Biodegradable superabsorbents

Abstract

The invention relates to a biodegradable superabsorbent based on polyglutamic acid (salt) and a preparation method thereof. The objective of the invention is to provide a biodegradable superabsorbent with better performance. Said problem has been solved by a method for producing a water-absorbing polyglutamic acid (salt), comprising i) providing an aqueous mixture of non-crosslinked polyglutamic acid (salt) and at least one crosslinking agent, ii) crosslinking the non-crosslinked polyglutamic acid (salt) to obtain a crosslinked polyglutamic acid (salt) gel, iii) drying the crosslinked polyglutamic acid (salt) gel, and iv) subjecting the dried cross-linked water-absorbing polyglutamic acid (salt) to a heat treatment in the presence of at least one accelerator so as to obtain a water-absorbing polyglutamic acid (salt), and iv) subjecting the dried cross-linked water-absorbing polyglutamic acid (salt) to a heat treatment in the presence of at least one accelerator so as to obtain a water-absorbing polyglutamic acid (salt).

Description

Technical Field

[0001] The present invention relates to a biodegradable superabsorbent based on polyglutamic acid (salt) and a preparation method thereof. Background Art

[0002] "Superabsorbent" or "superabsorbent" is a common commercial term that refers to polymer particles that can absorb large amounts of water without releasing the absorbed water under pressure. Other common terms include "superabsorbent material" (SAM), "superabsorbent polymer" (SAP), or "absorbent gelling material" (AGM).

[0003] When superabsorbents absorb water, they expand dramatically; water is trapped within their polymer network, causing the water-laden superabsorbent to form a hydrogel. Superabsorbents can absorb both saline and various bodily fluids, similar to water. This ability makes superabsorbents a key ingredient in personal hygiene products such as baby diapers, feminine care products, and incontinence products.

[0004] Most superabsorbents currently used in hygiene products are based primarily on lightly cross-linked synthetic polymers that are capable of absorbing large amounts of liquid, including water and body fluids such as urine, in a short period of time. These synthetic polymers, which include, for example, polymers and copolymers based on acrylic acid or acrylamide, are not traditionally renewable materials and do not biodegrade sufficiently or at all, necessitating incineration or landfill.

[0005] Attempts have been made to replace these polymers and copolymers with biodegradable and sustainable polymers. One area of focus has been the use of polysaccharides. However, the challenge in producing the raw materials for polysaccharide-based superabsorbents is that they are typically water-soluble and must be converted to a water-insoluble form before they can be used as superabsorbents in various applications.

[0006] For example, EP 0538904A1 and US Pat. No. 5247072 describe superabsorbents based on carboxyalkyl polysaccharides. The processes described involve a thermal crosslinking step that is very sensitive to slight variations in pH, temperature during the reaction, etc., resulting in absorbents with widely varying absorption properties and a tendency to have a shortened storage time.

[0007] However, in the polysaccharide crosslinking methods known in the prior art, in addition to a low aging stability, it has been observed that uniform crosslinking of the polysaccharides can hinder the biodegradability of the absorbents, since the restricted expansion reduces accessibility to microorganisms. Furthermore, in the crosslinking reactions known in the prior art, enzymatic degradation can be inhibited by additionally introduced substituents [Mehltretter et al., Journal of the American Oil Chemists Society, 47 (1970), pp. 522-524].

[0008] Due to its bio-based and biodegradable properties, polyglutamic acid (PGA) and its use as a superabsorbent have also been studied. For example, international application WO2021 / 242936A1 reports the manufacture of a superabsorbent based on polyglutamic acid, which can be additionally modified. However, this superabsorbent performed mediocrely in terms of the common parameters used to evaluate superabsorbents, such as centrifuge retention capacity (CRC), pressure absorption capacity (AAP), saline flow conductivity (SFC) and absorption rate (vortex and FSR), especially after the surface cross-linking step. Although good performance of the above parameters is crucial to the commercial success of superabsorbents used in personal hygiene products, the practical application of superabsorbents based on polyglutamic acid in commercial hygiene products is still unknown.

[0009] The object of the present invention is therefore to provide a biodegradable superabsorbent with improved properties. In particular, the properties with respect to centrifuge retention capacity (CRC), absorbency under pressure (AAP), saline flow conductivity (SFC) and absorption rate (vortex and FSR) should be improved and balanced. Summary of the Invention

[0010] The object is achieved by a method for producing water-absorbing polyglutamic acid (salt), which comprises the following steps:

[0011] i) providing an aqueous mixture of non-crosslinked polyglutamic acid (salt) and at least one crosslinking agent,

[0012] ii) cross-linking the non-cross-linked polyglutamic acid (salt) to obtain a cross-linked polyglutamic acid (salt) gel,

[0013] iii) drying the cross-linked polyglutamic acid (salt) gel to obtain dry cross-linked water-absorbing polyglutamic acid (salt),

[0014] 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).

