Water-absorbing material and method for producing same

Abstract

Provided are: a water-absorbing material which contains a mechanochemical reaction product of a raw material containing a plant-derived biomass with an esterification agent; a method for producing the water-absorbing material, the method including a step for causing a mechanochemical reaction to occur by applying mechanical energy to a mixture of a raw material containing a plant-derived biomass with an esterification agent; and a method for imparting water-absorbing capability to a raw material containing a plant-derived biomass, the method being characterized by causing a mechanochemical reaction of the raw material to occur. This water-absorbing material is used in various fields such as agricultural and horticultural products including soil water-retaining agents, sanitary products including paper diapers and sanitary napkins, pet supplies including pet sheets, food distribution industries including cooling gels, daily necessities including disposable body warmers and gel fragrances, and medical supplies including waste blood coagulating agents.

Description

Water-absorbent material and its manufacturing method

[0001] The present invention relates to a water-absorbing material used in various fields such as agricultural and horticultural products such as soil water retention agents, sanitary products such as disposable diapers and napkins, pet products such as pet sheets, food and distribution products such as ice-keeping gels, daily necessities such as disposable body warmers and gel air fresheners, and medical products such as waste blood coagulation agents, and a method for producing the same.

[0002] Currently, most of the superabsorbent resins (Super Absorbent Polymers (SAPs)) widely used as absorbent materials are made from petrochemical sodium polyacrylate, which is petroleum-derived and non-biodegradable, resulting in a significant environmental impact. Therefore, research and development is being conducted on absorbent materials made primarily from plant biomass, which are naturally derived and biodegradable SAPs with a low environmental impact.

[0003] Patent Document 1 describes a superabsorbent hydrogel comprising a crosslinked polymer network comprising polymer chains grafted onto particles of soy lees, the crosslinks being formed via the polymer chains and / or each soy lees particle being bonded to one or more polymer chains.

[0004] Patent Document 2 describes a water-retaining natural polymer that includes a biological waste material such as fruit waste containing pectin, a cross-linking agent such as sulfosuccinic acid, and a polysaccharide such as cellulose.

[0005] Special table 2020-536981 publication Special table 2022-542300 publication

[0006] However, the production of the superabsorbent hydrogel described in Patent Document 1 requires a reaction time of several hours, resulting in a problem of low production efficiency. Furthermore, the production of the water-retaining natural polymer described in Patent Document 2 requires a step of extracting pectin, and similarly to Patent Document 1, the reaction time requires several hours, resulting in a problem of low production efficiency. As described in Patent Documents 1 and 2, conventional biodegradable SAPs made from plant biomass as raw materials require multiple solvents and catalysts, and the high product price resulting from production costs such as long reaction times has hindered their widespread use, preventing them from being used as final products.

[0007] An object of the present invention is to provide a novel water-absorbent material that can be produced by a simple method and has excellent water-absorbing capacity.

[0008] The present invention provides: [1] a water-absorbing material containing a mechanochemical reaction product between a raw material containing plant biomass and an esterifying agent; [2] the water-absorbing material according to [1] above, in which the plant biomass contains a protein; [3] the water-absorbing material according to [1] above, in which the plant biomass contains a polysaccharide-containing plant biomass; [4] the water-absorbing material according to [1] above, in which the raw material contains a protein-containing plant biomass and a polysaccharide-containing plant biomass; [5] the water-absorbing material according to [2] or [4] above, in which the protein-containing plant biomass is at least one selected from the group consisting of soybean pulp, soybean meal, sake lees, corn meal, and wheat meal; [6] the water-absorbing material according to any one of [3] to [5] above, in which the polysaccharide-containing plant biomass is lignocellulose-based biomass; [7] [8] The water-absorbing material according to any one of [1] to [6] above, wherein the esterifying agent contains an organic acid; [8] The water-absorbing material according to [7] above, wherein the organic acid contains a carboxylic acid compound; [9] The water-absorbing material according to [8] above, wherein the carboxylic acid compound is at least one selected from the group consisting of succinic acid, maleic acid, citric acid, and anhydrides of these acids;

[10] The water-absorbing material according to any one of [1] to [9] above, wherein the mechanochemical reactant is a product obtained by causing a mechanochemical reaction using a twin-screw extruder mixer;

