JP4132993B2 - Water absorbent resin and method for producing the same - Google Patents

Description

【００４５】
表１より、実施例１、参考例１〜５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]
BACKGROUND 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-absorbent resin excellent in water-absorbing ability and biodegradability and having a low dissolved content, and a method for producing the same.
[0002]
[Prior art]
In recent years, water-absorbing resins have been used not only as sanitary materials such as paper diapers and sanitary products, but also in the medical field such as body fluid absorbing materials; civil engineering such as sealing materials (water-stopping 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 dehydrating agents that remove water from solvents; agriculture and horticultural fields such as greening. Various water-absorbing resins according to these uses have been proposed. Among them, polyacrylic acid (salt) -based water-absorbing resins are widely used because they are excellent in water-absorbing ability and inexpensive. However, the polyacrylic acid (salt) water-absorbing resin has little photodegradability in the water-absorbing state, but hardly has biodegradability. Therefore, when polyacrylic acid (salt) water-absorbing resin is treated as waste, for example, when landfill disposal is performed, there is a problem that it is difficult 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 biodegradability include, for example, water-absorbing resins obtained by crosslinking polysaccharides (Japanese Patent Laid-Open Nos. 56-5137 and 58-79006, JP-A-60-58443, JP-A-8-89796), a water-absorbent resin obtained by crosslinking a cellulose derivative using a cellulose derivative as a polysaccharide derivative (JP-A-49-128987, JP-A-5-89987). No. 50-85689, JP-A No. 54-163981, JP-B No. 55-5000785, JP-A No. 54-28755, JP-A No. 57-137301, JP-A No. 58-1701, JP-A-61-89364, JP-A-5-49925, JP-A-5-123573, JP-A-7-82301) and the like are known.
[0004]
However, the biodegradability of a water-absorbent resin obtained by crosslinking a polysaccharide or polysaccharide derivative is inferior to that of a polysaccharide or polysaccharide derivative that is a raw material. Furthermore, in order to increase the water absorption capacity of the water-absorbent resin, it is theoretically necessary to reduce the crosslinking density. However, if the crosslinking density is reduced, the uncrosslinked polysaccharide or polysaccharide derivative dissolves in water, There is a problem that becomes high. Therefore, a water-absorbing resin excellent in water-absorbing ability and biodegradability and having a low water-soluble content 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-absorbent resin excellent in 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-absorbent resin obtained by cross-linking polysaccharide and polyvinyl alcohol with a cross-linking agent is excellent in water-absorbing ability and biodegradability, and has a small amount of dissolution, thereby completing the present invention.
That is, the present invention relates to a water-absorbent resin obtained by crosslinking polysaccharide and polyvinyl alcohol with a crosslinking agent. Moreover, this invention relates to the manufacturing method of the water absorbing resin characterized by mixing polysaccharides, polyvinyl alcohol, and a crosslinking agent, and heating.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The polysaccharide used in the present invention is not particularly limited, and examples thereof include polysaccharides, polysaccharide derivatives, and alkali metal salts such as sodium salts and potassium salts thereof.
Examples of the polysaccharide include cellulose, methylcellulose, ethylcellulose, methylethylcellulose, hemicellulose, starch, methyl starch, ethyl starch, methylethyl 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 the polysaccharide derivative include carboxymethyl cellulose, hydroxyethyl cellulose, starch glycolic acid, agar derivative, and carrageenan derivative obtained by carboxyalkylating or hydroxyalkylating the polysaccharide.
In the present specification, the polysaccharide includes polysaccharide derivatives and metal salts thereof.
[0009]
These polysaccharides, polysaccharide derivatives and their metal salts may be used alone or in combination of two or more. Among these, 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 absorption ability.
[0010]
The degree of substitution with the alkali metal salt of the polysaccharide and the alkali metal salt of the polysaccharide derivative is 0.2 to 1.2, preferably 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. Moreover, when a substitution degree exceeds 1.2, there exists a possibility that the biodegradation rate of the water absorbent resin obtained may fall.
[0011]
The weight average molecular weight of the polyvinyl alcohol used for this invention is not specifically limited, Preferably it is 100,000 or less, More preferably, it is 90000 or less, More preferably, it is 80000-10000. When a weight average molecular weight exceeds 100,000, there exists a possibility that the biodegradability of the water absorbent resin obtained may fall.
[0012]
The saponification degree of polyvinyl alcohol is not particularly limited, and is preferably 60 to 99.9%, more preferably 80 to 99%. If the degree of saponification is less than 60% or exceeds 99.9%, the water-absorbing capacity of the resulting water-absorbent resin may be lowered.
