be in particulate form. The SAF provided in the present process can be virgin SAF, post-consumer recycled SAF (PCR SAF), post-industrial recycled SAF (PIR SAF), or a combination of these materials. "Post-consumer SAF" and "post-consumer recycled SAF" (PCR SAF) are used interchangeably herein and, as used herein, refer to SAF contained in an AHP, which AHP has been used by a consumer (e.g., worn by an incontinent user). After use, the AHP is recycled, and the PCR SAF is isolated from the AHP. However, in the present process, it is not necessary to purify the SAF so that other components of the post-consumer AHP are not included in the post-consumer SAF provided to the present process.

[0104] "Post-industrial SAF" and "post-industrial recycled SAF" (PIR SAF) are used interchangeably herein and, as used herein, refer to SAF that may or may not be included in an AHP. PIR SAF have not been previously used, e.g., have not been included in an AHP that is being used by a consumer. Alternatively, PIR SAF may originate from an AHP that has been sorted out during production, e.g., because they are defective. PIR SAF may also be sorted out during SAF production, e.g., because they do not meet required performance targets (volume, whiteness, etc.). Thus, in the latter scenario, the PIR SAF have not previously been included in an AHP.

[0105] Typical properties of SAF are mechanical properties, swelling capacity, and centrifuge retention capacity (CRC) measured according to the test methods set forth herein.

[0106] The SAF also contains more than 25% by weight but less than 95% by weight of other comonomers (i.e., other than acrylic acid). Suitable comonomers are, for example, methyl acrylate, methyl methacrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, or monomer groups comprising / consisting of polymers and copolymers such as polyacrylamide, polyvinyl alcohol, ethylene-maleic anhydride copolymers, polyvinyl ethers, hydroxypropyl cellulose, polyvinyl morpholinone, and vinyl sulfonic acid, polyacrylamide, polyvinylamine, polyallylamine, and polyvinylpyridine. Other suitable polymers in the SAF include hydrolyzed acrylonitrile-grafted starch, acrylic acid-grafted starch, and isobutylene-maleic anhydride copolymers, and mixtures thereof. The SAF is crosslinked to render the material substantially water-insoluble. Preferred monomers are methyl (meth)acrylate and / or monomers containing hydroxyl groups, such as hydroxyalkyl (meth)acrylates, e.g., hydroxyethyl methacrylate, tripropylene glycol monoacrylate, 5 glyceryl monoacrylate, etc. The SAF may comprise / consist of polymers formed from two types of monomers (including acrylic acid) or, more preferably, three or more types of monomers.

[0107] The SAF may have a sodium level greater than about 8 wt% Na, or 10 wt% to 20 wt%, or 15 wt% to 18 wt% Na. In yet another embodiment of the present invention, the SAF has a sodium level less than 12 wt% Na (for the avoidance of doubt, weight-%, wt-%, and wt% are used interchangeably herein). Also, or alternatively, the SAF may have a potassium level greater than about 13.5 wt% K, or 17 wt% to 34 wt%, or 25.5 wt% to 30.6 wt% K. The SAF may have a potassium level less than 20.4 wt% K. The Na and K contents can be measured, for example, using inductively coupled plasma (ICP) analytical techniques, as is well known to those skilled in the art.

[0108] Alternatively, the SAF may be a mixture of NH4 in wt. + ammonium levels above about 6.3 wt. % as an amount of NH4 + The SAF may have an ammonium level of 7.8% to 15.7% by weight, or 11.7% to 14.1% by weight. + % by weight.

[0109] The SAF provided to the method of the present invention may be in a dry form or may be partially swollen with water, saline, or urine (e.g., urine in PCR SAF). Thus, the SAF may be swollen with water, saline, or urine to 0.05 g / g to 20 g / g, preferably 0.05 g / g to 15 g / g, more preferably 0.10 g / g to 10 g / g, more preferably 0.20 g / g to 5 g / g, and even more preferably 0.50 g / g to 2 g / g. Completely dry SAF (i.e., 0 g / g per 1 g of water, saline, or urine) may not be advantageous for the method of the present invention because completely dry SAF takes longer to absorb an aqueous carrier containing dissolved salts therein. On the other hand, excessively swollen (or even completely swollen) SAF when provided to the method may also result in an increased time for salts dissolved in the aqueous carrier to be absorbed by the SAF. The SAF provided to the present method may have an absorption capacity CRC (measured as centrifuge retention capacity "CRC" as described herein) of between 70 g / g and 40 g / g.