[11] A method for producing the water-absorbing material according to any one of [1] to [9] above, comprising a step of applying mechanical energy to a mixture of a raw material containing plant biomass and an esterifying agent to cause a mechanochemical reaction;

[12] A method for producing the water-absorbing material according to

[11] above, wherein the step is carried out using a twin-screw extruder mixer;

[13] The present invention relates to the method for producing a water-absorbing material according to

[11] or

[12] above, wherein the esterifying agent contains an organic acid;

[14] the method for producing a water-absorbing material according to

[13] above, wherein the organic acid contains a carboxylic acid compound;

[15] the method for producing a water-absorbing material according to

[14] above, wherein the carboxylic acid compound is at least one selected from the group consisting of succinic acid, maleic acid, citric acid, and anhydrides of these acids; and

[16] a method for imparting water absorption ability to a raw material containing plant biomass, characterized by causing a mechanochemical reaction in the raw material.

[0009] The water-absorbent material of the present invention has excellent water-absorbing ability and can be obtained by a simple method.

[0010] 1 is a schematic cross-sectional view of a twin-screw extruder kneader that can be used to produce the water-absorbing material of the present invention.

[0011] The water-absorbent material of the present invention contains a mechanochemical reaction product between a raw material containing plant biomass and an esterifying agent. In this specification, the term "mechanochemical reaction product" refers to a reaction product obtained by a mechanochemical reaction, and "mechanochemical reaction" generally refers to the phenomenon of applying mechanical energy to a substance to cause a chemical reaction. The water-absorbent material of the present invention is also an invention that utilizes a mechanochemical reaction in the general sense, in which mechanical energy is applied to a raw material containing plant biomass, causing a chemical reaction and transforming the raw material into a structure with water-absorbing properties. More specifically, although not particularly limited, the "mechanochemical reaction product" of the present invention is presumed to exhibit a structure resulting from the application of mechanical energy to a raw material containing plant biomass, activating functional groups contained in the raw material and causing a chemical reaction with the esterifying agent.

[0012] Plant biomass is not particularly limited as long as it is a renewable resource derived from plants. The types and classifications of plant biomass are generally expressed in various ways depending on how they are perceived, but any of these are acceptable in the present invention. For example, based on the type of plant, it can be classified into herbaceous biomass and woody biomass. Specific examples include agricultural products, forestry products, wild plants, algae, and by-products generated during the processing of these. Based on the state of biomass, it can also be classified into waste biomass (food waste, waste paper, construction wood, sawmill residues, etc.), unused biomass (rice husks, wheat straw, rice straw, etc.), and resource crops (sugarcane, corn, rapeseed, etc.). Furthermore, based on the components, it may also be referred to as lignocellulosic biomass or polysaccharide-containing plant biomass. Depending on how it is perceived, substantially the same thing may fall into multiple categories. However, in the present invention, all biomass falling into the category of plant biomass is applicable, regardless of the classification or expression.

[0013] In the present invention, in one embodiment, the plant biomass is preferably at least one type selected from the group consisting of agricultural by-products, forestry by-products, food processing by-products, and textile processing by-products, from the viewpoints of environmental issues, effective use of waste, costs, etc., and by-products also include those that are treated as waste.

[0014] Examples of agricultural by-products include, but are not limited to, rice husks, wheat husks, rice straw, wheat straw, corn stalks and leaves (cornstarch), sugarcane bagasse, soybean meal, soybean husks, peanut husks, banana stalks (banana fiber), and kapok.

[0015] Examples of forestry by-products include, but are not limited to, thinned wood, lumber scraps, bark, branches, leaves, sawdust, wood chips, and the like.

[0016] Food processing by-products include, but are not limited to, soybean pulp, fruit peels and seeds (orange peel, apple peel, etc.), outer vegetable leaves and roots (cabbage outer leaves, carrot leaves, etc.), used tea leaves, coffee grounds, sake lees, oil cakes (soybean meal, canola meal, sunflower meal, peanut meal, cottonseed meal, flaxseed meal, rapeseed meal, etc.), algae meal, nut meal, soy milk cake (pressure residue), and zein (corn protein).

[0017] Examples of waste materials include, but are not limited to, waste cooking oil, brewer's dregs (beer dregs, wine dregs, corn residues generated during bioethanol production, etc.), discarded clothing (cotton, etc.), food waste, compost, etc.

