Bio-based and biodegradable superabsorbent polymer and preparation method thereof

Abstract

The present invention relates to a bio-based and biodegradable superabsorbent polymer (SAP) comprising sodium alginate, modified cellulose, at least one activator and at least one cross-linking agent. The SAP exhibits a high bio-based content of up to 93% and meets industrial composting standards such as EN 13432. The need for high thermal energy is eliminated by conducting the crosslinking reaction under mild conditions, including ambient temperature and neutral to alkaline pH. The produced SAP particles exhibit excellent liquid absorption properties, rapid swelling, high retention rate, and no observed toxicity or skin sensitization. The present invention provides a regimen for sustainable replacement of petroleum-based SAP for hygiene products, agricultural and other disposable applications.

Description

Cross Reference to Related Applications

[0001] This application claims priority to U.S. Provisional Patent Application 63 / 652,111, filed May 27, 2024, which is incorporated herein in its entirety by reference. TECHNICAL FIELD

[0002] The present invention relates to a formulation of a bio-based and biodegradable superabsorbent polymer and a method for its preparation, and in particular, but not exclusively, to a bio-based and biodegradable superabsorbent polymer formulation based on bio-sourced raw materials. BACKGROUND

[0003] Superabsorbent polymers (SAP) are hydrophilic and crosslinked polymers that absorb and retain a large amount of liquid relative to their own mass without dissolving. More than 90% of SAP is used in disposable products such as adult incontinence products, baby diapers, feminine hygiene products, and absorbent pads. Polyacrylates (PAA) from non-renewable and non-degradable petroleum-based acrylic acid (AA) are almost the only SAP material on the market. Due to global environmental motivations to reduce dependence on petroleum and eliminate permanent waste, the market demand for SAP materials from renewable resources and their substitutes as PAA is growing and increasingly popular.

[0004] For example, U.S. Patent Applications US5736595A and US5721295A disclose a 2-component SAP containing carboxymethyl cellulose and water-swellable polymers, but do not have proven biodegradability and have low total bio-based content. U.S. Patent Application US7144957B2 uses pure bio-based starch as a skeleton to graft monomers onto the skeleton by graft copolymerization, but these monomers are still mainly petroleum-based, and the resulting SAP also cannot show biodegradability.

[0005] In the invention of bio-based and biodegradable SAP, CN117545797A, KR20230009824A and US20230087087A1 disclose a method for preparing SAP based on starch and chitosan, which can achieve more than 90% degradation within 6 months according to the ISO 14855 standard. This invention uses carboxylic anhydride as the first crosslinking agent, and uses epoxy resin-based compounds as the second surface crosslinking agent, requiring a high reaction temperature of 80-140°C.

[0006] Further, US20200054782A1 discloses a starch-based SAP without synthetic polymer, which contains 60-95% bio-based carbon and can achieve more than 60% biodegradation within 90 days according to ASTM D5388 standard. The crosslinking agents used in this invention, such as citric acid, succinic acid, magnesium acetate, aluminum lactate, aluminum hydroxide, zinc chloride and glycerol, also require high crosslinking temperature of more than 85°C. Other crosslinking agents or surface crosslinking agents, such as maleic anhydride (mentioned in JP4880144B2), alkylene carbonate, various oxazolidinones (mentioned in US20180043052A1), boric acid, epichlorohydrin, diethylene sulfone (mentioned in JP4685017B2), acrylate polyol, glycerol ethoxylate (mentioned in EP2714775A1 and WO2012164018A1) and guanidylated polysaccharides (mentioned in US8012907B2) also require high temperature to successfully complete crosslinking or surface crosslinking.

[0007] Therefore, there is an urgent need in the art for a SAP that is both bio-based and biodegradable, while being manufactured under milder conditions without the need for crosslinking at high temperatures. SUMMARY

[0008] Therefore, the present invention provides a formulation of a bio-based and biodegradable SAP, and a method of making the bio-based and biodegradable SAP. The bio-based and biodegradable SAP contains at least 80% bio-based content according to the International Standard ASTM D6866 test conducted by a third-party testing laboratory, and is biodegradable by EN13432 industrial composting test, OECD 301B biodegradability test, REACH SVHC analysis, ISO 10993-10:2021 skin sensitization test and ISO 10993-23:2021 irritation test.

[0009] The bio-based and biodegradable SAP of the present invention is prepared by crosslinking reaction at a temperature lower than 80°C, thereby reducing energy consumption and achieving milder processing conditions compared to conventional petroleum-based superabsorbent polymers and other bio-based superabsorbent polymers in the prior art.

[0010] According to a first aspect of the invention, the present invention provides a formulation of a bio-based and biodegradable SAP. The bio-based and biodegradable SAP comprises sodium alginate (SA), modified cellulose, at least one activator, at least one crosslinking agent, and at least one pH adjuster. The bio-based and biodegradable superabsorbent polymer has a bio-based content of 0.1% to 93% and complies with at least one biodegradable regulation selected from EN 13432, ASTM D6400, OECD 301B, ISO 17088, EN14995, or AS 5810.

[0011] According to one embodiment, the bio-based and biodegradable superabsorbent polymer has a bio-based content of 20% to 93%.

[0012] According to one embodiment, the modified cellulose comprises carboxymethyl cellulose (CMC), carboxymethyl guar gum (CMG), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), carboxymethyl starch (CMS), or a combination thereof, in a content of 25 wt% to 85 wt%.

[0013] According to one embodiment, the at least one activator includes a nuclear activator or a surface activator.

[0014] According to one embodiment, the at least one activator comprises 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N,N'-dicyclohexylcarbodiimide, N-hydroxysuccinimide sulfonate, or a combination thereof, and is operable at pH 4 to 7 and ambient temperature.

[0015] According to one embodiment, the at least one crosslinking agent includes a core crosslinking agent or a surface crosslinking agent.

[0016] According to one embodiment, the core crosslinking agent includes gelatin, chitosan, diethylenetriamine, propane-1,2,3-triamine, polyethyleneimine, or combinations thereof; and the surface crosslinking agent includes diethylenetriamine, propane-1,2,3-triamine, tris(2-aminoethyl)amine, a polyetheramine having at least two terminal primary amine groups and having a backbone of polypropylene glycol or polyethylene glycol or polyoxyethylene polyoxypropylene copolymer, a polyetheramine with a molecular weight range of about 400 to 5000 g / mol, or any combination thereof.

[0017] According to one embodiment, the at least one pH adjuster comprises hydrochloric acid solution, acetic acid solution, phosphoric acid solution, nitric acid solution, ammonium solution, potassium hydroxide, potassium hydroxide solution, sodium hydroxide, sodium hydroxide solution, or a combination thereof.

[0018] According to another embodiment, the bio-based and biodegradable superabsorbent polymer further comprises at least one surfactant, itaconic acid (IA), acrylamide, at least one free radical initiator, and at least one diacrylate.

[0019] According to one embodiment, the at least one surfactant comprises an octylphenol ethoxylate with an average ethylene oxide chain length of about 7 to 70 ethylene oxide units, or an alkyl polyglucan, wherein the alkyl polyglucan comprises cocoyl glucoside, decyl glucoside, octyl glucoside, lauryl glucoside, sucrose cocoate, C6 alkyl glycoside, C6 alkyl glucoside, etc. 8-10 Alkyl glycosides or combinations thereof, in an amount of 0.1 wt% to 10 wt%.

[0020] According to one embodiment, the at least one free radical initiator comprises tert-butyl hydroperoxide, benzoyl peroxide, ammonium persulfate, di-tert-butyl peroxide, potassium persulfate, or a combination thereof.

[0021] According to one embodiment, the at least one diacrylate includes poly(propylene glycol) diacrylate, poly(ethylene glycol) diacrylate, N,N'-methylenebis(acrylamide), tri(ethylene glycol) diacrylate, 1,6-hexanediol diacrylate, or a combination thereof.

[0022] According to one embodiment, the bio-based and biodegradable superabsorbent polymer is formed into particles with a particle size of 20 to 100 mesh and exhibits a free swelling capacity (FSC) of at least 36 g / g saline solution, a centrifugal retention capacity (CRC) of at least 24 g / g saline solution, and an absorbance under pressure (AUL) of at least 8 g / g saline solution. The SAP particles pass ISO 10993-10:2021 skin sensitization test, ISO 10993-23:2021 irritation test, and REACH SVC analysis.