[0015] It has been found that superabsorbents based on polyglutamic acid (salts) have better properties in meeting the needs of users and manufacturers of personal hygiene products if produced according to the process of the invention. Since the superabsorbents obtained according to the process of the invention are derived from polyglutamic acid, they are biodegradable.

[0016] As used herein, "at least one" means one or more, i.e., 1, 2, 3, 4, 5, 6, 7, 8, 9 or more. For example, with respect to a cross-linking agent, the values stated relate to the cross-linking agent and not to the absolute number of cross-linking agent molecules used. Unless otherwise indicated, "%" refers to "wt%".

[0017] The above objects are achieved by means of a method for producing water-absorbing polyglutamate (salt), which comprises the following steps: i) providing an aqueous mixture of non-cross-linked polyglutamate (salt) and at least one cross-linking agent; ii) cross-linking the non-cross-linked polyglutamate (salt) to obtain a cross-linked polyglutamate (salt) gel; iii) drying the cross-linked polyglutamate (salt) gel to obtain a dried cross-linked water-absorbing polyglutamate (salt); and iv) heat-treating the dried cross-linked water-absorbing polyglutamate (salt) in the presence of at least one accelerator to obtain water-absorbing polyglutamate (salt), thereby providing sustainable and biodegradable water-absorbing polyglutamate (salt).

[0018] The non-crosslinked polyglutamic acid (salt) used in the present invention can be partially neutralized. Preferably, at least 50 mol%, more preferably at least 70 mol%, even more preferably at least 80 mol% of the non-crosslinked polyglutamic acid is neutralized and exists in the form of a salt. Neutralization can be achieved by using standard techniques and methods known to those skilled in the art. For example, an aqueous sodium hydroxide solution can be used. Suitable cations are lithium, sodium and potassium and mixtures thereof, preferably sodium and potassium. The non-crosslinked 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 molecular weight of the non-crosslinked polyglutamic acid (salt) is 200,000-3,000,000 Daltons, preferably 500,000-2,000,000 Daltons, more preferably 700,000-1,100,000 Daltons.

[0019] As used herein, "aqueous mixture" refers to a mixture comprising at least 40 wt%, preferably at least 50 wt%, more preferably at least 60 wt%, even more preferably 70 wt% water based on the total weight of the aqueous mixture.

[0020] The at least one crosslinking agent used in step i) is selected from glycidyl ethers such as diglycidyl ether, triglycidyl ether, polyglycidyl ethers containing 3 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 multifunctional 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(alkyl glycols), bio-based sorbitol glycidyl ethers (e.g., PEG-1000 from CVC Thermoset Specialties). GE-61), any type of cyclic and aromatic polyglycidyl ether, or a combination of multiple glycidyl ether crosslinking agents. The at least one crosslinking agent employed 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 crosslinking agent containing a carbodiimide functional group and other crosslinking agents (e.g., a glycidyl ether saccharide such as glucose, maltotriose or cyclodextrin in the presence of a water-soluble carbodiimide-containing compound). Further crosslinking agents such as water-soluble chitosan, polyethylene glycol or other organic polyols, aryl azide or diaziridine or other photoreactive chemical heterobifunctional crosslinking agents that act as receptor-ligand interaction complexes by two-step activation, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether and 1,4-butanediol diglycidyl ether can be used. Preferably, a crosslinker selected from ethylene glycol diglycidyl ether, poly(ethylene glycol) diglycidyl ether and 1,4-butanediol diglycidyl ether is used. If poly(ethylene glycol) diglycidyl ether is used, the average molecular weight of this crosslinker may be lower than 2000 g / mol, for example 500 g / mol.

[0021] In one embodiment of the present invention, the aqueous mixture contains a water-soluble polymer, which can be selected from the water-soluble polymers derived from ethylenically unsaturated monomers containing acid groups as defined in International Application WO2004 / 037903A2, which is incorporated herein by reference and therefore constitutes a part of the present disclosure. The polymer can be based on acrylic acid and methacrylic acid, acrylamides and methacrylamides. In addition to acrylamide and methacrylamide, preferred (meth) acrylamides are alkyl-substituted (meth) acrylamides or aminoalkyl-substituted (meth) acrylamide derivatives, such as N-hydroxymethyl (meth) acrylamide, N,N-dimethylamino (meth) acrylamide, dimethyl (meth) acrylamide or diethyl (meth) acrylamide. Possible vinylamides are, for example, N-vinylamide, N-vinyl formamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-methylformamide and vinyl pyrrolidone. In addition, water-soluble polymers can be based on alkoxypolyalkylene oxide (meth) acrylates (e.g., methoxypolyethylene glycol (meth) acrylate), acrylates, and methacrylates (e.g., 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.

[0022] Additionally, other biodegradable polymers, such as polysaccharides, may also be used.