[0018] The raw material preferably contains, as plant biomass, a plant biomass containing protein (hereinafter also referred to as protein-containing plant biomass) or a polysaccharide-containing plant biomass, and more preferably contains both a protein-containing plant biomass and a polysaccharide-containing plant biomass.

[0019] The term "protein-containing plant biomass" as defined in the present invention refers to a substance containing a certain amount or more of protein, and the protein content is preferably 10% by mass or more, more preferably 15 to 50% by mass, on a dry weight basis. In this specification, the protein content is a value measured by a method using a spectrophotometer.

[0020] Examples of protein-containing plant biomass include soybean pulp (approximately 20% by mass), soybean meal (approximately 45% by mass), sake lees (approximately 15% by mass), corn meal (approximately 28% by mass), wheat cake (approximately 38% by mass), rice bran, soy milk residue, and zein (corn protein). From the standpoint of availability (price, amount of waste), at least one selected from the group consisting of soybean pulp, soybean meal, sake lees, corn meal, and wheat cake is preferred. Note that wheat cake also includes lees from the production of beer, whiskey, etc. The values ​​in parentheses indicate general protein contents.

[0021] Polysaccharide-containing plant biomass is biomass containing polysaccharides including lignocellulose, plant-derived polysaccharides such as starch and pectin, and algae-derived polysaccharides such as agarose and carrageenan, and of these, it is preferable to use lignocellulose-based biomass containing lignocellulose as the raw material.

[0022] Lignocellulosic biomass contains at least one lignocellulosic component selected from the group consisting of cellulose, hemicellulose, and lignin, which are major components constituting lignocellulose, the main component of plant cell walls. The content of such lignocellulosic components is preferably 50% by mass or more, more preferably 70 to 80% by mass. The protein content of lignocellulosic biomass is low, preferably less than 10% by mass, and in this respect, it is distinguished from the protein-containing plant biomass in the present invention. In this specification, the content of lignocellulosic components is a value measured by sulfuric acid hydrolysis.

[0023] Examples of lignocellulosic biomass include, but are not limited to, conifers (cedar, spruce, larch, black pine, Abies sachalinensis, Himekomatsu, yew, fir, aspen, cypress, hemlock, tsuga, Japanese cypress, Japanese yew, etc.), hardwoods (asbestos, American black cherry, yellow poplar, walnut, birch, zelkova, ash, teak, Chinese maple, oak, hard maple, white ash, white oak, red oak), agricultural products (rice, wheat, corn, pineapple, oil palm, cassava, sugarcane, etc.) and waste products thereof, industrial plants (kenaf, cotton, kapok, etc.) and waste products thereof, forage crops (alfalfa, timothy, etc.), eriensus, bamboo, bamboo grass, etc.

[0024] In the present invention, the lignocellulosic biomass is not particularly limited, but for example, at least one selected from the group consisting of cotton, rice husks, wheat husks, rice straw, wheat straw, corn stalks and leaves (corn starch), sugarcane pomace (bagasse), soybean husks, peanut husks, banana stalks (banana fiber), banana pulp made from refined banana fiber, kapok, and waste paper powder is preferred.

[0025] The weight-average molecular weight of lignocellulosic biomass varies depending on the type, but from the viewpoint of water absorbency, it is preferably 30,000 or more, more preferably 100,000 to 2,000,000, even more preferably 200,000 to 1,000,000, and even more preferably 300,000 to 800,000. In this specification, the molecular weight of lignocellulosic biomass is a value measured by GPC (SEC). For example, the weight-average molecular weight of cotton is generally about 300,000 to 900,000, and the weight-average molecular weight of waste paper powder is generally about 50,000 to 100,000.

[0026] When both protein-containing plant biomass and polysaccharide-containing plant biomass are used, the mass ratio of the protein-containing plant biomass to the polysaccharide-containing plant biomass (protein-containing plant biomass / polysaccharide-containing plant biomass) is preferably 0.1 to 1.5, more preferably 0.2 to 1.3, even more preferably 0.2 to 1.2, and even more preferably 0.25 to 1.0.

[0027] It is preferable that the plant biomass be subjected to pretreatment such as washing and drying before being subjected to the mechanochemical reaction, but the plant biomass to be subjected to the mechanochemical reaction preferably has a low moisture content, and is more preferably in a dry state. The moisture content in the plant biomass is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0028] The raw material may contain one or more types of plant biomass, and may further contain other components suitable for various uses, such as fertilizer components when used for agricultural purposes, or fragrances, deodorizing components, antibacterial components, etc. when used in air fresheners, diapers, etc.