[0023] In a second aspect, the present invention provides a method for preparing a bio-based and biodegradable superabsorbent polymer. The method includes dissolving sodium alginate and modified cellulose in deionized water at a mass ratio of 1:0.3-6 to form a polysaccharide solution; subjecting the polysaccharide solution to core crosslinking to form a core-crosslinked gel; drying the core-crosslinked gel at 50°C to 110°C to form a core-superabsorbent polymer; grinding and sieving the core-superabsorbent polymer to form one or more core-superabsorbent polymer particles with a particle size less than 100 mesh; subjecting the one or more core-superabsorbent polymer particles to surface crosslinking to form one or more superabsorbent polymer particles; and drying the one or more superabsorbent polymer particles to form the bio-based and biodegradable superabsorbent polymer. The bio-based and biodegradable superabsorbent polymer exhibits a bio-based content of greater than 80%, a free swelling capacity of at least 36 g / g in physiological saline solution, and achieves at least 90% degradation within 180 days according to EN 13432, or at least 60% degradation within 28 days according to OECD 301B. The entire process is carried out at a temperature not exceeding 110°C, without using petroleum-derived acrylic acid, and produces a compostable SAP that is non-phytotoxic.

[0024] According to one embodiment, the step of dissolving sodium alginate and modified cellulose in deionized water to form the polysaccharide solution further includes adding at least one surfactant, itaconic acid, acrylamide, at least one free radical initiator, and at least one diacrylate to the polysaccharide solution.

[0025] According to one embodiment, the itaconic acid is further polymerized via free radical polymerization to form a polymer of itaconic acid, and the polymerization of the itaconic acid is carried out at a temperature of 50°C to 90°C under nitrogen, optionally with acrylamide in a molar ratio of 3-20:1 and one or more diacrylates.

[0026] According to one embodiment, the step of dissolving sodium alginate and modified cellulose in deionized water to form the polysaccharide solution includes: The sodium alginate and the modified cellulose are added to the deionized water and stirred until completely dissolved; and then at least one pH adjuster is added while stirring to adjust the pH of the polysaccharide solution to the range of 4 to 7.

[0027] According to one embodiment, the step of subjecting the polysaccharide solution to nuclear crosslinking to form a nuclear crosslinked gel includes: At least one nuclear activator is added to the polysaccharide solution; The polysaccharide solution was placed at room temperature for nuclear activation; Dissolve at least one nuclear crosslinking agent in deionized water to form a nuclear crosslinking agent solution; The nuclear crosslinking agent solution is mixed with the polysaccharide solution to form a mixture; At least one pH adjuster is added while stirring to adjust the pH of the mixture to the range of 7 to 12, and the mixture is placed at room temperature for core cross-linking to form a core-cross-linked gel.

[0028] According to one embodiment, the step of surface crosslinking the one or more core superabsorbent polymer particles includes: The core superabsorbent polymer particles were stirred in at least one solvent at room temperature; At least one surfactant was added to the nuclear superabsorbent polymer particles while stirring at room temperature to activate the surface. At least one surface crosslinking agent is added to the core superabsorbent polymer particles while stirring at room temperature to perform surface crosslinking, thereby forming the superabsorbent polymer particles; and The superabsorbent polymer particles are washed with at least one of the solvents.

[0029] According to one embodiment, the step of drying the one or more superabsorbent polymer particles to form the bio-based and biodegradable superabsorbent polymer includes drying the one or more superabsorbent polymer particles at a temperature of 50°C to 110°C. Attached Figure Description

[0030] Embodiments of the invention are described in more detail below with reference to the accompanying drawings, in which:

[0031] Figure 1 The nuclear activation reaction between a carboxyl group from sodium alginate or modified cellulose and at least one activator is schematically depicted, as well as the nuclear crosslinking reaction between the activated carboxyl group and the amine group of the nuclear crosslinking agent.

[0032] Figure 2 The surface activation reaction between carboxyl groups on the surface of core SAP particles and at least one activator is schematically depicted, as well as the surface crosslinking reaction between activated carboxyl groups and amine groups of a surface crosslinking agent.

[0033] Figures 3A-3B The free radical polymerization of IA alone and IA together with acrylamide is described in some embodiments;

[0034] Figure 4A The bio-based carbon content of the nuclear SAP particles from Example 3, as measured by ASTM D6866, is depicted, and Figure 4BThe bio-based carbon content of SAP particles from Example 8, as measured by ASTM D6866, is depicted; and

[0035] Figure 5 The main results of an EN 13432 industrial composting test of one embodiment of the bio-based and biodegradable SAP of the present invention are described. The test was conducted by a third-party testing laboratory.

[0036] Figure 6 The main results of the OECD 301B biodegradability test for one embodiment of the bio-based and biodegradable SAP of the present invention are described. This test was conducted by a third-party testing laboratory. Detailed Implementation

[0037] Definitions

[0038] Throughout this specification, unless the context otherwise requires, the word “comprise” or variations such as “comprises” or “comprising” should be understood to imply inclusion of the stated whole or group of wholes, but not to exclude any other whole or group of wholes. It should also be noted that in this disclosure and particularly in the claims and / or paragraphs, terms such as “comprises,” “comprised,” and “comprising” may have the meaning attributed to them under patent law, for example, allowing for elements not expressly listed, but excluding elements present in the prior art or affecting the essential or novel features of the invention.

[0039] Furthermore, throughout this specification and claims, unless the context otherwise requires, the word "include" or variations thereof, such as "includes" or "including," shall be understood to imply inclusion of the stated whole or group of wholes, but not to exclude any other whole or group of wholes.

[0040] As used herein and unless otherwise defined, the terms “substantially,” “basically,” “approximately,” and “about” are used to describe and explain small variations. When used in conjunction with an event or situation, the terms may cover instances where the event or situation occurs precisely or instances where the event or situation is close to occurring. For example, when used in conjunction with a numerical value, the terms may cover a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

[0041] References to "an embodiment," "an example embodiment," "exemplary embodiment," etc., in this specification indicate that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, it is assumed that the effect of such feature, structure, or characteristic in conjunction with other embodiments is within the knowledge of those skilled in the art, whether explicitly described or not.

[0042] In the preparation methods described herein, steps may be performed in any order without departing from the principles of the invention, except where the timing or order of operations is explicitly stated. A statement in a claim that implies performing a certain step first, followed by several other steps, should be interpreted as meaning that the first step is performed before any other steps, but the other steps may be performed in any suitable order unless the order is further stated within the other steps. For example, a claim element stating "step A, step B, step C, step D, and step E" should be interpreted as meaning that step A is performed first, and step E is performed last, and steps B, C, and D may be performed in any order between steps A and E, and such order still falls within the literal scope of the claimed process. A given step or subset of steps may also be repeated. Furthermore, unless the steps specified in the explicit claim language are performed separately, the specified steps may be performed in parallel.

[0043] As used herein, the term "bio-based content" refers to the percentage of organic carbon in materials derived from renewable biological sources, as measured by a certified third-party testing laboratory according to ASTM D6866.

[0044] As used herein, the term “biodegradability specification” refers to a standard protocol for assessing the biodegradability of a material, including but not limited to EN 13432, ASTM D6400, OEDC 301B, and OECD 208, wherein a material is deemed biodegradable if it meets the threshold criteria specified in the corresponding standard.

[0045] As used in this article, the term "modified cellulose" refers to cellulose that has been chemically modified to incorporate functional groups.

[0046] As used herein, the term "activator" refers to a chemical agent that alters the carboxyl groups on a polysaccharide to produce a reactive intermediate capable of further cross-linking with amine groups, and includes both nucleoactivators and surface activators.

[0047] As used herein, the term "crosslinking agent" refers to a molecule or polymer containing at least two reactive functional groups (such as amine groups) that react with an activated polysaccharide to form covalent bonds, thereby forming a three-dimensional network structure within the superabsorbent polymer.

[0048] As used herein, the terms “nuclear activator” and “surface activator” refer to activators used to activate carboxyl groups in the bulk matrix or on the surface of SAP particles for subsequent crosslinking reactions.

[0049] As used herein, the terms “core crosslinker” and “surface crosslinker” refer to crosslinkers that react with activated functional groups within the bulk matrix or on the surface of superabsorbent polymer particles to form covalent bonds and stabilize the polymer structure.