[0110] The amount of aqueous carrier provided in process step c) can be such that the SAF provided in step a) can swell to at least 20%, or at least 30%, or 50%, or at least 60%, or at least 70%, or at least 80% of its CRC upon absorption of all the aqueous carrier provided. If the SAF is provided in a pre-swollen state rather than a dry state (see further details below), less aqueous carrier is required to obtain the desired degree of SAF loading, i.e., the desired CRC.

[0111] As the liquid is absorbed, the polymer chains within the polymer network of the SAF begin to disentangle. Such disentanglement makes the polymer network more accessible to the radicals or radical ions formed from the salt, thus improving degradation. If the amount of aqueous carrier provided in step c) is not sufficient to allow the SAF to swell to at least 20% of its CRC upon absorption of the aqueous carrier, the polymer chains within the polymer network of the SAF will not disentangle sufficiently, resulting in slower or less effective degradation overall.

[0112] In the degradation process of the present invention, the use of post-consumer SAF can be advantageous over the use of virgin SAF. The polymer chains in the previously swollen polymer network, and then at least partially redried, are already disentangled. Re-swelling, and thus renewed disentanglement, is believed to be faster relative to the swelling of virgin SAF.

[0113] It is also advantageous that if the post-consumer SAF is provided to the method of the invention in a partially swollen form, the SAF does not need to be completely dried for use in the method, given the time and energy required to dry the post-consumer SAF. However, the post-consumer SAF may be sterilized before being provided to the method of the invention.

[0114] When post-consumer or post-industrial SAF is isolated from an AHP and provided to the method of the present invention, the SAF does not necessarily need to be purified to be free of other components of the AHP. The SAF may be contaminated with other components of the AHP, such as, for example, synthetic fiber materials or films (e.g., fibers, sheets, films, and fiber layers), cellulose fibers, adhesives, inks, dyes, surfactants, etc. The amount of these contaminants may be 20% or less by weight of the mixture of SAF and contaminants, or 15% or less by weight, or 10% or less by weight, or 5% or less by weight, or 2% or less by weight, or 1% or less by weight.

[0115] If the post-consumer SAF is still swollen, for example with urine or other liquid, this urine or other liquid contained by the SAF is not taken into account when calculating the amount of contaminant by weight of the mixture of SAF and contaminant.

[0116] When the SAF is provided as dry SAF of the present invention, the fiber size of the post-consumer or post-industrial SAF may optionally be reduced, for example, by cutting, crushing, grinding, or other suitable means, which may result in a reduced fiber length of about 50% or less of the unreduced fiber length, or from about 10% to about 70% of the unreduced fiber length.

[0117] If the SAF is provided in a pre-swollen form, such as post-consumer SAF that has not been dried or has only been partially dried after recycling, the SAF may be subjected to comminution to increase the surface area of ​​the SAF, thereby allowing for faster absorption of the aqueous carrier containing the salt dissolved therein. Such faster absorption may in turn result in faster degradation of the SAF. Comminution may be performed, for example, by wet grinding, dry grinding, or chopping.

[0118] Smaller fiber size can aid in faster and more uniform absorption of dissolved salts into the SAF, resulting in faster and more complete degradation of the SAF. Additionally, smaller fiber size can aid in mixing of the SAF with salts and aqueous carriers, especially in entangled fibers such as nonwovens.

[0119] Optional method step f) of separating the soluble polymer in the aqueous solution from other compounds and components in the mixture: Once the SAF has been decomposed into soluble polymers, the soluble polymers can be separated from the mixture of (possibly remaining undecomposed) SAF, salt, aqueous carrier, and optional additional components (e.g., hydrogen peroxide, and / or low molecular weight alcohol). The mixture can still contain a certain amount of undecomposed SAF that may be present in the mixture as a solid, insoluble component.

[0120] The soluble polymer can be extracted from the mixture via a number of processes. Non-limiting examples of these processes include water evaporation, filtration of the soluble polymer, water extraction, etc. Salts can also be removed by any desalination technique known to those skilled in the art. Non-limiting examples of desalination processes include membrane processes (e.g., reverse osmosis, forward osmosis, electrodialysis reversal (EDR), nanofiltration, etc.), freeze desalination, solar desalination, geothermal desalination, ion exchange, wave desalination, etc. The same techniques can also generally be applied to remove other low molecular weight compounds in the mixture, such as adhesives, inks, dyes, surfactants, and degradation products of these compounds, as well as other typical compounds of post-consumer AHPs.