[0029] The content of plant biomass in the raw material is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0030] As the esterifying agent, an organic acid is preferred, and a carboxylic acid compound is more preferred, since a crosslinked structure can be easily formed.

[0031] Examples of carboxylic acid compounds include saturated fatty acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and caproic acid; unsaturated fatty acids such as oleic acid and linoleic acid; hydroxy acids such as lactic acid and malic acid; aromatic carboxylic acids such as benzoic acid, phthalic acid, and gallic acid; dicarboxylic acids such as succinic acid, maleic acid, oxalic acid, and malonic acid; tricarboxylic acids such as aconitic acid; oxocarboxylic acids such as pyruvic acid; hydroxycarboxylic acids such as citric acid; and carboxylic acid derivatives such as anhydrides of these acids, with at least one selected from the group consisting of succinic acid, maleic acid, citric acid, and anhydrides of these acids being preferred.

[0032] The content of the organic acid in the esterifying agent is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0033] The mass ratio of the esterifying agent to the plant biomass in the raw material (esterifying agent / plant biomass in the raw material) is preferably 1.0 to 3.0, more preferably 2.4 to 2.7.

[0034] The present invention further provides a method for producing the water-absorbent material of the present invention, which includes a step of applying mechanical energy to a mixture of a raw material containing plant biomass and an esterifying agent to cause a mechanochemical reaction.

[0035] The means for imparting mechanical energy to the mixture of the raw material and the esterifying agent is not particularly limited as long as it is an apparatus that can impart at least one force selected from compressive force, impact force, grinding force, and shear force to the mixture as mechanochemical energy, and may be a continuous apparatus or a batch apparatus.

[0036] Examples of continuous apparatus include vibration kneaders, wheel rotary kneaders such as Muller mixers, vertical stirring blade kneaders, single-screw rotary kneaders (single-screw extrusion kneaders), and multi-screw rotary kneaders such as twin-screw extrusion kneaders.

[0037] Examples of batch-type devices include grinding devices using grinding balls such as planetary ball mills, rolling ball mills, and vibration ball mills, stirring kneaders (such as Laboplastomill (manufactured by Toyo Seiki Seisakusho)), and circulation-type twin-screw kneaders.

[0038] In the present invention, a continuous type device is preferred from the viewpoint of production efficiency, and a twin-screw extrusion kneader is more preferred because it is common and versatile.

[0039] The twin-screw extrusion kneader includes, for example, a mixture supply means 1, a mixture supply port 2, a barrel 4 equipped with a screw 3, and a mixture discharge port 5, as shown in FIG.

[0040] The mixture supply means 1 preferably includes a mixer 6 that mixes the raw material and the esterifying agent. The mixer 6 can be omitted, in which case separate supply means may be provided for the raw material and the esterifying agent, which are then separately introduced into the mixture supply port 2, and the raw material and the esterifying agent may be mixed in the barrel 4.

[0041] The screw shaft shape, rotation direction, etc. can be appropriately selected from various types in terms of workability, etc. For example, either a screw shaft having a parallel axis or a conical screw having an oblique axis may be used. The screws may be either intermeshing or non-intermeshing. The screw rotation direction may be either co-rotating or counter-rotating.

[0042] The screw rotation speed can be adjusted appropriately, but is preferably in the range of, for example, 30 to 150 r / min. By adjusting the screw rotation speed, the kneading time (residence time, reaction time) of the raw material mixture in the kneader can be adjusted.

[0043] The barrel 4 has, for example, a conveying section 7, a kneading section 8, and a conveying / extruding section 9. A mixture of the raw material and the esterifying agent introduced through a mixture supply port is conveyed by the conveying section 7 to the kneading section 8, kneaded, and then conveyed by the conveying / extruding section 9 to the kneaded mixture discharge port 5.

[0044] The twin-screw extruder kneader is preferably equipped with a temperature control mechanism. Known temperature control mechanisms such as heating, cooling, and storage can be used as the temperature control mechanism, and examples of the heating mechanism include, but are not limited to, electric and hot water heaters. For example, in FIG. 1, a cartridge-type heater 10 is installed.

