Water-absorbent crosslinked polycarboxylic acid polymer and method for producing same

Abstract

A method for producing a crosslinked polycarboxylic acid polymer by crosslinking a polycarboxylic acid polymer with a crosslinking agent including a polyepoxide and a polyhydrazide is disclosed. Also disclosed are the crosslinked polycarboxylic acid polymers made by the method and water-absorbing polymeric materials comprising the crosslinked polycarboxylic acid polymers.

Description

[Technical Field]

[0001] This application claims the benefit of U.S. Provisional Application No. 62 / 910,648, filed October 4, 2019, which is incorporated herein by reference.

[0002] This invention was made with government support under IIP 1660217 awarded by the National Science Foundation. The government has certain rights in this invention.

[0003] The present invention relates to a method for producing crosslinked polycarboxylic acid polymers and water-absorbent polymeric materials. [Background technology]

[0004] Water-absorbing polymers, which absorb water or aqueous fluids and retain them in the form of a gel, have been used in many applications, for example, hygiene products such as disposable diapers, agricultural products such as soil conditioners, and other applications where water absorption, retention, or distribution is useful.

[0005] Traditionally, such water-absorbent materials are made from synthetic petroleum-based polymers, such as the sodium salt of poly(acrylic acid) and polyacrylamide, which crosslink into water-insoluble networks that can absorb water and form hydrogels. While relatively inexpensive, petroleum-based polymers have adverse environmental impacts, particularly due to their non-renewable and non-degradable nature and the regulated emissions that result from the processes used to obtain their constituent monomers from petroleum sources.

[0006] Renewable alternatives to such conventional absorbent polymer materials are absorbent materials using biobased polymers, such as poly(amino acids) and polysaccharides. For example, gamma-poly(glutamic acid) (γ-PGA) is a water-soluble polycarboxylic acid polymer that can be commercially produced by a microbial fermentation process. γ-PGA has a hydrophilic polyamide backbone and, like poly(acrylic acid), has pendant carboxylic acid functional groups in each repeat unit. These characteristics make it suitable for crosslinking into materials for use in absorbent applications. For example, γ-PGA can be crosslinked with glycidyl ether crosslinkers, such as ethylene glycol diglycidyl ether and trimethylolpropane triglycidyl ether, to form water-absorbing products. However, the absorbency of glycidyl ether-crosslinked γ-PGA is not ideal due to its lower free swell capacity (FSC) and absorbency under load (AUL) compared to conventional crosslinked sodium polyacrylate, limiting its applications. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention relates to a method for producing crosslinked polycarboxylic acid polymers and water-absorbent polymeric materials. [Means for solving the problem]

[0008] A method for preparing a crosslinked polycarboxylic acid polymer by crosslinking the polycarboxylic acid polymer with a crosslinking agent including a polyepoxide and a polyhydrazide is disclosed. Also disclosed are the crosslinked polycarboxylic acid polymer made by this method, the water-absorbing crosslinked polycarboxylic acid polymer made by this method, and a water-absorbing material comprising the crosslinked polycarboxylic acid polymer. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 1 shows the free swell capacity (FSC) and absorbency under load (AUL) of an embodiment of crosslinked γ-PGA of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] <Detailed explanation> The singular nouns "at least one" and "one or more" are used interchangeably to indicate the presence of at least one of something. A plurality of such things may be present unless the context clearly indicates otherwise. "About" indicates that a stated numerical value allows for some imprecision (some references to the exactness of a value being "approximately" or "nearly" being reasonably close to that value). Unless the imprecision indicated by "about" is otherwise understood in the art in its ordinary meaning, "about," as used herein, at least accounts for the variation that may result from ordinary methods of measuring and using such parameters. Additionally, the disclosure of a range includes the disclosure of all values and further divided ranges within that entire range. The terms "comprise," "comprising," "containing," and "having" are inclusive and thus specify the presence of a stated feature, integer, step, operation, element, or component, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof. As used herein, the term "or" includes any and all combinations of one or more of the items listed in association with it. A "water-soluble" polymer is one that can be combined with water to form a clear solution, with or without the presence of a cosolvent and / or neutralizing agent. A "water-dispersible" polymer is one that can be combined with water to form a stable dispersion, with or without the presence of a cosolvent and / or neutralizing agent. A dispersion that has no visible settled sediment after 24 hours of storage at 25°C can be considered stable.

