Biodegradable superabsorbents

Abstract

The present invention relates to a biodegradable superabsorbent based on polyglutamic acid (salts) and its preparation. The aim was to provide a biodegradable superabsorbent with improved performance. This problem involved a method for preparing water-absorbing polyglutamic acid (salts), which method comprises: i) providing an aqueous mixture of uncrosslinked polyglutamic acid (salt) and at least one crosslinker; ii) cross-linking the uncross-linked polyglutamic acid (salt) to obtain a cross-linked polyglutamic acid (salt)-gel; iii) drying the cross-linked polyglutamic acid (salt)-gel to obtain a dried cross-linked water-absorbing polyglutamic acid (salt); iv) heat-treating the dried cross-linked water-absorbing polyglutamic acid (salt) in the presence of at least one accelerator to obtain the water-absorbing polyglutamic acid (salt). The problem was solved by the method including:

Description

[Technical Field]

[0001] The present invention relates to biodegradable superabsorbents based on polyglutamic acid (salts) and their preparation. [Background technology]

[0002] "Superabsorbent" or "superabsorber" is a common trade term that refers to polymer particles that can absorb large amounts of water under pressure without releasing the water. Other common terms are "superabsorbent materials" (SAMs), "superabsorbent polymers" (SAPs), or "absorbent gelling materials" (AGMs).

[0003] Upon absorbing water, superabsorbents swell rapidly, and the water becomes trapped within the polymer network of the superabsorbent, so that the water-laden superabsorbent forms a hydrogel. As well as water, superabsorbents absorb saline and various types of bodily fluids. Due to this ability, superabsorbents serve as central components for personal hygiene products such as baby diapers, feminine care products, and incontinence products.

[0004] Many of the superabsorbent materials currently used in hygiene products, which are capable of absorbing large amounts of liquids, especially body fluids such as water and urine, in a short time, are mainly based on slightly crosslinked synthetic polymers, including, for example, polymers and copolymers based on acrylic acid or acrylamide, which are not traditionally renewable materials and have poor or no biodegradability, requiring incineration or landfilling.

[0005] Attempts have been made to replace the above-mentioned polymers and copolymers with biodegradable, and therefore environmentally friendly, polymers. One of the most notable has been the use of polysaccharides. However, the challenge with the raw materials used to manufacture polysaccharide-based superabsorbents is that they are often water-soluble and must be converted into a water-insoluble form in order to be used as superabsorbents in various applications.

[0006] For example, European Patent No. 0538904 and U.S. Patent No. 5,247,072 describe superabsorbents based on carboxyalkyl polysaccharides, a process that involves a thermal crosslinking step that is highly sensitive to small changes in pH and reaction temperature, resulting in absorbents with widely varying absorption properties and prone to short shelf lives.

[0007] However, in the processes known from the prior art for cross-linking polysaccharides, it has been observed that the homogeneous cross-linking of polysaccharides hinders the biodegradability of the absorbent body, in part because of the poor aging stability, as well as the limited swelling, which reduces the accessibility of microorganisms. Furthermore, in the cross-linking reactions known from the prior art, the additional introduced substituents inhibit enzymatic degradation [Mehltretter et al., Journal of the American Oil Chemists Society, 47 (1970), pages 522-524].

[0008] Due to its bio-derived and biodegradable properties, polyglutamic acid (PGA) and its use as a superabsorbent material have also been investigated. For example, International Publication No. 2021 / 242936 reports the production of a polyglutamic acid-based superabsorbent that can be further modified. However, this superabsorbent, especially after a surface cross-linking process, exhibits mediocre performance with respect to common parameters used to evaluate superabsorbents, such as centrifugal retention capacity (CRC), absorption against pressure (AAP), saline flow conductivity (SFC), and absorption rate (vortex and FSR). Because adequate performance with respect to these parameters is crucial for the commercial success of superabsorbents used in personal hygiene products, the actual use of polyglutamic acid-based superabsorbents in commercial hygiene products is not yet known. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent No. 0538904 [Patent Document 2] U.S. Patent No. 5,247,072 [Patent Document 3] International Publication No. 2021 / 242936 [Non-patent literature]

[0010] [Non-Patent Document 1] Mehltretter et al., Journal of the American Oil Chemists Society, 47(1970), pages 522-524 Summary of the Invention [Problem to be solved by the invention]

[0011] It is therefore an object of the present invention to provide a biodegradable superabsorbent with improved performance, in particular with respect to centrifuge retention capacity (CRC), absorption against pressure (AAP), saline flow conductivity (SFC), and absorption rate (vortex and FSR), which should be improved and balanced. [Means for solving the problem]

[0012] The object is to provide a method for producing water-absorbing polyglutamic acid (salt), i) providing an aqueous mixture of uncrosslinked polyglutamic acid (salt) and at least one crosslinker; ii) cross-linking the uncross-linked polyglutamic acid (salt) to obtain a cross-linked polyglutamic acid (salt)-gel; iii) drying the cross-linked polyglutamic acid (salt)-gel to obtain a dried cross-linked water-absorbing polyglutamic acid (salt); iv) heat treating the dried cross-linked water-absorbing polyglutamic acid (salt) in the presence of at least one accelerator to obtain the water-absorbing polyglutamic acid (salt). The problem is solved by a method including:

[0013] It has been found that when produced according to the method of the present invention, superabsorbents based on polyglutamic acid (salts) achieve better performance with respect to the requirements of users and manufacturers of personal hygiene products. The superabsorbents obtained according to the method of the present invention are derived from polyglutamic acid and are therefore biodegradable.

