Recycling of superabsorbent polymers using an extensional flow device

Abstract

A poly(acrylic acid)-based superabsorbent polymer (SAP) in a feed stream is converted to poly(acrylic acid) (PAA) in an extensional flow device. The total energy used to degrade SAP to PAA is less than about 50 MJ / kg SAP.

Description

Technical Field

[0001] The present invention generally relates to the recovery of poly(acrylic acid)-based superabsorbent polymers (SAPs) using an extensional flow device with short residence times and optional and additional cavitation. More specifically, a feed stream comprising SAP is fed into the extensional flow device and produces a product stream comprising essentially poly(acrylic acid) (PAA). The concentration of SAP in the feed stream is greater than about 1 wt%, and the total energy used to convert the SAP to PAA is less than about 50 MJ / kg SAP. Background Art

[0002] Recycling absorbent hygiene products (AHPs) (i.e., baby diapers, feminine protection pads, and adult incontinence pads) is beneficial to the environment and is necessary to achieve the sustainability goals of many consumer product companies. These goals involve using 100% recycled materials and achieving zero landfill waste from consumer products and manufacturing. In addition to these goals, successful recycling also benefits the environment, stimulates the economy, improves human health and water quality, and provides needed energy for consumers in developing regions of the world.

[0003] The main component of AHP is typically superabsorbent polymer (SAP), while other components include binders, cellulose fibers, polyethylene, polypropylene, and polyester. SAP is a water-absorbing, water-swellable, and water-insoluble powdered solid that is a cross-linked and partially neutralized homopolymer of glacial acrylic acid. SAP has an exceptionally high ability to absorb aqueous liquids, such as contaminated water or urine. Approximately 97% of SAP produced today is used in AHP applications, while the remaining approximately 3% is used in other applications, such as agricultural or horticultural water retainers and industrial waterproofing agents.

[0004] Recycling AHP involves cleaning it from the soil that accumulates during its use and separating the various components into recycled material streams. More specifically, the recycled SAP material stream can be used in applications that require less than the AHP (because the properties of recycled SAP are inferior compared to virgin SAP; for example, agricultural or horticultural water retainers and industrial water repellents) and / or can be converted into essentially non-crosslinked and slightly branched or linear poly(acrylic acid) (PAA). This PAA can then be used as a feed material for a variety of applications. For example, PAA can be: 1) used as is in applications such as water treatment or corrosion inhibition; or 2) esterified and then used in adhesives, coatings, etc.; or 3) repolymerized and recrosslinked back into SAP; or 4) blended with virgin SAP. The first two groups of applications are part of efforts to recycle SAP into other products by replacing virgin acrylic-based compounds with compounds derived from recycled SAP, while the latter two groups of applications are part of the SAP circular economy (i.e., recycling SAP back into SAP). In all cases, the goal is to achieve the same properties as the virgin material.

[0005] Non-limiting examples of processes for producing a purified and separated spent SAP material stream from recovered AHP are disclosed and claimed in U.S. Patents 9,095,853 B2, issued August 4, 2015, and 9,156,034 B2, issued October 13, 2015, both assigned to Fater SpA, headquartered in Pescara, Italy.

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

[0007] The ultrasonic degradation of SAP is described in the following literature: (1) Ebrahimi, R. et al., Organic Chemistry Intl, 2012, article number 343768, 5 pages; and (2) Shukla, NB and Madras, G., J. Appl. Polym. Sci., 125 (2012), 630-639. The ultrasonic degradation of PAA is described in the following literature: (1) Shukla, NB et al., J. Appl. Polym. Sci., 112 (2009), 991-997; and (2) Prajapat, AL and Gogate, PR, Ultrason. Sonochem., 32 (2016), 290-299. Furthermore, a general description of the ultrasonic degradation of polymers in solution is given in Basedow, AM and Ebert, KH, Adv. Polym. Sci., 22 (1977), 83-148.

[0008] For the degradation of SAPs, both references use viscosity as a measure of degradation level and find that it takes about 5 to 10 minutes to reduce 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 this level of degradation. For the degradation of linear polymers, the main themes of these references (and others reporting the use of UV, thermal, and other forms of energy) are that (1) preferential cleavage occurs at the midpoint of the polymer chain, (2) higher molecular weight chains degrade at a higher rate than lower molecular weight chains, and (3) there is a minimum molecular weight below which no degradation or depolymerization occurs. In all cases, the sonication degradation of polymers is due to cavitation and the rapid growth and collapse of the resulting microbubbles.

[0009] Therefore, there is a need to recover AHP and its main component, which is SAP. For the recovery of SAP, it is necessary to degrade SAP to poly(acrylic acid) (PAA) in the following circumstances: within a short period of time; using low energy and electricity per unit mass of SAP; and under mild conditions, such as room temperature, so as to avoid decarboxylation of the degraded SAP. The low energy requirement per unit mass of SAP stems from the fact that recycling spent SAP and degrading it to PAA is only beneficial if the energy consumed during the conversion of SAP to PAA is lower than the energy used to produce fossil-derived acrylic acid (petro-AA) from propylene, which is about 50 MJ / kg AA. The PAA produced from SAP can then be incorporated back into the original SAP (thereby increasing its recycled content and supporting the circular economy of SAP) and / or derived into materials for other applications (such as adhesives, coatings, water treatment, fabric care, etc.). Summary of the Invention

[0010] In one embodiment of the present invention, a method for degrading a superabsorbent polymer (SAP) to poly(acrylic acid) (PAA) is provided. The method comprises flowing a feed stream comprising the SAP into an inlet of an extensional flow device and producing a product stream comprising the PAA at an outlet of the extensional flow device; wherein the feed stream comprises the SAP at a concentration greater than about 1 wt. %; wherein the feed stream has a residence time in the extensional flow device of less than about 120 seconds; and wherein the degradation of the SAP to the PAA requires a total energy of less than about 50 MJ / kg SAP.

[0011] In another embodiment of the present invention, a method for degrading superabsorbent polymer (SAP) to poly(acrylic acid) (PAA) is provided. The method comprises flowing a feed stream comprising the SAP into an inlet of an extensional flow device and producing a product stream comprising PAA at an outlet of the extensional flow device; wherein the feed stream comprises water and a concentration of greater than about 1 wt. % of the SAP; wherein the feed stream has a residence time in the extensional flow device of less than about 120 seconds; wherein the degradation of the SAP to the PAA requires a total energy of less than about 16 MJ / kg SAP; and wherein the PAA has a weight average molecular weight of less than about 1,000,000 g / mol.

[0012] In yet another embodiment of the present invention, a method for degrading superabsorbent polymer (SAP) to poly(acrylic acid) (PAA) is provided. The method comprises flowing a feed stream comprising the SAP into an inlet of an extensional flow device and producing a product stream comprising PAA at an outlet of the extensional flow device; wherein the feed stream comprises water and a concentration of greater than about 5% by weight of the SAP; wherein the feed stream has a residence time in the extensional flow device of less than about 120 seconds; wherein the degradation of the SAP to the PAA requires a total energy of less than about 16 MJ / kg SAP; and wherein the PAA has a weight average molecular weight of less than about 1,000,000 g / mol. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] While the specification concludes with claims particularly pointing out and distinctly claiming the invention, it is believed the present invention will be better understood from the following description taken in conjunction with the accompanying drawings, in which:

[0014] Figure 1is a graph showing the negative logarithm of the viscosity ratio between the feed stream and the product stream as a function of the residence time of the feed stream in the liquid whistle, for the case of orifices only without hydrodynamic cavitation (i.e., the blades are not engaged), and for a 2.5 wt% SAP and a 97.5 wt% reverse osmosis (RO) water feed stream.

[0015] Figure 2 is a graph showing the negative logarithm of the viscosity ratio between the feed stream and the product stream as a function of the residence time of the feed stream in the liquid whistle, in the presence of an orifice and hydrodynamic cavitation (i.e., the blades are engaged), and for a 2.5 wt% SAP and 97.5 wt% RO water feed stream.

[0016] Figure 3 is a graph showing the negative logarithm of the viscosity ratio between the feed stream and the product stream as a function of the residence time of the feed stream in the liquid whistle, in the presence of an orifice and hydrodynamic cavitation (i.e., the blades are engaged), and for the feed streams: 2.5 wt% SAP and 97.5 wt% RO water and 2.5 wt% SAP and 97.5 wt% of a 3 wt% H2O2 solution.

[0017] Figure 4 is a graph showing the negative logarithm of the viscosity ratio between the feed stream and the product stream as a function of the residence time of the feed stream in the liquid whistle for the case of orifices only without hydrodynamic cavitation (i.e., the blades are not engaged) and for the feed streams: 2.5 wt% SAP and 97.5 wt% RO water and 2.5 wt% SAP and 97.5 wt% of a 3 wt% H2O2 solution.

[0018] Figure 5 is shown by Thermo Scientific TM Nicolet TM Graph of the FTIR spectra of the feed stream SAP (Example 1) and the product stream PAA (Examples 1 to 5) collected on an iS50 FT-IR spectrometer (Golden Gate KRS5 ATR with diamond crystal, ZnSe lens). For neutralized PAA, COO - (Symmetrical) shown at approximately 1400 cm -1 At the COO - (Antisymmetric) displayed at approximately 1600 cm -1 and for unneutralized PAA, C=O is shown at approximately 1700 cm -1 (See Kirwan, LJ et al., Langmuir, 19 (2003), 5802–5807).

[0019] Figure 6is shown by Thermo Scientific TM Nicolet TM Graph of the FTIR spectra of the feed stream SAP (Example 6) and the product stream PAA (Examples 6 to 10) collected on an iS50 FT-IR spectrometer (Golden Gate KRS5 ATR with diamond crystal, ZnSe lens). For neutralized PAA, COO - (Symmetrical) shown at approximately 1400 cm -1 At the COO - (Antisymmetric) displayed at approximately 1600 cm -1 and for unneutralized PAA, C=O is shown at approximately 1700 cm -1 (See Kirwan, LJ et al., Langmuir, 19 (2003), 5802–5807). DETAILED DESCRIPTION

[0020] I Definition

[0021] As used herein, the term "SAP" refers to a cross-linked, partially neutralized superabsorbent polymer based on poly(acrylic acid). Examples of SAP are disclosed in U.S. Patents 8,383,746 B2 and 9,822,203 B2. Typically, SAP is capable of absorbing a 0.9 wt.% saline solution at 25°C, which is at least 10 times its dry weight. The typical absorption mechanism is osmotic pressure. SAP that absorbs water or an aqueous solution becomes a gel.

[0022] As used herein, the term "neutralization degree" or "DN" refers to the molar percentage of acid groups in a SAP or PAA that have been neutralized by reaction with a base (typically sodium hydroxide). A typical method for measuring the DN of a SAP is to measure the Na content using inductively coupled plasma (ICP) analysis, which is well known to those skilled in the art. If the amount of Na is expressed as wt% (Na), the degree of neutralization is calculated as DN = 100 x 72 / ((23 x 100 / wt% (Na)) - 22).

[0023] As used herein, the term "poly(acrylic acid)" or "PAA" or "acrylic acid polymer" refers to essentially non-crosslinked and slightly branched or linear poly(acrylic acid) molecules having acrylic acid as monomer units and a degree of polymerization that can be 2 or higher. For the purposes of the present invention, no distinction is made between acrylic acid polymers and acrylic acid oligomers.

[0024] As used herein, the term "degradation" refers to the conversion of SAP to PAA via partial depolymerization, decrosslinking, molecular backbone scission, or any combination thereof. For the purposes of this invention, the terms degradation, recovery, and conversion are used interchangeably, as long as they refer to the conversion of SAP to PAA. Furthermore, degradation substantially preserves the carboxyl groups of the SAP, and thus the product PAA contains these carboxyl groups. Note that complete depolymerization of SAP should yield acrylic acid (AA).

[0025] As used herein, the term "virgin SAP" refers to SAP produced from virgin glacial acrylic acid, which is the raw material used to make SAP today. Virgin acrylic acid can be produced from fossil-derived propylene or other bio-derived materials (non-limiting examples of bio-materials are: lactic acid, 3-hydroxypropionic acid, glycerol, bio-propylene, carbon dioxide, and sugars). Virgin SAP does not include any recycled SAP above about 1% by weight.

[0026] As used herein, the term "used SAP" refers to SAP that has been industrially produced and / or commercially used (e.g., for baby diapers, feminine pads, adult incontinence pads, or other articles and / or uses). Used SAP can be post-consumer SAP, post-industrial SAP, or a combination of the two. Unless otherwise specified herein, SAP refers to "used SAP" or "virgin SAP."

[0027] As used herein, the term "degraded SAP" refers to SAP that has been degraded into PAA. For the purposes of the present invention, the terms "degraded SAP" and "PAA" are used interchangeably.

[0028] As used herein, the term "recycled SAP" refers to SAP that contains at least 1 wt. % degraded SAP (or equivalently, PAA) that is incorporated into the SAP when it is produced from glacial acrylic acid using typical production methods. Thus, the recycled SAP is a blend of virgin SAP and at least 1 wt. % degraded SAP.

[0029] As used herein, the term "feed stream" refers to a body of fluid that flows in a specific direction and is fed to the inlet of an extensional flow device.

[0030] As used herein, the term "product stream" refers to the body of fluid produced at the outlet of an extensional flow device when a feed stream is fed to the inlet of the same device.