[0011] Crosslinked polycarboxylic acid polymers are prepared by crosslinking polycarboxylic acid polymers with polyepoxide compounds and polyhydrazide compounds. Polycarboxylic acid polymers are polymers having carboxylic acid groups (pendant carboxylic acid groups) pendant along the polymer backbone. The polycarboxylic acid polymers may optionally have carboxylic acid groups at one or both ends of the polymer chain. In various embodiments, the polycarboxylic acid polymers may have a pendant carboxylic acid group from about every tenth monomer unit, on average; or from about every sixth monomer unit, on average; or from about every fifth monomer unit, on average; or from about every fourth monomer unit, on average; or from about every third monomer unit, on average; or from about every other monomer unit, on average; or from all monomer units.

[0012] The weight average molecular weight of the polycarboxylic acid polymer, as measured by gel permeation chromatography (GPC) equipped with a light scattering detector, can be from about 1 kDa to about 50,000 kDa, preferably from about 5 kDa to about 50,000 kDa, more preferably from about 100 kDa to about 5,000 kDa, and even more preferably from about 200 kDa to about 600 kDa. In various embodiments, the weight average molecular weight of the polycarboxylic acid polymer is from about 1 kDa, or from about 5 kDa, or from about 10 kDa, or from about 20 kDa, or from about 30 kDa, or from about 50 kDa, or from about 100 kDa, or from about 150 kDa, or from about 200 kDa, or from about 250 kDa, or from about 300 kDa, to about 500 kDa, or to about 550 kDa, or to about 600 kDa, or to about 700 kDa. The polycarboxylic acid polymer may have a molecular weight of up to about 800 kDa, up to about 900 kDa, up to about 1000 kDa, up to about 2000 kDa, up to about 5000 kDa, up to about 7500 kDa, up to about 10,000 kDa, up to about 15,000 kDa, up to about 20,000 kDa, up to about 25,000 kDa, up to about 30,000 kDa, up to about 40,000 kDa, or up to about 50,000 kDa. The polycarboxylic acid polymer preferably contains a sufficient number of carboxylic acid groups to be water-soluble or water-dispersible. In certain embodiments, the average number of carboxylic acid groups per polycarboxylic acid polymer chain may be from about 2 to about 700,000, preferably from about 50 to about 50,000, and more preferably from about 1,500 to about 8,000.

[0013] Non-limiting examples of polycarboxylic acid polymers suitable for crosslinking include homopolymers and copolymers of ethylenically unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, 2-ethacrylic acid, 2-propylacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, etc., and their salts and anhydrides; carboxymethylcellulose and its salts; polyaspartic acid and its salts; polyglutamic acid and its salts; and carboxyethyldextran and its salts. In certain embodiments, the polycarboxylic acid polymer can be selected from the group consisting of α-poly(glutamic acid), γ-poly(glutamic acid), α-poly(aspartic acid), β-poly(aspartic acid), carboxymethylcellulose, poly(acrylic acid), poly(methacrylic acid), poly(2-carboxyethyl acrylate), poly(2-ethylacrylic acid), poly(2-propylacrylic acid), poly(maleic acid), copolymers thereof, and combinations thereof. In certain embodiments, the polycarboxylic acid polymer is or comprises a poly(amino acid), e.g., a homopolymer of aspartic acid or glutamic acid, e.g., L-α-poly(aspartic acid) or L-α-poly(glutamic acid), or a combination thereof, produced by ribosomal translation. Other non-limiting examples of useful poly(amino acids) include D,L-(α,β)-poly(aspartic acid) or D,L-(α,γ)-poly(glutamic acid), or a combination thereof, produced by condensation polymerization from aspartic acid and / or glutamic acid monomers, or D-γ-poly(glutamic acid), L-γ-poly(glutamic acid), D,L-γ-poly(glutamic acid), or a combination thereof, produced by nonribosomal synthesis in microbial culture or in vitro biochemical methods. Polycarboxylic acid polymers may be used in any combination in the crosslinking step.