[0014] As used herein, "at least one" refers to one or more, i.e., 1, 2, 3, 4, 5, 6, 7, 8, 9, or more. For example, with respect to crosslinkers, the value refers to the crosslinker and not the absolute number of molecules of crosslinker used. Unless otherwise stated, "%" refers to "% by weight." DETAILED DESCRIPTION OF THE INVENTION

[0015] A contribution to achieving this object is made by a method for producing a water-absorbing polyglutamic acid (salt), comprising the steps of: i) providing an aqueous mixture of uncrosslinked polyglutamic acid (salt) and at least one crosslinking agent; ii) crosslinking the uncrosslinked polyglutamic acid (salt) to obtain a crosslinked polyglutamic acid (salt)-gel; iii) drying the crosslinked polyglutamic acid (salt)-gel to obtain a dried crosslinked water-absorbing polyglutamic acid (salt); and iv) heat-treating the dried crosslinked water-absorbing polyglutamic acid (salt) in the presence of at least one accelerator to obtain the water-absorbing polyglutamic acid (salt), thereby providing an environmentally friendly and biodegradable water-absorbing polyglutamic acid (salt).

[0016] The uncrosslinked polyglutamic acid (salt) used in the present invention may be partially neutralized. Preferably, at least 50 mol%, more preferably at least 70 mol%, and even more preferably at least 80 mol% of the uncrosslinked polyglutamic acid is neutralized and exists as a salt. Neutralization can be achieved using standard techniques and methods known to those skilled in the art. For example, an aqueous solution of sodium hydroxide can be used. Suitable cations are lithium, sodium, and potassium, with sodium, potassium, and mixtures thereof being preferred. The uncrosslinked polyglutamic acid is selected from α-polyglutamic acid and γ-polyglutamic acid, preferably γ-polyglutamic acid. In a preferred embodiment of the present invention, the uncrosslinked polyglutamic acid (salt) has a molecular weight of 200,000 to 3,000,000 daltons, preferably 500,000 to 2,000,000 daltons, and more preferably 700,000 to 1,100,000 daltons.

[0017] As used herein, "aqueous mixture" refers to a mixture that contains at least 40% by weight, preferably at least 50% by weight, more preferably at least 60% by weight, and even more preferably 70% by weight water, based on the total weight of the aqueous mixture.

[0018] The at least one crosslinker used in step i) may be a glycidyl ether, such as diglycidyl ether, triglycidyl ether, polyglycidyl ethers containing three or more epoxy groups, diglycerol tetraglycidyl ether, dipentaerythritol tetraglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, isosorbide glycidyl ether, polyglycerol-3-glycidyl ether, or other aliphatic polyfunctional epoxides, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, polypropylene glycol diglycidyl ether, polyglycidyl ethers of alkane polyols, polyglycidyl ethers of poly(alkylene glycols), bio-based sorbitol glycidyl ether, such as CVC Thermoset The crosslinking agent is selected from the group consisting of ERISYS® GE-61 from Biotech Specialties, any type of cyclic and aromatic polyglycidyl ether, or a combination of two or more crosslinkers from the glycidyl ether class. At least one crosslinker used can be based on carbodiimide chemistry and can be selected from 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, dicyclohexylcarbodiimide, or other carbodiimide-containing compounds, or a combination of a carbodiimide-functionality-containing crosslinker with another crosslinker, for example, a crosslinker from the group of glycidyl ether sugars, such as glucose, maltotriose, or cyclodextrin, in the presence of a water-soluble carbodiimide-containing compound. Additional crosslinkers can be used, such as water-soluble chitosan, polyethylene glycol, or other organic polyalcohols, aryl azides, or diazirines, or other photoreactive chemical heterobifunctional crosslinkers that act as receptor-ligand interaction complexes through two-step activation, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and 1,4-butanediol diglycidyl ether.Preferably, a crosslinking agent selected from the group consisting of ethylene glycol diglycidyl ether, poly(ethylene glycol) diglycidyl ether, and 1,4-butanediol diglycidyl ether is used. When poly(ethylene glycol) diglycidyl ether is used, the average molecular weight of such a crosslinking agent may be less than 2000 g / mol, for example, 500 g / mol. In one embodiment of the present invention, the aqueous mixture contains a water-soluble polymer, which may be selected from the group consisting of water-soluble polymers derived from ethylenically unsaturated monomers containing acid groups, as defined in International Publication No. 2004 / 037903, which is incorporated herein by reference and thus forms part of the present disclosure. The polymer may be based on acrylic acid and methacrylic acid, acrylamide, and methacrylamide. Preferred (meth)acrylamides are acrylamides and methacrylamides, as well as alkyl-substituted (meth)acrylamides or aminoalkyl-substituted derivatives of (meth)acrylamides, such as N-methylol (meth)acrylamide, N,N-dimethylamino (meth)acrylamide, dimethyl (meth)acrylamide, or diethyl (meth)acrylamide. Possible vinylamides include, for example, N-vinylamide, N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-methylformamide, and vinylpyrrolidone. Additionally, the water-soluble polymers can be based on alkoxy-polyalkylene oxide (meth)acrylates such as methoxypolyethylene glycol (meth)acrylate, acrylic and methacrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, or butyl (meth)acrylate. These monomers can also include methyl polyethylene glycol allyl ether, vinyl acetate, styrene, and isobutylene.

[0019] Additionally, additional biodegradable polymers such as polysaccharides can be used.

[0020] Preferably, the aqueous mixture provided in step i) comprises: a) 10.0% to 50.0% by weight, preferably 20.0% to 40.0% by weight, more preferably 30.0% by weight, of polyglutamic acid (salt) based on the total weight of the aqueous mixture; b) 0.1% to 4.0% by weight, preferably 0.3% to 3.0% by weight, more preferably 0.5% to 2.0% by weight of at least one cross-linking agent, based on the total weight of the polyglutamic acid (salt); c) 0.0% to 10.0% by weight, preferably 0.0% to 5.0% by weight, more preferably 0.1 to 2.5% by weight of a water-soluble polymer, and d) 30.0% to 90.0% by weight, preferably 50.0% to 80.0% by weight, more preferably 60.0% to 70.0% by weight of water Includes.