[0121] For example, filtration can be used to remove solid compounds and components from the mixture, i.e., to separate the soluble polymer in the aqueous solution from other compounds and components in the mixture obtained by step c) in process step d). The solid compounds and components can be insoluble SAF and other components remaining in the post-consumer AHP, such as synthetic fiber materials or films (fibers, sheets / films / fiber layers) and cellulose. In particular, polyolefins (e.g., polypropylene, polyethylene) contained in other components of the post-consumer AHP, such as synthetic fiber materials or films, are not soluble or swellable in aqueous carriers. They react only negligibly with salts, i.e., polyolefins are not degraded or only slightly degraded in the process of the present invention. The same applies to PET, which can also be contained in synthetic fiber materials or films. Therefore, these materials remain as solid components in the mixture and can be filtered out.

[0122] PEG, another typical component of post-consumer AHPs, such as those found in surfactants, can be degraded by the method of the present invention. However, PEG is typically degraded into molecules with relatively low molecular weights, which are significantly smaller than the molecular weight of the soluble polymer. Therefore, the low molecular weight reaction products of PEG can be separated from the soluble polymer, for example, by the techniques described above.

[0123] Alternatively or additionally, the mixture of soluble polymer, (optionally remaining portion of) SAF, salt, and aqueous carrier, which may include compounds of post-consumer AHP, may also be mixed in a co-solvent in which the soluble polymer is insoluble, such that the soluble polymer precipitates and separates from the mixture. Prior to such mixing in the co-solvent, solid compounds in the mixture may be removed by filtration.

[0124] The soluble polymers obtained by the degradation method of the present invention may have different molecular weights. The soluble polymers may or may not contain oligomers. Preferably, the soluble polymers do not contain oligomers, i.e., the soluble polymers refer only to polymers. The average molecular weight Mw of the soluble polymers may be up to 10 MDa, or up to 5 MDa. The average molecular weight Mw of the soluble polymers may be at least 10 kDa, or at least 20 kDa, or between 30 kDa and 1 MDa. The soluble polymers may be linear or branched. However, the soluble polymers are not crosslinked, and therefore the soluble polymers are soluble, preferably water-soluble.

[0125] The soluble polymers obtained by the method of the present invention can be used in materials for other applications, such as adhesives, coatings, water treatment, or can be derivatized. In one embodiment of the present invention, the soluble polymers are used in adhesives, either as is or derivatized. In yet another embodiment of the present invention, the soluble polymers are used in fabric care applications, either as is or derivatized. In yet another embodiment of the present invention, the soluble polymers are used in water treatment applications, either as is or derivatized.

[0126] In one embodiment of the invention, the feed stream comprises SAF and an oxidizing water-soluble salt, the salt comprising at least one cation and at least one anion. In another embodiment of the invention, the feed stream comprises SAF and an oxidizing water-soluble salt, the salt comprising at least one cation and at least one anion, the anion being selected from the group consisting of peroxydisulfate, peroxymonosulfate, peroxydicarbonate, peroxydiphosphate, peroxydiborate, and combinations thereof. In yet another embodiment of the invention, the feed stream comprises SAF and an oxidizing water-soluble salt, the salt comprising at least one cation and at least one anion, the anion being selected from the group consisting of peroxydisulfate, peroxymonosulfate, peroxydicarbonate, peroxydiphosphate, peroxydiborate, and combinations thereof, the cation being Li + , Na + , K. + , Rb + , Cs + , NH4 + , organic substituted ammonium, Ca 2+ , Mg 2+ , Sr 2+ , Ba 2+ , Al 3+ , transition metal cations in the 1+ to 3+ oxidation states, and combinations thereof.

[0127] In one embodiment of the present invention, the feed stream is subjected to a biological process such that the negative decimal logarithm of the viscosity ratio between the feed stream and the product stream is greater than about 2. The biological process may involve an enzyme or microorganism that cleaves bonds present in the SAF, such as a carboxyl ester bond linking a soluble polymer to a poly(ethylene glycol) (PEG) crosslinker or an ether bond present in a PEG crosslinker. Breaking down such bonds may result in a decrease in the viscosity of the feed stream, which may allow for increased flow rates and / or reduced pressures as the feed stream flows through an extended flow device.

[0128] In one embodiment of the present invention, the feedstream comprises SAF and an enzyme, the enzyme having activity against the SAF. Non-limiting examples of enzymes are hydrolases and oxidases. Non-limiting examples of hydrolases are ester hydrolases, carboxyl ester hydrolases, ether hydrolases, cutinases, lipases, esterases, and carboyl esterases. In another embodiment of the present invention, the feedstream comprises SAF and an ester hydrolase. In yet another embodiment of the present invention, the feedstream comprises SAF and an ether hydrolase. Non-limiting examples of oxidases are peroxidases, peroxygenases, laccases, lipoxygenases, peroxidases, peroxygenases, monooxygenases, dioxygenases, and hydroxylases. In yet another embodiment of the present invention, the enzyme comprises an enzyme cocktail. In one embodiment of the present invention, the feedstream comprises SAF, the enzyme, and one or more of a cofactor, a cosubstrate, and a supplement.