[0045] The set temperature inside barrel 4, i.e., the heating temperature, differs depending on the types of raw materials and esterifying agent and cannot be determined in general, but is preferably 50 to 200°C, more preferably 70 to 150°C, and even more preferably 80 to 120°C.

[0046] A mechanochemical reaction between a raw material containing plant biomass and an esterifying agent results in a mechanochemical reaction product in which the raw material is endowed with water absorption capacity. Using this method, a mechanochemical reaction product can be easily obtained without the need for a solvent or the like. The occurrence of a mechanochemical reaction can be inferred, for example, by measuring the amount of unreacted functional groups (such as OH groups) using NMR or the like, without any particular limitation. The reaction rate is not particularly limited, and may be any rate at which the desired water absorption capacity is exhibited.

[0047] The mechanochemical reaction product can be used as a water-absorbing material, for example, by shredding it, dispersing the shredded material in water, neutralizing it with an alkali, and then appropriately performing post-treatments such as drying. Drying methods include drying in a vacuum oven (vacuum drying) and freeze-drying, but freeze-drying can reduce the moisture content more than vacuum drying, resulting in a higher water absorption rate for the water-absorbing material. Note that depending on the application of the water-absorbing material, the drying step may not be necessary, or the water-absorbing material may be used in a semi-dry state after drying in a short time.

[0048] The water absorption rate of the water-absorbent material of the present invention is preferably 200% or more, more preferably 300% or more, and even more preferably 1500% or more. A water-absorbent material having an appropriate water absorption rate can be selected depending on the application. In this specification, the water absorption rate is a value measured by the "Test method for water absorption of superabsorbent polymers" specified in JIS K 7223-1996, also known as the "tea bag method."

[0049] The water-absorbing material of the present invention, which is made from plant biomass as a raw material, is a renewable, naturally derived, biodegradable water-absorbing material that places little strain on the environment.

[0050] The water-absorbing material of the present invention can be used in various fields, such as agricultural and gardening supplies such as soil water retention agents, sanitary products such as disposable diapers and napkins, pet supplies such as pet sheets, food and distribution fields such as ice-keeping gels, daily necessities such as disposable body warmers and gel air fresheners, and medical supplies such as waste blood solidification agents.

[0051] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0052] Example 1: 29.7 g of soybean pulp (Ultrafine soybean pulp powder, manufactured by Yutec Co., Ltd., made from 100% domestic soybeans) dried overnight at 50°C in a vacuum oven was mixed with 79.6 g of succinic anhydride in a mixer to prepare a raw material mixture. Next, this raw material mixture was placed in an automatic feeder and fed into a twin-screw extrusion mixer (manufactured by Technovel Co., Ltd., model ULTnano20TW-KZU) with the barrel temperature set to 120°C. The raw material feed rate was 10 g / min, and the screw speed was 60 r / min. The time from when the raw material mixture was introduced into the mixer through the mixture inlet to when it was discharged from the mixer outlet was 30 minutes. The resulting mix (mechanochemical reaction product) was shredded using a mixer and dispersed in 1.5 liters of distilled water. The mechanochemical reaction product was neutralized with a 4% NaOH aqueous solution, filtered under reduced pressure, and dried at 50°C for 24 hours under reduced pressure to obtain a water-absorbing material. All of the soybean pulp used in this example was dried overnight at 50°C in a vacuum oven.

[0053] Examples 2 and 4 A water-absorbing material was obtained in the same manner as in Example 1, except that the soybean pulp, banana fiber (weight average molecular weight: 750,000), and succinic anhydride shown in Table 1 were mixed in a mixer to prepare a raw material mixture.

[0054] Example 3: 56 g of okara and 303 g of succinic anhydride were premixed in a mixer to prepare 359 g of a mixture of okara and succinic anhydride. Next, this mixture was placed in an automatic feeder and fed at a rate of 4.33 g / min into a twin-screw extrusion mixer (manufactured by Technovel Corporation, model ULTnano20TW-KZU) with the barrel temperature set to 120°C. Along with this mixture, 56 g of cotton was manually fed at a rate of 0.675 g / min. The total feed rate of the raw material mixture was 5 g / min, the raw material feed rate was 10 g / min, and the screw speed was 60 r / min. The time from when the raw material mixture was introduced into the mixer through the mixture inlet to when it was discharged from the mixer outlet was 30 minutes. The resulting mix (mechanochemical reaction product) was shredded using a mixer and dispersed in 2 liters of distilled water. The mechanochemical reaction product was neutralized with 4% NaOH aqueous solution, filtered under reduced pressure using filter paper, and dried in a vacuum oven at 50°C to a constant weight to obtain a water-absorbing material.