[0021] The crosslinking in step ii) of the method according to the present invention is preferably carried out within 10 to 50 minutes, preferably within 20 to 40 minutes, more preferably within 30 minutes. In a preferred embodiment, step ii) is carried out under atmospheric pressure. In another preferred embodiment, step ii) is carried out under stirring. More preferably, step ii) is carried out under stirring and at atmospheric pressure. Preferably, the crosslinking is carried out in a kneader reactor. The kneader reactor may be a single-shaft kneader reactor. In another embodiment, the kneader reactor has at least two kneading shafts. The kneader reactor is equipped with stirring means for disintegrating the polymerized material immediately within the reaction vessel. The use of a kneader reactor offers advantages over other common devices, such as belts, as it ensures effective mixing and provides a homogeneous mixture.

[0022] In a preferred embodiment, step ii) of the method of the present invention comprises a first stage and a second stage. The first stage is carried out under maximum agitation, and the second stage is carried out at 20% to 60%, preferably 30% to 50%, and more preferably 40% of the maximum agitation. The duration of the first stage is 50% to 82%, preferably 58% to 76%, and more preferably 66% of the total duration of step ii). Without wishing to be bound by any particular theory, the inventors conclude that the two stages address the changing viscosity, since the ongoing crosslinking leads to an increased viscosity of the material. Therefore, weakening the agitation in the second stage reduces material degradation. This method step is preferably carried out at a temperature of at least 80°C, more preferably at least 90°C, and even more preferably at least 100°C. The aforementioned temperatures refer to the temperatures of the chemical compounds present in step ii), including the crosslinked polyglutamic acid (salt) gel and the uncrosslinked polyglutamic acid (salt). The reaction vessel is ideally preheated to a particular temperature before the aqueous mixture is charged into the reaction vessel, a temperature of 120°C being preferred.

[0023] The use of 1,4-BDDGE as cross-linking agent, a polyglutamic acid concentration of 33.0% by weight based on the total weight of the aqueous solution, the application of a reactor temperature of -120°C in step ii), as well as the first and second stages described above and the use of a fill grade of at least 50% by volume, are advantageous for the cross-linked polyglutamic acid (salt) gel thus obtained and for the performance of the final product.

[0024] Instead of the kneader reactor, a reactor without stirring means, such as a belt reactor, can be used. In such a case, the crosslinked polyglutamic acid (salt) gel should be disintegrated before drying. This increases the drying efficiency. However, the gel obtained from the kneader reactor can also be disintegrated before drying.

[0025] The disintegration of the gel can be carried out, for example, by means of an extruder or a chopper or mincer or other common equipment.

[0026] The drying step iii) of the method according to the present invention can be achieved by conventional equipment and techniques. In particular, the gel can be dried using a bed dryer, a plate belt dryer, or a fluidized bed dryer, or by using a microwave or convection dryer. Preferably, the drying in step iii) is carried out at a temperature of 100°C to 160°C, preferably 115°C to 145°C, more preferably 130°C, for 5 to 15 minutes, more preferably 10 minutes. A shorter drying time and / or a lower drying temperature results in a wet material, while a longer drying time and / or a higher drying temperature results in an undesirable decrease in CRC and AAP of the water-absorbing polyglutamic acid (salt).

[0027] When a bed dryer is used, the cross-linked polyglutamic acid gel is preferably rotated 180° after 40% to 60%, preferably 50%, of the drying step has been completed, thereby ensuring uniform gel drying.

[0028] In step iii), the hot air flow used in the dryer to dry the cross-linked polyglutamic acid gel may have a speed of 4 m / s to 7 m / s, preferably 5.5 m / s.

[0029] According to a preferred embodiment, the dried polyglutamic acid gel is subjected to a grinding and sieving step before step iv).

[0030] Preferably, the sieving device used in the sieving step should have at least two sieves, the first sieve having a mesh size of 850 μm and the second sieve having a mesh size of 150 μm.

[0031] In step iv), the dried cross-linked, water-absorbing polyglutamic acid (salt) is heat-treated in the presence of at least one accelerator to obtain water-absorbing polyglutamic acid (salt). In this context, "in the presence of at least one accelerator" means that the accelerator is contacted with the dried cross-linked, water-absorbing polyglutamic acid (salt) before or during the heat treatment, preferably before the heat treatment. For this purpose, means known in the art, such as spraying the accelerator onto the dried cross-linked, water-absorbing polyglutamic acid (salt), and, if necessary, simultaneously or subsequently mixing the resulting mixture, can be used. Ideally, it should be ensured that the accelerator is uniformly spread over the dried cross-linked, water-absorbing polyglutamic acid (salt). The heat treatment of the dried cross-linked, water-absorbing polyglutamic acid (salt) in step iv) is carried out at a temperature ranging from 130°C to 170°C, preferably at 150°C, for 10 to 90 minutes, preferably 20 to 60 minutes.

[0032] The at least one accelerator according to the present invention may be selected from the group consisting of a surface cross-linking agent, water, and an additive.