[0023] Preferably, the aqueous mixture provided in step i) comprises:

[0024] a) 10.0-50.0 wt%, preferably 20.0-40.0 wt%, more preferably 30.0 wt% of polyglutamic acid (salt), based on the total weight of the aqueous mixture,

[0025] b) 0.1-4.0 wt%, preferably 0.3-3.0 wt%, more preferably 0.5-2.0 wt% of at least one cross-linking agent, based on the total weight of polyglutamic acid (salt),

[0026] c) 0.0-10.0 wt%, preferably 0.0-5.0 wt%, more preferably 0.1-2.5 wt% of a water-soluble polymer, and

[0027] d) 30.0-90.0 wt%, preferably 50.0-80.0 wt%, more preferably 60.0-70.0 wt% of water.

[0028] The crosslinking in step ii) of the method of the present invention is preferably carried out within 10-50 minutes, preferably within 20-40 minutes, and 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 atmospheric pressure. Preferably, crosslinking is carried out in a kneading reactor. The kneading reactor can be a single-shaft kneading reactor. In another embodiment, the kneading reactor has at least two kneading shafts. The kneading reactor is equipped with a stirring device for crushing the polymeric material in the reaction vessel. The use of a kneading reactor has advantages over other common equipment such as belt reactors because it can ensure effective mixing and provide a uniform mixture.

[0029] In a preferred embodiment, step ii) of the present method comprises a first and a second stage. The first stage is conducted under maximum agitation, while the second stage is conducted at 20-60%, preferably 30-50%, and more preferably 40%, of this maximum agitation. The duration of the first stage is 50-82%, preferably 58-76%, and more preferably 66%, of the total duration of step ii). Without wishing to be bound by a particular theory, we conclude that these two stages account for viscosity changes, as increased crosslinking leads to increased material viscosity. Therefore, by reducing agitation in the second stage, material degradation is reduced. These steps are preferably conducted at a temperature of at least 80°C, more preferably at least 90°C, and even more preferably at least 100°C. These temperatures refer to the temperature of the compound comprising the crosslinked polyglutamate gel and the non-crosslinked polyglutamate present in step ii). Ideally, the reaction vessel should be preheated to a specific temperature before the aqueous mixture is added to the reaction vessel. A preferred temperature is 120°C.

[0030] The use of 1,4-BDDGE as a crosslinking agent, a polyglutamic acid concentration of 33.0 wt% based on the total weight of the aqueous solution, a reaction vessel temperature of about 120° C. in step ii), and the use of the first and second stages as described above and a filling level of at least 50% by volume are beneficial for the crosslinked polyglutamic acid (salt) gel obtained therefrom and the properties of the final product.

[0031] Alternatively, a kneading reactor without a stirring device, such as a belt reactor, can be used. Even in this case, the crosslinked polyglutamic acid (salt) gel is pulverized before drying. This improves the drying efficiency. However, the gel obtained from the kneading reactor can also be pulverized before drying.

[0032] Gel comminution can be carried out, for example, by means of an extruder or a chopper or a mincer or other common equipment.

[0033] The drying step iii) of the method of the present invention can be accomplished using conventional equipment and techniques. Specifically, the gel can be dried using a bed dryer, a belt dryer, or a fluidized bed dryer, or using a microwave or convection dryer. The drying in step iii) is preferably performed at a drying temperature of 100-160°C, preferably 115-145°C, and more preferably 130°C, for 5-15 minutes, more preferably 10 minutes. Shorter drying times and / or lower drying temperatures result in a wet material, while longer drying times and / or higher drying temperatures can result in undesirable CRC and AAP losses of the hygroscopic polyglutamic acid (salt).

[0034] When using a bed dryer, the cross-linked polyglutamic acid gel is preferably turned 180° after 40-60%, preferably 50%, of the drying step. This ensures that the gel is dry.

[0035] In order to dry the cross-linked polyglutamic acid gel in step iii), the hot air flow rate used in the dryer may be 4-7 m / s, preferably 5.5 m / s.

[0036] According to a preferred embodiment, prior to step iv), the dried polyglutamic acid gel is subjected to a grinding step and a sieving step.

[0037] Preferably, the screening device used in the screening 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.

[0038] In step iv), the dried cross-linked hygroscopic polyglutamate (salt) is heat-treated in the presence of at least one accelerator to obtain the hygroscopic polyglutamate (salt). "In the presence of at least one accelerator" herein means that the accelerator is brought into contact with the dried cross-linked hygroscopic polyglutamate (salt) before or during the heat treatment, preferably before the heat treatment. To this end, methods known in the art can be used, such as spraying the accelerator onto the dried cross-linked hygroscopic polyglutamate (salt) and, if necessary, mixing the resulting mixture simultaneously or subsequently. Ideally, it should be ensured that the accelerator is evenly distributed over the dried cross-linked hygroscopic polyglutamate (salt). The heat treatment of the dried cross-linked hygroscopic polyglutamate (salt) in step iv) is carried out at a temperature of 130-170°C, preferably 150°C, for 10-90 minutes, preferably 20-60 minutes.