[0050] As used herein, the term "pH adjuster" refers to an acid or base, including but not limited to hydrochloric acid, acetic acid, sodium hydroxide, or ammonium solution, which is added to adjust the pH of the solution to a desired range to facilitate a chemical reaction.

[0051] As used herein, the term “superabsorbent polymer particles” refers to discrete particles of cross-linked polymer material with a particle size between 20 and 100 mesh that are capable of absorbing and retaining a large amount of liquid relative to their mass without dissolving.

[0052] As used herein, “free swelling capacity (FSC)” refers to the amount of liquid absorbed by a dry SAP sample under free swelling conditions; “centrifugation retention capacity (CRC)” refers to the amount of liquid retained in the SAP after centrifugation at a specified centrifugal force; and “absorption rate under pressure (AUL)” refers to the amount of liquid absorbed by an SAP sample under a specified mechanical load. These measurements are performed using physiological saline solutions unless otherwise stated. In this invention, the FSC, CRC, and AUL of SAP were determined according to EDANA 2002 test methods 440.2-02, 441.2-02, and 442.2-02, respectively.

[0053] As used herein, biodegradable standards EN 13432, ASTM D6400, OECD 301B, ISO 17088, EN 14995 and AS 5810 are each incorporated herein by reference in their entirety. These standards may be updated periodically; therefore, any reference to such standards is intended to cover all applicable versions unless otherwise stated.

[0054] As used in this article, "mesh size" refers to the number of holes per inch in a sieve. A larger mesh number corresponds to a smaller pore size, resulting in smaller particles; while a smaller mesh number corresponds to a larger pore size, resulting in larger particles.

[0055] Other definitions of the selected terms used herein can be found in the specific description of the invention and apply throughout. Unless otherwise defined, all other technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0056] In the following description, preferred examples are set forth, including formulations, compositions, and methods of their preparation and use. It will be apparent to those skilled in the art that modifications, including additions and / or substitutions, can be made without departing from the scope and spirit of the invention. Specific details may be omitted to avoid obscuring the invention; however, this invention is prepared to enable those skilled in the art to practice the teachings herein without requiring extensive experimentation.

[0057] This invention proposes a novel SAP formulation with high bio-based content and its preparation method. The bio-based and biodegradable SAP comprises sodium alginate (SA), modified cellulose, at least one activator, at least one crosslinking agent, and at least one pH adjuster. SA provides a high molecular weight to form the SAP framework for high volume expansion and provides carboxyl groups for crosslinking, particularly core crosslinking. Modified cellulose provides a high molecular weight to form the SAP framework for high volume expansion and provides carboxyl groups for crosslinking, particularly surface crosslinking. The pH adjuster is added to the polysaccharide solution to adjust the pH of the polysaccharide solution to pH 4 to 7, preferably pH 5, thereby protonating the carboxyl groups of SA and modified cellulose.

[0058] In one embodiment of the first aspect, the bio-based and biodegradable SAP contains 10% to 70% SA. Preferably, the viscosity of the SA is 100 cP to 4000 cP at room temperature.

[0059] In one embodiment of the first aspect, the bio-based and biodegradable SAP contains 25% to 85% by weight of modified cellulose. The modified cellulose may include carboxymethyl cellulose, carboxymethyl guar gum, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl starch, or combinations thereof.

[0060] Preferably, the viscosity of the modified cellulose is 500 cP to 5000 cP at room temperature.

[0061] In one embodiment of the first aspect, the bio-based and biodegradable SAP contains 1% to 15% by weight of at least one activator. The at least one activator includes a nuclear activator or a surface activator.

[0062] The nuclear activator reacts with a small number of carboxyl groups on the SA and modified cellulose chains to form covalently activated SA and activated modified cellulose. The activated SA and activated modified cellulose are semi-stable at room temperature and can be further reacted with a crosslinking agent. The activator reacts with protonated carboxyl groups. Therefore, the activation reaction is carried out under acidic to neutral conditions, and the reaction can be carried out at mild temperatures, such as room temperature. Figure 1 The nucleocrosslinking reaction between carboxyl groups from sodium alginate or modified cellulose and amine groups from a nucleocrosslinking agent is schematically depicted in some embodiments.

[0063] The surfactant reacts with a small number of carboxyl groups on the core SAP particles to form covalently activated core SAP particles. The activated core SAP particles are semi-stable at room temperature and can be further reacted with a surface crosslinking agent. The reaction can be carried out at mild temperatures, such as room temperature. Figure 2 The surface crosslinking reaction between carboxyl groups on the surface of the core SAP particles in some embodiments and amine groups from the surface crosslinking agent is schematically depicted.

[0064] Preferably, at least one activator may include 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N,N'-dicyclohexylcarbodiimide, N-hydroxysuccinimide sulfonate, or a combination thereof.

[0065] The crosslinking agent is a molecule or polymer containing at least two amine groups, which react with activated SA and activated modified cellulose via nucleophilic attack to form an amide bond between SA and modified cellulose. The crosslinking agent reacts in an aprotic state. Therefore, the crosslinking reaction is carried out under neutral to alkaline conditions, and the reaction can be carried out at mild temperatures, such as room temperature.

[0066] In one embodiment of the first aspect, the bio-based and biodegradable SAP contains 0.1% to 25% by weight of at least one crosslinking agent. The at least one crosslinking agent includes a core crosslinking agent or a surface crosslinking agent. The core crosslinking agent may include gelatin, chitosan, diethylenetriamine, propane-1,2,3-triamine, polyethyleneimine, or combinations thereof. The surface crosslinking agent may include diethylenetriamine, propane-1,2,3-triamine, tris(2-aminoethyl)amine, polyetheramine, etc. T-403, T-5000, T-3000, ED-600, ED-900, ED-2003 or combinations thereof.

[0067] In some embodiments, the surface crosslinking agent is a molecule or polymer containing at least two amine groups, which react with the activated core SAP particles to form amide bonds on the surface of the core SAP particles. The reaction can be carried out at a mild temperature, such as room temperature.

[0068] Following the surface crosslinking reaction, the SAP particles are washed with at least one solvent to remove impurities, said at least one solvent being a combination of at least two selected from deionized water, methanol, ethanol, propanol, or acetone. Water hydrolyzes the unreacted, activated core SAP particles and regenerates carboxyl groups, while methanol, ethanol, propanol, or acetone controls the degree of swelling to minimize water absorption by the SAP during the washing process.

[0069] In some embodiments, a pH adjuster is added after the addition of the nucleocrosslinker to adjust the pH of the nucleocrosslinker to pH 7 to 10, thereby promoting nucleophilic substitution of the amine groups of the activator to form covalent bonds with the activated SA and the activated modified cellulose.

[0070] In one embodiment of the first aspect, at least one pH adjuster may include hydrochloric acid solution, acetic acid solution, phosphoric acid solution, nitric acid solution, ammonium solution, potassium hydroxide, potassium hydroxide solution, sodium hydroxide, sodium hydroxide solution, or a combination thereof.

[0071] Optionally, the bio-based and biodegradable SAP includes at least one surfactant, itaconic acid (IA), acrylamide, at least one free radical initiator, and at least one diacrylate.

[0072] In one embodiment of the first aspect, the surfactant is used for pore formation or stabilization to create or stabilize micropores within the SAP particles, or to increase the surface area of ​​the SAP to facilitate increased liquid absorption rate via capillary action. At least one surfactant may include Triton X-100, X-102, X-114, X-165, X-305, X-705, cocoyl glucoside, decyl glucoside, octyl glucoside, lauryl glucoside, sucrose cocoate, C6 alkyl glycoside ... 8-10 Alkyl glycosides or combinations thereof.

[0073] In one embodiment of the first aspect, the bio-based and biodegradable SAP contains 0% to 50% by weight of IA. Preferably, the IA is derived from renewable plant sources, i.e., bio-based chemicals.

[0074] In another embodiment of the first aspect, the bio-based and biodegradable SAP contains 0% to 10% acrylamide by weight.

[0075] In one embodiment of the first aspect, a radical initiator is used to initiate radical polymerization. The radical initiator decomposes at a preferred temperature to form an active radical that attacks the C=C double bond of the acrylamide (IA) to transfer the radical site to the IA (or acrylamide). The radical-containing IA further attacks the remaining IA (or acrylamide) for chain propagation, thereby forming a PIA having a preferred molecular weight and monomer conversion. At least one radical initiator may include tert-butyl hydroperoxide, benzoyl peroxide, ammonium persulfate, di-tert-butyl peroxide, potassium persulfate, or combinations thereof.