[0031] As used herein, the term "Liquid Whistle" refers to a device of the Sonolator type (manufactured by Sonic Corporation, Stratford, CT), which uses an inlet chamber, an orifice, and a mixing chamber in the direction of flow, wherein the blade is in front of the orifice. The material flows through the orifice, and the jet impacts the blade, which then forces the blade to vibrate at its resonant frequency, and if the blade is within a range of 7 to 8 times the orifice hydraulic diameter from the orifice (i.e., the blade is engaged), the cavitation field is further enhanced. If the blade is outside the range of 7 to 8 times the orifice hydraulic diameter from the orifice, it is considered that the blade is not engaged. The closer the blade is to the orifice, and the lower the viscosity of the feed stream, the stronger the cavitation. The main purpose of liquid whistle (LW) is mixing, emulsification, depolymerization, and disinfection in household, personal care, and fine chemical industries (U.S. Patent No. 8,517,595B2 and Ryan, DJ et al., Chem. Engng Sci., 189 (2018), 369-379). For the purposes of this invention, LW is one type of extensional flow device that can be used.

[0032] As used herein, the term "extensional flow device" refers to a flow device that produces extensional flow, strain, and stress. Non-limiting examples of extensional flow devices are devices with converging and / or diverging channels, orifices, impinging jets, four-roll mills, screens, dies, and the like. For the purposes of the present invention, the terms "extension" and "elongation" are used interchangeably.

[0033] 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 in oscillatory mode with a parallel plate fixture, and the reported complex viscosity typically corresponds to a frequency of 1 rad / s. The viscosity of the product stream is measured in steady mode with a cup and oscillating fixture or in oscillatory mode with a parallel plate fixture. When the viscosity is measured in steady mode with a cup and oscillating fixture, the reported viscosity typically corresponds to a frequency of 4 s -1 These viscosity measurement techniques are well known to those skilled in the art. For the purposes of this invention, the negative value of the logarithm of the viscosity ratio indicates the degree of degradation of SAP to PAA in magnitude, as it is generally understood by those skilled in the art that, at a fixed concentration, the lower the viscosity of the PAA solution, the lower the molecular weight of the PAA.

[0034] As used herein, M n is the number average molecular weight in g / mol or equivalently in Da, M w is the weight average molecular weight in g / mol or equivalently in Da, M z is the z-average molecular weight in g / mol or equivalently in Da, and PDI is the polydispersity index, defined as M w / Mn .

[0035] "Disposable" is used in its ordinary sense to refer to an article that is disposed of or discarded after a limited number of uses of varying lengths of time (e.g., less than 20 uses, less than 10 uses, less than 5 uses, or less than 2 uses). If the disposable absorbent article is a diaper, pant, sanitary napkin, catamenial pad, or wet wipe for personal hygiene, the disposable absorbent article can be (and most typically is) intended to be disposed of after a single use.

[0036] II Feed Stream

[0037] Unexpectedly, it has been found that when a SAP feed stream (which is in the form of a gel) flows in an extensional flow device (e.g., LW) and undergoes extensional flow with a short residence time, the SAP degrades to PAA (i.e., substantially without decarboxylation). Without wishing to be bound by any theory, the applicant believes that the tensile stress generated in the SAP feed stream / gel as it flows through the orifice causes the crosslinker to stretch and break, attaching the crosslinker to the backbone and generating backbone bonding. The applicant expected that the gel would slide at the walls of the inlet chamber and the orifice, and therefore would not generate tensile stress because it would flow in the inlet chamber and the orifice in a plug flow manner (as is well known to those skilled in the art). Moreover, unexpectedly, it has been found that the PAA produced by the degradation of SAP by the extensional flow device has a narrow molecular weight distribution (MWD), i.e., a low PDI. This is expected for linear polymers, but unexpected for crosslinked polymers.

[0038] Typical properties of SAP are mechanical properties, swelling capacity, saline flow conductivity (SFC), absorption against pressure (AAP; INDA test method WSP 242.2), residual monomers, extractable polymers (amount of extractables), and centrifuge retention capacity (CRC). Moreover, for the purposes of the present invention, SAP may include other comonomers (such as itaconic acid, acrylamide, 2-acrylamido-2-methylpropane-1-sulfonic acid, etc.) or other materials (such as starch, cellulose fibers, clay, etc.).

[0039] SAP is usually prepared using a homogeneous solution polymerization process or by a multiphase polymerization technique (such as reverse emulsion or suspension polymerization). Polymerization reaction usually occurs in the presence of a relatively small amount of difunctional or multifunctional monomers (such as N, N'-methylenebisacrylamide, trimethylolpropane triacrylate, (poly) ethylene glycol di(meth)acrylate, triallylamine, etc.). Difunctional or multifunctional monomer compounds are used to slightly crosslink acrylate polymer chains, thereby making SAP water-insoluble, but water-swellable. In addition, SAP can be surface crosslinked with a suitable crosslinking agent (such as di / polyepoxide, di / polyalcohol, di / polyalkyl halide, etc.) after polymerization. SAP is usually in the form of microparticles, which are made by any typical size reduction technology (such as grinding) of a piece of material in the case of solution polymerization.

[0040] The SAP may be completely unneutralized (DN=0), completely neutralized (DN=100%), or partially neutralized. In one embodiment of the present invention, the SAP has a DN greater than about 50%. In another embodiment of the present invention, the SAP has a DN between about 65% and about 75%. In yet another embodiment of the present invention, the SAP has a DN greater than about 75%. In even another embodiment of the present invention, the SAP has a DN less than about 50%.

[0041] In one embodiment of the present invention, the feed stream comprises SAP. In another embodiment of the present invention, the feed stream comprises SAP and water. In yet another embodiment of the present invention, the feed stream comprises SAP and ethylene glycol (EG). In even yet another embodiment of the present invention, the feed stream comprises SAP, water, and ethylene glycol. The water in the feed stream can be RO water, ordinary tap water, or water containing dissolved inorganic salts of various salt concentrations. A non-limiting example of water with salt is 0.9 wt % sodium chloride solution. Other salts with monovalent cations but higher ionic strength can be used to reduce the viscosity of the feed stream or alternatively enable the use of higher SAP concentrations. A non-limiting example of a viscosity-reducing salt is sodium sulfate.

[0042] The feed stream may also contain any free radical generating chemical compound. Non-limiting examples of such chemical compounds are hydrogen peroxide (H2O2), persulfates (such as sodium persulfate 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.

[0043] In one embodiment of the present invention, the feed stream comprises SAP and H2O2. In another embodiment of the present invention, the feed stream comprises SAP and H2O2 solution.

[0044] In one embodiment of the present invention, the feed stream comprises SAP at a concentration of greater than about 1% by weight. In another embodiment of the present invention, the feed stream comprises SAP at a concentration of greater than about 5% by weight. In yet another embodiment of the present invention, the feed stream comprises SAP at a concentration of greater than about 10% by weight. In even yet another embodiment of the present invention, the feed stream comprises SAP at a concentration of about 2.5% by weight. In one embodiment of the present invention, the feed stream comprises SAP at a concentration of about 5% by weight.

[0045] In one embodiment of the present invention, the feed comprises SAP and an H2O2 solution, and the concentration of SAP is about 2.5% by weight, the concentration of the H2O2 solution is 97.5% by weight, and the concentration of H2O2 in the H2O2 solution is less than about 3% by weight. In another embodiment of the present invention, the feed comprises SAP and H2O2, and the concentration of SAP is about 5% by weight, the concentration of the H2O2 solution is about 95% by weight, and the concentration of H2O2 in the H2O2 solution is less than about 3% by weight. In yet another embodiment of the present invention, the feed comprises SAP and an H2O2 solution, and the concentration of SAP is about 2.5% by weight, the concentration of the H2O2 solution is 97.5% by weight, and the concentration of H2O2 in the H2O2 solution is about 3% by weight. In another embodiment of the present invention, the feed comprises SAP and H2O2, and the concentration of SAP is about 5% by weight, the concentration of the H2O2 solution is about 95% by weight, and the concentration of H2O2 in the H2O2 solution is about 3% by weight.

[0046] In one embodiment of the present invention, the feed comprises SAP and an H2O2 solution, and the concentration of SAP is about 2.5% by weight, the concentration of the H2O2 solution is 97.5% by weight, and the concentration of H2O2 in the H2O2 solution is about 0.3% by weight. In another embodiment of the present invention, the feed comprises SAP and H2O2, and the concentration of SAP is about 5% by weight, the concentration of the H2O2 solution is about 95% by weight, and the concentration of H2O2 in the H2O2 solution is about 0.3% by weight. In yet another embodiment of the present invention, the feed comprises SAP and an H2O2 solution, and the concentration of SAP is about 2.5% by weight, the concentration of the H2O2 solution is 97.5% by weight, and the concentration of H2O2 in the H2O2 solution is about 0.03% by weight. In another embodiment of the present invention, the feed comprises SAP and H2O2, and the concentration of SAP 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%.

[0047] In one embodiment of the present invention, the feed comprises SAP and an H2O2 solution, and the concentration of H2O2 in the H2O2 solution is less than about 3 wt%. In another embodiment of the present invention, the feed comprises SAP and H2O2, and the concentration of H2O2 in the H2O2 solution is less than about 0.3 wt%. In yet another embodiment of the present invention, the feed comprises SAP and an H2O2 solution, and the concentration of H2O2 in the H2O2 solution is less than about 0.03 wt%.

[0048] The viscosity of the feed stream is typically measured in oscillatory mode using a parallel plate fixture, and the reported complex viscosity typically corresponds to a frequency of 1 rad / s. Depending on the SAP concentration, the complex viscosity of the feed stream can be higher than 200 Pa.s (or equivalently, 200,000 cP). Depending on the SAP concentration, the feed stream can be in solution or gel form.

[0049] The non-renewable energy use (NREU) for producing acrylic acid (AA) from fossil-derived propylene is estimated to be approximately 50 MJ / kg SAP (equivalently, 50 MJ / kg AA). Therefore, any successful SAP recovery attempt would require consuming less energy to produce AA than the NREU, i.e., less than approximately 50 MJ / kg SAP. For the purposes of the NREU, it is assumed that the SAP is completely unneutralized (DN=0).

[0050] III. Extensional Flow Apparatus and Cavitation

[0051] Typically, the feed stream is in fluid communication with the extensional flow device via a tube or channel and a pump. Non-limiting examples of tubes or channels are glass tubes, metal tubes, alloy tubes (such as stainless steel tubes) and polymer tubes. Tubes or channels can have any cross-sectional shape, such as circular, rectangular, oval, diamond-shaped, etc. Moreover, the size of the cross-sectional area of ​​the tubes or channels can be the same or vary along the direction of flow. Non-limiting examples of the different cross-sectional shapes of tubes are corrugated tubes, which can cause the feed stream to experience tensile stress when flowing to the tube. These tensile stresses may be beneficial to the degradation of the SAP as a part of the feed stream. Moreover, the feed stream can be through a static mixer or other mixing elements placed in the tube and / or channel through which the feed stream flows.

[0052] Non-limiting examples of pumps are 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).The extensional flow device may employ one or more pumps.

[0053] In one embodiment of the present invention, the extensional flow device is a liquid whistle (LW). Typically, the LW comprises an inlet chamber, an orifice, and a mixing chamber in the direction of flow, wherein the blades are located in front of the orifice and at a certain distance therefrom. Also, typically, the extensional flow device comprises an inlet and an outlet. The feed stream enters the extensional flow device from the inlet, and the product stream leaves the extensional flow device from the outlet. A non-limiting example of an extensional flow device is the FLEX(R) from Sonic Corp. and from Microfluidics Corp (Newton, MA) In one embodiment of the invention, there are no vanes downstream of the orifice in the LW.

[0054] The non-limiting configurations of the orifice are slot-shaped, eye-shaped, oval, circular, triangular, square, rectangular and polygonal. The width of the orifice can be up to 1 inch (2.541 cm) or larger. The height of the orifice can be up to 0.5 inch (1.27 cm) or larger. In another embodiment of the present invention, the orifice is oval. 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 for making the orifice housing are stainless steel, titanium, ceramic, sintered tungsten carbide, various borides, various carbons, various carbides and various diborides. The forming section length of the orifice can be up to 10 mm. In one embodiment of the present invention, the forming section length of the orifice is between about 0.5 mm and about 5 mm. In another embodiment of the present invention, the forming section length of the orifice is about 1 mm.

[0055] When the blades of LW vibrate at their natural frequency, they produce intense cavitation, and the bubbles formed grow and collapse very quickly. Non-limiting examples of materials used to make the blades are stainless steel, titanium, ceramics, sintered tungsten carbide, various borides, various carbons, various carbides, and various diborides. The blades of LW can have a suitable configuration, such as, but not limited to, a cone, one or more sharp edges, a rectangular or square cross-section, etc. The blades of LW can have any suitable size. In one embodiment of the present invention, the length of the blades of LW is between about 1 mm and about 100 mm. In another embodiment of the present invention, the length of the blades of LW is between about 10 mm and about 50 mm. In yet another embodiment of the present invention, the thickness of the blades of LW is between about 7 μm and about 100 mm. In another embodiment of the present invention, the thickness of the blades of LW is between about 0.2 mm and about 50 mm.

[0056] The cavitation introduced by the vibrating blades of the LW can be hydrodynamic, acoustic (e.g., between 20 Hz and 20 kHz), or ultrasonic (e.g., above 20 kHz). In one embodiment of the invention, the blades of the LW are subjected to ultrasonic vibrations having a frequency between about 20 kHz and about 100 kHz.

[0057] The distance between the blades of the LW and the orifice can vary from about 0.1 mm to about 25 mm. In one embodiment of the present invention, the distance between the blades of the LW and the orifice is about 0.5 mm. In another embodiment of the present invention, the distance between the blades of the LW and the orifice is between about 0.5 mm and about 13 mm. In yet another embodiment of the present invention, the distance between the blades of the LW and the orifice is between about 1 mm and about 10 mm. In even another embodiment of the present invention, the distance between the blades of the LW and the orifice is between about 3 mm and about 6 mm.