[0129] In another embodiment of the invention, the feedstream comprises SAF and an enzyme cocktail. In yet another embodiment of the invention, the feedstream comprises SAF and an enzyme, wherein the enzyme comprises multiple catalytic activities, the activities being selected from the group consisting of carboxylesterases, ether hydrolases, and oxidases. The enzymes can be naturally occurring or engineered to improve properties such as substrate specificity, turnover, temperature stability, and pH stability. For example, hydrogen peroxide can be added to a peroxidase family enzyme or electron shuttle compound, such as, but not limited to, 1-hydroxybenzotriazole (HBT, synthetic grade), N-hydroxynaphthalimide (IMD-4, 99%), N-hydroxy-5-norbornene-2,3-dicarboxylic acid imide (NHND, 97%), N-hydroxyphthalimide (NPI, 97%), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), ABTS, or N,N'-dihydroxy-1,4,5,8-naphthaldiimide, IMD-8.

[0130] Non-limiting examples of bacterial microorganisms that degrade SAF in feedstreams include Bacillus cereus, Pseudomonas aureginosa, P. fluorescens, P. stutzeri, and Alcaligenes glycovorans. A non-limiting example of a fungal microorganism that degrades SAF is Phanerochaete chrysosporium. In another embodiment of the present invention, a combination or consortium of organisms, such as those listed herein, is utilized to degrade polymers in a feedstream. While not wishing to be bound by any theory, applicants believe that the microorganisms used in biological treatment express and produce at least one enzyme, such as the exemplary enzymes listed herein, that acts on the specific binding of SAF in the feedstream. The organism may also produce cofactors, cosubstrates, and / or allosteric modulators that enhance enzyme activity.

[0131] IV Product logistics A feed stream enters the inlet of the expansion device and produces a product stream at the outlet of the expansion flow device. In one embodiment of the invention, the product stream comprises a soluble polymer. In another embodiment of the invention, the product stream comprises a soluble polymer and an SAF.

[0132] In one embodiment of the invention, the soluble polymer has a weight average molecular weight of less than about 5,000,000 g / mol. In another embodiment of the invention, the soluble polymer has a weight average molecular weight of less than about 2,000,000 g / mol. In yet another embodiment of the invention, the soluble polymer has a weight average molecular weight of less than about 1,000,000 g / mol. In yet another embodiment of the invention, the soluble polymer has a weight average molecular weight of less than about 500,000 g / mol. In one embodiment of the invention, the soluble polymer has a weight average molecular weight of less than about 300,000 g / mol. In another embodiment of the invention, the soluble polymer has a weight average molecular weight of less than about 200,000 g / mol. In yet another embodiment of the invention, the soluble polymer has a weight average molecular weight of less than about 100,000 g / mol. In yet another embodiment of the invention, the soluble polymer has a weight average molecular weight of less than about 30,000 g / mol.

[0133] In one embodiment of the present invention, the soluble polymer has a weight average molecular weight of about 1,000,000 g / mol to about 5,000,000 g / mol. In another embodiment of the present invention, the soluble polymer has a weight average molecular weight of about 500,000 g / mol to about 2,000,000 g / mol. In yet another embodiment of the present invention, the soluble polymer has a weight average molecular weight of about 100,000 g / mol to about 1,000,000 g / mol. In yet another embodiment of the present invention, the soluble polymer has a weight average molecular weight of about 150,000 g / mol to about 500,000 g / mol. In one embodiment of the present invention, the soluble polymer has a weight average molecular weight of about 90,000 g / mol to about 300,000 g / mol. In another embodiment of the present invention, the soluble polymer has a weight average molecular weight of about 20,000 g / mol to about 200,000 g / mol. In yet another embodiment of the present invention, the soluble polymer has a weight average molecular weight of from about 10,000 g / mol to about 100,000 g / mol.

[0134] In one embodiment of the invention, the soluble polymer has a polydispersity index (PDI) of less than about 10. In another embodiment of the invention, the soluble polymer has a PDI of less than about 6. In yet another embodiment of the invention, the soluble polymer has a PDI of less than about 4. In yet another embodiment of the invention, the soluble polymer has a PDI of less than about 2. PDI is the ratio of weight average molecular weight to number average molecular weight, and these molecular weights are measured by GPC (described in Methods Section VII), as known to those skilled in the art.

