JP2004010634A - Water absorbing resin and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a water absorbing resin having an excellent water absorbing capacity, biodegradability and a low dissolution ratio, and to provide a method for producing the same. <P>SOLUTION: The water absorbing resin is obtained by crosslinking polysaccharides and polyvinyl alcohol using a crosslinking agent. A dialdehyde compound or a polyvalent carboxylic acid compound is used as the crosslinking agent. The water absorbing resin has ≥10 g/g water absorbing capacity for physiological saline, ≤30% dissolution ratio in the physiological saline and ≥15% biodegradation ratio. The method for producing the water absorbing resin comprises mixing the polysaccharides and polyvinyl alcohol with the crosslinking agent and heating the resultant mixture. <P>COPYRIGHT: (C)2004,JPO

Description

【００４５】
表１より、実施例１〜実施例６の吸水性樹脂は、吸水能および生分解性に優れ、しかも溶解分が少ないことがわかる。それに対して、多糖類のみを架橋させた比較例１の吸水性樹脂は、吸水能および生分解率に優れているものの、溶解分が多いことがわかる。また、ポリビニルアルコールのみを架橋させた比較例２の吸水性樹脂は、溶解分が少ないものの、吸水能および生分解率が低いことがわかる。
【００４６】
【発明の効果】
本発明によると、吸水能および生分解性に優れ、しかも溶解分が少ない吸水性樹脂およびその製造方法を提供することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a water absorbent resin and a method for producing the same. More specifically, the present invention relates to a water-absorbing resin having excellent water-absorbing ability and biodegradability and having a small amount of dissolved components, and a method for producing the same.
[0002]
[Prior art]
In recent years, water-absorbent resins have been used not only as sanitary materials such as disposable diapers and sanitary products, but also in the medical field such as body fluid absorbing materials; civil engineering such as sealing materials (water blocking materials) and anti-condensation materials; It is used in a wide variety of fields such as food fields such as holding materials; industrial fields such as a dehydrating agent for removing water from a solvent; and agriculture such as tree planting and horticulture. Various water-absorbing resins according to these uses have been proposed. Among them, polyacrylic acid (salt) -based water-absorbing resins are widely used because of their excellent water-absorbing ability and low cost. However, a polyacrylic acid (salt) -based water-absorbing resin has some photodegradability in a water-absorbing state, but has little biodegradability. Therefore, when the polyacrylic acid (salt) -based water-absorbent resin is treated as waste, for example, when it is landfilled, there is a problem that it is hard to be decomposed by bacteria and microorganisms in the soil and causes environmental pollution. .
[0003]
On the other hand, examples of the water-absorbing resin having excellent water-absorbing ability and having biodegradability include, for example, water-absorbing resins obtained by crosslinking polysaccharide itself (JP-A-56-5137, JP-A-58-79006, JP-A-60-58443, JP-A-8-89796), a water-absorbing resin obtained by using a cellulose derivative as a polysaccharide derivative and crosslinking the cellulose derivative (JP-A-49-128987, JP-A-50-85689, JP-A-54-163981, JP-B-55-500785, JP-A-54-28755, JP-A-57-137301, JP-A-58-1701, JP-A-61-89364, JP-A-5-49925, JP-A-5-123573, and JP-A-7-82301) are known.
[0004]
However, the biodegradability of the water-absorbent resin obtained by crosslinking the polysaccharide or the polysaccharide derivative is inferior to that of the raw material polysaccharide or polysaccharide derivative. Further, in order to increase the water absorbing ability of the water-absorbing resin, it is theoretically necessary to reduce the crosslink density, but if the crosslink density is reduced, the uncrosslinked polysaccharide or polysaccharide derivative is dissolved in water, Is high. Therefore, a water-absorbing resin which has excellent water-absorbing ability and biodegradability and has a low solubility in water, and a method for producing the same are desired.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a water-absorbing resin having excellent water-absorbing ability and biodegradability, and having a low dissolved content, and a method for producing the same.
[0006]
[Means for Solving the Problems]
The present inventors have found that a water-absorbing resin obtained by crosslinking a polysaccharide and polyvinyl alcohol with a crosslinking agent has excellent water-absorbing ability and biodegradability, and has a small amount of dissolved components, and has completed the present invention.
That is, the present invention relates to a water-absorbing resin obtained by crosslinking a polysaccharide and polyvinyl alcohol with a crosslinking agent. The present invention also relates to a method for producing a water-absorbent resin, which comprises mixing a polysaccharide, polyvinyl alcohol, and a crosslinking agent and heating the mixture.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
The polysaccharide used in the present invention is not particularly limited, but includes polysaccharides, polysaccharide derivatives, and alkali metal salts such as sodium salts and potassium salts thereof.