[0058] In one embodiment of the present invention, the blades are spaced apart from the orifice of the LW such that cavitation is not achieved when the fluid jet exits the orifice and impacts the blades. In another embodiment of the present invention, the blades are spaced apart from the orifice of the LW such that cavitation is achieved when the fluid jet exits the orifice and impacts the blades. In yet another embodiment of the present invention, the cavitation achieved in the extensional flow device is hydrodynamic. In yet another embodiment of the present invention, the cavitation achieved in the extensional flow device is ultrasonic. In one embodiment of the present invention, the cavitation achieved in the extensional flow device is acoustic.

[0059] In one embodiment of the present invention, the distance between the blades and the orifice of the LW is at least about 7 times the hydraulic diameter of the orifice. In another embodiment of the present invention, the distance between the blades and the orifice of the LW is less than about 7 times the hydraulic diameter of the orifice. In yet another embodiment of the present invention, the distance between the blades and the orifice of the LW is about 6 times the hydraulic diameter of the orifice. In even yet another embodiment of the present invention, the distance between the blades and the orifice of the LW is about 0.3 times the hydraulic diameter of the orifice.

[0060] The process can be carried out under any suitable pressure, and this pressure is measured at the feed stream place and orifice upstream.In one embodiment of the invention, pressure is between about 500psi (34.5 bar) and about 20,000psi (1379 bar).In another embodiment of the invention, pressure is higher than about 20,000psi (1379 bar).In another embodiment of the invention, pressure is between about 1000psi (68.9 bar) and about 10,000psi (689.5 bar).In even another embodiment of the present invention, pressure is between about 2,000psi (137.9 bar) and about 7,000psi (482.6 bar).In one embodiment of the invention, pressure is about 5,000psi (344.7 bar).

[0061] The flow rate at which the feed stream enters the extensional flow device can be any suitable value. In one embodiment of the invention, the flow rate at which the feed stream enters the extensional flow device is between about 1 L / min and about 1,000 L / min. In another embodiment of the invention, the flow rate at which the feed stream enters the extensional flow device is between about 2 L / min and about 500 L / min. In yet another embodiment of the invention, the flow rate at which the feed stream enters the extensional flow device is between about 3 L / min and about 200 L / min. In even yet another embodiment of the invention, the flow rate at which the feed stream enters the extensional flow device is between about 4 L / min and about 100 L / min. In one embodiment of the invention, the flow rate at which the feed stream enters the extensional flow device is about 5 L / min.

[0062] The residence time of the feed stream in the extensional flow device can be any suitable value. The residence time is defined as the average time that the feed stream spends in the extensional flow device as a whole (not only in the orifice, nor only in the inlet and mixing chamber). In one embodiment of the present invention, the residence time of the feed stream in the extensional flow device is less than about 120s. In another embodiment of the present invention, the residence time of the feed stream in the extensional flow device is less than about 60s. In yet another embodiment of the present invention, the residence time of the feed stream in the extensional flow device is less than about 15s. In one embodiment of the present invention, the residence time of the feed stream in the extensional flow device is between about 1.5s and about 50s. In another embodiment of the present invention, the residence time of the feed stream in the extensional flow device is between about 2s and about 20s. In yet another embodiment of the present invention, the residence time of the feed stream in the extensional flow device is between about 2.5s and about 10s. In even yet another embodiment of the present invention, the residence time of the feed stream in the extensional flow device is between about 3s and 5s.

[0063] The residence time of feed stream in the orifice of extensional flow device can be any suitable value. In one embodiment of the invention, the residence time of feed stream in orifice is between about 1ms and about 100ms. In another embodiment of the invention, the residence time of feed stream in orifice is between about 2ms and about 50ms. In another embodiment of the invention, the residence time of feed stream in orifice is between about 5ms and about 20ms. In even another embodiment of the invention, the residence time of feed stream in orifice is between about 7ms and about 15ms. In one embodiment of the invention, the residence time of feed stream in orifice is about 11ms.

[0064] Total energy is the electrical energy supplied to the extensional 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 within the extensional flow device to convert SAP to PAA and is based on the pressure drop of the feed stream as it flows through the extensional flow system. Calculations of total energy and specific energy are exemplified in Methods Section VII (as they are well known to those skilled in the art).

[0065] In one embodiment of the present invention, the specific energy used to convert SAP to PAA is less than about 30 MJ / kg SAP. In another embodiment of the present invention, the specific energy used to convert SAP to PAA is less than about 20 MJ / kg SAP. In yet another embodiment of the present invention, the specific energy used to convert SAP to PAA is less than about 10 MJ / kg SAP. In even yet another embodiment of the present invention, the specific energy used to convert SAP to PAA is less than about 5 MJ / kg SAP. In one embodiment of the present invention, the specific energy used to convert SAP to PAA is less than about 1 MJ / kg SAP.

[0066] In one embodiment of the present invention, the total energy used to convert SAP to PAA is less than about 50 MJ / kg SAP. In another embodiment of the present invention, the total energy used to convert SAP to PAA is less than about 32 MJ / kg SAP. In yet another embodiment of the present invention, the total energy used to convert SAP to PAA is less than about 16 MJ / kg SAP. In even yet another embodiment of the present invention, the total energy used to convert SAP to PAA is less than about 10 MJ / kg SAP. In one embodiment of the present invention, the total energy used to convert SAP to PAA is less than about 2 MJ / kg SAP.

[0067] Extensional flow can be carried out at room temperature or any other temperature. In addition, extensional flow can be carried out before or after other degradation processes (such as microwave heating, ultraviolet irradiation, infrared heating, ultrasound / cavitation, extrusion, stretching and stretching, etc.).

[0068] Extensional flow can also occur simultaneously with oxidative degradation, enzymatic degradation, or biological degradation.

[0069] Oxidative degradation method

[0070] Surprisingly, it has been discovered that SAP can be degraded into soluble PAAs, particularly polymers of acrylic acid, by mixing the SAP with an oxidizing, water-soluble salt (hereinafter referred to as the "salt"). The salt comprises at least one cation and at least one anion. The SAP and salt are mixed with an aqueous carrier such as water or saline.

[0071] By heating the mixture to a temperature of 30°C to 200°C (hereinafter referred to as "high temperature"), at least some of the anions decompose into free radicals. The high temperature may 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 high temperature may be less than 190°C, or less than 180°C, or less than 150°C. Generally, at high temperatures exceeding 200°C, the SAP begins to decompose and decay in an uncontrolled manner, which is undesirable for the present invention. Upon heating, hydrogen atoms of the salt, more specifically: hydrogen atoms of one or more anions of the salt, are abstracted, and the anions form free radicals. The high temperature to which the mixture is heated may be at least 10°C lower than the decomposition temperature of the salt (resulting in the formation of free radicals), or the mixture may be heated to a high temperature that is at least the decomposition temperature, or may be heated to a high temperature that is at least 10°C higher than the decomposition temperature of the salt.

[0072] As used herein, "decomposition temperature" is the 10 hour half-life temperature in water, which is, for example, 69°C for ammonium persulfate and 60°C for potassium persulfate.

[0073] Therefore, the selection of the optimal temperature range depends in particular on the selection of salt, because different salts (especially different anions) have different decomposition temperatures. The free radicals that have been formed can react with SAP, for example by reacting with the aliphatic CH groups contained in the polymer chain of SAP. As a result of this free radical reaction, the polymer chain of SAP is disconnected, and carbon-centered free radicals are formed at the disconnected SAP polymer chain. This reaction can also occur at the carboxyl group of SAP, which also leads to carbon-centered free radicals. Still alternatively or in addition to this, the reaction can occur at a nitrogen atom, which can be included in the cross-linking agent used for the initial preparation of SAP. If the reaction occurs at a nitrogen atom, nitrogen-centered free radicals are formed instead of carbon-centered free radicals.

[0074] Without wishing to be bound by theory, it is believed that the following reaction scheme exemplifies the process of degradation of SAP into soluble PAA (ie, the "decrosslinked polymer product" hereinafter):

[0075]

[0076] wherein R is H, or a basic cation, an ammonium cation, or a cross-linking residue.

[0077] The mixture can be maintained at the elevated temperature for a period of 10 minutes to 5 hours, preferably 10 minutes to 4 hours, and more preferably 10 minutes to 3 hours. Shorter times are preferred from an economical perspective. Shorter treatment times can be achieved, for example, by using higher salt concentrations, higher temperatures (however, below 200° C.), and / or by optimizing the mixing of the SAP and salt. The time the mixture is maintained at the elevated temperature also depends on the desired degree of degradation (i.e., the average molecular weight of the PAA obtained by the process). Generally, once the SAP has been degraded such that no or only trace amounts of insoluble SAP are present, indicating that most of the SAP has been broken down into soluble PAA, the mixture may no longer need to be maintained at the elevated temperature and the temperature can be reduced to room temperature (25° C.) or lower.

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

[0079] As an alternative to premixing the aqueous carrier with the salt so that the salt dissolves in the aqueous carrier, the aqueous carrier and salt can also be provided to the SAP separately so that the salt only dissolves in the aqueous carrier after mixing with the SAP. Importantly, the salt must be able to dissolve in the aqueous carrier after contact with the SAP or, preferably, before contact with the SAP.

[0080] The aqueous carrier may be preheated to an elevated temperature before being mixed with the salt and SAP. Such preheating may accelerate the degradation process. Alternatively, however, the aqueous carrier may be preheated to a temperature below the elevated temperature before being mixed with the salt and SAP. Still further alternatively, the aqueous carrier may not be preheated before being mixed with the salt and SAP, and heating to the elevated temperature may be completed after the aqueous carrier, salt, and SAP are mixed.

[0081] If the salt is dissolved in the aqueous carrier before mixing with the SAP, the aqueous carrier can be preheated to a temperature below the elevated temperature to prevent the anions from prematurely forming free radicals, which would cause the anions to degrade by autolysis and subsequently be unavailable to degrade the SAP after mixing with the SAP. However, if the salt is dissolved in the aqueous carrier only for a short period of time or immediately before mixing with the SAP, the aqueous carrier can be preheated to an elevated temperature before mixing with the SAP. Preheating can accelerate the time it takes for the salt to dissolve in the aqueous carrier.

[0082] Alternatively or additionally, the SAP can be preheated to an elevated temperature or below before mixing with the aqueous carrier and salt. Preheating the SAP can result in a shorter swelling time for the SAP, thereby accelerating the absorption of the aqueous carrier and dissolved salt into the SAP particles, enabling faster degradation. Faster absorption of dissolved salt into the SAP can also improve the uniform dispersion of the dissolved salt within the SAP, which can contribute to more uniform degradation, thereby preventing undegraded SAP fragments from remaining in the mixture.

[0083] Alternatively still, the mixture obtained in process step d) may be heated to the elevated temperature only after at least 50% by weight, or at least 70% by weight, or at least 90% by weight, or all of the aqueous carrier in which the salt is dissolved has been absorbed into the SAP. However, some preheating to a temperature below the elevated temperature may have already been done before.

[0084] The ratio of salt to SAP may be from 0.001 g salt to 0.05 g salt per 1 g SAP, or from 0.005 g salt to 0.03 g salt per 1 g SAP, or from 0.01 g salt to 0.03 g salt per 1 g SAP.

[0085] The ratio of aqueous carrier to SAP may be 2 g to 20 g aqueous carrier per 1 g SAP, or may be 5 g to 15 g aqueous carrier per 1 g SAP. The SAP may be provided in method step a) dry or swollen to less than 20 g, or less than 15 g, or less than 10 g, or less than 5 g liquid (such as water or saline) per gram SAP.

[0086] The total amount of liquid absorbed into (i.e., contained in) the SAP in method step e) - including the liquid contained in the swollen SAP as provided in method step a) (if the SAP is not provided as dry SAP) and the amount of aqueous carrier absorbed into and thus contained by the SAP in method step e) - can be from 2 g to 25 g per 1 g of SAP, or from 2 g to 20 g per 1 g of SAP, or from 5 g to 15 g per 1 g of SAP, or from 8 g to 13 g per 1 g of SAP. As used herein, "dry SAP" means that the SAP has a liquid content (referred to as "water content") of less than 0.20 g per 1 g of SAP, preferably less than 0.15 g per 1 g of SAP. The moisture content of the SAP is measured according to the EDANA moisture content test method NWSP 230.0.R2 (15) or via a moisture analyzer (HX204 from Mettler Toledo, drying temperature 130° C., starting superabsorbent weight 3.0 g (±0.5 g), stop standard 1 mg / 140 s). If the moisture content of the superabsorbent polymer particles is greater than 3% by weight, the SAP is dried to a moisture content of <3% by weight, for example in an oven at 105° C. for 3 hours or, for example, at 120° C. for 2 hours.

[0087] To ensure that the salt is available for effective degradation of the SAP, it is desirable that a significant amount of the aqueous carrier in which the salt is dissolved is absorbed into the SAP in method steps d) and e). At least 50% by weight, or at least 60% by weight, or at least 75% by weight, or at least 90% by weight, or 100% by weight of the aqueous carrier in which the salt is dissolved provided in step c) can be absorbed into the SAP. Absorption of the aqueous carrier in which the salt is dissolved in method steps d) and e) means that the aqueous carrier in which the salt is dissolved is absorbed only in method step d) (which would be the case if 100% by weight is absorbed in particular), or is absorbed primarily in method step e) (which may be the case if heating is already initiated when the SAP, salt, and aqueous carrier are mixed), or that a portion of the aqueous carrier in which the salt is dissolved is absorbed into the SAP in method step d) while another portion of the aqueous carrier in which the salt is dissolved is absorbed into the SAP in method step e).

[0088] The SAP provided in process step a) may have a centrifuge retention capacity (CRC) value of 10 g / g to 50 g / g, or 10 g / g to 40 g / g. If drying is required for recycling the AGM, the CRC is measured, as measured according to the CRC test method (EDANA method NWSP 241.0.R2).

[0089] If the SAP provided in method step a) is post-consumer recycled SAP, (a sample of) the SAP must first be dried and then the CRC of this sample measured to determine the CRC of the SAP.