[0039] The at least one accelerator according to the present invention may be selected from surface crosslinking agents, water and additives.

[0040] The surface crosslinking agent that can be used in step iv) is selected from the group consisting of polyols such as ethylene glycol, polyethylene glycols such as diethylene glycol, triethylene glycol and tetraethylene glycol, propylene glycol, polypropylene glycols such as 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), glycerol, polyglycerol, trimethylolpropane, polyoxypropylene, oxyethylene-oxypropylene block copolymers, sorbitan fatty acid esters, polyoxyethylene dehydrate Sorbitol-fatty acid esters, pentaerythritol, polyvinyl alcohol and sorbitol; amino alcohols such as ethanolamine, diethanolamine, triethanolamine or propanolamine; polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine or pentaethylenehexamine; polyglycidyl ether compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, hexylene glycol glycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether Glyceryl ether, diglycidyl phthalate, diglycidyl adipate, 1,4-phenylenebis(2-oxazoline), glycidol; polyisocyanates, preferably diisocyanates, such as 2,4-toluene diisocyanate and hexamethylene diisocyanate; polyaziridine compounds, such as 2,2-bis(hydroxymethyl)butanol-tris[3-(1-aziridinyl)propionate], 1,6-hexamethylenediethyleneurea and diphenylmethane-bis-4,4'-N,N'-diethyleneurea; halogen epoxides, such as epichlorohydrin and epibromohydrin and α-methylepichlorohydrin; alkylene carbonates, such as 1,3-dioxolane-2-one ( ethylene carbonate), 4-methyl-1,3-dioxolane-2-one (propylene carbonate), 4,5-dimethyl-1,3-dioxolane-2-one, 4,4-dimethyl-1,3-dioxolane-2-one, 4-ethyl-1,3-dioxolane-2-one, 4-hydroxymethyl-1,3-dioxolane-2-one, 1,3-dioxane-2-one, 4-methyl-1,3-dioxane-2-one, 4,6-dimethyl-1,3-dioxane-2-one, 1,3-dioxolane-2-one, poly-1,3-dioxolane-2-one; polyquaternary amines, for example, condensation products of dimethylamine and epichlorohydrin. Further preferred surface crosslinking agents are polyoxazolines such as 1,2-ethylenebisoxazoline, crosslinking agents with silane groups such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane, oxazolidinones such as 2-oxazolidinone, bis- and poly-2-oxazolidinones, and diethylene glycol silicate. Preferably, the surface crosslinking agent is selected from ethylene glycol diglycidyl ether (EGDGE) and 1,4-butanediol diglycidyl ether (BDDGE).

[0041] Based on the total amount of dry cross-linked water-absorbing polyglutamic acid (salt), 0.10-2.00 wt%, preferably 0.25-1.40 wt%, more preferably 0.50-0.80 wt% of the surface cross-linking agent is usually used.

[0042] As an accelerator according to the present invention, water can also be used in step iv). Typically, 1.0-5.0 wt. %, preferably 2.0-4.0 wt. %, and more preferably 3.0 wt. % of water is used, based on the total amount of the dried, cross-linked, water-absorbing polyglutamic acid (salt). Without wishing to be bound by a particular theory, water facilitates thermal processing, which has beneficial effects on the properties of the final product, particularly centrifuge retention capacity and pressurized absorption capacity. 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 crosslinking 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. "Absent" means that the water used contains less than 1.0 wt. %, preferably less than 0.5 wt. %, and more preferably less than 0.1 wt. % of any other chemical compounds relative to the total amount of water used.

[0043] In addition, as promoters, additives can be used to improve properties such as gel strength, permeability, processability, odor control, 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.

[0044] The water-absorbing polyglutamic acid (salt) according to the present invention can comprise 0.01-5.00wt% or 0.01-1.00wt% or 0.01-0.05wt% of a penetration modifier based on the total weight of the cross-linked water-absorbing polyglutamic acid (salt) of the dry. Suitable examples of penetration modifiers include compounds that change the depth of penetration of the surface modifier into the water-absorbing polyglutamic acid (salt), fiber, film, foam or bead by changing the viscosity, surface tension, ionic properties or adhesion of the medium to which the surface modifier or these modifiers are applied. Penetration modifiers can include polyethylene glycol, tetraethylene glycol dimethyl ether, monovalent metal salts, surfactants and water-soluble polymers.