[0076] In one embodiment of the first aspect, the diacrylate is a crosslinking agent for free radical polymerization containing two C=C double bonds to link the two polymer chains of IA (and acrylamide) together, thereby forming the resulting PIA network. At least one diacrylate may comprise poly(propylene glycol) diacrylate, poly(ethylene glycol) diacrylate, N,N'-methylenebis(acrylamide), tri(ethylene glycol) diacrylate, 1,6-hexanediol diacrylate, or combinations thereof.

[0077] In one embodiment of the first aspect, the bio-based and biodegradable SAP has a bio-based content of 0.1% to 93%.

[0078] In some embodiments, nitrogen is used to purge oxygen dissolved in the IA solution, since oxygen can terminate free radical polymerization.

[0079] After cross-linking and drying, the core SAP particles are ground into particles with a suitable particle size (preferably between 20 mesh and 100 mesh).

[0080] This invention also demonstrates excellent and proven biodegradability and safety for human use. This SAP is primarily derived from renewable resources, exhibits high biodegradability in accordance with international standards, and utilizes an environmentally friendly crosslinking agent that enables efficient gel formation at lower temperatures. This will meet the growing market demand for sustainable alternatives to petroleum-based SAPs, reduce the environmental footprint of single-use hygiene products, and align with global efforts in environmentally friendly material innovation.

[0081] According to a second aspect of the present invention, a method for preparing a bio-based and biodegradable SAP is provided. The method for preparing a bio-based and biodegradable SAP comprises:

[0082] (1) Dissolve SA and modified cellulose in deionized water to form a polysaccharide solution;

[0083] (2) The polysaccharide solution is subjected to nuclear cross-linking to form a nuclear cross-linked gel;

[0084] (3) Dry the cross-linked gel to form a core SAP;

[0085] (4) Grind the core SAP to form core SAP particles;

[0086] (5) To perform surface cross-linking of the core SAP particles to form SAP particles; and

[0087] (6) Dry the SAP particles.

[0088] The crosslinking and surface crosslinking methods used are mild and effective, and can be successfully crosslinked even at room temperature to produce a large capacity to absorb and retain water, brine solutions, biological fluids, etc. under normal pressure or load.

[0089] Optionally, the method for preparing bio-based and biodegradable SAP further includes performing IA radical polymerization to form a polymer of itaconic acid (PIA).

[0090] In one embodiment of the second aspect, the step of dissolving SA and modified cellulose in deionized water to form a polysaccharide solution comprises: 1) adding SA and modified cellulose to deionized water and stirring until they are completely dissolved; and 2) adding at least one pH adjuster while stirring to adjust the pH of the solution to 4 to 7.

[0091] In one embodiment of the second aspect, the step of subjecting the polysaccharide solution to core crosslinking to form a core-crosslinked gel comprises:

[0092] (1) Add at least one nuclear activator to the polysaccharide solution while stirring;

[0093] (2) Place the polysaccharide solution at room temperature for 15 minutes to 2 hours to activate the nucleus;

[0094] (3) Dissolve at least one nuclear crosslinking agent in deionized water;

[0095] (4) Add the nuclear cross-linking agent solution to the polysaccharide solution while stirring;

[0096] (5) While stirring, add at least one pH adjuster to adjust the pH of the solution to 7 to 12; and

[0097] (6) Place the polysaccharide solution at room temperature for 15 minutes to 2 hours to allow for nuclear cross-linking and form a nuclear cross-linked gel.

[0098] Optionally, the method includes adding at least one surfactant to the polysaccharide solution while stirring.

[0099] Optionally, the method includes adding PIA to a polysaccharide solution under stirring. PIA contains a high concentration of anionic carboxyl groups (two carboxyl groups per monomer unit) in its polymer chain. This provides strong charge repulsion when PIA comes into contact with an aqueous medium.

[0100] In some embodiments, PIA is synthesized via free radical polymerization of IA (and acrylamide). Acrylamide is added to undergo free radical polymerization with IA because acrylamide is more reactive than IA and produces a higher molecular weight than IA alone. Preferably, the molar ratio of IA to acrylamide is 3-20:1.

[0101] Preferably, IA is produced by fermentation of plant-based raw materials (such as corn starch). Figures 3A-3B The figure shows the free radical polymerization reaction of IA alone or with acrylamide.

[0102] In one embodiment of the second aspect, the step of drying the core-crosslinked gel to form a core SAP includes drying the core-crosslinked gel in an oven at 50°C to 110°C.

[0103] In one embodiment of the second aspect, the step of grinding the core SAP to form core SAP particles includes: 1) grinding the core SAP into particle form, and 2) sieving the core SAP particles to remove core SAP particles with a mesh size greater than 100 mesh.

[0104] In one embodiment of the second aspect, the step of crosslinking the surface of the core SAP particles to form SAP particles includes:

[0105] (1) Stir the core SAP particles in at least one solvent at room temperature for 1 to 55 minutes;

[0106] (2) Add at least one surfactant to the core SAP particles with stirring and continue at room temperature for 1 to 55 minutes to perform surface activation;

[0107] (3) At least one surface crosslinking agent is added to the core SAP particles under stirring and allowed to continue at room temperature for 0.5 to 3 hours to perform surface crosslinking, thereby forming SAP particles; and

[0108] (4) Wash the SAP particles with at least one solvent.

[0109] In one embodiment of the second aspect, the step of drying the SAP particles includes drying the SAP particles in an oven at 50°C to 110°C.

[0110] In one embodiment of the second aspect, the step of performing itaconic acid radical polymerization to form PIA includes:

[0111] (1) Add IA to deionized water and stir;

[0112] (2) Add at least one pH adjuster while stirring to partially neutralize IA;

[0113] (3) Purge the stirred mixture with nitrogen for 10 to 40 minutes;

[0114] (4) Increase the temperature of the stirred mixture to 50°C to 90°C under continuous nitrogen purging;

[0115] (5) Dissolve at least one free radical initiator in deionized water and add the solution of at least one free radical initiator to the stirred mixture to start polymerization;

[0116] (6) Stir at 50°C to 90°C for another 2 to 6 hours under nitrogen purging to form PIA solid;

[0117] (7) Cut the solid PIA into small pieces;

[0118] (8) Dry the PIA solid in an oven at 50°C to 110°C; and

[0119] (9) Grind PIA solid to form PIA.

[0120] Optionally, the method further includes adding acrylamide to the stirred mixture.

[0121] Optionally, the method further includes adding at least one diacrylate after the reaction has lasted for 5 to 60 minutes.

[0122] Optionally, the method further includes adding at least one pH adjuster to further neutralize the PIA solids.

[0123] In one embodiment of the second aspect, the step of performing IA radical polymerization to form PIA precedes the step of dissolving SA and modified cellulose in deionized water to form a polysaccharide solution.

[0124] In one embodiment of the second aspect, the modified cellulose may include CMC, CMG, HEC, HPC, CMS, or a combination thereof.

[0125] In one embodiment of the second aspect, at least one nuclear activator may include 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N,N'-dicyclohexylcarbodiimide, N-hydroxysuccinimide sulfonate, or a combination thereof.

[0126] In one embodiment of the second aspect, at least one nuclear crosslinking agent may include gelatin, chitosan, diethylenetriamine, propane-1,2,3-triamine, polyethyleneimine, or a combination thereof.

[0127] In one embodiment of the second aspect, at least one surface crosslinking agent may include diethylenetriamine, propane-1,2,3-triamine, tris(2-aminoethyl)amine, polyetheramine, etc. T-403, T-5000, T-3000, ED-600, ED-900, ED-2003 or combinations thereof.

[0128] In one embodiment of the second aspect, at least one pH adjuster may include hydrochloric acid solution, acetic acid solution, phosphoric acid solution, nitric acid solution, ammonium solution, potassium hydroxide, potassium hydroxide solution, sodium hydroxide solution, or a combination thereof.

[0129] In one embodiment of the second aspect, at least one solvent may include deionized water, methanol, ethanol, propanol, acetone, or a combination thereof.

[0130] In one embodiment of the second aspect, at least one surfactant may include Triton X-100, X-102, X-114, X-165, X-305, X-705, cocoyl glucoside, decyl glucoside, octyl glucoside, lauryl glucoside, sucrose cocoate, C6 alkyl glycoside, C 8-10 Alkyl glycosides or combinations thereof.