[0135] The viscosity of the product stream is typically measured using either a parallel plate fixture in oscillatory mode or a cup and bob fixture in steady mode. Reported oscillatory viscosities typically correspond to 1 rad / s, and reported steady-state viscosities typically correspond to 4 s -1 Depending on the concentration and molecular weight of the soluble polymer, the viscosity of the product stream can be as low as 1 mPa.s (or equivalently, 1 cP; i.e., the viscosity of water).

[0136] The ratio of the viscosity of the product stream to the viscosity of the feed stream is the viscosity reduction ratio (or simply viscosity ratio), which indicates the extent of SAF degradation into soluble polymers by the UV flow system. The negative decimal logarithm of the viscosity ratio measures the order of magnitude of viscosity change between the feed stream and the product stream. In one embodiment of the invention, the feed stream has a viscosity, the product stream has a viscosity, the ratio of the viscosity of the product stream to the viscosity of the feed stream is the viscosity ratio, and the negative decimal logarithm of the viscosity ratio is less than about 6. In another embodiment of the invention, the feed stream has a viscosity, the product stream has a viscosity, the ratio of the viscosity of the product stream to the viscosity of the feed stream is the viscosity ratio, and the negative decimal logarithm of the viscosity ratio is less than about 4. In yet another embodiment of the invention, the feed stream has a viscosity, the product stream has a viscosity, the ratio of the viscosity of the product stream to the viscosity of the feed stream is the viscosity ratio, and the negative decimal logarithm of the viscosity ratio is less than about 2.

[0137] The soluble polymers from the product stream can be derivatized into materials for various applications, such as adhesives, coatings, water treatment, etc. In one embodiment of the invention, the soluble polymers from the product stream are used as adhesives, either as is or derivatized. In yet another embodiment of the invention, the soluble polymers from the product stream are used in fabric care applications, either as is or derivatized. In yet another embodiment of the invention, the soluble polymers from the product stream are used in water treatment applications, either as is or derivatized.

[0138] In one embodiment of the invention, the soluble polymer from the product stream is used as a ply glue in a paper product. In another embodiment of the invention, the soluble polymer from the product stream is used as a ply glue in a paper towel product. In yet another embodiment of the invention, the soluble polymer from the product stream is used as a ply glue in a toilet paper product. In yet another embodiment of the invention, the soluble polymer from the product stream has an M of greater than about 350 kDa. w In one embodiment of the present invention, the soluble polymer from the product stream has an M of about 400 kDa to about 500 kDa and is used as a ply glue in paper products. w It is used as a ply glue in paper products.

[0139] In another embodiment of the present invention, the soluble polymer from the product stream is used as a glue between a paper core and a paper towel product. In yet another embodiment of the present invention, the soluble polymer from the product stream is used as a glue between a paper core and a toilet paper product.

[0140] Soluble polymers can be extracted from the product stream via a number of processes. Non-limiting examples of these processes include water evaporation, soluble polymer filtration, water extraction, etc. Additionally, salts present in the product stream from the use of SAF in AHP can be removed by any desalination technique known to those skilled in the art. Non-limiting examples of desalination processes include membrane processes (e.g., reverse osmosis, forward osmosis, electrodialysis reversal (EDR), nanofiltration, etc.), freeze desalination, solar desalination, geothermal desalination, ion exchange, wave desalination, etc.

[0141] V Recycled SAF The soluble polymer from the product stream can be fed to a process to make SAF using acrylic acid, thus producing recycled SAF. In one embodiment of the present invention, the soluble polymer is used to make recycled SAF.

[0142] In one embodiment of the present invention, the recycled SAF has a CRC, measured using the CRC test method described herein, of about 7 g / g to about 45 g / g. In another embodiment of the present invention, the recycled SAF has a CRC, measured using the CRC test method described herein, of about 10 g / g to about 35 g / g. In yet another embodiment of the present invention, the recycled SAF has a CRC, measured using the CRC test method described herein, of about 15 g / g to about 35 g / g.

[0143] VII Method NMR content method The NMR content method detects the presence of alkene terminal moieties, alkoxy groups (-O-CHR1-, where R1 is one of H, alkyl, aryl, heteroaryl, alkoxy, or halogen groups), aliphatic groups (-CHR1-, where R1 is one of H, alkyl, aryl, heteroaryl, or halogen groups), and / or other groups. 1 It is used to determine the molar ratio of functional groups with different NMR signals, such as H-NMR active groups.