[0033] Surface crosslinking agents which can be applied in step iv) are polyols, for example polyethylene glycols such as ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol, polypropylene glycols such as propylene glycol, dipropylene glycol, tripropylene glycol or tetrapropylene glycol, ethylene glycol diglycidyl ether (EGDGE), 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2,4-pentanediol, 1,6-hexanediol, 2,5-hexanediol, 1,4-butanediol diglycidyl ether (BDDGE), glycerin, polyglycerin, trimethylolpropane, polyoxypropylene, oxyethylene-oxypropylene-block copolymers, sorbitan-fatty acid esters, polyoxyethylenesorbitan-fatty acid esters, pentaerythritol, polyvinyl alcohol and sorbitol, amino alcohols, for example ethanolamine, diethanolamine, triethanolamine or propanolamine, polyamine compounds. compounds such as ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine or pentaethylenehexamine, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin polyglycidyl ether, pentaerythritol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, hexanediol glycidyl ether, polyglycidyl ether compounds such as trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, phthalic acid diglycidyl ester, adipic acid diglycidyl ether, 1,4-phenylenebis(2-oxazoline), glycidol, polyisocyanates, preferably diisocyanates such as 2,4-toluene diisocyanate (diioscyanate) and hexamethylene diisocyanate, 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate], 1,Polyaziridine compounds such as 6-hexa-methyl-enediethyleneurea and diphenylmethane-bis-4,4'-N,N'-diethyleneurea, halogen epoxides such as epichloro- and epibromohydrin and alpha-methylepichlorohydrin, 1,3-dioxolan-2-one (ethylene carbonate), 4-methyl-1,3-dioxolan-2-one (propylene carbonate), 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one The surface crosslinking agent is preferably selected from the group consisting of alkylene carbonates such as 1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,6-dimethyl-1,3-dioxolan-2-one, 1,3-dioxolan-2-one, poly-1,3-dioxolan-2-one, and polyquaternary amines such as the condensation product of dimethylamine and epichlorohydrin. Further preferred surface crosslinking agents are polyoxazolines such as 1,2-ethylenebisoxazoline, crosslinkers with silane groups such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane, oxazolidinones such as 2-oxazolidinone, bis- and poly-2-oxazolidinone, and diglycol silicates. Preferably, the surface cross-linking agent is selected from ethylene glycol diglycidyl ether (EGDGE) and 1,4-butanediol diglycidyl ether (BDDGE).

[0034] Based on the total amount of dried cross-linked water-absorbing polyglutamic acid (salt), 0.10 wt % to 2.00 wt % of the surface cross-linking agent is generally used, preferably 0.25 wt % to 1.40 wt %, more preferably 0.50 wt % to 0.80 wt % of the surface cross-linking agent is used.

[0035] Water can also be used as an accelerator in step iv) according to the present invention. Typically, 1.0% to 5.0% by weight, preferably 2.0% to 4.0% by weight, and more preferably 3.0% by weight of water is used based on the total amount of dried cross-linked, water-absorbing polyglutamic acid (salt). Without wishing to be bound by any particular theory, water aids in the heat treatment, which is beneficial to the performance of the final product, particularly its centrifuge retention capacity and absorption against pressure. In a preferred embodiment, water is used as an accelerator in the absence of any other chemical compounds, such as organic compounds including, but not limited to, organic solvents, organic surface cross-linking agents, organic additives, or organometallic salts, and in the absence of inorganic compounds, such as, but not limited to, metal salts, water-soluble and water-insoluble inorganic compounds. By "absent," we mean that the water used contains less than 1.0% by weight, preferably less than 0.5% by weight, and more preferably less than 0.1% by weight of any other chemical compounds relative to the total amount of water used.

[0036] Additives can also be used as accelerators to improve properties such as gel strength, permeability, processability, odor resistance, color, etc. For example, these additives can be applied before, during, or after the surface cross-linking step. They can also be applied without surface cross-linking.

[0037] The water-absorbing polyglutamic acid (salt) of the present invention may contain 0.01% to 5.00%, or 0.01% to 1.00%, or 0.01% to 0.05% by weight of a penetration modifier, based on the total weight of the dried cross-linked water-absorbing polyglutamic acid (salt). Suitable examples of penetration modifiers include surface modifiers or compounds that modify the penetration depth of the surface modifier into the water-absorbing polyglutamic acid (salt), fibers, films, foams, or beads by changing the viscosity, surface tension, ionic properties, or adhesive properties of the medium to which the surface modifier is applied. Examples of penetration modifiers include polyethylene glycol, tetraethylene glycol dimethyl ether, monovalent metal salts, surfactants, and water-soluble polymers.

[0038] The water-absorbing polyglutamic acid (salt) according to the present invention may contain 0.01% to 5.00% by weight, or 0.01% to 1.00% by weight, or 0.01% to 0.05% by weight of a polyvalent metal salt, based on the total weight of the dried cross-linked water-absorbing polyglutamic acid (salt). The polyvalent metal salt is preferably water-soluble. Examples of metal cations include, but are not limited to, Al, Fe, Zr, Mg, Ce, and Zn cations. Preferably, the polyvalent metal salt has a valence of +3, with Al(+3) being most preferred. Examples of anions in the polyvalent metal salt include halides, sulfates, nitrates, lactates, and acetates, with chlorides, sulfates, acetates, and lactates being preferred, and sulfates and lactates being more preferred. Aluminum sulfate and aluminum lactate are examples of polyvalent metal salts that are readily commercially available and exhibit excellent performance. The preferred form of aluminum sulfate is hydrated aluminum sulfate, preferably aluminum sulfate having 12 to 14 water molecules. Mixtures of polyvalent metal salts may also be used. The dried cross-linked water-absorbent polyglutamic acid (salt) and the polyvalent metal salt are preferably mixed by dry blending or in solution using means well known to those skilled in the art. For dry blending, a binder may be used in an amount sufficient to ensure a substantially uniform mixture of the salt and superabsorbent polymer. The binder may be water or a low-volatile organic compound having a boiling point of at least 150°C. Examples of binders include water, polyols such as propylene glycol, glycerin, and poly(ethylene glycol).

[0039] The water-absorbing polyglutamic acid (salt) according to the present invention may contain 0.01% to 5.00% by weight, or 0.01% to 1.00% by weight, or 0.01% to 0.05% by weight of a water-insoluble inorganic powder, based on the total weight of the dried cross-linked water-absorbing polyglutamic acid (salt). Examples of insoluble inorganic powders include silicon dioxide, silicic acid, silicate, titanium dioxide, aluminum oxide, magnesium oxide, zinc oxide, talc, calcium phosphate, clay, diatomaceous earth, zeolite, bentonite, kaolin, hydrotalcite, activated clay, and apatite. The insoluble inorganic powder additive may be a single compound or a mixture of compounds selected from the above list. An example of silica is SIPERNAT® 22S fumed silica, commercially available from Evonik Industries. The preferred particle size of the inorganic particles is 10 x 10 -9 m~10×10 -6 The range is m.