[0090] The at least one anion of the salt may be selected from the group consisting of peroxodisulfate, peroxomonosulfate, peroxydicarbonate, peroxypyrophosphate, peroxodiborate, or mixtures thereof.

[0091] The at least one cation of the salt is not critical because cations do not dissociate into free radicals. Therefore, the choice of cation does not directly affect the degradation process because cations do not form free radicals. The at least one cation can be selected to have sufficient solubility in the aqueous carrier and it should be available at a relatively low cost. The at least one cation can be selected from: Li + 、Na + , K + , Rb + 、Cs + NH4 + , organically substituted ammonium, Ca2+, Mg2+, Sr2+, Ba2+, Al3+, transition metal cations in the 1+ to 3+ oxidation states, or mixtures thereof (e.g., combinations of different salts with different cations). Most preferred are one or more basic cations and NH4 + cation.

[0092] At least 50 wt%, or at least 60 wt%, or at least 70 wt%, or at least 80 wt%, or at least 90 wt%, or 100 wt% of the total weight of the salt can be alkaline persulfate salt.

[0093] Hydrogen peroxide may be added during the process. Hydrogen peroxide can help increase the yield per time of PAA, i.e., the degradation rate. Hydrogen peroxide can also help decolorize degraded contaminants. Hydrogen peroxide can be added to the SAP as a separate aqueous solution, or it can be added to an aqueous carrier before mixing with the SAP, with or without a salt dissolved in the aqueous carrier. The amount of hydrogen peroxide used in the process of the present invention can be from 10% to 200% by weight, based on the weight of the salt, or from 20% to 100% by weight, based on the weight of the salt, or from 30% to 80% by weight, based on the weight of the salt.

[0094] Process step e) can be carried out at a pH of 3 to 7. Generally, no further special measures are required to achieve a pH within this range. Persulfate radicals are less stable, for example, at a pH above 7.

[0095] Additives can 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, glycerol, or mixtures thereof can be added to the aqueous carrier provided in method step c), or added to the mixture in method step d). These additives can support the initial wettability of the aqueous carrier and the salts dissolved therein to the SAP. They can also improve the stability of the aqueous carrier against bacterial contamination. Other additives, such as antimicrobial additives, can also be added. The total amount of the additives can be no more than 10% by weight, or no more than 8% by weight, or no more than 5% by weight, or no more than 3% by weight, based on the weight of the aqueous carrier.

[0096] The method of the present invention can be carried out in a continuous process or an intermittent process. Generally, from a commercial / cost perspective, a continuous process is generally preferred. In a continuous process, the SAP can be provided, for example, in a continuous stream on a carrier belt or the like, and, for example, by spraying an aqueous carrier and a salt (and optionally hydrogen peroxide) onto the SAP, the aqueous carrier and the salt are mixed with the SAP. The mixture of the SAP, the salt and the aqueous carrier can be transferred to a belt after method step d) (for example, after the aqueous carrier in which the salt is dissolved has been partially or completely absorbed into the SAP) and heated in a continuous or intermittent manner.

[0097] Alternatively, the aqueous carrier can be provided in a batch container or similar container (wherein the salt is dissolved therein before or after the aqueous carrier is provided to the container). The SAP can then be added to the container already filled with the aqueous carrier and dissolved salt, and the SAP can be allowed to absorb the aqueous carrier and the salt dissolved therein, and the mixture can be heated to an elevated temperature simultaneously or subsequently.

[0098] With SAP, especially if provided as dry SAP particles, air tends to become "trapped" between the particles, i.e., in the spaces between the SAP particles as they absorb liquid and swell. Consequently, the swollen SAP tends to "float" in the liquid. As the SAP degrades, the dissolved PAA can sink in the container, where it can be (continuously) removed. To prevent undegraded or partially degraded SAP from being removed along with the PAA (since some SAP can sink in the container), a screen or the like can be installed in the container to prevent undegraded or fully degraded SAP particles from sinking further to the bottom of the container, as they will be trapped in the screen until they are more completely degraded and able to pass through the screen.

[0099] Alternatively, the mixture of SAP, salt, and aqueous carrier can be agitated so that the swollen SAP particles sink to the bottom of the container, and the soluble PAA, the product of the process, can be removed from the upper portion of the container.

[0100] The obtained solution with PAA dissolved therein can be transferred, for example via a pump, to different containers, pipes, or any other suitable means for any post-treatment that may be desired for the solution. Possible post-treatments are filtration, desalination, evaporative concentration or many other treatments.

[0101] The energy consumption of the degradation process depends particularly on the high temperature. The higher the temperature, the higher the energy consumption per time (i.e., a shorter treatment time at a higher temperature may require less energy overall than a relatively lower temperature at a relatively longer treatment time). For example, for a batch process in an insulated container (i.e., where the heating to the high temperature is completed only once), the energy consumption for a high temperature of about 100°C is about 3.5 MJ / kg of dry AGM.

[0102] The SAP provided in method step a) may be in the form of particles. The SAP provided in the method may be virgin SAP, post-consumer recycled SAP (PCR SAP), post-industrial recycled SAP (PIR SAP), or a combination of those materials. "Post-consumer SAP" and "post-consumer recycled SAP" (PCR SAP) are used interchangeably herein and, as used herein, refer to SAP that is contained by AHP and that has been used by a consumer (e.g., worn by an incontinent user). After use, the AHP is recycled and the PCR SAP is separated from the AHP. However, for the method of the present invention, it is not necessary to purify the SAP so that the post-consumer SAP provided for the method of the present invention does not contain other components of the post-consumer AHP.

[0103] "Post-industrial SAP" and "post-industrial recycled SAP" (PIR SAP) are used interchangeably herein and, as used herein, refer to SAP that may or may not be contained by an AHP. PIR SAP has not been previously used, for example, it has not been contained by an AHP that has been used by a consumer. Conversely, PIR SAP may be derived from AHPs that have been sorted out during production, for example, because they are defective. PIR SAP may also be sorted out during SAP production, for example, because they do not meet desired performance targets (such as capacity, whiteness, etc.). Therefore, in the latter case, the PIR SAP has not been previously contained by an AHP.

[0104] Typical properties of SAP are mechanical properties, swelling capacity, saline flow conductivity (SFC), absorption against pressure (AAP), residual monomers, extractables, and cylinder retention capacity (CRC). Furthermore, for the purposes of the present invention, SAP may include other comonomers such as itaconic acid, acrylamide, etc. The amount of comonomer may be less than 20 wt%, or less than 10 wt%, or less than 1 wt%, or less than 0.5 wt%, based on the total weight of the dry SAP.

[0105] SAP is typically prepared using a homogeneous solution polymerization process or by a multiphase polymerization technique (such as inverse emulsion or suspension polymerization). The polymerization reaction is typically completed in the presence of a relatively small amount of difunctional monomers or multifunctional monomers, such as N,N'-methylenebisacrylamide, triacrylate, ethylene glycol di(meth)acrylate, triallylamine, etc. The difunctional monomer or multifunctional monomer compound is used to slightly crosslink the acrylate polymer chain, thereby making the SAP water-insoluble but water-swellable. In addition, the SAP can be surface crosslinked after polymerization by reacting with a suitable crosslinking agent, such as di / polyepoxide, di / polyol, di / polyhalogenated alkane, etc. The SAP provided for the method of the present invention may be in the form of particles. The particle form can be produced from a material block using any typical size reduction technique (such as grinding).

[0106] The SAP may be completely unneutralized (in which case, DN=0), completely neutralized (in which case, DN=100%), or partially neutralized. In one embodiment of the present invention, the SAP has a DN greater than about 50%. In another embodiment of the present invention, the SAP has a DN between about 65% and about 75%. In yet another embodiment of the present invention, the SAP has a DN greater than about 75%. In even another embodiment of the present invention, the SAP has a DN less than about 50%.

[0107] The SAP 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 PCRSAP). Thus, the SAP may be swollen 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 with water, saline or urine. Complete drying (i.e., 0 g / g of water, saline or urine) may be less advantageous for the method of the present invention because it takes longer for a completely dry SAP to absorb the aqueous carrier in which the salt is dissolved. On the other hand, an SAP that is excessively swollen (or even completely swollen) when provided to the method may also result in an increase in time until the salt dissolved in the aqueous carrier is absorbed into the SAP. The SAP provided to the process may have a absorption capacity CRC (measured as Centrifuge Retention Capacity "CRC" according to EDANA method NWSP 241.0.R2) of 10 g / g to 50 g / g.

[0108] The amount of aqueous carrier provided in method step c) can be such that the SAP provided in step a) is capable of swelling to at least 20%, or at least 30%, or at least 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 SAP is not provided dry but pre-swollen (see further details below), less aqueous carrier is required to obtain the desired degree of SAP loading, i.e. the desired CRC.

[0109] Upon absorption of liquid, the polymer chains within the SAP's polymer network begin to disentangle. This disentanglement makes the polymer network more accessible to free radicals formed by the anions of the salt. Consequently, degradation is improved. If the amount of aqueous carrier provided in step c) does not allow the SAP to swell to at least 20% of its CRC upon absorption of the aqueous carrier, the polymer chains within the SAP's polymer network may not disentangle sufficiently, resulting in slower or less effective degradation overall.

[0110] For the degradation methods of the present invention, using post-consumer SAP may be advantageous over using virgin SAP: the polymer chains in the polymer network of SAP that has been previously swollen and then at least partially redried have already been disentangled. It is believed that reswelling, and thus re-disentanglement, is faster than swelling of virgin SAP. It has been found that SAP that has been previously swollen and then redried has a higher CRC when swollen after redrying than the CRC measured when the SAP was first swelled from virgin SAP.

[0111] If the post-consumer SAP is provided for use in the process of the present invention in a partially swollen form, it is also advantageous not to completely dry the SAP used in the process, given that drying the post-consumer SAP is time-consuming and energy-intensive. However, the post-consumer SAP may be sterilized before providing it to the process of the present invention.

[0112] If post-consumer or post-industrial SAP is separated from AHP to provide for use in the methods of the present invention, the SAP does not necessarily need to be purified so that other components of the AHP are absent. Instead, it has been found that the SAP may be contaminated by other components of the AHP, such as synthetic fiber materials or films (e.g., fibers, sheets, membranes, and fiber layers), cellulose fibers, adhesives, inks, dyes, surfactants, etc. The amount of these contaminants may not exceed 20% by weight of the mixture of SAP and contaminants, or may not exceed 15% by weight, or not exceed 10% by weight, or not exceed 5% by weight, or not exceed 2% by weight, or not exceed 1% by weight.

[0113] If after consumption the SAP remains swollen, for example with urine or other liquids, this urine or other liquid contained by the SAP is not taken into account when calculating the amount of contaminant by weight of the mixture of SAP and contaminant.

[0114] If the SAP is provided for use in the present invention as dry SAP, the average particle size of the post-consumer SAP may optionally be reduced, for example, by grinding, milling, or other suitable means. The dry SAP provided for use in the present invention (whether PCR SAP, PIR SAP, or freshly manufactured SAP) may have a D50 average particle size of 100 μm to 1,000 μm, as measured according to ISO method 13322-2. The particle size distribution (PSD) of the dry SAP may be 40 μm to 5,000 μm, or 50 μm to 2,000 μm, or 50 μm to 1,000 μm, or 50 μm to 800 μm.

[0115] If the SAP is provided in a pre-swollen form, for example, as post-consumer SAP that has not been dried or has only been partially dried after recycling, the SAP can be subjected to comminution to increase the surface area of ​​the SAP, which can result in faster absorption of the aqueous carrier in which the salt is dissolved. Such faster absorption can, in turn, lead to faster degradation of the SAP. Comminution can be accomplished, for example, by wet grinding.

[0116] Smaller particle size can aid in the rapid and uniform absorption of dissolved salts into the SAP, leading to faster and more complete degradation of the SAP.

[0117] Optional process step f) of separating the soluble polyacrylic acid polymer in aqueous solution from other compounds and components in the mixture:

[0118] Once the SAP has been decomposed into PAA, the PAA can be separated from the mixture of (possibly remaining undecomposed) SAP, salt, aqueous carrier and optional additional components (such as hydrogen peroxide). The mixture may still contain a certain amount of undecomposed SAP, which may be present in the mixture as a solid insoluble component.

[0119] PAA can be extracted from the mixture by a variety of methods. Non-limiting examples of these methods include water evaporation, filtration of PAA, water extraction, and the like. Furthermore, salts can be removed by any desalination technique known to those skilled in the art. Non-limiting examples of desalination methods include membrane methods (e.g., reverse osmosis, forward osmosis, electrodialysis reverse (EDR), nanofiltration, etc.), cryo-desalination, solar desalination, geothermal desalination, ion exchange, wave-powered desalination, and the like. The same techniques can generally be applied to remove other low molecular weight compounds from the mixture, for example, other typical compounds of post-consumer AHP, such as adhesives, inks, dyes, surfactants, and degradation products of these compounds.

[0120] For example, filtration can be used to eliminate solid compounds and components from the mixture, i.e., process step d) for separating the soluble polyacrylic acid polymer in the aqueous solution from the other compounds and components in the mixture obtained by step c). The solid compounds and components may be the remaining insoluble SAP and other components of post-consumer AHP, such as synthetic fiber materials or films (fibers, sheets / films / fibrous layers) and cellulose. It is worth noting that polyolefins (e.g., polypropylene, polyethylene) contained in other components of post-consumer AHP (such as synthetic fiber materials or films) are insoluble or non-swellable in the aqueous carrier. They react with the salt only to a negligible extent, i.e., the polyolefin is not degraded or only insignificantly degraded by the process of the present invention. The same applies to PET, which may also be contained in the synthetic fiber materials or films. Therefore, these materials will remain in the mixture as solid components and can be filtered out.