[0144] In this method, proton NMR spectroscopy is used to analyze samples of soluble materials in deuterated water to identify different 1 The peaks in the H-NMR domains are integrated and the ratios are taken to determine the functional groups or different 1 Determine the mole percentage of protons in each H-NMR domain.

[0145] The soluble polymer is dried in a vacuum oven (Heraeus Vacutherm model, Thermo Scientific™) at 40° C. and 10-50 mbar pressure for 3 hours. Any low molecular weight alcohols, esters, or ethers are removed from the soluble polymer.

[0146] A fluid solution is prepared by dissolving less than 10% by weight of the sample in DO and adjusting the pH to 5.5-6.5. The solution is transferred to an NMR glass-grade tube and placed in the sample holder (bore) of a proton NMR instrument. An example of a suitable instrument is a Bruker NMR device with a 400 MHz field strength. Instruments from other manufacturers and with other field strengths, including "low-field" instruments operating as low as 60 MHz, can also be successfully used to perform this method. A nosy-presat sequence is used to acquire data and suppress residual water signals. Those skilled in the art will be familiar with the appropriate selection of other specific data collection parameters. Suitable parameters used with the exemplary 400 MHz Bruker instrument described above are a 4.1-second acquisition time (FID length), an 8-second relaxation time, a 90-degree pulse width, a 20 ppm spectral width, 64 k points in the FID, and 64 repeated scans. In the Fourier transform step, exponential apodization is used with 0.3 Hz line broadening, and the spectrum is absorbed stepwise. Spline baseline correction is used to ensure a flat baseline on either side of the integrated peak.

[0147] The following peak areas are typically used and integrated for content determination: 1) One of two terminal alkene protons at chemical shifts in the range of approximately 5-6 ppm, typically one terminal alkene proton at approximately 5.35 ppm + / - 0.5 ppm. (To confirm the identification of such proton peaks as terminal alkene protons, use standard edited 1 H- 13 Using the C HSQC sequence (e.g., according to W. Wilker, D. Leibfritz, R. Kerssebaum & W. Bermel, Magn. Reson. Chem. 31, 287-292 (1993)), it can be determined that both alkene signals seen in the 1D-1H spectrum are attached to the same methylene (secondary) carbon (-CH2). The resulting integral is called "integral_alkene." 2) Alkoxy protons at chemical shifts in the range of about 3.2-3.8 ppm, typically about 3.6 ppm. The resulting integral is called "integral_3.6." If multiple signals appear around 3.6 ppm, i.e., in the range of about 3.2-3.8 ppm, the signal with the largest integral value is selected to obtain "integral_3.6." 3) Methylene protons of aliphatic CH groups, typically at about 1.5 ppm and 2.1 ppm, or about 1.8 ppm. The integral obtained is called "integral_CH." 4) Other aliphatic groups at chemical shifts in the range of approximately 1.0 to 2.6 ppm. 5) Different under the following conditions 1 Other groups or peaks of H-NMR domains can be analyzed similarly. a) It is a separated signal; b) have peak maxima at a distance of at least 0.5 ppm; 6) Identify peaks in the NMR spectrum corresponding to classes 1), 2), 3), and / or 4) and integrate them if present. If no such peaks are present, this is reported as no measurable content of classes 1), 2), 3), or 4), respectively. As known to those skilled in the art, the integral ranges from baseline (start of signal) to baseline (end of signal), or, if broad and / or complex, the boundary of the integral originates from the start of the next adjacent signal.

[0148] The ratio "3.6:CH" is calculated by the following formula: ratio 3.6:CH=integral_3.6 / integral_CH The ratio 3.6:CH is a unitless number and represents the ratio of protons at approximately 3.6 ppm.

[0149] The alkene content "% alkene" is calculated by the following formula: %alkene=[integral_alkene / (integral_alkene+integral_3.6+integral_CH)] * 100%

[0150] The methylene content "% CH" is calculated by the following formula: %CH=[integral_CH / (integral_alkene+integral_3.6+integral_CH)] * 100%

[0151] The content of approximately 3.6 ppm protons (e.g., alkoxy protons) "%3.6 ppm" is calculated by the following formula: %3.6=[integral_3.6 / (integral_alkene+integral_3.6+integral_CH)] * 100%

[0152] The ratio "3.6:CH" is reported to the nearest 0.001.

[0153] Alkene, methylene, and proton contents at approximately 3.6 ppm are reported in % to the nearest 0.01%.