Examples of polysaccharides include cellulose, methyl cellulose, ethyl cellulose, methyl ethyl cellulose, hemicellulose, starch, methyl starch, ethyl starch, methyl ethyl starch, agar, carrageenan, alginic acid, pectic acid, guar gum, tamarind gum, locust bean gum, konjac mannan Dextran, xanthan gum, pullulan, gellan gum, chitin, chitosan, chondroitin sulfate, heparin, hyaluronic acid and the like.
[0008]
Examples of polysaccharide derivatives include carboxyalkylated or hydroxyalkylated carboxymethyl cellulose, hydroxyethyl cellulose, starch glycolic acid, agar derivatives, carrageenan derivatives and the like.
In this specification, the polysaccharide also includes a polysaccharide derivative and a metal salt thereof.
[0009]
These polysaccharides, polysaccharide derivatives, and metal salts thereof may be used alone, or two or more kinds may be appropriately mixed. Among them, carboxymethylcellulose and alkali metal salts such as sodium salt and potassium salt thereof are preferably used from the viewpoint of obtaining a water-absorbing resin having high water absorbing ability.
[0010]
The degree of substitution of the alkali metal salt of the polysaccharide and the alkali metal salt of the polysaccharide derivative by the salt is preferably from 0.2 to 1.2, and more preferably from 0.4 to 0.9. If the degree of substitution is less than 0.2, the water-absorbing ability of the resulting water-absorbent resin may be reduced. If the degree of substitution exceeds 1.2, the biodegradability of the resulting water-absorbent resin may be reduced.
[0011]
The weight average molecular weight of the polyvinyl alcohol used in the present invention is not particularly limited, and is preferably 100,000 or less, more preferably 90,000 or less, and further preferably 80,000 to 10,000. If the weight average molecular weight exceeds 100,000, the biodegradability of the resulting water-absorbent resin may be reduced.
[0012]
The saponification degree of the polyvinyl alcohol is not particularly limited, and is preferably 60 to 99.9%, more preferably 80 to 99%. When the saponification degree is less than 60% or more than 99.9%, the water absorbing ability of the resulting water-absorbent resin may be low.
[0013]
The preferred ratio of polyvinyl alcohol is 0.1 to 200 parts by weight, more preferably 1 to 150 parts by weight, and still more preferably 10 to 120 parts by weight, based on 100 parts by weight of the polysaccharide. If the proportion of polyvinyl alcohol is less than 0.1 parts by weight, the resulting water-absorbent resin may have a large amount of dissolved components. If the proportion of polyvinyl alcohol exceeds 200 parts by weight, the water absorbing ability of the resulting water absorbent resin may be reduced.
[0014]
The crosslinking agent used in the present invention is not particularly limited, and examples thereof include dialdehydes, polycarboxylic acids, and epoxy compounds. Among them, dialdehydes and polycarboxylic acids are preferred.
[0015]
Examples of dialdehydes include glyoxal, glutaraldehyde, terephthalaldehyde and the like. Among them, glyoxal and glutaraldehyde are preferably used from the viewpoint of easy availability and low cost.
[0016]
Examples of the polycarboxylic acids include oxalic acid, maleic acid, succinic acid, aspartic acid, polyacrylic acid and the like. Among them, succinic acid is preferably used from the viewpoint of high safety.
[0017]
Epoxy compounds include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol diglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol, γ- Glycidoxypropyltrimethoxysilane and the like can be mentioned.
[0018]
The preferred amount of the crosslinking agent is 0.05 to 50 parts by weight, more preferably 0.1 to 20 parts by weight, and still more preferably 1 to 10 parts by weight, based on 100 parts by weight of the total amount of the polysaccharide and polyvinyl alcohol. is there. If the amount of the crosslinking agent used is less than 0.05 parts by weight, the amount of dissolved water-absorbent resin obtained may increase. When the amount of the cross-linking agent exceeds 50 parts by weight, not only the effect corresponding to the amount used is not obtained, but also the water absorbing ability of the obtained water-absorbing resin may be reduced.
[0019]
The water-absorbent resin of the present invention can be produced by mixing a polysaccharide, polyvinyl alcohol, and a crosslinking agent, heating and crosslinking.
When the polysaccharide and polyvinyl alcohol are cross-linked by a cross-linking agent, it is preferable to mix them uniformly and sufficiently so that a uniform cross-linking reaction is performed. For example, a method of mixing powders, a method of mixing in a slurry state, a method of mixing in a solution state, and the like are exemplified. Among them, a method of mixing in a solution state is preferably used from the viewpoint of more uniform and sufficient mixing.