[0014] In addition to the polycarboxylic acid polymer or combination of polycarboxylic acid polymers, the above reaction can further include a second polymer having multiple groups reactive with the crosslinker, such as multiple reactive groups selected from the group consisting of carboxylic acid groups, amine groups, hydroxyl groups, and combinations thereof. In various embodiments, the second polymer is water-soluble or water-dispersible. Non-limiting examples of polymers suitable as the second polymer include starch, guar gum, xanthan gum, carrageenan, pectin, glucomannan, inulin, cellulose, β-glucan, dextrin, galactomannan, alginic acid, chitosan, ethylenically unsaturated carboxylic acids, amines, and alcohols, such as homopolymers and copolymers of acrylic acid, methacrylic acid, 2-ethacrylic acid, 2-propylacrylic acid, acrylamide, 2-hydroxyethyl acrylate, N-(2-hydroxyethyl)acrylamide, maleic acid, and 2-aminoethyl methacrylate, and combinations of such polymers.

[0015] A polycarboxylic acid polymer or a combination of polycarboxylic acid polymers is crosslinked by reaction with a crosslinking agent containing a polyepoxide and a polyhydrazide. This crosslinking agent has been found to enhance the water absorption of water-soluble or water-dispersible polycarboxylic acid polymers when crosslinked. In particular, the use of a crosslinking agent containing a polyepoxide and a polyhydrazide increases both the free swell capacity and the absorbency under load compared to the use of a polyepoxide crosslinker alone. To determine the free swell capacity, a tea bag containing 0.1 g of crosslinked polycarboxylic acid polymer is immersed in 100 mL of 0.9% NaCl solution at room temperature (23±2°C) for 5 minutes. The tea bag is then removed from the saline solution and hung to remove surface moisture for 5 minutes. The swollen crosslinked product is then weighed. The free swell capacity is defined as the ratio of the mass of water absorbed (the difference between the wet weight and the dry weight) to the dry weight. To determine the absorbency under load, 0.1 g of cross-linked polycarboxylic acid polymer was placed in a plastic cylinder with a screen cloth at the bottom, and a plastic piston was placed on the product (0.3 psi). The filter sponge was placed in a glass container, and the container was filled with 0.9% NaCl solution up to the edge of the filter sponge. The assembly containing the above product was then placed on the filter sponge for 90 minutes at room temperature (23 ± 2 °C). The absorbency under load was calculated as the ratio of the mass of absorbed water (difference between wet weight and dry weight) to the dry mass.

[0016] Suitable polyepoxide crosslinking molecules contain two or more reactive epoxide groups. Non-limiting examples of these include polyglycidyl ethers of alkane polyols and poly(alkylene glycols), including, by way of further example, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether and triglycidyl ether, propylene glycol diglycidyl ether, butanediol diglycidyl ether, and polyglycidyl ethers of erythritol, trimethylolethane, pentaerythritol, and trimethylpropane; diepoxyalkanes and diepoxyaralkanes (including 1,2,3,4-diepoxybutane, 1,2,4,5-diepoxypentane, 1,2,5,6-diepoxyhexane, 1,2,7,8-diepoxyoctane, 1,4- and 1,3-divinylbenzene diepoxide); poly(alkylene glycols) and ... and polyglycidyl esters of polycarboxylic acids, such as oxalic acid diglycidyl ester, succinic acid diglycidyl ester, adipic acid diglycidyl ester, glutaric acid diglycidyl ester, phthalic acid diglycidyl ester, terephthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, 2,6-naphthalenedicarboxylic acid diglycidyl ester, and epoxide esters of polyunsaturated fatty acids and their oligomers, such as polyepoxidized dimeric linoleic acid, polyepoxidized linoleic acid, polyepoxidized linoleic acid, and polyepoxidized derivatives of linseed oil, soybean oil, their alkyl esters, and their oligomers.

[0017] In certain embodiments, the crosslinker comprises a polyepoxide selected from the group consisting of a polyepoxide having a structure shown in formula (I) and a polyepoxide having a structure shown in formula (II). [ka] (In the formula, n is 1 to 150.) [ka] (Wherein R1 is H, CH3, CH2CH3, OH, CH2OH, [ka] and R2, R3, and R4 are [ka] (It is).

[0018] Polyepoxides include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,3-butanediol diglycidyl ether, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, resorcinol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, and poly(ethylene glycol) diglycidyl ether. The glycerol may be selected from the group consisting of glycerol, poly(propylene glycol) diglycidyl ether, trimethylolpropane diglycidyl ether, trimethylolethane triglycidyl ether, triethylolpropane diglycidyl ether, triethylolethane triglycidyl ether, glycerol propoxylate triglycidyl ether, pentaerythritol tetraglycidyl ether, castor oil polyglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, and combinations thereof.