[0121] For example, PEG contained in surfactants (i.e., another typical component of post-consumer AHP) is degraded by the methods of the present invention. However, PEG is typically degraded into relatively small molecular weight molecules that are significantly smaller than the molecular weight of PAA. Therefore, the small molecular weight reaction products of PEG can be separated from the soluble PAA polymer, for example, by the above-described techniques.

[0122] Alternatively or in addition, a mixture of PAA, (possibly the remainder of) SAP, salt, and an aqueous carrier (which may contain compounds of post-consumer AHP) may be mixed in a co-solvent in which the PAA is insoluble, such that the PAA will precipitate to separate it from the mixture. Prior to such mixing in the co-solvent, the solid compounds in the mixture may be removed by filtration.

[0123] The PAA obtained by the degradation method of the present invention can have different molecular weights. The PAA may or may not contain oligomers. Preferably, the PAA does not contain oligomers, i.e., the PAA is comprised solely of polymers. The average molecular weight (Mw) of the PAA may be at most 10 MDa or at most 5 MDa. The average molecular weight (Mw) of the PAA may be at least 10 kDa or at least 20 kDa. The PAA may be linear or branched. However, the PAA is not cross-linked and, therefore, is water-soluble.

[0124] The PAA obtained by the method of the present invention can be used or derivatized into materials for other applications such as adhesives, coatings, water treatment, etc. In one embodiment of the present invention, the PAA, as is or derivatized, is used in adhesives. In yet another embodiment of the present invention, the PAA, as is or derivatized, is used in fabric care applications. In even yet another embodiment of the present invention, the PAA, as is or derivatized, is used in water treatment applications.

[0125] In one embodiment of the present invention, the feed stream comprises SAP and an oxidizing water-soluble salt; and wherein the salt comprises at least one cation and at least one anion. In another embodiment of the present invention, the feed stream comprises SAP and an oxidizing water-soluble salt; wherein the salt comprises at least one cation and at least one anion; and wherein the anion is selected from the group consisting of: peroxydisulfate, peroxymonosulfate, peroxydicarbonate, peroxypyrophosphate, peroxydiborate, and combinations thereof. In yet another embodiment of the present invention, the feed stream comprises SAP and an oxidizing water-soluble salt; wherein the salt comprises at least one cation and at least one anion; wherein the anion is selected from the group consisting of: peroxydisulfate, peroxymonosulfate, peroxydicarbonate, peroxypyrophosphate, peroxydiborate, and combinations thereof; and wherein the cation is selected from the group consisting of: 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.

[0126] IV Product Stream

[0127] The feed stream flows into the inlet of the extensional flow device and produces a product stream at the outlet of the extensional flow device. In one embodiment of the present invention, the product stream comprises PAA. In another embodiment of the present invention, the product stream comprises PAA and SAP.

[0128] In one embodiment of the present invention, the PAA has a weight average molecular weight of less than about 5,000,000 g / mol. In another embodiment of the present invention, the PAA has a weight average molecular weight of less than about 2,000,000 g / mol. In yet another embodiment of the present invention, the PAA has a weight average molecular weight of less than about 1,000,000 g / mol. In even yet another embodiment of the present invention, the PAA has a weight average molecular weight of less than about 500,000 g / mol. In one embodiment of the present invention, the PAA has a weight average molecular weight of less than about 300,000 g / mol. In another embodiment of the present invention, the PAA has a weight average molecular weight of less than about 200,000 g / mol. In yet another embodiment of the present invention, the PAA has a weight average molecular weight of less than about 100,000 g / mol. In even yet another embodiment of the present invention, the PAA has a weight average molecular weight of less than about 30,000 g / mol.

[0129] In one embodiment of the present invention, the PAA has a weight average molecular weight between about 1,000,000 g / mol and about 5,000,000 g / mol. In another embodiment of the present invention, the PAA has a weight average molecular weight between about 500,000 g / mol and about 2,000,000 g / mol. In yet another embodiment of the present invention, the PAA has a weight average molecular weight between about 100,000 g / mol and about 1,000,000 g / mol. In even yet another embodiment of the present invention, the PAA has a weight average molecular weight between about 150,000 g / mol and about 500,000 g / mol. In one embodiment of the present invention, the PAA has a weight average molecular weight between about 90,000 g / mol and about 300,000 g / mol. In another embodiment of the present invention, the PAA has a weight average molecular weight between about 20,000 g / mol and about 200,000 g / mol. In yet another embodiment of the present invention, the PAA has a weight average molecular weight between about 10,000 g / mol and about 100,000 g / mol.

[0130] In one embodiment of the present invention, the PAA has a polydispersity index (PDI) of less than about 10. In another embodiment of the present invention, the PAA has a PDI of less than about 6. In yet another embodiment of the present invention, the PAA has a PDI of less than about 4. In even yet another embodiment of the present invention, the PAA 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.

[0131] The viscosity of the product stream is typically measured in oscillatory mode with a parallel plate fixture or in steady mode with a cup and swing fixture. The reported oscillatory viscosity typically corresponds to 1 rad / s, and the reported steady viscosity typically corresponds to 4 s -1 Depending on the PAA concentration and molecular weight, the viscosity of the product stream can be as low as 1 mPa.s (or equivalently, 1 cP; i.e., the viscosity of water).

[0132] The ratio of the viscosity of the product stream to the viscosity of the feed stream is the viscosity reduction ratio (or simply, the viscosity ratio). It indicates the extent to which the UV flow system degrades SAP into PAA. The negative logarithm of the viscosity ratio measures the order of magnitude change between the viscosities of the feed stream and the product stream. In one embodiment of the present 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 logarithm of the viscosity ratio is less than about 6. In another embodiment of the present 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 logarithm of the viscosity ratio is less than about 4. In yet another embodiment of the present 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 logarithm of the viscosity ratio is less than about 2.

[0133] The PAA from the product stream can be derivatized into materials for various applications such as adhesives, coatings, water treatment, etc. In one embodiment of the present invention, the PAA from the product stream (as is or derivatized) is used as an adhesive. In yet another embodiment of the present invention, the PAA from the product stream (as is or derivatized) is used in fabric care applications. In even yet another embodiment of the present invention, the PAA from the product stream (as is or derivatized) is used in water treatment applications.

[0134] In one embodiment of the present invention, the PAA from the product stream is used as a layer size in a paper product. In another embodiment of the present invention, the PAA from the product stream is used as a layer size in a tissue product. In yet another embodiment of the present invention, the PAA from the product stream is used as a layer size in a sanitary paper product. In even yet another embodiment of the present invention, the PAA from the product stream used as a layer size in a paper product has an M of greater than about 350 kDa. w In one embodiment of the present invention, the PAA from the product stream used as a layer size in a paper product has an M of between about 400 kDa and about 500 kDa. w .

[0135] In another embodiment of the present invention, the PAA from the product stream is used as glue between a paper core and a tissue product.In even another embodiment of the present invention, the PAA from the product stream is used as glue between a paper core and a hygiene paper product.

[0136] PAA can be extracted from the product stream via a variety of processes. Non-limiting examples of such processes include water evaporation, PAA filtration, water extraction, and the like. Furthermore, salts present in the product stream due to the use of SAPs in AHP can be removed via any desalination technology known to those skilled in the art. Non-limiting examples of desalination processes include membrane processes (e.g., reverse osmosis, forward osmosis, electrodialysis reverse (EDR), nanofiltration, etc.), cryo-desalination, solar desalination, geothermal desalination, ion exchange, wave-powered desalination, and the like.

[0137] V Recycled SAP

[0138] PAA from the product stream can be fed into a process for making SAP from glacial acrylic acid, thereby producing recycled SAP. Examples 21 and 23 illustrate the incorporation of PAA into virgin SAP. In one embodiment of the present invention, PAA is used to produce recycled SAP.

[0139] In one embodiment of the present invention, the SAP comprises a concentration of PAA, wherein the PAA concentration is less than about 60 wt %. In another embodiment of the present invention, the SAP comprises a concentration of PAA, wherein the PAA concentration is less than about 50 wt %. In yet another embodiment of the present invention, the SAP comprises a concentration of PAA, wherein the PAA concentration is less than about 45 wt %. In even yet another embodiment of the present invention, the SAP comprises a concentration of PAA, wherein the PAA concentration is less than about 40 wt %. In one embodiment of the present invention, the SAP comprises a concentration of PAA, wherein the PAA concentration is less than about 30 wt %. In another embodiment of the present invention, the SAP comprises a concentration of PAA, wherein the PAA concentration is less than about 20 wt %. In yet another embodiment of the present invention, the SAP comprises a concentration of PAA, wherein the PAA concentration is less than about 15 wt %. In even yet another embodiment of the present invention, the SAP comprises a concentration of PAA, wherein the PAA concentration is less than about 10 wt %.

[0140] In one embodiment of the present invention, the recovered SAP has an amount of extractables, and the amount of the extractables is less than about 20% by weight. In another embodiment of the present invention, the recovered SAP has an amount of extractables, and the amount of the extractables is less than about 15% by weight. In yet another embodiment of the present invention, the recovered SAP has an amount of extractables, and the amount of the extractables is less than about 10% by weight. In even yet another embodiment of the present invention, the recovered SAP has an amount of extractables, and the amount of the extractables is less than about 7% by weight.

[0141] In one embodiment of the present invention, the recovered SAP has a swelling ratio, and wherein the swelling ratio is greater than about 50 g / g. In another embodiment of the present invention, the recovered SAP has a swelling ratio, and wherein the swelling ratio is greater than about 45 g / g. In yet another embodiment of the present invention, the recovered SAP has a swelling ratio, and wherein the swelling ratio is greater than about 40 g / g. In even yet another embodiment of the present invention, the recovered SAP has a swelling ratio, and wherein the swelling ratio is greater than about 35 g / g.

[0142] In one embodiment of the present invention, the recovered SAP has a swelling ratio, and wherein the swelling ratio is about 50 g / g. In another embodiment of the present invention, the recovered SAP has a swelling ratio, and wherein the swelling ratio is about 45 g / g. In yet another embodiment of the present invention, the recovered SAP has a swelling ratio, and wherein the swelling ratio is about 42 g / g. In even yet another embodiment of the present invention, the recovered SAP has a swelling ratio, and wherein the swelling ratio is about 40 g / g.

[0143] In one embodiment of the present invention, the recovered SAP has a CRC, and wherein the CRC is between about 20 g / g and about 45 g / g. In another embodiment of the present invention, the recovered SAP has a CRC, and wherein the CRC is between about 25 g / g and about 40 g / g. In yet another embodiment of the present invention, the recovered SAP has a CRC, and wherein the CRC is between about 30 g / g and about 35 g / g.

[0144] In one embodiment of the present invention, the recovered SAP has an AAP, and wherein the AAP is between about 15 g / g and about 40 g / g. In another embodiment of the present invention, the recovered SAP has an AAP, and wherein the AAP is between about 20 g / g and about 35 g / g. In yet another embodiment of the present invention, the recovered SAP has an AAP, and wherein the AAP is between about 25 g / g and about 30 g / g.

[0145] VI Embodiment

[0146] Unless otherwise stated, the SAP used in the following examples is designated as "GIC31187," obtained from Procter & Gamble Co. (Cincinnati, OH), prepared according to the procedure described in Methods Section VII, having a particle size between 63 μm and 150 μm, a DN of 68 mol%, and its typical properties are shown in Methods Section VII.

[0147] Inventive Examples 1 to 5 show that for a 2.5 wt% SAP and 97.5 wt% RO water feed stream, the negative logarithm of the product stream to feed stream viscosity ratio (i.e., the order of magnitude decrease in product stream viscosity relative to feed stream viscosity) increases with increasing residence time in LW (no hydrodynamic cavitation). The results for these inventive examples are also reported in Tables 1 and Figure 1 Shown in.

[0148] Example 1

[0149] SAP was mixed with RO water overnight to produce a feed stream (in gel form) having 2.5 wt% SAP and 97.5 wt% RO water. 400 mL of the feed stream was loaded into a liquid whistle apparatus (LW; Sonolator Model A; Sonic Corp., Stratford, CT; oval orifice dimensions: width 2×0.0375 inches=1.9 mm, height 2×0.012 inches=0.6 mm (calculated hydraulic diameter 1.7 mm), segment length 1 mm, volume V=π×(width)×(height)×(segment length) / 4=0.9 mm). 3 ), operated at a flow rate of about 4899 mL / min and a pressure of about 4945 psi (about 341 bar), and the product stream was collected in a beaker. A stainless steel blade was placed about 10.7 mm from the LW orifice because this distance exceeded 6 times the hydraulic diameter of the orifice, so it was believed that the blade would not cause any significant cavitation. The residence time of the feed stream in the LW was about 4.9 s, and the residence time of the feed stream in the orifice was about 11 ms. Under these conditions, the total energy was about 2.10 MJ / kg SAP, and the specific energy was 1.36 MJ / kg SAP (therefore, the energy efficiency of the LW was about 1.36 / 2.1=64.8%). The viscosities of the feed and product streams were measured in oscillation mode with a parallel plate fixture. The complex viscosity of the feed stream was measured to be 672.4 Pa.s at 1 rad / s, and the complex viscosity of the product stream was measured to be 109.9 Pa.s at 1 rad / s. Therefore, the viscosity ratio of the two streams is 1.63×10 -1 , and its negative logarithm is 0.79. PAA in the product stream is not decarboxylated, as Figure 5The PAA in the product stream was analyzed using MWD analysis as described in Methods Section VII and yielded the following values: M n =1082 kDa; M w =1680 kDa; and PDI =1.6.