[0040] In some embodiments, the water-absorbent polyglutamic acid (salt) of the present invention comprises, based on the total weight of the dried cross-linked water-absorbent polyglutamic acid (salt), 0.01% to 5.00%, or 0.01% to 1.00%, or 0.01% to 0.05% by weight of a polymeric coating, such as a thermoplastic coating, a cationic coating, or a combination of a thermoplastic coating and a cationic coating. In some specific embodiments, the polymeric coating is a polymer that can be in a solid, emulsion, suspension, colloidal, or solubilized form, or a combination thereof. Polymeric coatings suitable for the present invention can include, but are not limited to, thermoplastic coatings having a thermoplastic melting temperature, which are applied to the particle surface at or subsequent to the temperature of the treated superabsorbent polymer particles. Examples of thermoplastic polymers include polyolefins, polyethylene, polyesters, polyamides, polyurethanes, styrene polybutadiene, linear low-density polyethylene (LLDPE), ethylene acrylic acid copolymer (EAA), ethylene alkyl methacrylate copolymer (EMA), polypropylene (PP), maleated polypropylene, ethylene vinyl acetate copolymer (EVA), polyesters, and polyamides. Blends of all polyolefin families, such as blends of PP, EVA, EMA, EEA, EBA, HDPE, MDPE, LDPE, LLDPE, and / or VLDPE, may also be advantageously used. In certain embodiments, maleated polypropylene is a preferred thermoplastic polymer for use in the present invention. Thermoplastic polymers may be functionalized to provide additional benefits, such as water solubility or water dispersibility. As used herein, a cationic polymer refers to a polymer or mixture of polymers containing one or more functional groups capable of ionizing into positively charged ions in aqueous solution. Suitable functional groups for cationic polymers include, but are not limited to, primary, secondary or tertiary amino groups, imino groups, imido groups, amide groups, and quaternary ammonium groups.Examples of synthetic cationic polymers include salts or partial salts of poly(vinylamine), poly(allylamine), poly(ethyleneimine), poly(aminopropanol vinyl ether), poly(acrylamidopropyltrimethylammonium chloride), and poly(diallyldimethylammonium chloride). Examples of naturally occurring cationic polymers include partially deacetylated chitin, chitosan, and chitosan salts. Synthetic polypeptides such as polyasparagine, polylysine, and polyarginine are also suitable cationic polymers.

[0041] Additionally, additives may be used to improve the whiteness or long-term color stability of the polymer, such as resistance to darkening, yellowing, or browning. Such additives are well known in the art and include antioxidants, sulfur- and phosphorus-containing compounds, chelating agents, optical brighteners, and the like. Preferred additives for color stability are 2-hydroxy-2-sulfonatoacetic acid, bisulfites, phosphonates, ethylenediaminetetraacetic acid, ethylenediamine-N,N'-disuccinic acid, diethylenediaminepentaacetic acid, salts and derivatives thereof, and mixtures thereof.

[0042] In some embodiments, additional surface additives may optionally be used with the particulate superabsorbent polymer composition, including odor-binding or deodorizing substances such as cyclodextrins, zeolites, inorganic or organic salts, similar materials, and tannins, anti-caking additives, flow modifiers, surfactants, viscosity modifiers, etc., as described in EP 2 176 325, which is incorporated herein by reference and therefore forms part of this disclosure. Furthermore, surface additives that perform several roles during surface modification may be used. For example, a single additive may be a surfactant, a viscosity modifier, and react to crosslink polymer chains. In another embodiment, the additional surface additive may include a chelating agent. The chelating agent may preferably be selected from organic polyacids, phosphorus polyacids, and their salts. Preferably, the chelating agent may be selected from nitrilotriacetic acid, ethylenediaminetetraacetic acid, cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, diethylenetriaminepenta(methylenephosphonic acid), ethylene glycol-bis-(aminoethyl ether)-N,N,N'-triacetic acid, N-(2-hydroxyethyl)-ethylenediamine-N,N,N'-triacetic acid, triethylenetetraaminehexaacetic acid, tartaric acid, citric acid, iminodisuccinic acid, gluconic acid, phosphonates and salts thereof.

[0043] The steps of the method according to the present invention are carried out in the following order: step i), step ii), step iii), and then step iv).

[0044] The present invention also relates to a water-absorbing polyglutamic acid (salt) obtainable by the method described herein. Preferably, the water-absorbing polyglutamic acid (salt) has a particulate form and / or a particle size distribution of 150 μm to 850 μm. Preferably, at least 80% by weight, more preferably at least 90% by weight, of the water-absorbing polyglutamic acid (salt) has a particle size distribution of 150 μm to 850 μm.

[0045] Preferably, the water-absorbing polyglutamic acid (salt) obtainable by this method has the following performance parameters: an absorption at a pressure of 4.83 kPa (0.7 psi) greater than 9 g / g and less than 30 g / g or less than 26 g / g, preferably less than 25 g / g, when measured as defined herein; 0 cm when measured as defined herein 3 ·s·g -1 Larger and 150x10 -7 ·cm 3 ·s·g -1 Less than 10 cm, preferably 3 ·s·g -1 Larger and 100x10 -7 ·cm 3 ·s·g -1 Saline flow conductivity less than 0.01; a centrifuge retention capacity, when measured as defined herein, of greater than 20 g / g and less than 46 g / g, preferably greater than 25 g / g and less than 42 g / g; 0.5 g g when measured as defined herein -1 ·s -1 Larger and 1.5g g -1 ·s -1 Less than 0.7 g g -1 ·s -1 Larger and 1.2g g -1 ·s -1 Free swelling rate of less than ; A vortex of less than 50 seconds and more than 10 seconds, preferably less than 30 seconds and more than 15 seconds, when measured as defined herein. Achieve at least one of the following.