[0013]
A preferred ratio of the 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 with respect to 100 parts by weight of the polysaccharide. When the ratio of polyvinyl alcohol is less than 0.1 part by weight, there is a possibility that the amount of the water-absorbing resin to be obtained increases. Moreover, when the ratio of polyvinyl alcohol exceeds 200 weight part, there exists a possibility that the water absorption ability of the water-absorbing resin obtained may fall.
[0014]
Although it does not specifically limit as a crosslinking agent used for this invention, Dialdehydes, polyhydric carboxylic acids, an epoxy compound, etc. are mentioned. Of these, dialdehydes and polycarboxylic acids are preferred.
[0015]
Examples of dialdehydes include glyoxal, glutaraldehyde, terephthalaldehyde, and the like. Among these, glyoxal and glutaraldehyde are preferably used from the viewpoint of easy availability and low cost.
[0016]
Examples of polyvalent carboxylic acids include oxalic acid, maleic acid, succinic acid, aspartic acid, polyacrylic acid, and the like. Among these, succinic acid is preferably used from the viewpoint of high safety.
[0017]
As epoxy compounds, 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- Examples thereof include glycidoxypropyltrimethoxysilane.
[0018]
The preferred use amount of the crosslinking agent is 0.05 to 50 parts by weight, more preferably 0.1 to 20 parts by weight, and even more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the total amount of polysaccharide and polyvinyl alcohol. is there. When the usage-amount of a crosslinking agent is less than 0.05 weight part, there exists a possibility that the melt | dissolution content of the water-absorbing resin obtained may increase. Moreover, when the usage-amount of a crosslinking agent exceeds 50 weight part, the effect corresponding to the usage-amount will not be acquired, but there exists a possibility that the water absorption ability of the water-absorbing resin obtained may fall.
[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 the cross-linking agent, it is preferable to mix uniformly and sufficiently so that a uniform cross-linking reaction is performed. Examples thereof include a method of mixing powders, a method of mixing in a slurry state, a method of mixing in a solution state, and the like. Especially, the method of mixing in a solution state is used suitably from a viewpoint which can mix more uniformly and fully.
[0020]
Examples of the solvent used in the mixing method include water or hydrophilic organic solvents such as lower alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol.
[0021]
When making polysaccharide and polyvinyl alcohol into a solution, it is preferable that the density | concentration of the solution is 0.1 to 20 weight%, More preferably, it is 0.5 to 10 weight%. When the concentration is less than 0.1% by weight, the amount of the solution increases, and it takes a long time to remove the solvent, which may reduce the production efficiency. Moreover, when a density | concentration exceeds 20 weight%, there exists a possibility that the viscosity of aqueous solution may become high and it may become difficult to mix polysaccharide and polyvinyl alcohol uniformly and fully.
[0022]
Moreover, when making a crosslinking agent into a solution, it is preferable that the density | concentration of the solution is 1 weight%-saturation concentration, More preferably, it is 5 weight%-saturation concentration. When the concentration is less than 1% by weight, the amount of the solution increases, and it takes a long time to remove the solvent, which may reduce the production efficiency.
[0023]
The heating temperature at the time of crosslinking by heating is preferably 60 to 180 ° C, more preferably 70 to 150 ° C. When heating temperature is less than 60 degreeC, there exists a possibility that a crosslinking reaction may become difficult to advance. Moreover, when heating temperature exceeds 180 degreeC, there exists a possibility that polysaccharide may color or a crosslinking reaction may advance too much and water absorption ability may fall. The heating method is not particularly limited, and examples thereof include a method of irradiating far infrared rays, microwaves, and the like, a method using a hot air dryer, a vacuum dryer, and the like.
The heating time is not particularly limited, and may be appropriately set according to the type and combination of polysaccharide, polyvinyl alcohol, crosslinking agent, and solvent, the heating temperature, and the desired physical properties of the water-absorbent resin. 1 to 20 hours.
[0024]
In the present invention, if necessary, a crosslinking reaction may be performed by adding a catalyst in order to smoothly advance the crosslinking reaction. As the catalyst, acids such as sulfuric acid, hydrochloric acid, phosphoric acid and nitric acid are preferably used.
It is preferable that the usage-amount of a catalyst is 1-200 weight part with respect to 100 weight part of crosslinking agents. When the usage-amount of a catalyst is less than 1 weight part, there exists a possibility that reaction may become difficult to advance. Moreover, when the usage-amount of a catalyst exceeds 200 weight part, there is no effect corresponding to a usage-amount and it is not economical.
[0025]
In the method for producing the water-absorbent resin of the present invention, for example, each of polysaccharide, polyvinyl alcohol, and crosslinking agent is used as an aqueous solution, and after the polysaccharide and polyvinyl alcohol aqueous solution are mixed in advance, the aqueous solution of the crosslinking agent is added again. Mix. The resulting aqueous solution is heated to remove the water from the aqueous solution while allowing the crosslinking reaction to proceed, and then dried to obtain a dried product. The water-absorbing resin can be produced by pulverizing the obtained dried product.