[0019] The crosslinking agent further includes a polyhydrazide having at least two hydrazide functional groups. Non-limiting examples of suitable polyhydrazides include polyhydrazides of aliphatic and aromatic dicarboxylic and tricarboxylic acids, such as adipic acid dihydrazide, citric acid dihydrazide and trihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, phthalic acid dihydrazide, terephthalic acid dihydrazide, hexahydrophthalic acid dihydrazide, and 2,6-naphthalenedicarboxylic acid dihydrazide.

[0020] In certain embodiments, the cross-linking agent comprises a polyhydrazide selected from the group consisting of a polyhydrazide having the structure shown in formula (III) and a polyhydrazide having the structure shown in formula (IV). [ka] (wherein n is 1 to 10.) [ka] (wherein R is H, OH, or CH3).

[0021] The polyhydrazide may be selected from the group consisting of oxalic acid dihydrazide (oxalyl dihydrazide), succinic acid dihydrazide, malonic acid dihydrazide, ethylmalonic acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, dodecanedioic acid dihydrazide, sebacic acid dihydrazide, phthalic acid dihydrazide, terephthalic acid dihydrazide, isophthalic acid dihydrazide, carbohydrazide, thiocarbohydrazide, citric acid trihydrazide, ethylenediaminetetraacetic acid tetrahydrazide, and combinations thereof.

[0022] The crosslinker may comprise multiple polyepoxides or multiple polyhydrazides, or multiple polyhydrazides and multiple polyepoxides. The crosslinker may comprise a small amount, for example, up to about 10 mole %, of an additional reactant based on the total moles of the crosslinker compound. Examples of such additional reactants include compounds having multiple aziridine groups, carbodiimide compounds, amine compounds having at least two active hydrogens, and polycarboxylic acid monomers.

[0023] In certain embodiments, the amount of polyepoxide and the amount of polyhydrazide used in the crosslinking reaction are each independently preferably about 0.1 to about 10% by weight, more preferably about 0.5 to about 5% by weight, and even more preferably about 1 to about 3% by weight, based on the weight of the polycarboxylic acid polymer. In certain embodiments, the amount of polyepoxide and the amount of polyhydrazide used in the crosslinking reaction are each independently preferably about 0.1 to about 10% by weight, more preferably about 0.5 to about 5% by weight, and even more preferably about 1 to about 3% by weight, based on the acid equivalent weight of the polycarboxylic acid polymer. In certain embodiments, the molar ratio between polyepoxide and polyhydrazide is preferably about 0.1 to about 10, more preferably about 0.2 to about 5, and even more preferably about 0.5 to about 2.

[0024] In an exemplary embodiment, all components for the crosslinking reaction are dissolved in an aqueous medium, and the reaction solution is heated in an oven. The concentration of the polycarboxylic acid polymer in the reaction solution may be about 10 to about 300 g / L, preferably about 50 to about 200 g / L, and more preferably about 80 to about 150 g / L. The pH of the reaction solution may be about 3 to about 9, preferably about 4 to about 8, and more preferably about 5 to about 7. Useful neutralizing agents include alkali metal bases, ammonia, and / or amines. The oven temperature may be about 50 to about 200°C, preferably about 80 to about 180°C, and more preferably about 100 to about 150°C. The reaction mixture may be held in the oven for about 1 to about 12 hours, preferably about 1.2 to about 6 hours, and more preferably about 1.5 to about 3 hours.

[0025] If desired, drying can be carried out in an oven, such as a forced air oven, at any of the oven temperatures described above, or by infrared heating at a temperature of from about 20 to about 180°C.

[0026] The crosslinking reaction can be carried out in an aqueous medium. The crosslinked polycarboxylic acid polymer product can then be dried, ground, and classified to obtain particulate crosslinked polycarboxylic acid polymers of a desired average particle size and / or particle size distribution. Non-limiting examples of grinders include vertical grinders, pulverizers, rotary cutter mills, disk mills, and other such cutting, grinding, or crushing devices. In one example, the crosslinked polycarboxylic acid polymer can be further dried after coarse grinding, and then ground or crushed, for example, in a suitable mill, and classified to a final desired average particle size.