[0046] Even more preferably, the water-absorbing polyglutamic acid (salt) exhibits the above-mentioned AAP and CRC values.

[0047] The above performance parameters are often used to qualify water-absorbing polymers for use in personal hygiene products. The quoted values ​​are obtained from the preparation method of the present invention.

[0048] Yet another object of the present invention is an article comprising a water-absorbing polyglutamic acid (salt) having at least one of the above performance parameters or obtainable by the method of the present invention.

[0049] The article is preferably a personal hygiene product such as a diaper, sanitary napkin, or napkin. Alternatively, the article may be a wound dressing. Further applications of the water-absorbent polyglutamic acid (salt) of the present invention include medical / pharmaceutical applications in which the water-absorbent polyglutamic acid (salt) of the present invention can be used as or in biological adhesives, dental carriers, bone regeneration, cartilage regeneration, vaccine development scaffolds in tissue engineering, drug delivery systems, and biological control agents. Further applications include agriculture, for example, to improve soil water availability, as a biofertilizer, in wastewater treatment, as a bioflocculant, in the food industry as a thickener, oil reducer, flavoring agent, cryoprotectant, and in cosmetics such as sunscreens, hair growth serums, anti-aging serums, mouthwashes, and contact lens care solutions. Test Methods

[0050] Superabsorbents are typically purchased by manufacturers of personal hygiene products. The overall performance profile of a superabsorbent is crucial for the purchasing decision. The required performance profile strongly depends on the type and purpose of the hygiene product. Over the past few decades, market participants have established numerous performance parameters to compare the suitability of different SAP qualities for their intended purposes. Some of these performance parameters are standardized by independent organizations, while others are defined by specific manufacturers of hygiene products solely for their own individual needs. In reality, both types of performance parameters are important within the real SAP market. Furthermore, the patent literature is replete with parameters that have no impact outside of specific patent rights.

[0051] In the present invention, the following performance parameters are relevant and have been determined as follows:

[0052] Centrifuge holding capacity (CRC) Centrifuge retention capacity refers to the fluid retention capacity without pressure. The method WSP 241.2(05) recommended by EDANA (European Disposables and Nonwovens Associations) was applied.

[0053] Absorption Against Pressure (AAP) Absorption against pressure refers to the ability to absorb urine when subjected to external pressure. AAP was measured at a pressure of 4.83 kPa (equivalent to 0.7 psi). Method WSP 242.2(05) recommended by EDANA (European Disposables and Nonwovens Associations) was applied.

[0054] Saline Flow Conductivity (SFC) Saline flow conductivity refers to the ability of a gel to transfer fluid upon initial contact with body fluids. The test method is disclosed on pages 69-75 of WO 95 / 26209, except that 1.5 g of the superabsorbent material to be tested was used instead of 0.9 g.

[0055] Free Swell Rate (FSR) This parameter relates to the swelling rate of the water-absorbing polymer. 1.00 g (= W1) of dry water-absorbing material is weighed into a 25 ml glass beaker and evenly distributed at the bottom of the glass beaker. 20 ml of 0.9 wt. % aqueous sodium chloride solution is then dispensed into a second glass beaker, and the contents of this beaker are quickly added to the first beaker, and a stopwatch is started. The stopwatch is stopped as soon as the last drop of salt solution is absorbed, as confirmed by the disappearance of reflection on the liquid surface. The exact amount of liquid poured from the second beaker and absorbed by the polymer in the first beaker is accurately determined by weighing the second beaker (= W2). The time required for absorption, measured by the stopwatch, is represented by t. The disappearance of the last drop of liquid on the surface is defined as time t. The free swelling rate (FSR) is calculated as follows: Formula

[0056] TIFF2025541787000001.tif16122 However, if the moisture content of the tested material exceeds 3% by weight, the weight W1 must be corrected for this moisture content. The FSR is expressed in g g -1 ·s -1 is.

[0057] Vortex Time Vortex time refers to the time, in seconds, until the vortex disappears after adding 2 g of water-absorbing polymer to 50 mL of saline solution and stirring the mixture at 600 rpm. A 100 mL glass beaker (Pyrex #1060-100 or Fisher Brand #FB-102-100) was used with a magnetic stir bar (size 38.4 mm x 8 mm). The saline temperature was set to 24°C to 25°C, and the room temperature was above 21°C. Humidity was set to be within the limits of EDANA Standard Test WSP 241.2(05).

[0058] The invention will now be further illustrated by the following examples. [Example]

[0059] Preparation of dried cross-linked water-absorbing polyglutamic acid (salt) (Table 1) Preparation of aqueous crosslinker solution At room temperature, 1,000 g of deionized water and 10 g of diglycidyl ether-type crosslinker were carefully mixed in a beaker with the aid of a magnetic stirrer. The crosslinkers used were polyethylene glycol diglycidyl ether (poly-EGDGE) or 1,4-butanediol diglycidyl ether (BDDGE), used in an amount of 2 wt.% based on the amount of uncrosslinked polyglutamic acid (salt). Further information is shown in Table 1 below.

[0060] Batch crosslinking in a kneader reactor The crosslinking reaction was carried out in a single-shaft kneader reactor, Discotherm Batch, type DTB1.5, obtained from List AG, Switzerland, with a total volume of 3.1 liters. The reactor was equipped with a jacket for heating and cooling, a vacuum system, a nitrogen supply system, and a reactor control unit.

[0061] The water / crosslinker solution prepared above is charged into the reactor through the dome, and then 500 g of γ-PGA in solid form (obtained from Lubon Industry Co. Ltd., China, MW=700,000 Daltons; or obtained from Bonding Chemical, USA, MW=1,100,000 Daltons; see Table 1 below) is added under full stirring (65 rpm). The reactor is preheated to above 110°C (heating device set temperature: 120°C). The temperature is measured in the jacket of the kneader reactor. The pressure in the vessel is atmospheric. The reactor is open and maintained at the aforementioned temperature throughout the reaction.