[0026]
The water-absorbent resin thus obtained has a water absorption capacity of 10 g / g or more, preferably 15 to 80 g / g, with respect to physiological saline. When the water absorption capacity is less than 10 g / g, the amount of water-absorbing resin used is increased, which is not preferable. The water absorption capacity in the present invention refers to a water absorbent resin obtained by placing 1 g of a water absorbent resin in 200 ml of 0.9% by weight saline, sufficiently swelled, and then filtering the water absorbent resin with a 200 mesh wire mesh. When the weight A (g) is measured, it is a value calculated by the following equation.
Water absorption capacity (g / g) = A / 1
[0027]
Moreover, the soluble part with respect to the physiological saline of the water absorbing resin of this invention is 30% or less, Preferably it is 25% or less. If the dissolved content exceeds 30%, the water absorption capacity is lowered, which is not preferable. The dissolved content in the present invention means that 1 g of water-absorbing resin is placed in 250 ml of 0.9 wt% saline, stirred with a stirrer for 3 hours, then filtered through a 200-mesh wire mesh, and 50 ml of the collected filtrate is used. It is a value calculated by the following equation when the weight B (g) after accurately measuring in a beaker of known weight A (g) dried in advance and drying at 140 ° C. for 16 hours is measured.
Dissolved content (%) = [(B−A) /50×250−250×0.009] × 100
[0028]
Furthermore, the biodegradation rate 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 inferior and there is a risk of causing problems such as environmental pollution. The biodegradation rate in the present invention is based on 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. Then, 80 mg of water-absorbent resin was added to 400 ml of 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 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 obtained, while the total amount B (mg) of carbon dioxide generated from the culture solution to which no water-absorbent resin was added was similarly determined. Further, when the calculated value C (mg) of the amount of carbon dioxide generated when the water-absorbent resin is completely decomposed is obtained, it is a value calculated by the following equation.
Biodegradation rate (%) = (A−B) / C × 100
[0029]
In order to improve processability and quality performance, the water-absorbent resin of the present invention includes inorganic fine particles such as silica fine particles, fillers made of pulp fibers, etc., activated carbon, iron phthalocyanine derivatives, vegetable properties, as necessary. Deodorant mainly composed of zeolite adsorbed with essential oil, etc., fragrance, antibacterial agent mainly composed of metals such as silver, copper and zinc, bactericidal agent, antifungal agent, antiseptic agent, oxygen scavenger (oxidation) An additive such as an inhibitor), a surfactant, a foaming agent, and a fragrance may be added. The addition amount of the additive is not generally determined depending on the type of the additive, but is usually about 0.01 to 5 parts by weight with respect to 100 parts by weight of the water absorbent resin.
[0030]
The water-absorbent resin of the present invention is not only used in the hygiene field such as sanitary materials such as paper diapers and sanitary products, but also in the medical field such as body fluid absorbing materials and wound protection materials during surgical operations; sealing materials during shield construction, concrete curing Civil engineering and construction fields such as wood, gel water sacs, anti-condensation materials; food fields such as drip absorbent materials such as meat and fish, freshness preservation materials, freshness preservation materials such as vegetables, etc .; dehydration materials that remove water from solvents Industrial field: Agricultural and horticultural fields such as soil water retention material, plant cultivation water retention material, seed coating material, etc. for greening, oil / water separation material, waste liquid absorbent, vibration proofing material, soundproofing material, household use It can be used in a wide variety of fields such as general goods, toys, and artificial snow.
[0031]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, this invention is not limited only to these Examples.
[0032]
( Reference Example 1)
400 g of a 5 wt% aqueous solution of carboxymethylcellulose (Aldrich, substitution degree 0.7) and 100 g of a 5 wt% aqueous solution of polyvinyl alcohol (Wako Pure Chemical Industries, Ltd., molecular weight 44000, saponification degree 88%) at 80 ° C. And stirred for 5 hours. Next, 5 g of a 40 wt% aqueous glyoxal solution and 0.25 g of concentrated sulfuric acid were added, and the mixture was further stirred and mixed. The obtained mixed solution was allowed to stand in a hot air drier set at 100 ° C. for 7 hours, and water was removed from the mixed solution 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]
( Reference Example 2)
In Reference Example 1, 23.8 g of a water-absorbent resin was obtained in the same manner as in Reference Example 1, except that the standing time in the hot air dryer was changed from 7 hours to 10 hours.
[0034]
( Reference Example 3)
In Reference Example 1, 23.4 g of a water-absorbent resin was obtained in the same manner as in Reference Example 1 except that the set temperature of the hot air dryer was changed from 100 ° C to 140 ° C.
[0035]
( Reference Example 4)
In Reference Example 1, 24.4 g of a water-absorbent resin was obtained in the same manner as in Reference Example 1 except that glyoxal was changed to glutaraldehyde.