[0027] The ground crosslinked polycarboxylic acid polymer is not limited to a particular particle shape or form. The particulate crosslinked polycarboxylic acid polymer may be in the form of a powder, flake, aggregate, granule, irregular granular particle, sphere, ellipsoid, cylindrical particle (or whisker), fiber, or another shape suitable for its intended use. Examples of uses include, but are not limited to, baby diapers and adult hygiene products, soil additives, oil treatment and industrial dehydration, medical applications such as drug delivery devices and tissue engineering implants, thickeners for aqueous media, including personal care and food applications, and other applications requiring the absorption, desorption, or thickening of water or aqueous fluids.

[0028] In some embodiments, the crosslinked polycarboxylic acid polymer particle composition further comprises an excipient or additive that enhances the performance or ease of use in the end use. The type of excipient or additive is not particularly limited. Suitable examples include, but are not limited to, other molecular species crosslinked with the polycarboxylic acid polymer to alter the material properties, surfactants or emulsifiers to enhance dispersion, inorganic fillers to enhance mechanical properties, coating the crosslinked polycarboxylic acid polymer particles with an active pharmaceutical ingredient, or impregnating the crosslinked polycarboxylic acid polymer particles with an active pharmaceutical ingredient.

[0029] Tests have shown that when both polyepoxide and polyhydrazide are used for the crosslinking reaction, the crosslinked polycarboxylic acid polymer exhibits much higher water absorption than when only polyepoxide is used as a crosslinking agent. Furthermore, the use of polyhydrazide as the only crosslinking agent did not result in a crosslinked product. Without wishing to be bound by a particular theory, it is believed that the improved properties are due to the reaction between polyepoxide and polyhydrazide, which forms unique bonds between the crosslinked polycarboxylic acid polymer chains.

[0030] The present invention is further illustrated by the following examples. It should be noted that the examples are not intended to limit the scope of the present invention, but are provided to illustrate the present invention. [Example]

[0031] The weight-average molecular weight of the γ-PGA used in the examples was 255 kDa, as determined by gel permeation chromatography with a light scattering detector. The γ-PGA (10 g) was dispersed in DI water (100 mL) using an immersion blender, and the pH of the solution was adjusted to 5.5 by adding 4 M HCl (100 μL). Next, trimethylolpropane triglycidyl ether (TTE) (200 μL) and adipic acid dihydrazide (ADH) (100 mg) were added. The mixture was poured onto a silicone mat and heated at 150°C for 2 hours. The product was then purified by soaking in a large amount of DI water overnight, dried in a dehydrator at 45°C for 48 hours, and then crushed into particles (20-100 mesh). The crosslinked product was then tested for its water absorption, including free swell capacity (FSC) and absorbency under load (AUL).

[0032] For comparison, crosslinking of γ-PGA was also attempted using trimethylolpropane triglycidyl ether under the same conditions. Linear γ-PGA (10 g) was dispersed in DI water (100 mL) using an immersion blender, and the pH of the solution was adjusted to 5.5 by adding 4 M HCl (100 μL). Next, trimethylolpropane triglycidyl ether (TTE) (200 μL) was added. The mixture was poured onto a silicone mat and heated at 150°C for 2 hours. The product was then purified by soaking in a large amount of DI water overnight, dried in a dehydrator at 45°C for 48 hours, and then crushed into particles (20-100 mesh).

[0033] For comparison, crosslinking of γ-PGA was also attempted using adipic acid dihydrazide under the same conditions. Linear γ-PGA (10 g) was dispersed in DI water (100 mL) using an immersion blender, and the pH of the solution was adjusted to 5.5 by adding 4 M HCl (100 μL). Next, adipic acid dihydrazide (ADH) (100 mg) was added. The mixture was poured onto a silicone mat and heated at 150 °C for 2 hours. However, the preparation of γ-PGA crosslinked with adipic acid dihydrazide was unsuccessful. The resulting product was water-soluble and did not form a gel.

[0034] To determine the free swelling capacity (FSC), a tea bag containing 0.1 g of the above product was immersed in 100 mL of 0.9% NaCl solution at room temperature (23±2°C) for 5 minutes. The tea bag was then removed from the saline solution and hung at an angle for 5 minutes to allow excess saline to drip off. The swollen cross-linked product was then weighed. The free swelling capacity is calculated by the ratio of the weight of absorbed water (difference between wet weight and dry weight) to the dry weight. The free swelling capacity of the examples is shown in the figures.