[0154] Centrifuge Retention Capacity (CRC) Test Method The capacity of superabsorbent fibers is determined in accordance with the Centrifuge Retention Capacity (CRC) test method set forth in EDANA NWSP 241.0.R2(19). In deviation from EDANA NWSP 241.0.R2(19), sampling of superabsorbent fibers, superabsorbent nonwovens, and / or superabsorbent cores (Chapter 8 of EDANA NWSP 241.0.R2(19)) is as follows:

[0155] The superabsorbent fibers, superabsorbent nonwoven fabric, and / or superabsorbent core are cut into small pieces with a maximum dimension of approximately 5 mm. Cutting can be done manually, for example, with scissors. Care is taken to ensure that the fibrous structure (core, nonwoven fabric, or bulk of fibers) is not significantly compressed before or during the cutting process. This ensures sufficient void space between the superabsorbent fibers, so that the superabsorbent fibers can be primarily wetted by the swelling medium over their entire surface area.

[0156] Further deviations or additions from EDANA NWSP 241.0.R2(19) in the procedures for superabsorbent fibers, superabsorbent nonwovens, and / or superabsorbent cores (Chapters 9.1-9.5 of EDANA NWSP 241.0.R2(19)) are as follows:

[0157] The sample for measurement is carefully taken, for example using laboratory tweezers, and placed in a tea bag. Using the laboratory tweezers, the fibers are carefully distributed into the tea bag to avoid clumps, and any clumps of fibers are carefully opened.

[0158] When sealing the tea bag, care is taken to ensure that the sealed area is free of superabsorbent fiber, superabsorbent nonwoven, and / or superabsorbent core material, to ensure a complete and sufficiently strong seal of the tea bag.

[0159] All other aspects of the test method will be performed as described in EDANA NWSP 241.0.R2(19).

[0160] Total Energy Calculation The total energy is the electrical energy supplied to the extended flow device and is based on the voltage and amperage of the device and the residence time of the feed stream. Extended flow devices typically calculate the total energy from the motor torque and speed and the residence time of the feed stream in the extended flow device. The total energy per unit mass of SAF is then calculated from the total energy and the amount of SAF in the feed stream.

[0161] Specific Energy Calculation Specific energy is the energy dissipated in the feed stream used to convert the SAF to soluble polymer and is based on the pressure drop in the feed stream as it flows through an expanded flow system. As an example, if the pressure drop in the feed stream is 4945 psi (341 bar), the volume of the feed stream is 400 mL, and the feed stream density is 1 g / mL, the specific energy is calculated as follows: (341 (bar) × 0.4 (L)) / (400 (mL) × 0.025 (g SAF / g) × 1 (g / mL)) = 1.36 MJ / kg SAF.

[0162] Molecular Weight Distribution (MWD) analysis This is performed using gel permeation chromatography (GPC) with multi-angle light scattering (MALS) and refractive index (RI) detection. Samples are prepared at a concentration of 1 mg / mL in 0.1 M NaNO3 / 0.02 wt% sodium azide (NaN3) and allowed to hydrate overnight with gentle mixing at room temperature. Samples are then filtered through a 0.8 μm filter prior to GPC-MALS / RI analysis. Absolute MWD distributions are calculated using a dn / dc value of 0.15.

[0163] It should be understood that the foregoing description has been given for clarity of understanding only, and that no unnecessary limitations should be implied therefrom, since modifications within the scope of the invention will be apparent to those skilled in the art.

[0164] The dimensions and values ​​disclosed herein should not be understood 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."

[0165] All documents cited herein, including any cross-references or related patents or applications, are incorporated herein by reference in their entirety unless expressly excluded or otherwise limited. The citation of any document shall not be deemed to be prior art to any invention disclosed or claimed herein, or to teach, suggest, or disclose any such invention, either alone or in combination with any other reference(s). Furthermore, 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.

[0166] While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

1. 1. A method for decomposing superabsorbent fibers (SAF) into soluble polymers, the soluble polymers comprising 5% to 75% by weight of polymerized acrylic acid monomer units, based on the total weight of the soluble polymers, the method comprising: flowing a feed stream in the form of a gel comprising the SAFs into an inlet of an extended flow device; and producing a product stream comprising the soluble polymers at an outlet of the extended flow device, the feed stream comprising the SAFs at a concentration greater than about 1% by weight, the feed stream having a residence time in the extended flow device of less than about 120 seconds, the decomposition of the SAFs into the soluble polymers requiring a total energy of less than about 50 MJ / kg SAF, the extended flow device comprising, in a flow direction, an inlet chamber, an orifice, and a mixing chamber, the mixing chamber having a blade, the blade being positioned before and spaced apart from the orifice in the mixing chamber.