[0055] Example 5 A mixture of 1.23 g of soybean pulp and 3.3 g of succinic anhydride was placed in a circulation-type twin-screw mixer (Xplore MC5, manufactured by Leo Lab Co., Ltd.) preheated to 100°C and mixed for 30 minutes at a twin screw speed of 60 r / min. The resulting mixture (mechanochemical reaction product) was then added to 200 mL of distilled water. The mechanochemical reaction product was completely dispersed in water and then neutralized with a 4% aqueous NaOH solution. The mixture was vacuum filtered through filter paper and dried in a vacuum oven at 50°C until a constant weight was obtained, yielding a water-absorbing material.

[0056] Example 6: 0.11 g of 10% by mass water was added to 1.12 g of soybean pulp. 1.23 g of this soybean pulp was mixed with 3.3 g of succinic anhydride. The resulting mixture was placed in a circulating twin-screw mixer (Xplore MC5, manufactured by Leo Lab Co., Ltd.) preheated to 100°C and kneaded for 10 minutes at a twin screw speed of 60 r / min. The resulting kneaded mixture (mechanochemical reaction product) was then added to 200 mL of distilled water. The mechanochemical reaction product was completely dispersed in water and then neutralized with a 4% NaOH aqueous solution. The mixture was vacuum filtered through filter paper and dried in a vacuum oven at 50°C for 24 hours to obtain a water-absorbing material.

[0057] Example 7 A mixture of 1.46 g of soybean pulp and 3.46 g of maleic anhydride was placed in a circulation-type twin-screw mixer (Xplore MC5, manufactured by Leo Lab Co., Ltd.) preheated to 80°C and mixed for 30 minutes at a twin screw speed of 60 r / min. The resulting mixture (mechanochemical reaction product) was then added to 200 mL of distilled water. The mechanochemical reaction product was completely dispersed in water and then neutralized with a dilute aqueous sodium hydroxide solution. The mixture was vacuum filtered through filter paper and dried in a vacuum oven at 50°C until a constant weight was obtained, yielding a water-absorbing material.

[0058] Examples 8 to 26, 33, 36, and 37: Protein-containing plant biomass, lignocellulosic biomass, and succinic anhydride were mixed as shown in Tables 1 and 2. The resulting mixture was placed in a circulating twin-screw mixer (Xplore MC5, manufactured by Leo Labs) preheated to the temperatures shown in Tables 1 and 2, and mixed for 10 minutes at a twin screw speed of 60 r / min. The resulting mixture (mechanochemical reactant) was then added to 200 mL of distilled water. After the mechanochemical reactant was completely dispersed in water, it was neutralized with a 4% aqueous NaOH solution. The mixture was vacuum filtered through filter paper and dried in a vacuum oven at 50°C for 24 hours to obtain a water-absorbent material. The banana pulp used in this example was obtained by treating banana fiber (banana stems) with alkali (boiling in NaOH) to remove lignin, then shredding the pulp, washing it with distilled water, and drying it (weight-average molecular weight: 750,000).

[0059] Example 27: 1.23 g of banana pulp and 3.3 g of succinic anhydride were placed in a circulating twin-screw mixer (Xplore MC5, manufactured by Leo Labo Co., Ltd.) preheated to 120°C and mixed in the same manner as in Example 5. The resulting mixture (mechanochemical reaction product) was then placed in 200 mL of distilled water. After the mechanochemical reaction product was completely dispersed in water, it was neutralized to pH 7.0 with a 1 M aqueous NaOH solution. The mixture was vacuum filtered through filter paper and dried in a vacuum oven at 50°C until a constant weight was obtained, yielding a water-absorbing material.

[0060] Examples 28, 30, 31, 32, 34, and 35 Water-absorbent materials were obtained in the same manner as in Example 5, except that no soybean pulp was used, and the lignocellulosic biomass shown in Table 2 was used, and the esterifying agent shown in Table 2 was used, and the materials were kneaded using a circulation-type twin-screw kneader (Xplore MC5, manufactured by Leo Labo Co., Ltd.) preheated to the temperature shown in Table 2.