[0131] In one embodiment of the second aspect, IA is derived from renewable plant sources, i.e., bio-based chemicals.

[0132] In one embodiment of the second aspect, at least one free radical initiator may include tert-butyl hydroperoxide, benzoyl peroxide, ammonium persulfate, di-tert-butyl peroxide, potassium persulfate, or a combination thereof.

[0133] In one embodiment of the second aspect, at least one diacrylate may include poly(propylene glycol) diacrylate, poly(ethylene glycol) diacrylate, N,N'-methylenebis(acrylamide), tri(ethylene glycol) diacrylate, 1,6-hexanediol diacrylate, or a combination thereof.

[0134] In the following description, specific details are provided to provide a full understanding of the invention, for illustrative purposes, and are not intended to be limiting.

[0135] Example

[0136] Example 1 - Synthesis of PIA containing only IA

[0137] 50 g of IA and 25 g of deionized water were mixed in a round-bottom flask with magnetic stirring. 15 g of sodium hydroxide was slowly added to the mixture to dissolve the solid. The solution mixture was then purged with nitrogen for 30 minutes, and the flask, equipped with a condenser, was placed in an oil bath with magnetic stirring. The oil bath temperature was increased to 80°C. 0.25 g of ammonium persulfate was dissolved in 1 mL of deionized water, and this solution was added dropwise to the IA solution to initiate polymerization. The mixture was maintained at 80°C with continuous stirring for 4 hours. After this, the solid product was removed. The PIA solid was cut into small pieces and then ground into granules. The degree of neutralization of PIA was 50%.

[0138] To measure monomer conversion, the PIA solution was freeze-dried and redissolved in deuterium dioxide. The solution was measured by proton nuclear magnetic resonance (NMR). Monomer conversion was calculated using the proton integral ratio of monomer IA to polymer PIA. Monomer conversion ranged from 88% to 99%.

[0139] The molecular weight of PIA was determined by gel permeation chromatography using a pH 7 phosphate-buffered saline (PBS) solution and polyacrylic acid standards as the mobile phase. The number-average molecular weight ranged from 22 kg / mol to 34 kg / mol.

[0140] Example 2 - Synthesis of PIA with IA, acrylamide, and diacrylate

[0141] 50 g of IA and 31 g of deionized water were mixed in a capped plastic bottle with magnetic stirring. 15 g of sodium hydroxide was slowly added to the mixture to dissolve the solid. The solution mixture was then purged with nitrogen for 20 minutes, and the flask was placed in a water bath with magnetic stirring. 8 g of acrylamide was added to the mixture. The temperature of the water bath was increased to 70°C. 0.25 g of ammonium persulfate was dissolved in 0.5 mL of deionized water, and this solution was added dropwise to the IA solution to initiate polymerization. After 10 minutes, 0.313 g of polyethylene glycol diacrylate was added to the mixture. The mixture was maintained at 70°C and stirred continuously for 4 hours. After this, the solid product was removed. The PIA solid was cut into small pieces and then ground into granules. The degree of neutralization of PIA was 50%.

[0142] To obtain PIA with 70% neutralization, solid PIA was cut into small pieces and placed in 810 mL of 0.2 M sodium hydroxide solution for absorption. The PIA gel was then dried in a 70°C oven, and the solid was ground into granules. The degree of neutralization of PIA was 70%.

[0143] Example 3 - Forming core SAP with PIA and SA grain Particle - diethylene triamine as core crosslinker

[0144] SA was dissolved in deionized water to form a 4% solution. The pH of the SA solution was adjusted to 5 using NaOH solution. 1-Ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) was added and dissolved in the SA solution at a weight percentage of 10%. The SA / EDC mixture was subjected to a nucleoactivation reaction at room temperature for 1 hour. PIA (IA only) was dissolved in deionized water, and the solution was adjusted to pH 8 using NaOH solution. The two solutions were then mixed at a PIA:SA mass ratio of 1:3. After this, diethylenetriamine was mixed into the mixture at a molar ratio of 25% EDC. The mixture was placed at room temperature for an additional hour to allow for a nucleocrosslinking reaction. After this, the mixture was placed in a 70°C oven to dry for 2 to 4 hours.

[0145] The dried solid was ground into particles using a centrifugal grinder. The core SAP particles were classified by sieving based on their particle size. The free swelling capacity (FSC), centrifugal retention capacity (CRC), and absorbance under pressure (AUL) of the SAP were measured. The FSC, CRC, and AUL were 47 g, 40 g, and 7.3 g brine / g SAP, respectively.

[0146] The biodegradability of SAP was measured according to industrial composting tests according to EN 13432 and conducted by a third-party testing laboratory. As specified in EN 13432, SAP showed a degradation rate of 90.6% over 90 days and a disintegration rate of 93.2% after 84 days, and exhibited no observable phytotoxicity according to Annex E of OECD 208 as amended to EN 13432. CO2 evolution analysis showed that the cumulative carbon dioxide released from SAP reached more than 90% of the theoretical maximum within 90 days, thus meeting the biodegradability requirements of EN 13432. Disintegration analysis confirmed that after 84 days of composting, more than 93% of the SAP particles were physically broken down into particles smaller than 2 mm. Furthermore, phytotoxicity assessment using watercress seed germination and biomass analysis showed no significant growth inhibition compared to the control group, indicating the absence of phytotoxicity. These combined results confirm that SAP particles meet all the key criteria for industrial compostability.

[0147] Figure 5The main experimental results of the EN 13432 industrial composting test of the bio-based and biodegradable SAP of the present invention are shown. It comprises three sub-sections: (1) the percentage of biodegradation over composting time, indicating that CO2 evolution exceeds 90% within 90 days; (2) the disintegration rate, confirming that over 93% of the SAP fragments passed through a 2 mm sieve after 84 days; and (3) the results of a phytotoxicity test based on OECD 208 seed germination and biomass analysis, indicating no toxic effects on plant growth. These results visually demonstrate that the SAP meets industrial composting standards, supporting its environmental friendliness and suitability for compostable sanitary or agricultural applications.

[0148] Example 4 - Forming SAP grain Particle - diethylene triamine as surface crosslinker

[0149] The core SAP particles from Example 3 were immersed in an acetone / water (9:1 v / v) solution and stirred for 10 minutes. Following this, EDC was added to a 2.5% (w / w) acetone / water solution of the core SAP particles at room temperature with continuous stirring for 20 minutes to initiate a surface activation reaction. Then, diethylenetriamine was added to the mixture at a 25% (w / w) molar ratio of EDC, followed by continuous stirring at room temperature for 20 minutes to initiate a surface crosslinking reaction. The SAP particles were separated from the solution and washed with acetone. The SAP particles were then dried in a 60°C oven for 30 minutes. The FSC, CRC, and AUL values ​​were 36 g, 24 g, and 12.2 g brine / g SAP, respectively.

[0150] Example 5 - Forming core SAP with SA and modified cellulose grain Particle - gelatin as core crosslinker

[0151] SA and CMC were dissolved together in deionized water at a 1:1 weight ratio to form a 3.8% solution. The pH of the solution was adjusted to 5 using NaOH solution. EDC was added and dissolved in a 1.75% (by weight) solution of SA and CMC. The mixture was allowed to undergo a nucleoactivation reaction at room temperature for 1 hour. After this, gelatin was dissolved in deionized water and added to the mixture at a 20% (by weight) weight of SA. NaOH solution was added to the mixture to deprotonate the amine groups of the gelatin. The mixture was left at room temperature for another hour to allow for a nucleocrosslinking reaction. After this, the mixture was placed in a 70°C oven to dry for 4 to 6 hours.

[0152] The dried solid was ground into particles using a centrifugal grinder. The core SAP particles were classified by sieving based on their particle size. The FSC and CRC values ​​were 58 g brine and 22 g SAP, respectively.