[0020]
Examples of the solvent used in the mixing method include water and hydrophilic organic solvents such as lower alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol.
[0021]
When a polysaccharide and polyvinyl alcohol are used as a solution, the concentration of the solution is preferably 0.1 to 20% by weight, and more preferably 0.5 to 10% by weight. If the concentration is less than 0.1% by weight, the amount of the solution increases, and a long time of heating is required to remove the solvent, which may lower the production efficiency. On the other hand, when the concentration exceeds 20% by weight, the viscosity of the aqueous solution increases, and it may be difficult to uniformly and sufficiently mix the polysaccharide and polyvinyl alcohol.
[0022]
When the crosslinking agent is used as a solution, the concentration of the solution is preferably 1% by weight to a saturated concentration, more preferably 5% by weight to a saturated concentration. When the concentration is less than 1% by weight, the amount of the solution increases, and a long time of heating is required to remove the solvent, which may lower the production efficiency.
[0023]
The heating temperature at the time of heating and crosslinking is preferably from 60 to 180 ° C, more preferably from 70 to 150 ° C. When the heating temperature is lower than 60 ° C., the crosslinking reaction may not easily proceed. If the heating temperature exceeds 180 ° C., the polysaccharide may be colored, or the crosslinking reaction may proceed too much, resulting in a decrease in water absorption capacity. The heating method is not particularly limited, and examples thereof include a method of irradiating far infrared rays, microwaves, and the like, and a method of using a hot air dryer, a reduced pressure dryer, and the like.
The heating time is not particularly limited, and may be appropriately set according to the type and combination of the polysaccharide, polyvinyl alcohol, the crosslinking agent, and the solvent, the heating temperature, and the desired physical properties of the water-absorbing resin. , About 1 to 20 hours.
[0024]
In the present invention, a crosslinking reaction may be carried out by adding a catalyst, if necessary, to allow the crosslinking reaction to proceed smoothly. As the catalyst, acids such as sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid are suitably used.
The use amount of the catalyst is preferably 1 to 200 parts by weight based on 100 parts by weight of the crosslinking agent. If the amount of the catalyst used is less than 1 part by weight, the reaction may not easily proceed. On the other hand, if the amount of the catalyst exceeds 200 parts by weight, there is no effect corresponding to the amount of the catalyst and it is not economical.
[0025]
In the method for producing a water-absorbent resin of the present invention, for example, each of a polysaccharide, polyvinyl alcohol, and a crosslinking agent is used as an aqueous solution. Mix. The obtained aqueous solution is heated to remove the water from the aqueous solution and dried while the crosslinking reaction proceeds to obtain a dried product. A water-absorbent resin can be produced by pulverizing the obtained dried product.
[0026]
The water-absorbing resin thus obtained has a water-absorbing ability for physiological saline of 10 g / g or more, preferably 15 to 80 g / g. If the water absorbing ability is less than 10 g / g, the amount of the water absorbing resin used is undesirably increased. The water-absorbing ability in the present invention refers to a water-absorbent resin obtained by putting 1 g of a water-absorbent resin in 200 ml of 0.9% by weight saline solution, sufficiently swelling, and then filtering the water-absorbent resin through a 200-mesh wire net. Is a value calculated by the following equation when the weight A (g) is measured.
Water absorption capacity (g / g) = A / 1
[0027]
The dissolved amount of the water-absorbent resin of the present invention in physiological saline is 30% or less, preferably 25% or less. If the dissolved content exceeds 30%, the water absorption capacity is undesirably reduced. In the present invention, 1 g of the water-absorbent resin was placed in 250 ml of 0.9% by weight saline solution, stirred for 3 hours with a stirrer, and then filtered through a 200-mesh wire gauze. It is a value calculated by the following equation when accurately measuring in a beaker of a known weight A (g) previously dried and measuring the weight B (g) after drying at 140 ° C. for 16 hours.
Dissolution (%) = [(BA) /50×250-250×0.009] × 100
[0028]
Furthermore, the biodegradability of the water-absorbent resin of the present invention is 15% or more, preferably 20% or more. When the biodegradation rate is less than 15%, the biodegradability is poor, and there is a possibility of causing problems such as environmental pollution. In addition, the biodegradation rate in the present invention is based on JIS K 6951 and is based on 8.5 g of anhydrous potassium dihydrogen phosphate, 21.75 g of anhydrous dipotassium hydrogen phosphate, and 33.4 g of disodium hydrogen phosphate dihydrate. Then, 80 mg of a water-absorbent resin was added to 400 ml of a standard test culture solution prepared by dissolving 0.5 g of ammonium chloride in distilled water to 1000 ml, and then the culture solution to which standard activated sludge was added to be 30 ppm was stirred with a stirrer. Meanwhile, the total amount A (mg) of carbon dioxide generated when cultured at 25 ° C. for 28 days was determined, and the total amount B (mg) of carbon dioxide generated from a culture solution to which no water-absorbing resin was added was determined in the same manner. When the calculated value C (mg) of the amount of carbon dioxide generated when the water-absorbent resin is completely decomposed is calculated, the value is calculated by the following equation.