[0035] To determine the absorbency under load (AUL), 0.1 g of the above product was placed in a plastic cylinder with a screen cloth at the bottom, and a plastic piston was placed on top of the product (0.3 psi). The filter sponge was placed in a glass container, and the container was filled with 0.9% NaCl solution up to the edge of the filter sponge. The assembly including the product was then placed on the filter sponge for 90 minutes at room temperature (23±2°C). The absorbency under load was calculated by the ratio of the weight of absorbed water (difference between wet weight and dry weight) to the dry weight. The absorbency under load of the examples is shown in the figures.

[0036] As shown in the figure, compared to γ-PGA cross-linked with TTE, γ-PGA cross-linked with TTE / ADH exhibited much higher FSC (33 g / g vs. 25 g / g) and AUL (31 g / g vs. 24 g / g), which is a 32% improvement in FSC and a 29% improvement in AUL.

[0037] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in selected embodiments even if not specifically shown or described. They can also be varied in many ways. Such variations should not be considered a departure from the invention, and all such modifications are intended to be included within the scope of the invention.

Claims

1. 1. A method for producing a water-absorbing crosslinked polycarboxylic acid polymer, comprising the step of crosslinking a polycarboxylic acid polymer with a crosslinking agent comprising a polyepoxide and a polyhydrazide, The method of manufacturing, wherein the polycarboxylic acid polymer is selected from the group consisting of α-poly(glutamic acid), γ-poly(glutamic acid), α-poly(aspartic acid), β-poly(aspartic acid), copolymers thereof, and combinations thereof.

2. The method of claim 1 , wherein the crosslinking agent comprises a component selected from the group consisting of polyepoxides and combinations thereof and a component selected from the group consisting of polyhydrazides and combinations thereof.

3. The method according to claim 1 or 2, wherein the polycarboxylic acid polymer has a weight average molecular weight of 1 kDa to 50,000 kDa.

4. The method of any one of claims 1 to 3, wherein the polycarboxylic acid polymer comprises gamma-poly(glutamic acid).

5. The method according to any one of claims 1 to 4, wherein the polycarboxylic acid polymer is water-soluble or water-dispersible.

6. The method of any one of claims 1 to 5, wherein a second polymer having multiple groups reactive with the crosslinker is crosslinked with the polycarboxylic acid polymer.

7. The polyepoxide is selected from the group consisting of ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,3-butanediol diglycidyl ether, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, resorcinol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, poly(ethylene glycol) diglycidyl ether, poly(propylene glycol) diglycidyl ether, 7. The method of claim 1, wherein the component is selected from the group consisting of triglycidyl ether, triethylolpropane diglycidyl ether, trimethylolethane triglycidyl ether, triethylolpropane diglycidyl ether, triethylolethane triglycidyl ether, glycerol propoxylate triglycidyl ether, pentaerythritol tetraglycidyl ether, castor oil polyglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, and combinations thereof.

8. The method according to any one of claims 1 to 7, wherein the polyhydrazide is a component selected from the group consisting of oxalic acid dihydrazide, succinic acid dihydrazide, malonic acid dihydrazide, ethylmalonic acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, dodecanedioic acid dihydrazide, sebacic acid dihydrazide, phthalic acid dihydrazide, terephthalic acid dihydrazide, isophthalic acid dihydrazide, carbohydrazide, thiocarbohydrazide, citric acid trihydrazide, ethylenediaminetetraacetic acid tetrahydrazide, and combinations thereof.

9. The method according to any one of claims 1 to 8, wherein the crosslinking agent comprises 0.1 to 10% by weight of a polyepoxide and / or 0.1 to 10% by weight of a polyhydrazide, based on the weight of the polycarboxylic acid polymer.

10. The process according to any one of claims 1 to 9, wherein the molar ratio between the polyepoxide and the polyhydrazide is between 0.1 and 10.

11. The method of any one of claims 1 to 10, wherein the polyepoxide and polyhydrazide are simultaneously reacted with the polycarboxylic acid polymer to form a crosslinked polycarboxylic acid polymer.

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