[0153] Example 6 - Forming SAP with SA and modified cellulosegrain Particle - gelatin as core crosslinker and diethylene triamine as surface crosslinker Example 7 - Forming SAP with SA, modified cellulose, and surfactant

[0154] SA and CMC were dissolved together in deionized water at a weight ratio of 1:3 to form a 3.5% solution. The pH of the solution was adjusted to 5 using NaOH solution. EDC was added and dissolved in the SA and CMC solution at a weight percentage of 5%. The mixture was allowed to undergo a nucleoactivation reaction at room temperature for 1 hour. After this, gelatin was dissolved in deionized water and added to the SA and CMC mixture at a weight percentage of 25%. NaOH solution was added to the mixture to deprotonate the amine groups of the gelatin. The mixture was left at room temperature for another hour to allow for a nucleocrosslinking reaction. After this, the mixture was placed in a 70°C oven to dry for 4 to 6 hours. The dried solids were ground into particles using a centrifugal mill. The core SAP particles were classified by sieving based on their particle size.

[0155] Core SAP particles with a mesh size between 20 and 60 were immersed in an acetone / water (9:1 v / v) solution and stirred for 10 minutes. Following this, EDC was added to a 7% (w / w) acetone / water solution of the core SAP particles at room temperature with continuous stirring for 15 minutes to initiate a surface activation reaction. Then, diethylenetriamine was added to the mixture at a 4% (w / w) molar ratio of EDC, followed by continuous stirring at room temperature for 40 minutes to initiate a surface crosslinking reaction. The SAP particles were separated from the solution and washed with an ethanol / water (7:3 v / v) solution. The SAP particles were then dried in a 70°C oven for 30 minutes. The FSC, CRC, and AUL values ​​were 61 g, 46 g, and 11.3 g brine / g SAP, respectively.

[0156] The absorption rate of SAP particles was measured using the vortex method. In this method, 25 mL of physiological saline was magnetically stirred at 600 rpm in a 50 mL beaker using a 2.5 cm long and 0.5 cm diameter magnetic stir bar to generate a vortex. 1.0 g of SAP particles was then poured into the saline solution, and the SAP particles began to absorb the saline, causing the vortex to disappear. The time between the addition of the SAP particles and the disappearance of the vortex was recorded as the absorption rate. The absorption rate for 20-60 mesh SAP particles was 67 seconds, while the absorption rate for 60-80 mesh SAP particles was 19.5 seconds.

[0157] The liquid permeability of SAP particles was measured using the column method. SAP particles were immersed in excess physiological saline at room temperature for 1 hour to allow them to swell into a gel. The SAP gel was placed in a glass column and pressed into a 2 cm thick gel layer. A metal mesh was used to cover the SAP gel to secure it to the bottom of the column. Physiological saline was poured into the column, maintaining a saline level of 9 cm. The time it took for 20 mL of physiological saline to pass through was measured. The liquid permeability of the SAP particles was calculated based on the volume of saline passing through per minute. The liquid permeability of 20-60 mesh SAP particles was 6.0 mL / min, and the liquid permeability of 60-80 mesh SAP particles was 10.7 mL / min.

[0158] The bio-based content of the SAP was measured according to the ASTM D6866 international standard test, and the measurement was conducted by a third-party testing laboratory. The bio-based content of the surface-crosslinked SAP particles was 84.61%.

[0159] Particle - gelatin as core crosslinker and T5000 as surface crosslinker grain Example 8 - Forming SAP with SA, modified cellulose, and PIA Particle - gelatin as core crosslinker and diethylene triamine as surface crosslinker

[0160] SA and CMC were dissolved together in deionized water at a weight ratio of 1:3 to form a 3.5% solution. The pH of the solution was adjusted to 5 using NaOH solution. EDC was added and dissolved in the SA and CMC solution at a weight percentage of 5%. The mixture was allowed to undergo a nucleoactivation reaction at room temperature for 1 hour. After this, gelatin was dissolved in deionized water and added to the SA and CMC mixture at a weight percentage of 25%. NaOH solution was added to the mixture to deprotonate the amine groups of the gelatin. Decyl glucoside was added to the SA and CMC mixture at a weight percentage of 6.25%. The mixture was left at room temperature for another hour to undergo a nucleocrosslinking reaction. After this, the mixture was placed in a 70°C oven to dry for 4 to 6 hours. The dried solids were ground into particles using a centrifugal grinder. The nucleo-SAP particles were classified by sieving based on their particle size.

[0161] Core SAP particles with a mesh size between 20 and 60 were immersed in an acetone / water (9:1 v / v) solution and stirred for 10 minutes. Following this, EDC was added to a 10% (w / w) acetone / water solution of the core SAP particles at room temperature with continuous stirring for 15 minutes to initiate the surface activation reaction. Then... T5000 was added to a 4% molar mixture of EDC, followed by continuous stirring at room temperature for 45 minutes to allow for surface crosslinking. The SAP particles were then separated from the solution and washed with an ethanol / water (7:3 v / v) solution. The SAP particles were then dried in a 70°C oven for 30 minutes.

[0162] The FSC, CRC, and AUL of the SAP particles were measured. The FSC, CRC, and AUL were 46 g, 32 g, and 20 g saline / g SAP, respectively. The absorption rate of the SAP particles was measured using the vortex method described in Example 6. The absorption rate for 20-60 mesh SAP particles was 95 seconds, while that for 60-80 mesh SAP particles was 41 seconds. The liquid permeability of the SAP particles was measured using the column method described in Example 6. The liquid permeability for 20-60 mesh SAP particles was 103 mL / min.

[0163] The bio-based content of the SAP was measured according to the ASTM D6866 international standard test, and the measurement was conducted by a third-party testing laboratory. The bio-based content of the surface-crosslinked SAP particles is 85.15%.

[0164] Figures 4A-4B grain Figure 6 Example 9 - Forming SAP with SA, modified cellulose, PIA, and surfactant

[0165] SA and CMC were dissolved together in deionized water at a weight ratio of 1:3 to form a 3.5% solution. The pH of the solution was adjusted to 5 using NaOH solution. EDC was added and dissolved in the SA and CMC solution at a weight percentage of 5%. The mixture was allowed to undergo a nucleoactivation reaction at room temperature for 1 hour. After this, gelatin was dissolved in deionized water and added to the SA and CMC mixture at a weight percentage of 25%. NaOH solution was added to the mixture to deprotonate the amine groups of the gelatin. 70% neutralized PIA at a weight percentage of 2% of SA and CMC was added to the mixture. The mixture was left at room temperature for another hour to allow for a nucleocrosslinking reaction. After this, the mixture was placed in a 70°C oven to dry for 4 to 6 hours. The dried solids were ground into particles using a centrifugal mill. The nucleo-SAP particles were classified by sieving based on their particle size.

[0166] Core SAP particles with a mesh size between 20 and 60 were immersed in an acetone / water (9:1 v / v) solution and stirred for 10 minutes. Following this, EDC was added to a 5% (w / w) acetone / water solution of the core SAP particles at room temperature with continuous stirring for 15 minutes to initiate a surface activation reaction. Then, diethylenetriamine was added to the mixture at a 4% (w / w) molar ratio of EDC, followed by continuous stirring at room temperature for 1 hour to initiate a surface crosslinking reaction. The SAP particles were then separated from the solution and washed with an ethanol / water (7:3 v / v) solution. The SAP particles were then dried in a 70°C oven for 30 minutes.

[0167] The FSC, CRC, and AUL of the SAP particles were measured. The FSC, CRC, and AUL were 63 g, 49 g, and 11.4 g saline / g SAP, respectively. The absorption rate of the SAP particles was measured using the vortex method described in Example 6. The absorption rate of 20-60 mesh SAP particles was 68 seconds, while that of 60-80 mesh SAP particles was 27 seconds. The liquid permeability of the SAP particles was measured using the column method described in Example 6. The liquid permeability of 20-60 mesh SAP particles was 18.2 mL / min, while that of 60-80 mesh SAP particles was 3.8 mL / min.

[0168] Particle - gelatin as core crosslinker and T5000 as surface crosslinker The bio-based content testing of the bio-based and biodegradable SAP of the present invention is described. The bio-based content of the SAP was measured according to the ASTM D6866 international standard test, and the measurements were performed by a third-party testing laboratory. The bio-based content of the core SAP particles in the formulation of Example 3 was 93%, and the bio-based content of the surface-crosslinked SAP particles in the formulation of Example 8 was 84.47%. These results confirm that the SAP is primarily derived from renewable plant-based sources.

[0169] SAP’s biodegradability was measured according to the OECD 301B CO2 evolution biodegradability test and tested by a third-party testing laboratory. Example 10 - Forming SAP with SA, modified cellulose, and PIA The main experimental results of the bio-based and biodegradable SAP of this invention were presented in the OECD 301B CO2 evolution biodegradability test. According to the OECD 301B standard, the SAP showed a 93% degradation rate within 28 days.