[0062] The agitation was set to maximum (100% of the potentiometer, 65 rpm) for 20 minutes to completely dissolve the PGA and allow the mixture to reach the desired temperature. After this, the agitator was set to 40% of the potentiometer, at 24 rpm, for an additional 10 minutes. The reactor end plate was then removed, and the free-flowing, granular gel was discharged from the reactor. The resulting polymer was then further processed.

[0063] The granular gel obtained from crosslinking in the DTB 1.5 l reactor is extruded in a kitchen-type meat mincer (Mado Kuchen Fleischwolf MEW 710-R70) equipped with an 8 mm thick die plate having 45 holes with a diameter of 6 mm each.

[0064] Drying the cross-linked polyglutamic acid (salt) gel Gel drying was carried out in a batch-operated fluidized-bed dryer, model CTL (delivered by Allgaier-Werke KG, Uhingen, Germany). This dryer was equipped with the same plates as the plant's plate belt dryer, i.e., perforated stainless steel plates with 20 x 3 mm holes, 20 cm diameter, ventilation, air heater, fresh air filter and exhaust air filter with automatic dust removal, and a conical fluidization chamber with a control box at the bottom. The air flow was from bottom to top and was not circulated.

[0065] A portion of the extruded gel (600-900 grams) is then placed in the fluidization chamber of the dryer. The gel to be dried is placed on a plate, a gel bed approximately 5-8 cm thick, and dried in a hot air stream at 130°C or 140°C with an air inlet speed of 5.5 m / s for 15 or 20 minutes, respectively. After 10 minutes, the pre-dried material is rotated 180° and allowed to dry evenly on both sides for an additional 5 or 10 minutes. The resulting dried polymer is ground in a Bauermeister lab roll mill and sieved through a Retsch sieve tower equipped with sieves with 850 and 150 micron mesh sizes to obtain the particle size distribution percentage for analysis of the precursor superabsorbent.

[0066] The dried cross-linked water-absorbent polyglutamic acid (salt) is heat-treated (Table 2). The dried cross-linked water-absorbing polyglutamic acid (salt) obtained after drying, grinding and sieving was heat treated in the presence of an accelerator to improve its properties, see Table 2.

[0067] To prepare the surface cross-linking solution, 0.3 wt% to 1.5 wt% of cross-linking agent was dissolved in 3 wt% demineralized water, based on 100 g of dried cross-linked water-absorbing polyglutamic acid (salt), respectively.

[0068] Ethylene glycol diglycidyl ether (EGDGE) or 1,4-butanediol diglycidyl ether (BDDGE) was used as a cross-linking agent. Additives such as isopropanol and aluminum lactate were used. Water was also used as an accelerator.

[0069] While vigorously stirring in a Krupps 3 Mix 7000 mixer, 60 g of dried cross-linked water-absorbing polyglutamic acid (salt) was coated with the above amount of surface cross-linking solution in a household Krupps blender cup using a syringe equipped with a 0.4 mm cannula and stirred for an additional 1 minute.

[0070] Details of the promoters used, amounts and reaction conditions are given in Table 2 below.

[0071] The coated precursor was divided into three portions and heated in a circulating air drying oven Heraeus UT6120 at 150 °C for 20–60 min.

[0072] The surface cross-linked polymer thus obtained was sieved through a Retsch sieve with a mesh size of 850 microns in order to remove agglomerates formed by the coating.

[0073] result The performance data of the prepared water-absorbing polyglutamic acid (salt) is shown in the table.

[0074] [Table 1]

[0075] [Table 2] When water is the only accelerator used, water-absorbent polyglutamic acid (salts) show good simultaneous performance in terms of AAP and CRC. The overall performance is comparable to that of acrylic acid-based superabsorbent polymers, but polyglutamic acid (salts)-based polymers are environmentally friendly.

Claims

1. A method for producing a water-absorbing polyglutamic acid (salt), comprising the steps of: i) providing an aqueous mixture of uncrosslinked polyglutamic acid (salt) and at least one crosslinker; ii) cross-linking the uncross-linked polyglutamic acid (salt) to obtain a cross-linked polyglutamic acid (salt)-gel; iii) drying the cross-linked polyglutamic acid (salt)-gel to obtain a dried cross-linked water-absorbing polyglutamic acid (salt); iv) heat treating the dried cross-linked water-absorbing polyglutamic acid (salt) in the presence of at least one accelerator to obtain the water-absorbing polyglutamic acid (salt). A method comprising:

2. The uncrosslinked polyglutamic acid (salt) has a molecular weight of 200,000 to 3,000,000 daltons. The method of claim 1 ,

3. The crosslinking agent may be a glycidyl ether, such as a diglycidyl ether, a triglycidyl ether, a polyglycidyl ether containing three or more epoxy groups, diglycerol tetraglycidyl ether, dipentaerythritol tetraglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, isosorbide glycidyl ether, polyglycerol-3-glycidyl ether, or other aliphatic polyfunctional epoxides, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, polypropylene glycol diglycidyl ether, polyglycidyl ethers of alkane polyols, polyglycidyl ethers of poly(alkylene glycols), bio-derived sorbitol glycidyl ether, cyclic and aromatic polyglycidyl ethers, or a combination of two or more crosslinking agents from the class of glycidyl ethers. the class of carbodiimides, such as 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, dicyclohexylcarbodiimide or other carbodiimide-containing compounds; combinations of carbodiimide functionality-containing crosslinkers with other crosslinkers, for example, crosslinkers of the glycidyl ether sugar, e.g., glucose, maltotriose or cyclodextrin class in the presence of water-soluble carbodiimide-containing compounds; water-soluble chitosan, polyethylene glycol or other organic polyalcohols; aryl azides or diazirines or other photoreactive chemical heterobifunctional crosslinkers that act as receptor-ligand interaction complexes by two-step activation; other crosslinkers, such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether and 1,4-butanediol diglycidyl ether, preferably from the group consisting of ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether and 1,4-butanediol diglycidyl ether.