[0061] Example 29 A water-absorbing material was obtained in the same manner as in Example 27, except that 7 g of banana pulp and 7 g of succinic anhydride were used and an Xplore 15HT (manufactured by Leo Labo Co., Ltd.) was used as the circulation type twin-screw kneader.

[0062] Example 38 A water-absorbent material was obtained in the same manner as in Example 10, except that the amounts of soybean pulp and banana pulp used were changed to those shown in Table 2, citric acid shown in Table 2 was used instead of succinic anhydride, and the preheating temperature was set to 130°C.

[0063] Example 39 A water-absorbing material was obtained in the same manner as in Example 12, except that the amount of soy pulp and banana fiber used was changed to the amount shown in Table 2, citric acid shown in Table 2 was used instead of succinic anhydride, and the preheating temperature was 130°C.

[0064] Examples 40 and 41 Water-absorbent materials were obtained in the same manner as in Example 3, except that the amount of soy pulp used was changed to the amount shown in Table 2, that waste paper powder shown in Table 2 was used instead of cotton, that citric acid shown in Table 2 was used instead of succinic anhydride, and that the preheating temperature was 130°C.

[0065] The water-absorbing materials obtained in Examples 1 to 41 and the dried kneaded material of Comparative Example 1 were processed into powder using an electric mixer, and the water absorption rate was measured according to the method specified in JIS K 7223-1996. The results are shown in Tables 1 and 2.

[0066]

[0067]

[0068] From the above results, it can be seen that the water-absorbent materials of Examples 1 to 41 all have high water absorption rates.

[0069] The water-absorbing material of the present invention is used in various fields, such as agricultural and gardening supplies such as soil water retention agents, sanitary products such as disposable diapers and napkins, pet supplies such as pet sheets, food and distribution fields such as ice-keeping gels, daily necessities such as disposable body warmers and gel air fresheners, and medical supplies such as waste blood coagulation agents.

[0070] REFERENCE SIGNS LIST 1 mixture supply means 2 mixture supply port 3 screw 4 barrel 5 kneaded material discharge port 6 mixer 7 conveying section 8 kneading section 9 conveying / extrusion section 10 heater

Claims

1. A water-absorbing material containing a mechanochemical reaction product of a raw material containing plant biomass and an esterifying agent.

2. The water-absorbing material according to claim 1, wherein the plant biomass contains protein.

3. The water-absorbing material according to claim 1, wherein the plant biomass comprises polysaccharide-containing plant biomass.

4. The water-absorbent material according to claim 1, wherein the raw materials contain a protein-containing plant biomass and a polysaccharide-containing plant biomass.

5. The water-absorbent material according to claim 2 or 4, wherein the protein-containing plant biomass is at least one selected from the group consisting of soybean lees, soybean meal, sake lees, corn meal, and wheat meal.

6. The water-absorbent material according to any one of claims 3 to 5, wherein the polysaccharide-containing plant biomass is lignocellulose-based biomass.

7. The water-absorbing material according to any one of claims 1 to 6, wherein the esterifying agent contains an organic acid.

8. The water-absorbing material according to claim 7, wherein the organic acid comprises a carboxylic acid compound.

9. The water-absorbent material according to claim 8, wherein the carboxylic acid compound is at least one selected from the group consisting of succinic acid, maleic acid, citric acid, and anhydrides of these acids.

10. The water-absorbing material according to any one of claims 1 to 9, wherein the mechanochemical reaction product is produced by a mechanochemical reaction using a twin-screw extruder kneader.

11. A method for producing the water-absorbing material according to any one of claims 1 to 9, comprising the step of applying mechanical energy to a mixture of a raw material containing plant biomass and an esterifying agent to cause a mechanochemical reaction.

12. The method for producing a water-absorbent material according to claim 11, wherein the step is carried out using a twin-screw extruder kneader.

13. The method for producing a water-absorbent material according to claim 11 or 12, wherein the esterifying agent contains an organic acid.

14. The method for producing a water-absorbent material according to claim 13, wherein the organic acid comprises a carboxylic acid compound.

15. The method for producing a water-absorbent material according to claim 14, wherein the carboxylic acid compound is at least one selected from the group consisting of succinic acid, maleic acid, citric acid, and anhydrides of these acids.

16. A method for imparting water absorption capacity to a raw material containing plant biomass, comprising causing a mechanochemical reaction in the raw material.

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