[0170] The material safety of SAP particles was analyzed in accordance with REACH SVHC regulations. SAP particles meet the regulatory requirements. The material safety of SAP particles was evaluated by an accredited third-party laboratory based on REACH SVHC (Substances of Very High Concern) analysis. The analysis confirmed that the SAP particles do not contain any of the 241 substances currently listed in the REACH candidate list, indicating full compliance with EU REACH regulations and suitability for use in hygiene and skin contact products.

[0171] The skin compatibility of SAP particles was analyzed according to the requirements of ISO 10993-10:2021 Skin Sensitization Tests and ISO 10993-23:2021 Irritation Tests. The analysis was conducted by a third-party testing laboratory. SAP particles were extracted using polar (0.9% sodium chloride solution) and non-polar (corn oil) extractants according to the ISO 10993-10:2021 Skin Sensitivity Test (Guinea Pig Maximize Test, GPMT Method) at 37°C for 72 hours. The extracts were applied to test animals via intradermal injection followed by topical application. The results, based on the degree of erythema, showed a 0% positive reaction rate in all test groups using both polar and non-polar extractants. The positive reaction rate was 0% in all negative control groups and 100% in all positive control groups. These results indicate no sensitization in the test animals, confirming that SAP is non-sensitizing and safe for human use. In addition, SAP particles were tested for skin irritation using an intradermal injection model according to ISO 10993-23:2021. SAP particles were extracted using polar (0.9% sodium chloride solution) and non-polar (corn oil) extractants according to ISO 10993-23:2021 at 37°C for 72 hours. The extracts were then injected intradermally into test animals, and the degree of erythema and edema was observed at several time intervals after injection. The results showed that the final irritation scores for both polar and non-polar extractants were 0. The final irritation score (polar) for the positive control group was 5.0, and the final irritation score (non-polar) for the positive control group was 3.5. The test results revealed no observable signs of erythema or edema, and the irritation index fell within the acceptable range defined by the standard, further supporting its biocompatibility.

[0172] Particle - gelatin as core crosslinker and T5000 as surface crosslinker grain Comparative Example 1 Comparative Example 2 ​

[0173] SA and CMC were dissolved together in deionized water at a weight ratio of 1:3 to form a 3.5% solution. The pH of the solution was adjusted to 5 using NaOH solution. EDC was added and dissolved in the SA and CMC solution at a weight percentage of 5%. The mixture was allowed to undergo a nucleoactivation reaction at room temperature for 1 hour. After this, gelatin was dissolved in deionized water and added to the SA and CMC mixture at a weight percentage of 25%. NaOH solution was added to the mixture to deprotonate the amine groups of the gelatin. 2% PIA (50% neutralization) and 6.25% decyl glucoside (SA and CMC) were added to the mixture. The mixture was left at room temperature for another hour to allow for a nucleocrosslinking reaction. After this, the mixture was placed in a 70°C oven to dry for 4 to 6 hours. The dried solids were ground into particles using a centrifugal mill. The nucleo-SAP particles were classified by sieving based on their particle size.

[0174] The cored SAP particles, with a mesh size between 20 and 60, were immersed in an acetone / water (9:1 v / v) solution and stirred for 10 minutes. Following this, EDC was added to a 5% (w / w) acetone / water solution of the cored SAP particles at room temperature with continuous stirring for 15 minutes to initiate the surface activation reaction. Then... T5000 was added to a 4% molar mixture of EDC, followed by continuous stirring at room temperature for 60 minutes to allow for surface crosslinking. The SAP particles were then separated from the solution and washed with an ethanol / water (7:3 v / v) solution. The SAP particles were then dried in a 70°C oven for 30 minutes.

[0175] The FSC, CRC, and AUL of the SAP particles were measured. The FSC, CRC, and AUL were 48 g, 33 g, and 20.8 g saline / g SAP, respectively. The absorption rate of the SAP particles was measured using the vortex method described in Example 6. The absorption rate of 20-60 mesh SAP particles was 45 seconds, while that of 60-80 mesh SAP particles was 25 seconds. The liquid permeability of the SAP particles was measured using the column method described in Example 6. The liquid permeability of 20-60 mesh SAP particles was 64 mL / min, while that of 60-80 mesh SAP particles was 34 mL / min.

[0176] The bio-based content of the SAP was measured according to the ASTM D6866 international standard test, and the measurement was conducted by a third-party testing laboratory. The bio-based content of the surface-crosslinked SAP particles was 85.83%.

[0177] The material safety of SAP particles was analyzed in accordance with REACH SVHC regulations. SAP particles meet the specified requirements.

[0178] The skin compatibility of SAP particles was analyzed according to the requirements of ISO 10993-10:2021 Skin sensitization test and ISO 10993-23:2021 Irritation test. The analysis was conducted by a third-party testing laboratory. The ISO 10993-10 skin sensitization test (GPMT method) showed that the SAP particles had no skin sensitization reaction, while the ISO 10993-23 intradermal reaction test showed that the SAP particles met the standard requirements.

[0179] ​ grain ​ ​

[0180] SA and CMC were dissolved together in deionized water at a weight ratio of 1:3 to form a 3.5% solution. The pH of the solution was adjusted to 5 using NaOH solution. EDC was added and dissolved in the SA and CMC solution at a weight percentage of 5%. The mixture was allowed to undergo a nucleoactivation reaction at room temperature for 1 hour. After this, gelatin was dissolved in deionized water and added to the SA and CMC mixture at a weight percentage of 25%. NaOH solution was added to the mixture to deprotonate the amine groups of the gelatin. 2% PIA with a 50% neutralization degree was added to the mixture at a weight percentage of 2% of SA and CMC. The mixture was left at room temperature for another hour to allow for a nucleocrosslinking reaction. After this, the mixture was placed in a 70°C oven to dry for 4 to 6 hours. The dried solids were ground into particles using a centrifugal mill. The core SAP particles were classified by sieving based on their particle size.

[0181] Core SAP particles with a mesh size between 20 and 60 were immersed in an acetone / water (9:1 v / v) solution and stirred for 10 minutes. After this, EDC was added to a 3% (w / w) acetone / water solution of the core SAP particles at room temperature with continuous stirring for 15 minutes to carry out the surface activation reaction. Then... T5000 was added to a 4% molar mixture of EDC, followed by continuous stirring at room temperature for 60 minutes to allow for surface crosslinking. The SAP particles were then separated from the solution and washed with an ethanol / water (7:3 v / v) solution. The SAP particles were then dried in a 70°C oven for 30 minutes.

[0182] The FSC, CRC, and AUL of the SAP particles were measured. The FSC, CRC, and AUL were 45 g, 31 g, and 20.6 g saline / g SAP, respectively. The absorption rate of the SAP particles was measured using the vortex method described in Example 6. The absorption rate for 20-60 mesh SAP particles was 110 seconds, while that for 60-80 mesh SAP particles was 57 seconds. The liquid permeability of the SAP particles was measured using the column method described in Example 6. The liquid permeability for 20-60 mesh SAP particles was 35 mL / min, while that for 60-80 mesh SAP particles was 63 mL / min.

[0183] The biodegradability of this SAP was measured according to the OECD 301B CO2 evolution biodegradability test and tested by a third-party testing laboratory. According to the OECD 301B standard, the SAP showed a degradation rate of 68% within 16 days.

[0184] ​

[0185] The FSC, CRC, and AUL of the reference SAP 1, composed of polyacrylate, were measured. The FSC, CRC, and AUL were 62 g, 37 g, and 21.8 g saline / g SAP, respectively. The absorption rate of the SAP particles was measured using the vortex method described in Example 6. The absorption rate for 20-60 mesh SAP particles was 48 seconds, while that for 60-80 mesh SAP particles was 25 seconds. The liquid permeability of the SAP particles was measured using the column method described in Example 6. The liquid permeability for 20-60 mesh SAP particles was 120 mL / min, while that for 60-80 mesh SAP particles was 29 mL / min.