[0036]
(Example 1 )
In Reference Example 1, 24.4 g of a water-absorbent resin was obtained in the same manner as in Reference Example 1, except that glyoxal was changed to succinic acid.
[0037]
( Reference Example 5 )
In Reference Example 1, 24.2 g of a water-absorbent resin was obtained in the same manner as in Reference Example 1 except that the amounts of a 5% by weight aqueous solution of carboxymethyl cellulose and a 5% by weight aqueous solution of polyvinyl alcohol were changed to 250 g.
[0038]
(Comparative Example 1)
500 g of a 5 wt% aqueous solution of carboxymethylcellulose (Aldrich, substitution degree 0.7), 5 g of 40 wt% glyoxal aqueous solution, and 0.25 g of concentrated sulfuric acid were mixed with stirring. The obtained mixed solution was allowed to stand in a hot air drier set at 100 ° C. for 7 hours, and water was removed from the mixed solution 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 5 wt% aqueous solution of polyvinyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight 44000, saponification degree 88%), 5 g of 40 wt% glyoxal aqueous solution, and 0.25 g of concentrated sulfuric acid were mixed with stirring. The obtained mixed solution was allowed to stand in a hot air drier set at 100 ° C. for 7 hours, and water was removed from the mixed solution 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 property values of the water-absorbing resins obtained in each Example and Comparative Example 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-absorbent resin was placed in 200 ml of 0.9% by weight saline and sufficiently swollen. Next, the water-absorbent resin was filtered off with a 200-mesh wire mesh. The weight A (g) of the obtained water-absorbing resin was measured, and the water absorption capacity (g / g) was calculated according to the following formula.
Water absorption capacity (g / g) = A / 1
[0042]
(2) 1 g of the dissolved water-absorbing resin was placed in 250 ml of 0.9 wt% saline and stirred with a stirrer for 3 hours. Next, the mixture was filtered through a 200 mesh wire net, and the filtrate was recovered. The recovered filtrate (50 ml) was accurately measured in a beaker with a known weight (A) (g) that had been dried in advance, and the weight B (g) after drying at 140 ° C. for 16 hours was measured. .
Dissolved content (%) = [(B−A) /50×250−250×0.009] × 100
[0043]
(3) Biodegradation rate In accordance with JIS K 6951, anhydrous potassium dihydrogen phosphate 8.5 g, anhydrous dipotassium hydrogen phosphate 21.75 g, disodium hydrogen phosphate dihydrate 33.4 g, ammonium chloride 0.8. 80 mg of a water-absorbing resin was added to 400 ml of a standard test culture solution prepared by dissolving 5 g in distilled water to 1000 ml, and then added so that standard activated sludge (manufactured by Chemicals Evaluation and Research Institute) was 30 ppm. . This culture solution was cultured at 25 ° C. for 28 days while stirring with a stirrer. The amount of carbon dioxide generated during the period was periodically measured to determine the total amount A (mg) of carbon dioxide generated. Further, the total amount B (mg) of carbon dioxide generated from the culture solution to which no water-absorbent resin was added was determined in the same manner. Furthermore, 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 (%) = (A−B) / C × 100
[0044]
[Table 1]

[0045]
From Table 1, it can be seen that the water-absorbent resins of Example 1 and Reference Examples 1 to 5 are excellent in water-absorbing ability and biodegradability and have a small amount of dissolution. In contrast, it can be seen that the water-absorbent resin of Comparative Example 1 in which only polysaccharides are cross-linked is excellent in water-absorbing ability and biodegradability but has a large amount of dissolution. Moreover, although the water absorbing resin of the comparative example 2 which bridge | crosslinked only polyvinyl alcohol has few melt | dissolution contents, it turns out that water absorption ability and a biodegradation rate are low.
[0046]
【The invention's effect】
According to the present invention, it is possible to provide a water-absorbent resin excellent in water absorption ability and biodegradability and having a low dissolved content, and a method for producing the same.

Claims (5)

A water-absorbent resin obtained by crosslinking polysaccharide and polyvinyl alcohol with polyvalent carboxylic acids . The water-absorbent resin according to claim 1, wherein the ratio of polyvinyl alcohol is 0.1 to 200 parts by weight with respect to 100 parts by weight of the polysaccharide. The water-absorbent resin according to claim 1 or 2 , wherein the polycarboxylic acid is used in an amount of 0.05 to 50 parts by weight with respect to 100 parts by weight of the total amount of polysaccharide and polyvinyl alcohol. The water absorbent resin according to any one of claims 1 to 3 , wherein the polysaccharide is carboxymethylcellulose. A method for producing a water-absorbent resin, comprising mixing a polysaccharide, polyvinyl alcohol, and polyvalent carboxylic acids and heating the mixture.