2. The method of claim 1 , wherein the residence time is less than about 60 seconds.

3. 3. The method of claim 1 or 2, wherein the total energy is less than about 16 MJ / kg SAF.

4. The method of any one of claims 1 to 3, wherein the feed stream comprises SAF and water.

5. The method of any one of claims 1 to 4, wherein the feed stream comprises SAF and hydrogen peroxide.

6. 6. The method of any one of claims 1 to 5, wherein the SAF has a sodium level of about 10% to about 20% by weight as the amount of Na.

7. 7. The method of any one of claims 1 to 6, wherein the feed stream has a viscosity, the product stream has a viscosity, the ratio of the viscosity of the product stream to the viscosity of the feed stream is a viscosity ratio, and the negative decimal logarithm of the viscosity ratio is less than about 4.

8. 8. The method of any one of claims 1 to 7, wherein the feed stream has a viscosity, the product stream has a viscosity, the ratio of the viscosity of the product stream to the viscosity of the feed stream is a viscosity ratio, and the negative decimal logarithm of the viscosity ratio is less than about 2.

9. The method of any one of claims 1 to 8, wherein the soluble polymer has a weight average molecular weight of less than about 2,000,000 g / mol.

10. The method of any one of claims 1 to 9, wherein the soluble polymer has a weight average molecular weight of less than about 1,000,000 g / mol.

11. The method of any one of claims 1 to 10, wherein the soluble polymer has a polydispersity index (PDI) of less than about 4.

12. 12. The method of any one of claims 1 to 11, wherein the SAF has a centrifuge retention capacity of at least 15 g / g as measured using the CRC test method.

13. 1. A method for degrading superabsorbent fibers (SAF) into soluble polymers, the soluble polymers comprising 5% to 75% by weight of polymerized acrylic acid monomer units, based on a total weight of the soluble polymer, the method comprising: flowing a feed stream in the form of a gel comprising the SAF into an inlet of an extended flow device; and producing a product stream comprising the soluble polymer at an outlet of the extended flow device, the feed stream comprising water and SAF at a concentration greater than about 1% by weight, the feed stream having a residence time in the extended flow device of less than about 120 seconds, and the decomposition of the SAF into the soluble polymers is greater than about 16 MJ / kg. A method for producing a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol, the method requiring a total energy of less than SAF, the method comprising: a) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; b) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; c) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; d) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; e) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; f) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; g ...

14. 1. A method for degrading superabsorbent fibers (SAF) into soluble polymers, the soluble polymers comprising 5% to 75% by weight of polymerized acrylic acid monomer units, based on the total weight of the soluble polymer, the method comprising: flowing a feed stream in the form of a gel comprising the SAF into an inlet of an extended flow device; and producing a product stream comprising the soluble polymer at an outlet of the extended flow device, the feed stream comprising water and SAF at a concentration greater than about 5% by weight, the feed stream having a residence time in the extended flow device of less than about 120 seconds, and the decomposition of the SAF into the soluble polymers is greater than about 16 MJ / kg. A method for producing a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol, the method requiring a total energy of less than SAF, the method comprising: a) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; b) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; c) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; d) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; e) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; f) forming a soluble polymer having a weight average molecular weight of less than about 1,000,000 g / mol; g ...

15. 15. The method of claim 14, wherein the feed stream has a viscosity, the product stream has a viscosity, the ratio of the viscosity of the product stream to the viscosity of the feed stream is a viscosity ratio, and the negative decimal logarithm of the viscosity ratio is less than about 4.

16. 16. The method of claim 14 or 15, wherein the SAF has a sodium level of about 10% to about 20% by weight as the amount of Na.

17. The method of any one of claims 14 to 16, wherein the feed stream comprises SAF and hydrogen peroxide.

18. The method of any one of claims 1 to 17, wherein the SAF is provided as loose fibers.

19. The method of any one of claims 1 to 17, wherein the SAF is provided in the form of a nonwoven web, the nonwoven web comprising the SAF.

20. 20. The method of claim 19, wherein the nonwoven web is cut, shredded, or comminuted before being subjected to the method or during the performance of the method.

21. 5. The method of any one of claims 1 to 4, wherein the SAF has a sodium level greater than 8% by weight as the amount of Na.

22. 10. The method of claim 1, wherein the feed stream has a viscosity, the product stream has a viscosity, the ratio of the viscosity of the product stream to the viscosity of the feed stream is a viscosity ratio, and the negative decimal logarithm of the viscosity ratio is less than about 6.

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