3. The method according to claim 1 or 2, characterized in that

4. the at least one cross-linking agent is selected from the group consisting of ethylene glycol diglycidyl ether, poly(ethylene glycol) diglycidyl ether, and 1,4-butanediol diglycidyl ether. The method according to claim 3, characterized in that

5. The aqueous mixture a) 10.0% to 50.0% by weight, preferably 20.0% to 40.0% by weight, more preferably 30.0% by weight, of polyglutamic acid (salt), based on the total weight of the aqueous mixture; b) 0.1 wt. % to 4.0 wt. %, preferably 0.3 wt. % to 3.0 wt. %, more preferably 0.5 wt. % to 2.0 wt. % of said at least one crosslinker, based on the total weight of said aqueous mixture; c) 0.0% to 10.0% by weight, preferably 0.0% to 5.0% by weight, more preferably 0.1 to 2.5% by weight of a water-soluble polymer; and d) 30.0% to 90.0% by weight, preferably 50.0% to 80.0% by weight, more preferably 60.0% to 70.0% by weight of water The method according to any one of claims 1 to 4, characterized in that it comprises:

6. the aqueous mixture contains 25.0 wt % to 50.0 wt %, preferably 30.0 wt % to 40.0 wt %, more preferably 33.3 wt %, of a mixture comprising the polyglutamic acid (salt) and the at least one cross-linking agent, based on the total weight of the aqueous mixture; The method according to any one of claims 1 to 5, characterized in that

7. step ii) is carried out within 10 to 50 minutes, preferably within 20 to 40 minutes, more preferably within 30 minutes; and / or step ii) is carried out under atmospheric pressure, and / or step ii) is carried out under stirring, and / or Step ii) is carried out in a kneader reactor The method according to any one of claims 1 to 6, characterized in that

8. Step ii) comprises a first stage and a second stage, the duration of the first stage being 50% to 82%, preferably 58% to 76%, more preferably 66% of the total duration of step ii), the first stage being carried out under maximum agitation, and the second stage being carried out at 20% to 60%, preferably 30% to 50%, more preferably 40% of the maximum agitation. The method of claim 7, characterized in that

9. The cross-linked polyglutamic acid (salt) gel collapses before drying. The method according to any one of claims 1 to 8, characterized in that

10. 10. The method of claim 9, wherein the disintegrating is carried out by means of an extruder or a chopper or a mincer.

11. Step iii) is carried out using a bed dryer, a belt dryer, a fluidized bed dryer, a microwave or a convection dryer. The method according to any one of claims 1 to 10, characterized in that

12. Step iii) is carried out at a temperature of 100°C to 160°C, preferably 115°C to 145°C, more preferably 130°C, for 5 minutes to 15 minutes, preferably 10 minutes. The method according to any one of claims 1 to 11, characterized in that

13. Prior to step iv), the dried polyglutamic acid (salt) gel is subjected to a crushing step and a sieving step. The method according to any one of claims 1 to 12, characterized in that

14. In the sieving step, a sieving device is used, and the sieving device has at least two sieves, the first sieve having a mesh size of 850 μm and the second sieve having a mesh size of 150 μm. The method of claim 13, wherein:

15. In step iv), at least one accelerator selected from the group consisting of a surface cross-linking agent, water, and an additive is used. The method according to any one of claims 1 to 14, characterized in that

16. the at least one accelerator used in step iv) is selected from the group consisting of ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether and water; The method of claim 15, wherein:

17. The surface cross-linking agent is used in an amount of 0.10% by weight to 2.00% by weight, preferably 0.25% by weight to 1.40% by weight, more preferably 0.50% by weight to 0.80% by weight, based on the total amount of the dried water-absorbing polyglutamic acid (salt).

17. The method according to claim 15 or 16,

18. The promoter is water. The method according to any one of claims 1 to 17, characterized in that

19. Based on the total amount of the dried water-absorbing polyglutamic acid (salt), 1.0% by weight to 5.0% by weight, preferably 2.0% by weight to 4.0% by weight, more preferably 3.0% by weight of water is used.

20. The method of claim 18, wherein:

20. A water-absorbing polyglutamic acid (salt) obtained by the method according to any one of claims 1 to 19.

21. The water-absorbing polyglutamic acid (salt) has the following characteristics: an absorption at a pressure of 4.83 kPa (0.7 psi) greater than 9 g / g and less than 30 g / g or less than 26 g / g, preferably less than 25 g / g, when measured as defined herein; 0 cm when measured as defined herein ３ ・s・g －１ Larger and 150x10 －７ cm ３ ・s・g －１ Less than 10 cm ３ ・s・g －１ Larger and 100x10 －７ ・cm ３ ・s・g －１ Saline flow conductivity of less than a centrifuge retention capacity, when measured as defined herein, of greater than 20 g / g and less than 46 g / g, preferably greater than 25 g / g and less than 42 g / g; 0.5 g g when measured as defined herein －１ ・s －１ Larger and 1.5g.g －１ ・s －１ Less than 0.7 g·g －１ ・s －１ Cutlet 1.2g.g －１ ・s －１ a free swelling rate of less than A vortex of less than 50 seconds and more than 10 seconds, preferably less than 30 seconds and more than 15 seconds, when measured as defined herein. A water-absorbing polyglutamic acid (salt) characterized by having at least one of the following.

22. An article comprising the water-absorbing polyglutamic acid (salt) according to claim 20 or 21.

23. The article is or includes a diaper, a hygiene product, a sanitary napkin, a napkin, or a wound dressing.

23. The article of claim 22, characterized in that:

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