[0045] The water-absorbing polyglutamate (salt) according to the present invention may contain 0.01-5.00wt% or 0.01-1.00wt% or 0.01-0.05wt% of a polyvalent metal salt based on the total weight of the dried cross-linked water-absorbing polyglutamate (salt). The polyvalent metal salt is preferably water-soluble. Examples of metal cations include, but are not limited to, cations of Al, Fe, Zr, Mg, Ce and Zn. Preferably, the valence of the polyvalent metal salt is +3, most preferably Al(+3). Examples of anions in the polyvalent metal salt include halides, sulfates, nitrates, lactates and acetates, of which chlorides, sulfates, acetates and lactates are preferred, and sulfates and lactates are more preferred. Aluminum sulfate and aluminum lactate are examples of polyvalent metal salts, which are easily available on the market and have good performance. The preferred form of aluminum sulfate is hydrated aluminum sulfate, preferably aluminum sulfate containing 12-14 water molecules. Mixtures of polyvalent metal salts can be used. The dry, cross-linked, water-absorbing polyglutamic acid (salt) and the multivalent metal salt are suitably mixed by dry blending or in solution, using methods well known to those skilled in the art. For dry blending, a sufficient amount of a binder may be used to ensure a substantially uniform mixture of the salt and the 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, glycerol, and polyethylene glycol.

[0046] The water-absorbing polyglutamic acid (salt) according to the present invention may contain 0.01-5.00 wt% or 0.01-1.00 wt% or 0.01-0.05 wt% of water-insoluble inorganic powder based on the total weight of the dry cross-linked water-absorbing polyglutamic acid (salt). Examples of insoluble inorganic powders include silicon dioxide, silicic acid, silicates, 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 selected from the above compounds. An example of silicon dioxide is available from Evonik Industries 22S fumed silica. The preferred particle size range of the inorganic particles is 10x10 -9 -10x10 -6 m.

[0047] In some aspects, the water-absorbing polyglutamic acid (salt) of the present invention comprises 0.01-5.00 wt% or 0.01-1.00 wt% or 0.01-0.05 wt% of a polymer coating, such as a thermoplastic coating, or a cationic coating, or a combination of a thermoplastic coating and a cationic coating, based on the total weight of the dry cross-linked water-absorbing polyglutamic acid (salt). In some specific aspects, the polymer coating is a polymer that can be in a solid, emulsion, suspension, colloid or dissolved form, or a combination thereof. Polymer coatings suitable for the present invention may include, but are not limited to, thermoplastic coatings having a certain thermoplastic melting temperature, wherein the temperature of the treated superabsorbent polymer particles is brought to the thermoplastic melting temperature simultaneously or subsequently with the application of the polymer coating to the particle surface. Examples of thermoplastic polymers include polyolefins, polyethylene, polyesters, polyamides, polyurethanes, styrene polybutadiene, linear low density polyethylene (LLDPE), ethylene acrylic acid copolymers (EAA), ethylene alkyl methacrylate copolymers (EMA), polypropylene (PP), maleated polypropylene, ethylene vinyl acetate copolymers (EVA), polyesters, polyamides, and blends of all polyolefin families, such as blends of PP, EVA, EMA, EEA, EBA, HDPE, MDPE, LDPE, LLDPE and / or VLDPE, can also be advantageously used. In particular aspects, maleated polypropylene is a preferred thermoplastic polymer for use in the present invention. Thermoplastic polymers can be functionalized to obtain additional advantages, such as water solubility or dispersibility. Cationic polymers, as used herein, refer to polymers or polymer mixtures containing one or more functional groups that have the potential to become positively charged ions upon ionization in aqueous solution. Suitable functional groups for cationic polymers include, but are not limited to, primary, secondary or tertiary amino groups, imino groups, imide 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), poly(diallyldimethylammonium chloride). Examples of natural cationic polymers include partially deacetylated chitin, chitosan, and chitosan salts. Synthetic polypeptides such as polyasparagine, polylysine, and polyarginine are also suitable cationic polymers.

[0048] In addition, additives that enhance the whiteness or long-term color stability of the polymer (e.g., to prevent darkening, yellowing, or browning) may also be used. Such additives are well known in the art and include antioxidants, sulfur- and phosphorus-containing compounds, chelating agents, fluorescent whitening agents, and the like. Preferred additives for color stability are 2-hydroxy-2-sulfonated acetic acid, bisulfites, phosphonates, ethylenediaminetetraacetic acid, ethylenediamine-N,N'-disuccinic acid, diethylenediaminepentaacetic acid, their salts and derivatives, and mixtures thereof.

[0049] In some aspects, additional surface additives can optionally be used with the particulate superabsorbent polymer composition, including odor binding or odor control substances, such as cyclodextrins, zeolites, inorganic or organic salts, similar materials, and the tannins described in European Patent EP2176325B1 (which is incorporated herein by reference and therefore forms a part of this disclosure), anti-caking additives, flow modifiers, surfactants, viscosity modifiers, etc. In addition, surface additives can play a variety of roles in the surface modification process. For example, a single additive can be a surfactant, a viscosity modifier, and can react to crosslink the polymer chains. On the other hand, the additional surface additives can include a chelating agent. The chelating agent can preferably be selected from organic polyacids, phosphoric acid polyacids, and salts thereof. Preferably, the chelating agent can 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.

[0050] The steps of the method of the present invention are carried out in the order of step i), step ii), step iii) and step iv).