[0150] Example 2

[0151] The feed stream of this Example 2 is the product stream of Example 1. 400 mL of feed stream is loaded into the equipment of Example 1 and run the second pass at a flow rate of about 4899 mL / min and a pressure of about 4341 psi (299.3 bar). The residence time of the feed stream in the LW is about 4.9 s. The cumulative (1st and 2nd pass) residence time of the feed stream is about 9.2 s. The calculated total energy is 1.92 MJ / kg SAP, the calculated cumulative (1st and 2nd pass) total energy is 4.02 MJ / kg SAP, the calculated specific energy is 1.20 MJ / kg SAP, the calculated cumulative (1st and 2nd pass) specific energy is 2.56 MJ / kg SAP, and therefore the energy efficiency of the LW for the 1st and 2nd pass is 2.56 / 4.02=63.7%. The viscosity of the product stream was measured in oscillatory mode using a parallel plate fixture and was found to be 38.7 Pa.s at 1 rad / s. The viscosity ratio of the two streams was therefore 5.76 × 10 -2 , and its negative logarithm is 1.24. PAA in the product stream is not decarboxylated, as Figure 5 The PAA in the product stream has: n =750 kDa; M w =1120 kDa; and PDI =1.5.

[0152] Example 3

[0153] The feed stream of this Example 3 is the product stream of Example 2. 400 mL of feed stream is loaded into the equipment of Example 1 and is run for the 3rd pass at a flow rate of about 4899 mL / min and a pressure of about 4195 psi (289.2 bar). The residence time of the feed stream in the LW is about 4.9 s. The cumulative (1st to 3rd pass) residence time of the feed stream is about 13.8 s. The calculated total energy is 1.89 MJ / kg SAP, the calculated cumulative (1st to 3rd pass) total energy is 5.91 MJ / kg SAP, the calculated specific energy is 1.16 MJ / kg SAP, the calculated cumulative (1st to 3rd pass) specific energy is 3.72 MJ / kg SAP, and the energy efficiency of the LW for the 1st to 3rd pass is therefore calculated to be 3.72 / 5.91=62.9%. The viscosity of the product stream was measured in oscillatory mode using a parallel plate fixture and was found to be 15.2 Pa.s at 1 rad / s. The viscosity ratio of the two streams was therefore 2.26 × 10 -2 , and its negative logarithm is 1.65. PAA in the product stream is not decarboxylated, as Figure 5 The PAA in the product stream has: n =1254kDa; M w =1566 kDa; and PDI =1.2.

[0154] Example 4

[0155] The feed stream of this Example 4 is the product stream of Example 3. 300 mL of the feed stream was loaded into the apparatus of Example 1 and run for the 4th pass at a flow rate of about 4899 mL / min and a pressure of about 4143 psi (285.6 bar). The residence time of the feed stream in the LW was about 3.7 s. The cumulative (1st to 4th pass) residence time of the feed stream was about 17.5 s. The LW total energy was calculated to be 1.86 MJ / kg SAP, the cumulative (1st to 4th pass) LW total energy was calculated to be 7.77 MJ / kg SAP, the specific energy was calculated to be 1.14 MJ / kg SAP, the cumulative (1st to 4th pass) specific energy was calculated to be 4.86 MJ / kg SAP, and therefore the energy efficiency of the LW for the 1st to 4th pass was calculated to be 4.86 / 7.77=62.5%. The viscosity of the product stream was measured in stable mode with a cup and swing fixture and at 4 s -1 Under the condition of , it is measured to be 6.31Pa.s. Therefore, the viscosity ratio of the two flows is 9.38×10 -3 , and its negative logarithm is 2.03. PAA in the product stream is not decarboxylated, as Figure 5 The PAA in the product stream has: n =1419 kDa; Mw =1697 kDa; and PDI =1.2.

[0156] Example 5

[0157] The feed stream of this Example 5 is the product stream of Example 4. 300 mL of the feed stream was loaded into the apparatus of Example 1 and run for the 5th pass at a flow rate of about 4899 mL / min and a pressure of about 4101 psi (282.8 bar). The residence time of the feed stream in the LW was about 3.7 s. The cumulative (1st and 2nd pass) residence time of the feed stream was about 21.2 s. The total LW energy was calculated to be 1.85 MJ / kg SAP, the cumulative (1st to 5th pass) LW total energy was calculated to be 9.62 MJ / kg SAP, the specific energy was calculated to be 1.13 MJ / kg SAP, the cumulative (1st to 5th pass) specific energy was calculated to be 5.99 MJ / kg SAP, and therefore the energy efficiency of the LW for the 1st to 4th pass was calculated to be 5.99 / 9.62=62.3%. The viscosity of the product stream was measured in stable mode with a cup and swing fixture and at 4 s -1 Under the condition of , it is measured to be 3.23Pa.s. Therefore, the viscosity ratio of the two flows is 4.8×10 -3 , and its negative logarithm is 2.32. PAA in the product stream is not decarboxylated, as Figure 5 The PAA in the product stream has: n =1318kDa; M w =1653 kDa; and PDI =1.3.

[0158] Inventive Examples 6 to 10 show that for a 2.5 wt% SAP and 97.5 wt% RO water feed stream, the negative logarithm of the product stream to feed stream viscosity ratio (i.e., the order of magnitude decrease in product stream viscosity relative to feed stream viscosity) increases with residence time in LW (with hydrodynamic cavitation). The results for these inventive examples are also reported in Tables 1 and Figure 2 Shown in.

[0159] Example 6

[0160] The feed stream of this Example 6 was the same as that of Example 1 and was run in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as Example 1. The only difference in the apparatus of Example 1 was that in this Example 6 the stainless steel blade was placed 0.5 mm from the LW orifice (i.e., this distance was 0.3 times the hydraulic diameter of the orifice and therefore cavitation was expected to occur). The viscosities of the feed and product streams were measured in oscillatory mode using a parallel plate fixture. The complex viscosity of the feed stream at 1 rad / s was measured to be 648.2 Pa.s and the complex viscosity of the product stream at 1 rad / s was measured to be 115.7 Pa.s. Therefore, the viscosity ratio of the two streams was 1.78×10 -1 , and its negative logarithm is 0.75. PAA in the product stream is not decarboxylated, as Figure 6 The PAA in the product stream has: n =646kDa; M w =939 kDa; and PDI =1.5.

[0161] Example 7

[0162] The feed stream of this Example 7 was the product stream of Example 6, and it was run in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as in Example 2. The only difference in the apparatus of Example 2 was that in this Example 7 the stainless steel blade was placed 0.5 mm from the LW orifice. The viscosity of the product stream was measured in oscillatory mode using a parallel plate fixture and was found to be 26.9 Pa.s at 1 rad / s. Therefore, the viscosity ratio of the two streams was 4.15×10 -2 , and its negative logarithm is 1.38. PAA in the product stream is not decarboxylated, as Figure 6 The PAA in the product stream has: n =814 kDa; M w =1308 kDa; and PDI =1.6.

[0163] Example 8

[0164] The feed stream of this Example 8 was the product stream of Example 7, and it was run in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as in Example 3. The only difference in the apparatus of Example 3 was that in this Example 8 the stainless steel blade was placed 0.5 mm from the LW orifice. The viscosity of the product stream was measured in oscillatory mode using a parallel plate fixture and was found to be 10.8 Pa.s at 1 rad / s. Therefore, the viscosity ratio of the two streams was 1.67×10 -2 , and its negative logarithm is 1.78. PAA in the product stream is not decarboxylated, as Figure 6 The PAA in the product stream has: n =1026kDa; M w =1498 kDa; and PDI =1.4.

[0165] Example 9

[0166] The feed stream for this Example 9 was the product stream of Example 8 and was run in the same equipment and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as Example 4. The only difference in the equipment of Example 4 was that in this Example 9 the stainless steel blade was placed 0.5 mm from the LW orifice. The viscosity of the product stream was measured using a cup and an oscillating fixture in steady mode and was measured at 4 s. -1 Under the condition of , it is measured to be 2.75Pa.s. Therefore, the viscosity ratio of the two flows is 4.24×10 -3 , and its negative logarithm is 2.37. PAA in the product stream is not decarboxylated, as Figure 6 The PAA in the product stream has: n =1277kDa; M w =1532 kDa; and PDI =1.2.

[0167] Example 10

[0168] The feed stream for this Example 10 was the product stream of Example 9, and it was run in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as Example 5. The only difference in the apparatus of Example 5 was that in this Example 10 the stainless steel blade was placed 0.5 mm from the LW orifice. The viscosity of the product stream was measured using a cup and an oscillating fixture in steady mode and was measured at 4 s. -1 Under the condition of , it is measured to be 2.1Pa.s. Therefore, the viscosity ratio of the two flows is 3.24×10 -3 , and its negative logarithm is 2.49. PAA in the product stream is not decarboxylated, as Figure 6 The PAA in the product stream has: n =1434kDa; M w =1703 kDa; and PDI =1.2.

[0169] Inventive Examples 11 to 15 show that for 2.5 wt% SAP and 97.5 wt% of a 3 wt% H2O2 solution, the negative logarithm of the viscosity ratio of the product stream to the feed stream (i.e., the order of magnitude decrease in the viscosity of the product stream relative to the viscosity of the feed stream) increases with increasing residence time in LW (no hydrodynamic cavitation). The results of these inventive examples are also reported in Tables 1 and Figure 3 Shown in.

[0170] Example 11

[0171] A feed stream having 2.5 wt% SAP and 97.5 wt% of a 3 wt% hydrogen peroxide solution was prepared as in Example 1 and operated in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as in Example 1. The viscosities of the feed and product streams were measured using a parallel plate fixture in oscillatory mode. The complex viscosity of the feed stream at 1 rad / s was measured to be 628.6 Pa.s, and the complex viscosity of the product stream at 1 rad / s was measured to be 78 Pa.s. Therefore, the viscosity ratio of the two streams was 1.24×10 -1 , and its negative logarithm is 0.91. The PAA in the product stream has: M n =373kDa; M w =624 kDa; and PDI =1.7.

[0172] Example 12

[0173] The feed stream for this Example 12 was the product stream of Example 11, and it was run in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as in Example 2. The viscosity of the product stream was measured using a parallel plate fixture in oscillatory mode and was found to be 28.6 Pa.s at 1 rad / s. Thus, the viscosity ratio of the two streams was 4.55×10 -2 , and its negative logarithm is 1.34. The PAA in the product stream has: M n =666 kDa; M w =1005 kDa; and PDI =1.5.

[0174] Example 13

[0175] The feed stream for this Example 13 was the product stream of Example 12, and it was run in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as in Example 3. The viscosity of the product stream was measured using a parallel plate fixture in oscillatory mode and was found to be 10.6 Pa.s at 1 rad / s. Therefore, the viscosity ratio of the two streams was 1.69×10 -2 , and its negative logarithm is 1.77. The PAA in the product stream has: M n =833kDa; M w =1208 kDa; and PDI =1.4.

[0176] Example 14

[0177] The feed stream for this Example 14 was the product stream of Example 13, and it was run in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as Example 4. The viscosity of the product stream was measured using a parallel plate fixture in oscillatory mode and was found to be 3.9 Pa.s at 1 rad / s. Therefore, the viscosity ratio of the two streams was 6.20×10 -3 , and its negative logarithm is 2.21. The PAA in the product stream has: M n =891kDa; M w =1239 kDa; and PDI =1.4.

[0178] Example 15

[0179] The feed stream for this Example 15 was the product stream of Example 14 and was run in the same equipment and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as Example 5. The viscosity of the product stream was measured using a cup and swing fixture in steady mode and was measured at 4 s. -1 Under the condition of , it is measured to be 2.1Pa.s. Therefore, the viscosity ratio of the two flows is 3.34×10 -3 , and its negative logarithm is 2.48. The PAA in the product stream has: M n =967kDa; M w =1332 kDa; and PDI =1.4.

[0180] Inventive Examples 16 to 20 show that for 2.5 wt% SAP and 97.5 wt% of a 3 wt% H2O2 solution, the negative logarithm of the viscosity ratio of the product stream to the feed stream (i.e., the order of magnitude decrease in the viscosity of the product stream relative to the viscosity of the feed stream) increases with increasing residence time in LW (with hydrodynamic cavitation). The results of these inventive examples are also reported in Tables 1 and Figure 4 Shown in.

[0181] Example 16

[0182] The feed stream of this Example 16 was the same as that of Example 11, and it was run in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as Example 6. The viscosities of the feed and product streams were measured using a parallel plate fixture in oscillatory mode. The complex viscosity of the feed stream at 1 rad / s was measured to be 628.6 Pa.s, and the complex viscosity of the product stream at 1 rad / s was measured to be 51.7 Pa.s. Therefore, the viscosity ratio of the two streams was 8.11×10 -2 , and its negative logarithm is 1.08. The PAA in the product stream has: M n =525kDa; M w=849 kDa; and PDI =1.6.

[0183] Example 17

[0184] The feed stream for this Example 17 was the product stream of Example 16, and it was run in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as Example 7. The viscosity of the product stream was measured using a parallel plate fixture in oscillatory mode and was found to be 14.5 Pa.s at 1 rad / s. Therefore, the viscosity ratio of the two streams was 2.31×10 -2 , and its negative logarithm is 1.64. The PAA in the product stream has: M n =792kDa; M w =1162 kDa; and PDI =1.5.

[0185] Example 18

[0186] The feed stream for this Example 18 was the product stream of Example 17, and it was run in the same equipment and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as Example 8. The viscosity of the product stream was measured using a parallel plate fixture in oscillatory mode and was found to be 6.68 Pa.s at 1 rad / s. Therefore, the viscosity ratio of the two streams was 1.06×10 -2 , and its negative logarithm is 1.97. The PAA in the product stream has: M n =1074kDa; M w =1405 kDa; and PDI =1.3.

[0187] Example 19

[0188] The feed stream for this Example 19 was the product stream of Example 18, and it was run in the same apparatus and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as Example 9. The viscosity of the product stream was measured using a parallel plate fixture in oscillatory mode and was found to be 2.96 Pa.s at 1 rad / s. Therefore, the viscosity ratio of the two streams was 4.71×10 -3 , and its negative logarithm is 2.33. The PAA in the product stream has: M n =1074kDa; M w =1406 kDa; and PDI =1.3.