[0186] ​

[0187] The FSC, CRC, and AUL of the reference SAP 2, composed of polyacrylate, were measured. The FSC, CRC, and AUL were 52 g, 28 g, and 25.6 g saline / g SAP, respectively. The absorption rate of the SAP particles was measured using the vortex method described in Example 6. The absorption rate of the 20- to 60-mesh SAP particles was 43 seconds. The liquid permeability of the SAP particles was measured using the column method described in Example 6. The liquid permeability of the 20- to 60-mesh SAP particles was 164 mL / min. Industrial applicability:

[0188] The bio-based and biodegradable superabsorbent polymer (SAP) or particles disclosed herein can absorb a large amount of liquid relative to their own mass without dissolving in water. They have many different potential applications, such as agricultural water-retaining agents, baby diapers, adult incontinence diapers, or feminine hygiene products. Bio-based and biodegradable SAPs have a very high bio-based content because they are synthesized from bio-based polymers or monomers using very small amounts of petroleum-based reagents. Bio-based and biodegradable SAPs also meet biodegradability requirements and are non-phytotoxic, making them a more sustainable alternative to petroleum-based SAPs, particularly for single-use applications.

Claims

1. A bio-based and biodegradable superabsorbent polymer, characterized in that, The bio-based and biodegradable superabsorbent polymer comprises sodium alginate, modified cellulose, at least one activator, at least one crosslinking agent, and at least one pH adjuster, wherein the bio-based content of the bio-based and biodegradable superabsorbent polymer is from 0.1% to 93%, and meets at least one biodegradability requirement selected from EN 13432, ASTM D6400, OECD 301B, ISO 17088, EN 14995, or AS 5810.

2. The bio-based and biodegradable superabsorbent polymer according to claim 1, wherein the bio-based content of the bio-based and biodegradable superabsorbent polymer is 20% to 93%.

3. The bio-based and biodegradable superabsorbent polymer according to claim 1, wherein the modified cellulose comprises carboxymethyl cellulose, carboxymethyl guar gum, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl starch or a combination thereof, and the modified cellulose content is from 25 wt% to 85 wt%.

4. The bio-based and biodegradable superabsorbent polymer according to claim 1, wherein the at least one activator comprises a nucleoactivator or a surface activator.

5. The bio-based and biodegradable superabsorbent polymer according to claim 4, wherein the at least one activator comprises 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N,N'-dicyclohexylcarbodiimide, N-hydroxysuccinimide sulfonate, or a combination thereof, and is operable at pH 4 to 7 and ambient temperature.

6. The bio-based and biodegradable superabsorbent polymer according to claim 1, wherein the at least one crosslinking agent comprises a core crosslinking agent or a surface crosslinking agent.

7. The bio-based and biodegradable superabsorbent polymer according to claim 6, wherein the core crosslinking agent comprises gelatin, chitosan, diethylenetriamine, propane-1,2,3-triamine, polyethyleneimine, or a combination thereof; and the surface crosslinking agent comprises diethylenetriamine, propane-1,2,3-triamine, tris(2-aminoethyl)amine, having at least two terminal primary amine groups and having a backbone of polypropylene glycol or polyethylene glycol or polyoxyethylene polyoxypropylene copolymer, a polyetheramine with a molecular weight range of 400 to 5000 g / mol, or any combination thereof.

8. The bio-based and biodegradable superabsorbent polymer according to claim 1, wherein the at least one pH adjuster comprises hydrochloric acid solution, acetic acid solution, phosphoric acid solution, nitric acid solution, ammonium solution, potassium hydroxide, potassium hydroxide solution, sodium hydroxide, sodium hydroxide solution, or a combination thereof.

9. The bio-based and biodegradable superabsorbent polymer of claim 1, wherein the bio-based and biodegradable superabsorbent polymer further comprises at least one surfactant, itaconic acid, acrylamide, at least one free radical initiator, and at least one diacrylate.

10. The bio-based and biodegradable superabsorbent polymer according to claim 9, wherein the at least one surfactant comprises an octylphenol ethoxylate with an average ethylene oxide chain length of 7 to 70 ethylene oxide units, or an alkyl polyglucan, wherein the alkyl polyglucan comprises cocoyl glucoside, decyl glucoside, octyl glucoside, lauryl glucoside, sucrose cocoate, C6 alkyl glycoside ... 8-10 Alkyl glycosides or combinations thereof, and the content of the at least one surfactant is from 0.1 wt% to 10 wt%.

11. The bio-based and biodegradable superabsorbent polymer of claim 9, wherein the at least one free radical initiator comprises tert-butyl hydroperoxide, benzoyl peroxide, ammonium persulfate, di-tert-butyl peroxide, potassium persulfate, or a combination thereof.

12. The bio-based and biodegradable superabsorbent polymer according to claim 9, wherein the at least one diacrylate comprises poly(propylene glycol) diacrylate, poly(ethylene glycol) diacrylate, N,N'-methylenebis(acrylamide), tri(ethylene glycol) diacrylate, 1,6-hexanediol diacrylate, or a combination thereof.

13. The bio-based and biodegradable superabsorbent polymer of claim 1, wherein the bio-based and biodegradable superabsorbent polymer is formed into particles with a particle size of 20-100 mesh and exhibits a free swelling capacity (FSC) of at least 36 g / g, a centrifugal retention capacity (CRC) of at least 24 g / g and an absorption rate under pressure (AUL) of at least 8 g / g.

14. A method for preparing a bio-based and biodegradable superabsorbent polymer, characterized in that, The method includes: Sodium alginate and modified cellulose are dissolved in deionized water at a mass ratio of 1:0.3-6 to form a polysaccharide solution; The polysaccharide solution is subjected to nuclear cross-linking to form a nuclear cross-linked gel; The core-crosslinked gel is dried at 50°C to 110°C to form a core-superabsorbent polymer; The nuclear superabsorbent polymer is ground and sieved to form one or more nuclear superabsorbent polymer particles with a mesh size of less than 100 mesh; The one or more core superabsorbent polymer particles are surface crosslinked to form one or more superabsorbent polymer particles; and The one or more superabsorbent polymer particles are dried to form the bio-based and biodegradable superabsorbent polymer. The bio-based and biodegradable superabsorbent polymer described herein exhibits a bio-based content of greater than 80%, a free swelling capacity of at least 36 g / g physiological saline solution, and achieves at least 90% degradation within 180 days according to EN 13432, or at least 60% degradation within 28 days according to OECD 301B.

15. The method of claim 14, wherein the step of dissolving sodium alginate and modified cellulose in deionized water to form the polysaccharide solution further comprises adding at least one surfactant, itaconic acid, acrylamide, at least one free radical initiator and at least one diacrylate to the polysaccharide solution.

16. The method of claim 15, wherein the itaconic acid is further polymerized via free radical polymerization to form a polymer of itaconic acid, and the polymerization of the itaconic acid is carried out at a temperature of 50°C to 90°C under nitrogen, optionally with acrylamide in a molar ratio of 3-20:1 and one or more diacrylates.

17. The method of claim 14, wherein the step of dissolving sodium alginate and modified cellulose in deionized water to form the polysaccharide solution comprises: The sodium alginate and the modified cellulose were added to the deionized water and stirred until completely dissolved; and Then, at least one pH adjuster is added while stirring to adjust the pH of the polysaccharide solution to the range of 4 to 7.

18. The method of claim 14, wherein the step of subjecting the polysaccharide solution to core crosslinking to form a core-crosslinked gel comprises: At least one nuclear activator is added to the polysaccharide solution; The polysaccharide solution was placed at room temperature for nuclear activation; Dissolve at least one nuclear crosslinking agent in deionized water to form a nuclear crosslinking agent solution; The nuclear crosslinking agent solution is mixed with the polysaccharide solution to form a mixture; At least one pH adjuster is added while stirring to adjust the pH of the mixture to the range of 7 to 12, and the mixture is placed at room temperature for core cross-linking to form the core-cross-linked gel.

19. The method of claim 14, wherein the step of surface crosslinking the one or more core superabsorbent polymer particles comprises: The core superabsorbent polymer particles were stirred in at least one solvent at room temperature; At least one surfactant was added to the nuclear superabsorbent polymer particles while stirring at room temperature to activate the surface. At least one surface crosslinking agent is added to the core superabsorbent polymer particles while stirring at room temperature to perform surface crosslinking, thereby forming the superabsorbent polymer particles; as well as The superabsorbent polymer particles are washed with at least one of the solvents.

20. The method of claim 14, wherein the step of drying the one or more superabsorbent polymer particles to form the bio-based and biodegradable superabsorbent polymer comprises drying the one or more superabsorbent polymer particles at a temperature of 50°C to 110°C.

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