[0051] The present invention also relates to a water-absorbing polyglutamate (salt) obtainable by the method described herein. Preferably, the water-absorbing polyglutamate (salt) is in granular form and / or has a particle size distribution of 150-850 μm. Preferably, at least 80 wt%, more preferably at least 90 wt%, of the water-absorbing polyglutamate (salt) has a particle size distribution of 150-850 μm.

[0052] Preferably, the water-absorbing polyglutamic acid (salt) obtainable according to the method of the present invention achieves at least one of the following performance parameters:

[0053] The absorption capacity under a pressure of 4.83 kPa (0.7 psi) measured according to the method defined in the specification is greater than 9 g / g and less than 30 g / g or less than 26 g / g, preferably less than 25 g / g;

[0054] · According to the method defined in the manual, the conductivity of the saline water is greater than 0 and less than 150x10 -7 cm 3 ·s·g -1 , preferably greater than 10 and less than 100x10 -7 cm 3 ·s·g -1 ;

[0055] The centrifuge retention capacity measured according to the method defined in the instructions is greater than 20 and less than 46 g / g, preferably greater than 25 and less than 42 g / g;

[0056] The free swelling rate is greater than 0.5 and less than 1.5 g·g measured according to the method defined in the instructions. -1 ·s -1 , preferably 0.7 and less than 1.2 g·g -1 ·s -1 ;

[0057] • The vortex time is less than 50 and greater than 10 seconds, preferably less than 30 and greater than 15 seconds, measured according to the method defined in the specification.

[0058] More preferably, the water-absorbing polyglutamate (salt) exhibits the above-mentioned AAP and CRC values.

[0059] The performance parameters described are generally used to identify water-absorbing polymers for use in personal hygiene articles. The values cited are derived from the preparation process of the present invention.

[0060] Another object of the present invention is to provide a product comprising water-absorbing polyglutamic acid (salt), wherein the product has at least one of the above-mentioned performance parameters or can be obtained according to the method of the present invention.

[0061] The article is preferably a personal hygiene article, such as a diaper, sanitary napkin or napkin. In addition, the article can also be a wound cover. Further applications of the water-absorbing polyglutamic acid (salt) of the present invention include medical / pharmaceutical applications, wherein it can be used as or in biological glue, dental carrier, bone regeneration, cartilage regeneration, vaccine development scaffold in tissue engineering, drug delivery system and biological control agent. Further applications are agriculture, for example for improving the availability of soil moisture, as a biofertilizer, for wastewater treatment, as a bioflocculant, in the food industry as a thickener, oil reducer, flavoring, cryoprotectant, and in cosmetics, such as sunscreen, hair growth serum, anti-aging serum, mouthwash and contact lens care solution.

[0062] Test Method

[0063] Superabsorbents are typically purchased by manufacturers of personal hygiene products. The overall performance of the superabsorbent is crucial in purchasing decisions. The desired performance profile depends largely on the type and intended use of the hygiene product. Over the past few decades, market participants have established a series of performance parameters to compare the suitability of different SAP qualities for their intended use. Some of these performance parameters are standardized by independent organizations, while others are defined by individual hygiene product manufacturers based on their individual needs. In reality, both types of performance parameters are crucial in the real-world SAP market. Furthermore, the patent literature is replete with parameters that have no impact outside of a particular patent.

[0064] For the present invention, the following performance parameters are relevant and are determined as follows.

[0065] Centrifuge retention capacity (CRC)

[0066] Centrifuge retention capacity refers to the fluid retention capacity under no pressure. The method recommended by the European Disposables and Nonwovens Association (EDANA) WSP 241.2 (05) was used.

[0067] Absorption under pressure (AAP)

[0068] Absorbency under pressure is the ability of a fabric to absorb urine when subjected to external pressure. AAP is measured at a pressure of 4.83 kPa (equivalent to 0.7 psi) using the method WSP 242.2 (05) recommended by the European Disposables and Nonwovens Association (EDANA).

[0069] Saline Flow Conductivity (SFC)

[0070] Saline conductivity refers to the ability of a gel to transport fluid after initial contact with body fluid. The test method is disclosed on pages 69-75 of International Publication WO-A-95 / 26209, except that 1.5 g of the superabsorbent under investigation is used instead of 0.9 g.

[0071] Free Swell Ratio (FSR)

[0072] The parameter is related to the swelling rate of the absorbent polymer. 1.00 g (= W1) of dry absorbent material is weighed into a 25 mL glass beaker and evenly distributed on the bottom of the glass beaker. Then 20 mL of a 0.9 wt% sodium chloride aqueous solution is dispensed into a second glass beaker, the contents of which are quickly added to the first beaker, and a stopwatch is started. When the last drop of salt solution is confirmed to be absorbed by the disappearance of the reflection on the liquid surface, the stopwatch is stopped. By weighing the second beaker (= W2), the exact amount of liquid poured out of the second beaker and absorbed by the polymer in the first beaker can be accurately determined. The time required for absorption, measured with a stopwatch, is recorded as 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:

[0073] FSR[g·g -1 ·s -1 ]=W2 / (W1·t)

[0074] However, when the moisture content of the material under consideration exceeds 3 wt%, the weight W1 must be corrected according to the moisture content. The unit of FSR is g·g -1 ·s -1 .