Biodegradation rate (%) = (AB) / C × 100
[0029]
In the water-absorbent resin of the present invention, in order to improve processability and quality performance, if necessary, inorganic fine particles such as silica fine particles, a filler composed of pulp fiber and the like, activated carbon and iron phthalocyanine derivative, vegetable Deodorant mainly composed of zeolite or the like to which essential oil is adsorbed, fragrance, antibacterial agent mainly composed of metals such as silver, copper, zinc, etc., bactericide, fungicide, preservative, deoxidizer (oxidation Additives such as a surfactant, a surfactant, a foaming agent, and a fragrance. The amount of the additive is not generally determined by the type of the additive, but is usually about 0.01 to 5 parts by weight based on 100 parts by weight of the water-absorbing resin.
[0030]
The water-absorbent resin of the present invention is used not only in the field of hygiene such as sanitary materials such as disposable diapers and sanitary products, but also in the medical field such as body fluid absorbing materials during surgical operations and wound protection materials; sealing materials during shield method, concrete curing, etc. Materials, gel blisters, anti-condensation materials, etc .; civil engineering and construction fields; drip absorbing materials such as meat and fish, and freshness preserving materials such as vegetables, vegetables and other freshness preserving materials; dehydrating materials that remove water from solvents, etc. Industrial field; Agricultural and horticultural fields, such as soil water retention materials for planting trees, water retention materials for plant cultivation, seed coating materials, etc., as well as oil / water separation materials, waste liquid absorbents, vibration damping materials, soundproofing materials, household use It can be used in a wide variety of fields such as miscellaneous goods, toys, artificial snow, and the like.
[0031]
【Example】
Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to only these Examples.
[0032]
(Example 1)
400 g of a 5% by weight aqueous solution of carboxymethylcellulose (manufactured by Aldrich, substitution degree 0.7) and 100 g of a 5% by weight aqueous solution of polyvinyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight: 44000, saponification degree: 88%) were heated to 80 ° C. For 5 hours to mix. Next, 5 g of a 40% by weight glyoxal aqueous solution and 0.25 g of concentrated sulfuric acid were added, followed by sufficient stirring and mixing. The obtained mixture was allowed to stand in a hot-air drier set at 100 ° C. for 7 hours, and water was removed from the mixture and dried while the crosslinking reaction proceeded. The obtained dried product was pulverized using a mixer to obtain 24.5 g of a water absorbent resin.
[0033]
(Example 2)
In Example 1, 23.8 g of a water-absorbent resin was obtained in the same manner as in Example 1, except that the standing time in the hot air dryer was changed from 7 hours to 10 hours.
[0034]
(Example 3)
In Example 1, 23.4 g of a water-absorbent resin was obtained in the same manner as in Example 1 except that the set temperature of the hot air dryer was changed from 100 ° C to 140 ° C.
[0035]
(Example 4)
In Example 1, 24.4 g of a water-absorbent resin was obtained in the same manner as in Example 1 except that glyoxal was changed to glutaraldehyde.
[0036]
(Example 5)
In Example 1, 24.4 g of a water-absorbent resin was obtained in the same manner as in Example 1, except that succinic acid was used instead of glyoxal.
[0037]
(Example 6)
In Example 1, 24.2 g of a water-absorbent resin was obtained in the same manner as in Example 1 except that the amounts of the 5% by weight aqueous solution of carboxymethyl cellulose and the 5% by weight aqueous solution of polyvinyl alcohol were changed to 250 g, respectively.
[0038]
(Comparative Example 1)
500 g of a 5% by weight aqueous solution of carboxymethylcellulose (manufactured by Aldrich, substitution degree 0.7), 5 g of a 40% by weight glyoxal aqueous solution, and 0.25 g of concentrated sulfuric acid were stirred and mixed. The obtained mixture was allowed to stand in a hot-air drier set at 100 ° C. for 7 hours, and water was removed from the mixture and dried while the crosslinking reaction proceeded. The obtained dried product was pulverized using a mixer to obtain 24.3 g of a water absorbent resin.