[0189] Example 20

[0190] The feed stream for this Example 20 was the product stream of Example 19 and was run in the same equipment and using the same conditions (i.e., flow rate, pressure, total energy, and specific energy) as Example 10. The viscosity of the product stream was measured using a cup and swing fixture in steady mode and was measured at 4 s. -1 Under the condition of , it is measured to be 1.4Pa.s. Therefore, the viscosity ratio of the two flows is 2.23×10 -3 , and its negative logarithm is 2.65. The PAA in the product stream has: M n =1093kDa; M w =1391 kDa; and PDI =1.3.

[0191] The feed stream compositions, experimental conditions, and results for Examples 1 to 20 of the present invention are summarized in Table 1 below.

[0192] Table 1

[0193]

[0194] Inventive Example 23 shows that the amount of extractables from SAP produced by incorporating about 4.8% PAA (a portion of the product stream; from degraded SAP) into virgin SAP (Comparative Example 21) is about half the amount of extractables from SAP produced by incorporating about 5.1% commercial PAA into virgin SAP (Comparative Example 22).

[0195] Example 21 - Comparative

[0196] 112.7 g of distilled water was placed in a 500 mL round bottom flange neck flask equipped with a 4-neck flange lid and a water-cooled condenser. The flask was cooled in an ice water bath. 46 g of acrylic acid (Cat#213040; 99.5%, low water, stabilized); Beantown Chemical, Hudson, NH) was added and stirred with a football-shaped magnetic stirrer. 34.73 g of sodium hydroxide (Cat#415413; 50% aqueous solution; Sigma-Aldrich, St Louis, MO) was added in small aliquots, maintaining the temperature of the mixture between 17°C and 30°C. After this addition, the ice bath was removed. 0.335 g of polyethylene glycol diacrylate (Cat#455008; M n700 Da; Sigma-Aldrich) was dissolved in 3.16 g of distilled water and added to the flask. The flask was purged with nitrogen for 1 hour by bubbling nitrogen through a stainless steel needle inserted through the septum into the stirring contents. 0.0113 g of L-ascorbic acid (Cat# A0278; reagent grade; Sigma-Aldrich) was dissolved in 0.5 mL of distilled water and added to the flask. 0.0518 g of potassium persulfate (Cat# 216224; ACS Reagent >99%; Sigma-Aldrich) and 0.0021 g of hydrogen peroxide (stable, 1%; Kroger; Topical Solution USP) were dissolved in 2.5 mL of distilled water and added to the flask within 1 minute of the L-ascorbic acid. The flask was observed and the stirrer was turned off when the viscosity increased enough to prevent the stir bar. The temperature was monitored and after the peak exotherm, the condenser was removed and the flask was sealed and placed in an oven at 60°C for 18 hours. The flask was removed, cooled, and the gelled contents were broken into approximately 1 cm round pieces by hand and spread onto an aluminum pan. The gel was dried in a fan oven at 120°C for 6 hours, removed, cooled, and ground using an IKA Al 1 Basic S1 grinder (IKA Works, Inc., Wilmington, NC). The ground powder was sieved, and the fraction between 152 μm and 508 μm was collected and placed in a controlled environment room at 73°F and 50% relative humidity for 24 hours. 1 g of this powder was analyzed for extractables content according to EDANA method NWSP 270.0.R2 (15). The amount of extractables for this sample was 5.85%.

[0197] Example 22 - Comparative

[0198] 115.54 g of 2.5 wt% PAA prepolymer solution ( PA 110S; ChemPoint Inc., Bellevue, WA; prepared by diluting 10 g of a 35 wt% solution to 140 g with distilled water) was charged to a 500 mL round bottom flange neck flask equipped with a 4-neck flange lid and a water-cooled condenser. The flask was cooled in an ice water bath. 43.18 g of acrylic acid (Cat# 213040; 99.5%, low water, stabilized); Beantown Chemical) was added and stirred with a football-shaped magnetic stirrer. 34.73 g of sodium hydroxide (Cat# 415413; 50% aqueous solution, Sigma-Aldrich) was added in small aliquots, maintaining the temperature of the mixture between 17°C and 30°C. After this addition, the ice bath was removed. 0.335 g of polyethylene glycol diacrylate (Cat# 455008; M n700 Da; Sigma-Aldrich) was dissolved in 3.16 g of distilled water and added to the flask. The flask was purged with nitrogen for 1 hour by bubbling nitrogen through a stainless steel needle inserted through the septum into the stirring contents. 0.0113 g of L-ascorbic acid (Cat# A0278; reagent grade; Sigma-Aldrich) was dissolved in 0.5 mL of distilled water and added to the flask. 0.0518 g of potassium persulfate (Cat# 216224; ACS Reagent >99%; Sigma-Aldrich) and 0.0021 g of hydrogen peroxide (stable, 1%, Kroger, Topical Solution USP) were dissolved in 2.5 mL of distilled water and added to the flask within 1 minute of the L-ascorbic acid. The flask was observed and the stirrer was turned off when the viscosity increased enough to prevent the stir bar. The temperature was monitored and after the peak exotherm, the condenser was removed and the flask was sealed and placed in an oven at 60°C for 18 hours. The flask was removed, cooled, and the gelled contents were broken into approximately 1 cm round pieces by hand and spread onto an aluminum pan. The gel was dried in a fan oven at 120°C for 6 hours, removed, cooled, and ground using an IKA A11 Basic S1 grinder (IKA Woks, Inc.). The ground powder was sieved, and the fraction between 152 μm and 508 μm was collected and placed in a controlled environment chamber at 73°F and 50% relative humidity for 24 hours. 1 g of this powder was analyzed for extractables content according to EDANA method NWSP 270.0.R2 (15). The amount of extractables for this sample was 14.02%.

[0199] Example 23

[0200] 10.54 g of distilled water and 105 g of the product stream of Example 10 (i.e., a 2.5 wt% PAA solution (M w 1703 kDa), which is produced when the feed stream flows in the LW and the blade is set at 0.5 mm from the LW orifice) was charged into a 500 mL round bottom flange neck flask equipped with a 4-neck flange cap and a water-cooled condenser. The flask was cooled in an ice water bath. 43.18 g of acrylic acid (Cat#213040; 99.5%, low water, stabilized); Beantown Chemical) was added and stirred with a football-shaped magnetic stirrer. 33.08 g of sodium hydroxide (Cat#415413; 50% aqueous solution, Sigma-Aldrich) mixed with 1.64 g of distilled water was added in small aliquots, maintaining the temperature of the mixture between 17°C and 30°C. After this addition, the ice bath was removed. 0.335 g of polyethylene glycol diacrylate (Cat#455008; M n700 Da; Sigma-Aldrich) was dissolved in 3.16 g of distilled water and added to the flask. The flask was purged with nitrogen for 1 hour by bubbling nitrogen through a stainless steel needle inserted through the septum into the stirring contents. 0.0113 g of L-ascorbic acid (Cat# A0278; reagent grade; Sigma-Aldrich) was dissolved in 0.5 mL of distilled water and added to the flask. 0.0518 g of potassium persulfate (Cat# 216224; ACS Reagent >99%; Sigma-Aldrich) and 0.0021 g of hydrogen peroxide (stable, 1%, Kroger, Topical Solution USP) were dissolved in 2.5 mL of distilled water and added to the flask within 1 minute of the L-ascorbic acid. The flask was observed and the stirrer was turned off when the viscosity increased enough to prevent the stir bar. The temperature was monitored and after the peak exotherm, the condenser was removed and the flask was sealed and placed in an oven at 60°C for 18 hours. The flask was removed, cooled, and the gelled contents were broken into approximately 1 cm round pieces by hand and spread onto an aluminum tray. The gel was dried in a fan oven at 120°C for 6 hours, removed, cooled, and ground using an IKA A11 Basic S1 grinder (IKA Works, Inc.). The ground powder was sieved, and the fraction between 150 μm and 500 μm was collected and placed in a controlled environment chamber at 73°F and 50% relative humidity for 24 hours. 1 g of this powder was analyzed for extractables according to EDANA method NWSP 270.0.R2 (15). The amount of extractables for this sample was 7.56%.

[0201] The SAP compositions and results for Examples 21 to 23 are summarized in Table 2 below.

[0202] Table 2

[0203]

[0204] Inventive Example 26 shows that the swelling ratio of the SAP produced by incorporating about 5% PAA (a portion of the product stream; from degraded SAP) into the original SAP is the same as that of the original SAP (Comparative Example 24).

[0205] Example 24 - Comparative

[0206] 0.5 to 1 g of the dried, unground gel prepared as in Example 11 was selected, accurately weighed, and placed in a glass jar containing approximately 200 mL of a 0.9 wt % aqueous NaCl solution. The jar was allowed to stand for 3 days without stirring. The free liquid was then decanted, and the swollen gel in the jar was reweighed. The swelling ratio (in g / g) was calculated as (weight of swollen gel - weight of dried gel) / weight of dried gel and was found to be 42.0 g / g.

[0207] Example 25 - Comparative

[0208] 0.5 to 1 g of the dry, unground gel prepared as in Example 12 was selected, accurately weighed, and placed in a glass jar containing approximately 200 mL of a 0.9 wt % aqueous NaCl solution. The jar was allowed to stand for 3 days without stirring. The free liquid was then decanted, and the swollen gel in the jar was reweighed. The swelling ratio (in g / g) was calculated as (weight of swollen gel - weight of dried gel) / weight of dried gel and was found to be 55.3 g / g.

[0209] Example 26

[0210] 0.5 to 1 g of the dried, unground gel prepared as in Example 13 was selected, accurately weighed, and placed in a glass jar containing approximately 200 mL of a 0.9 wt % aqueous NaCl solution. The jar was allowed to stand for 3 days without stirring. The free liquid was then decanted, and the swollen gel in the jar was weighed again. The swelling ratio (in g / g) was calculated as (weight of swollen gel - weight of dried gel) / weight of dried gel and was found to be 47.5 g / g.

[0211] Example 27

[0212] Several samples of SAP were subjected to the method of the present invention. The SAP used in all examples was a polyacrylic acid-based SAP with a capacity (CRC) of 27.6 g / g, a water content of 0.4%, and a D50 average particle size of 398 μm, as measured according to ISO method 13322-2 (particle size distribution PSD of 63-710 μm). The SAP had an absorption against pressure (AAP) of 25.5 g / g, as determined by EDANA method WSP 442.2-02. In a deviation from EDANA WSP 442.2-02, a pressure of 0.7 psi was applied (while the EDANA method specifies a pressure of only 0.3 psi).

[0213] The deionized water used below was Millipore Q. The conductivity was measured using a laboratory conductivity meter COND 70 instrument (without CELL, #50010522, equipped with Cell VPT51-01 C=0.1, obtained from XS Instruments) or via LF 320 / Set (#300243, equipped with 325, obtained from WTW), the conductivity was <160 μS / cm at 0°C. Therefore, similar equipment for measuring conductivity can be used. The deionized water used in the examples represents the aqueous carrier. The actual amount of deionized water (= aqueous carrier) in the sample is shown in the "m_w_total" column in Table 3.

[0214] Unless otherwise stated, experimental procedures were performed in a climate-conditioned room under standard conditions of 23°C ± 2°C temperature and 45% ± 10% relative humidity.

[0215] program :

[0216] 1. By 1L plastic bottle (made of HDPE, Nalgene TM A 0.5 wt % potassium persulfate (KPS) stock solution was prepared by stirring 5.0 g of dry salt (Sigma-Aldrich, >= 99.0% purity, stock number 216224-500G) in 1% argon (5% argon / 1% argon / 1% argon) and completely dissolving it in 995.0 g of deionized water (i.e., the aqueous carrier). Complete dissolution of the KPS salt was observed when no visible salt crystals remained in the solution.

[0217] 2. A 1.0 wt% hydrogen peroxide (HPO) stock solution (30.0 g) was prepared by adding 1.0 g of 30 wt% HPO (also known as strong hydrogen peroxide, Sigma-Aldrich, stock number 216763-500ML) to 29.0 g of deionized water in a 40 ml glass vial with a plastic snap cap and used fresh (within 24 hours).

[0218] 3. For all examples, an amount of 2.00 g ± 0.02 g of dry SAP of weight "M0" was measured on a balance into a glass vial of 40 ml volume.

[0219] 4. Separately, in a 100 ml glass beaker (Pyrex), a corresponding amount of an aqueous vehicle with diluted salts therein (as described according to point 2 above) having a mass "Ms0" for each example was prepared, containing the corresponding volume in ml (density of all solutions being 1.0 g / ml) of a 0.5 wt.-% stock solution of the corresponding oxidizing salt ("m_salt_solution") and additional deionized water ("m_water") (i.e., a further amount of aqueous vehicle), and (for those examples comprising HPO as indicated in Table 3) a 1.0 wt.-% hydrogen peroxide solution ("m_HPO"), measured by means of an Eppendorf pipette equipped with a 10 ml plastic pipette tip, such that the effective final weight concentrations as given in Table 3, i.e. "w_salt" for the salts and "w_HPO" for the HPO, were obtained.

[0220] 5. Add an amount of the aqueous carrier with dissolved salt, "Ms0," prepared according to step 4, to the dry SAP in the glass vial, ensuring that all SAP particles come into contact with the aqueous carrier with dissolved salt. The amount of "Ms0" for each example is listed in Table 3. Gentle manual shaking, if necessary, was used to improve wetting and uniform swelling of all SAP particles in each sample. Typically, it took 10 to 60 seconds for the entire amount of the aqueous carrier with dissolved salt to be absorbed into the SAP. Therefore, the amount of aqueous carrier with dissolved salt in the SAP is Ms0 / M0.