[0075] Vortex time

[0076] The vortex time is the time (in seconds) from the addition of 2 g of the water-absorbing polymer to 50 mL of a saline solution and the subsequent stirring of the mixture at 600 rpm until the vortex disappears. A 100 mL glass beaker (Pyrex #1060-100 or Fisher Brand #FB-102-100) and a magnetic stirring bar (dimensions 38.4 mm x 8 mm) were used. The saline temperature was set between 24 and 25°C, with the room temperature above 21°C. The humidity was set within the limits of EDANA standard test WSP 241.2 (05).

[0077] The present invention will now be further illustrated by the following examples. Example

[0078] Preparation of dry cross-linked water-absorbent polyglutamic acid (salt) (Table 1)

[0079] Preparation of crosslinker aqueous solution

[0080] At room temperature, 1000 g of deionized water and 10 g of a diglycidyl ether crosslinker were carefully mixed in a beaker using a magnetic stirrer. The crosslinker used was polyethylene glycol diglycidyl ether (poly-EGDGE) or 1,4-butanediol diglycidyl ether (BDDGE), and the amount used was 2 wt % based on the non-crosslinked polyglutamic acid (salt). Table 1 below provides more information.

[0081] Batch crosslinking in a kneading reactor

[0082] The crosslinking reaction was carried out in a Discotherm Batch, DTB1.5 uniaxial kneading reactor obtained from List AG, Switzerland, with a total volume of 3.1 L. The reactor was equipped with a heating and cooling jacket, a vacuum system, a nitrogen supply system and a reactor control unit.

[0083] The water / crosslinker solution prepared as described above was filled into the reactor through the dome, and then 500 g of solid γ-PGA (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) was added under full stirring (65 rpm). The reactor was preheated to greater than 110° C. (set temperature of the heating device: 120° C.). The temperature was measured in the jacket of the kneading reactor. The pressure inside the vessel was atmospheric pressure. Throughout the reaction, the reactor remained open and maintained at the aforementioned temperature.

[0084] The stirring was set to maximum (100% of the potentiometer, 65 rpm) for 20 minutes to allow the PGA to completely dissolve and the mixture to reach the desired temperature. Thereafter, the stirrer was set to 40%, i.e. 24 rpm, for 10 minutes. Afterwards, the end plate of the reactor was removed to drain the free-flowing and granular gel from the reactor. The resulting polymer was further processed.

[0085] The granular gel obtained by crosslinking in the DTB 1.5 L reactor was extruded into a kitchen-type meat grinder (Mado Küchen Fleischwolf MEW 710-R70) equipped with an 8 mm thick die plate with 45 holes, each with a diameter of 6 mm.

[0086] Drying of cross-linked polyglutamic acid gel

[0087] Gel drying was performed in a batch-operated fluidized bed dryer, model CTL (supplied by Allgaier-Werke KG, Uhingen, Germany). The dryer was equipped with a conical fluidizing chamber (the bottom of which consisted of a perforated stainless steel plate with 20 x 3 mm holes and a diameter of 20 cm, similar to the plate-belt dryer used in the factory), a ventilator, an air heater, a fresh air and exhaust filter with automatic dust removal, and a control box. The air flow was from bottom to top and was not circulated.

[0088] 600-900 g of the extruded gel is then placed in the fluidization chamber of the dryer. The gel to be dried is placed on a flat plate, with a gel bed thickness of approximately 5-8 cm, and dried for 15 or 20 minutes in a stream of hot air at 130°C or 140°C, respectively, with an air inlet velocity of 5.5 m / s. After 10 minutes, the pre-dried material is rotated 180° to allow for further uniform drying on both sides for 5 or 10 minutes. The resulting dry polymer is ground in a Bauermeister laboratory roller mill and sieved in a Retsch sieve tower equipped with sieves with mesh sizes of 850 and 150 μm to obtain the particle size fraction used for analysis of the precursor superabsorbent.

[0089] Heat treatment of dried cross-linked water-absorbing polyglutamic acid (salt) (Table 2)

[0090] 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. To prepare the surface cross-linking solution, 0.3-1.5 wt% of the cross-linking agent was dissolved in 3 wt% of deionized water, each amount based on 100 g of the dried cross-linked water-absorbing polyglutamic acid (salt).

[0091] Ethylene glycol diglycidyl ether (EGDGE) or 1,4-butanediol diglycidyl ether (BDDGE) was used as a crosslinking agent. Additives such as isopropyl alcohol and aluminum lactate were also used. Water was also used as an accelerator.