[0039]
(Comparative Example 2)
500 g of a 5% by weight aqueous solution of polyvinyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight: 44000, saponification degree: 88%), 5 g of a 40% by weight glyoxal aqueous solution, and 0.25 g of concentrated sulfuric acid were mixed by stirring. The obtained mixture was allowed to stand in a hot-air drier set at 100 ° C. for 7 hours, and water was removed from the mixture and dried while the crosslinking reaction proceeded. The obtained dried product was pulverized using a mixer to obtain 24.1 g of a water absorbent resin.
[0040]
The physical properties of the water-absorbing resins obtained in each of the examples and comparative examples were measured by the following methods. The results are shown in Table 1.
[0041]
(1) Water absorption capacity (g / g)
1 g of the water-absorbing resin was placed in 200 ml of 0.9% by weight saline solution and sufficiently swelled. Next, the water-absorbing resin was filtered off with a 200-mesh wire net. The weight A (g) of the obtained water-absorbent resin was measured, and the water absorption capacity (g / g) was calculated by the following equation.
Water absorption capacity (g / g) = A / 1
[0042]
(2) 1 g of the water-absorbent resin for the dissolved component was placed in 250 ml of 0.9% by weight saline solution, and stirred for 3 hours with a stirrer. Then, the mixture was filtered through a 200-mesh wire net, and the filtrate was recovered. 50 ml of the collected filtrate was accurately measured in a beaker of a known weight A (g) which had been dried in advance, and the weight B (g) after drying at 140 ° C. for 16 hours was measured. .
Dissolution (%) = [(BA) /50×250-250×0.009] × 100
[0043]
(3) Biodegradation rate According to JIS K 6951, 8.5 g of anhydrous potassium dihydrogen phosphate, 21.75 g of anhydrous dipotassium hydrogen phosphate, 33.4 g of disodium hydrogen phosphate dihydrate, and 0.3% of ammonium chloride were used. 80 mg of a water-absorbent resin was added to 400 ml of a standard test culture solution in which 5 g was dissolved in distilled water to make 1000 ml, and then standard activated sludge (manufactured by Chemicals Evaluation and Research Institute) was added to 30 ppm. . This culture was cultured at 25 ° C. for 28 days while stirring with a stirrer. The amount of carbon dioxide generated during the period was measured periodically, and the total amount A (mg) of generated carbon dioxide was determined. In addition, the total amount B (mg) of carbon dioxide generated from the culture solution to which no water-absorbing resin was added was similarly obtained. Further, from the calculated value C (mg) of the amount of carbon dioxide generated when the water-absorbent resin was completely decomposed, the biodegradation rate (%) was calculated by the following equation.
Biodegradation rate (%) = (AB) / C × 100
[0044]
[Table 1]

[0045]
Table 1 shows that the water-absorbent resins of Examples 1 to 6 are excellent in water-absorbing ability and biodegradability, and have a small amount of dissolved components. In contrast, the water-absorbent resin of Comparative Example 1 in which only the polysaccharide was crosslinked was excellent in the water-absorbing ability and the biodegradability, but had a large amount of dissolved components. Further, it can be seen that the water-absorbing resin of Comparative Example 2 in which only polyvinyl alcohol was crosslinked had a low water-absorbing ability and a low biodegradation rate, though the amount of dissolved components was small.
[0046]
【The invention's effect】
According to the present invention, it is possible to provide a water-absorbing resin which is excellent in water-absorbing ability and biodegradability and has a small amount of dissolved components, and a method for producing the same.

Claims (7)

A water-absorbent resin obtained by crosslinking a polysaccharide and polyvinyl alcohol with a crosslinking agent. The water-absorbent resin according to claim 1, wherein the water-absorbent resin has a water-absorbing capacity of 10 g / g or more in physiological saline, a dissolved content in physiological saline of 30% or less, and a biodegradability of 15% or more. The water-absorbent resin according to claim 1 or 2, wherein the ratio of the polyvinyl alcohol is 0.1 to 200 parts by weight based on 100 parts by weight of the polysaccharide. The water-absorbent resin according to any one of claims 1 to 3, wherein the amount of the crosslinking agent used is 0.05 to 50 parts by weight based on 100 parts by weight of the total amount of the polysaccharide and polyvinyl alcohol. The water-absorbing resin according to any one of claims 1 to 4, wherein the crosslinking agent is a dialdehyde or a polycarboxylic acid. The water-absorbing resin according to any one of claims 1 to 5, wherein the polysaccharide is carboxymethyl cellulose. A method for producing a water-absorbent resin, comprising mixing a polysaccharide, polyvinyl alcohol, and a crosslinking agent and heating the mixture.