[0221] 6. Then, the samples in the glass vials were sealed with snap-on plastic caps and allowed to stand for 10 minutes.

[0222] 7. Preheat a circulation oven (Binder GmbH, Germany, Model 1 FED 720) to the temperature shown in the "Temperature T" column (i.e., "high temperature") in Table 3. When temperature is reached, place the corresponding vials with samples on the aluminum tray and start a stopwatch.

[0223] 8. After the time shown in the "Time" column in Table 3 has elapsed, remove the corresponding sample from the glass vial and allow it to cool for 10 minutes.

[0224] 9. Then, transfer the sample from the glass vial to a centrifuge vial (plastic 100 ml centrifuge vial with a screw cap). Place the centrifuge vial in a laboratory centrifuge (Multifuge X1m Thermo Scientific TM , equipped with BIOshield TMThe samples were placed in a 720 rotor and centrifuged at 5000 rpm for 30 minutes (equivalent to 4528 g-force for this setup). Centrifugation precipitated any remaining undegraded and insoluble portion of the SAP from the clear solution formed during degradation. When no liquid formation was observed, centrifugation was not performed, for example, in Comparative Examples C1 to C4.

[0225] 10. For all centrifuged samples, the clear solution was decanted into individual glass vials (40 ml) and thus separated from any remaining non-degraded and insoluble portion of the SAP.

[0226] 11. Measure the net weight of the clear solution "Ms". Measure an aliquot of the clear solution of mass "m_a" into a pre-weighed 10 ml empty (without snap cap) glass vial of mass "m_sc" via a 5 ml plastic syringe. Then, place the 10 ml vial with the clear solution into a vacuum oven (Heraeus Vacutherm model, Thermo Scientific) at 40°C and a pressure of 10 mbar to 50 mbar. TM ) for 3 h to ensure significant evaporation of water. The dry polymer residue was weighed and its mass "Mp" was used to calculate the degradation yield "Y%" via the following formula:

[0227] Y = 100*(Mp×Ms) / (m_a×M0), in weight %

[0228] Thus, the yield Y represents the ratio of the amount of extracted soluble polymer as a product of the SAP degradation solution to the amount of initial dry SAP. Considering that SAP is a cross-linked network of polyacrylic acid, the extracted soluble polymer is substantially soluble polyacrylic acid.

[0229] 12. Sample A8 was tested under the same conditions as Sample A18** to determine the reproducibility of the test procedure.

[0230] Details and results are given in Table 3.

[0231]

[0232] Method VII

[0233] Preparation of SAP "GIC 31187"

[0234] Deionized water with a resistance of >5 MΩ·cm at 25° C. and ice made from this deionized water were used. A sample of approximately 100 g of ice was melted in a 250 mL glass beaker (VWR International Ltd, Leicestershire, UK; part number LENZ07001049) and the conductivity at 0° C. was measured (e.g., via a COND70 INSTRUMENT without a CELL, No. 50010522, equipped with a Cell VPT51-01 C=0.1 from XS Instruments (Carpi MO, Italy), or via a LF 320 / Set, No. 300243, equipped with a TetraCon 325 from WTW (Xylem Inc., Rye Brook, NY, USA)) to be 1.6 μS / cm.

[0235] About 8713.2g of ice prepared as described above is loaded into a 20L resin pot (equipped with a four-necked glass lid closed with a septum, suitable for introducing a thermometer and a syringe needle). A magnetic stirrer capable of mixing the entire contents (when liquid) is added and stirring is started (e.g., an elliptical magnetic stirring bar from VWR, part number 442-0507). Stirring can be carried out at 250-600rpm. 315.6g of deionized water is taken and 33.52g of "PEG700-DA" (e.g., poly (ethylene glycol)-diacrylate with a number average molecular weight of about 700g / mol, from Sigma-Aldrich, CAS#26570-48-9) is dissolved in a 500mL glass beaker. The glass beaker containing the "PEG700-DA" solution is covered with paraffin film and set aside. 5.175 g of "KPS" (potassium persulfate from Sigma-Aldrich, CAS#7727-21-1) was dissolved in a 500 mL glass beaker using 250.0 g of deionized water. To this solution, approximately 0.208 g of a 1 wt % aqueous hydrogen peroxide solution (prepared by diluting a 30 wt % aqueous hydrogen peroxide solution (from Sigma-Aldrich, CAS#7722-84-1) with deionized water) was added. The "KPS" solution thus obtained was sealed and set aside. This solution must be used within 6 hours of preparation. 1.128 g of ascorbic acid (from Sigma-Aldrich, CAS#50-81-7) was dissolved in a 100 mL glass vial with a plastic cap using 50.0 g of deionized water. The solution "ascorbic acid" was sealed and set aside. 4599.600 g of glacial acrylic acid (GAA, CAS #79-10-7; synthetic acrylic acid from Merck, #800181) was added to the ice in the resin kettle while continuing to stir. A thermometer was introduced into the resin kettle, followed by the addition of a total of 3472.600 g of 50 wt% NaOH solution (for analysis, from Merck, #158793, CAS #1310-73-2) and approximately 250.0 g of ice (prepared from deionized water) in portions, bringing the temperature to a range of approximately 15°C to 30°C. The mixture was continued to stir. At a temperature of approximately 15°C to 30°C, the "PEG700-DA" solution was added to the mixture of acrylic acid (AA), NaOH solution, and ice while continuing to stir. The container containing the "PEG700-DA" solution was washed twice with deionized water, each wash containing approximately 3% of the volume of the "PEG700-DA" solution. The wash water from both washes was added to the stirred mixture. Deionized water (the remaining amount needed to achieve a total of 11887.47 g (ice + water)) (e.g., about 2308.67 g deionized water) is added to the stirred mixture. The resin kettle is then closed and the pressure is released, for example, by piercing the septum with two syringe needles.The argon gas of about 200-300 microliters is stirred at 400-600 rpm.Then under about 0.4 bar via injection needle (stainless steel 304 syringe, long 36 inches, size 16, from Sigma-Aldrich, part number Z152404-1EA) with argon violent purge solution, simultaneously with about 250-600 rpm stirring.Argon gas flow is placed on the position near agitator, to effectively and quickly remove dissolved oxygen.After about minimum 1 hour and maximum 2 hours in argon purge and stirring, at a temperature of about 20 ℃-25 ℃, via syringe, " ascorbic acid " solution is added in the reaction mixture, while continuing to stir and argon purge.In 1 minute, also by one of the 4 necks in the glass cover via funnel, add " KPS " solution, " KPS " covers this neck quickly after adding and completing.After initiator solution (" ascorbic acid " and " KPS " solution) is mixed with reaction mixture, continue to stir and argon purge, but purge needle is moved above reaction mixture and record temperature. As polymerization begins (as indicated by a small temperature increase), more specifically after the gel point (characterized by a sudden increase in viscosity), stirring is stopped. The temperature is monitored; typically, it rises from about 23°C to about 70°C-95°C over 60 minutes. Once the temperature reaches a maximum (the reaction mixture can reach, for example, up to about 105°C) and begins to decrease, the resin kettle is transferred to a circulation oven (Binder FED 720) and maintained at about 60°C for about 20 hours.

[0236] After the polymerization completion time of the circulation oven, the oven is closed and the resin pot is cooled to about 20 ℃ to 40 ℃ while remaining in the oven. After this, the gel is taken out and manually broken or cut into smaller pieces with scissors. The gel is ground with a grinder (X70G from Scharfen, which has an Unger R70 plate system: 3 pre-cutter kidney-shaped plates with straight holes of 17 mm in diameter), placed on a perforated stainless steel plate (aperture 4.8 mm, 50 cm × 50 cm, 0.55 mm caliper, 50% open area, from RS; the maximum height of the gel before drying: about 3 cm), and transferred to a circulation oven (e.g., Binder FED 720) equipped with a condensation trap from DAMM (condensing via a heat exchanger cooled to below the dew point) with dry circulating air, cooled to 5 ℃ at about 120 ℃ via a thermostat (Julabo FP 50) for about 20 hours. The dried gel is then ground using a centrifugal grinder (e.g., a Retsch ZM 200 with a vibrating feeder DR 100 (setting 50-60), the opening of the interchangeable screens set to 1.5 mm, and a rotation speed of 8000 rpm). The ground polymer is then sieved to a screen cut containing >90% by weight of material between 150 μm and 850 μm via a sieving machine (e.g., an AS 400 control from Retsch, with screens DIN / ISO 3310-1 of 150 μm and 710 μm, at about 250 rpm for about 10 minutes) to obtain the matrix polymer "SK-002-A". The particles that passed the 150 μm screen were collected under the name "RD 5717". The procedure described here was repeated twice more, and the SAP particles with a cut of 150-710 μm were stored under the names "SK-002-E" and "SK-002-K", respectively. As described for "SK-002-A", the corresponding grindings below 150 μm were collected under the names "GIC 31749" and "GIC 30266", respectively. To prepare the material "GIC 31187", the materials "RD 5717", "GIC 31749" and "GIC 30266" (all particle sizes below 150 μm) were combined and sieved again as described above, but using a sieve DIN / ISO 3310-1 with mesh sizes of 63 μm and 150 μm, respectively.

[0237] SAP "GIC 31187" Features

[0238] The SAP material thus obtained was analyzed for capacity, moisture, and extractable polymer using the Centrifuge Retention Capacity (CRC) test method (EDANA Method WSP 241.2.R3), the Moisture Test Method (EDANA Method WSP 230.2.R3), and the Extractable Polymer (Amount of Extractables) Test Method (EDANA Method WSP 270.2.R3), respectively. The results were as follows: CRC = 50.3 g / g; Moisture = 0.3 wt%; and Extractable Polymer = 15.03 wt%.

[0239] Total energy calculation

[0240] Total energy is the electrical energy supplied to the extensional flow device and is based on the device's voltage and amperage as well as the residence time of the feed stream. Extensional flow devices typically calculate total energy based on motor torque and speed and the residence time of the feed stream in the device. Total energy per unit mass of SAP is then calculated based on the total energy and the amount of SAP in the feed stream.

[0241] Specific energy calculation

[0242] Specific energy is the energy dissipated in the feed stream to convert SAP to PAA and is based on the pressure drop of the feed stream as it flows through the extensional flow system. As an example, if the pressure drop of 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: (341 (bar) × 0.4 (L)) / (400 (mL) × 0.025 (g SAP / g) × 1 (g / mL)) = 1.36 MJ / kg SAP.

[0243] Molecular weight distribution (MWD) analysis

[0244] Gel permeation chromatography (GPC) with multi-angle light scattering (MALS) and refractive index (RI) detection was used. Samples were prepared at a concentration of 1 mg / mL in 0.1 M NaNO3 / 0.02 wt% sodium azide (NaN3) and hydrated overnight with gentle mixing at room temperature. The samples were then filtered through a 0.8 μm filter prior to GPC-MALS / RI analysis. Absolute MWD distributions were calculated using a dn / dc value of 0.15.

[0245] The foregoing description has been given for clearness of understanding only, and no unnecessary limitations are to be understood therefrom, as modifications within the scope of the invention will be apparent to one skilled in the art.

[0246] The dimensions and values ​​disclosed herein are not to be understood as being strictly limited to the exact numerical values ​​recited. Instead, unless otherwise specified, 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."

[0247] Unless expressly excluded or otherwise limited, each document cited herein, including any cross-referenced or related patent or application, is hereby incorporated by reference in its entirety. The citation of any document is not an admission that it is prior art with respect to any of the present inventions disclosed or claimed herein, or that it, by itself or in combination with any one or more of the references, proposes, suggests, or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

[0248] Although specific embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various other changes and modifications may be made without departing from the spirit and scope of the present invention. It is therefore intended that all such changes and modifications within the scope of the present invention be encompassed in the appended claims.

Claims

1. A method for degrading a superabsorbent polymer (SAP) to poly(acrylic acid) (PAA), the method comprising flowing a feed stream comprising said SAP into an inlet of an extensional flow device, and producing a product stream comprising PAA at an outlet of said extensional flow device; wherein said feed stream comprises water and a concentration of SAP greater than 1 wt. %; wherein said feed stream has a residence time in said extensional flow device of less than 120 s; wherein said degradation of said SAP to said PAA requires a total energy of less than 16 MJ / kg SAP; and wherein said PAA has a weight average molecular weight of less than 1,000,000 g / mol, wherein the SAP is a cross-linked, partially neutralized, poly(acrylic acid)-based superabsorbent polymer, and the extensional flow device has an orifice, wherein the tensile stress generated therein as the feed stream of SAP flows through the orifice causes the cross-linking agent to stretch and break, attach the cross-linking agent to the backbone and generate backbone bonding, and The extensional flow occurs simultaneously with oxidative degradation, enzymatic degradation or biological degradation.

2. The method according to claim 1, wherein the residence time is less than 60 s.

3. The process of claim 1, wherein the feed stream comprises SAP and water.

4. The process of claim 1, wherein the feed stream comprises SAP and hydrogen peroxide.

5. The method of claim 1, wherein the SAP has a degree of neutralization greater than 50%.

6. The method of claim 5, wherein the SAP has a degree of neutralization between 65% and 75%.

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

8. The method of claim 7, wherein the negative logarithm of the viscosity ratio is less than 4.

9. The method of claim 7, wherein the negative logarithm of the viscosity ratio is less than 2.

10. The method of claim 1, wherein the PAA has a polydispersity index of less than 4.

11. The method of claim 1, wherein the PAA is used to produce recycled SAP; the SAP comprises a concentration of PAA; and wherein the PAA concentration is less than 30%.

12. The method of claim 11, wherein the PAA concentration is less than 15%.

13. The method of claim 1, wherein the PAA is used to produce a recycled SAP; wherein the recycled SAP has a swelling ratio; and wherein the swelling ratio is greater than 45 g / g.

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