[0092] 60 g of dry crosslinked hydrophilic polyglutamic acid (salt) were coated with the above amount of surface crosslinking solution in a household Krupps mixing cup using a syringe with a 0.4 mm cannula while stirring vigorously with a Krupps 3Mix 7000 mixer and stirred for a further minute.

[0093] The details of the promoters used, their amounts and reaction conditions are shown in Table 2 below.

[0094] The coated precursor was divided into three parts and heated in a circulating air drying oven Heraeus UT6120 at 150° C. for 20-60 minutes.

[0095] The surface-crosslinked polymer thus obtained was sieved with a Retsch sieve having a mesh size of 850 μm to remove aggregates formed by the coating material.

[0096] result

[0097] The performance data of the prepared water-absorbing polyglutamic acid (salt) are shown in the table below.

[0098]

[0099]

[0100]

[0101]

Claims

1. A method for producing water-absorbing polyglutamic acid (salt), comprising the following steps: i) providing an aqueous mixture of non-crosslinked polyglutamic acid (salt) and at least one crosslinking agent, ii) cross-linking the non-cross-linked polyglutamic acid (salt) to obtain a cross-linked polyglutamic acid (salt) gel, iii) drying the cross-linked polyglutamic acid (salt) gel to obtain dry 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).

2. The method according to claim 1, characterized in that The molecular weight of the non-cross-linked polyglutamate (salt) is 200,000-3,000,000 Daltons.

3. The method according to claim 1 or 2, characterized in that The crosslinking agent is selected from the group consisting of glycidyl ethers such as diglycidyl ether, triglycidyl ether, polyglycidyl ether containing 3 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 multifunctional 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, cyclic and aromatic polyglycidyl ethers, or a combination of glycidyl ether-based crosslinking agents; carbodiimides, For example, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, dicyclohexylcarbodiimide, other carbodiimide-containing compounds, or a combination of a cross-linking agent containing a carbodiimide functional group and other cross-linking agents, such as a cross-linking agent of glycidyl ether saccharides (such as glucose, maltotriose or cyclodextrin) in the presence of a water-soluble carbodiimide-containing compound; other cross-linking agents, such as water-soluble chitosan, polyethylene glycol or other organic polyols, aryl azide or diaziridine or other photoreactive chemical heterobifunctional cross-linking agents 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 selected from ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether and 1,4-butanediol diglycidyl ether.

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

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

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

7. The method according to any one of claims 1 to 6, characterized in that Step ii) is carried out within 10-50 minutes, preferably within 20-40 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 kneading reactor.

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

9. The method according to any one of claims 1 to 8, characterized in that The cross-linked polyglutamate gel was crushed before drying.

10. The method according to claim 9, characterized in that The comminution is performed by an extruder, a chopper or a mincer.

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

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

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

14. The method according to claim 13, characterized in that A sieving device is used in the sieving step, wherein the sieving device has at least two sieves, wherein the mesh size of the first sieve is 850 μm, and the mesh size of the second sieve is 150 μm.

15. The method according to any one of claims 1 to 14, characterized in that In step iv) at least one accelerator selected from the group consisting of surface crosslinking agents, water and additives is used.

16. The method according to claim 15, characterized in that The at least one accelerator used in step iv) is selected from ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether and water.

17. The method according to claim 15 or 16, characterized in that Based on the total amount of the dry water-absorbing polyglutamic acid (salt), 0.10-2.00 wt%, preferably 0.25-1.40 wt%, more preferably 0.50-0.80 wt% of the surface crosslinking agent is used.

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

19. The method according to claim 18, characterized in that Based on the total amount of the dry hygroscopic polyglutamic acid (salt), 1.0-5.0 wt%, preferably 2.0-4.0 wt%, more preferably 3.0 wt% of water is used.

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

21. A water-absorbing polyglutamic acid (salt), characterized in that The water-absorbing polyglutamic acid (salt) has at least one of the following characteristics: The absorption capacity under a pressure of 4.83 kPa (0.7 psi) measured according to the method defined in the specification is greater than 9 g / g and less than 30 g / g or less than 26 g / g, preferably less than 25 g / g; · According to the method defined in the manual, the conductivity of the saline water is greater than 0 and less than 150x 10 -7 cm 3 ·s·g -1 , preferably greater than 10 and less than 100 x 10 -7 cm 3 ·s·g -1 ; The centrifuge retention capacity measured according to the method defined in the instructions is greater than 20 and less than 46 g / g, preferably greater than 25 and less than 42 g / g; The free swelling rate is greater than 0.5 and less than 1.5 g·g measured according to the method defined in the instructions. -1 ·s -1 , preferably greater than 0.7 and less than 1.2 g·g -1 ·s -1 ; • The vortex time is less than 50 and greater than 10 seconds, preferably less than 30 and greater than 15 seconds, measured according to the method defined in the specification.

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

23. The article according to claim 22, characterized in that The article is or comprises a diaper, a sanitary article, a sanitary napkin, a napkin, a wound cover.

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