JP2008280429A - Highly water-absorptive resin and its preparation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly water-absorptive resin being excellent in biodegradability and saline- and seawater-absorption capacities, and its preparation method. <P>SOLUTION: The highly water-absorptive resin satisfies the following conditions: (1) the cellulose or cellulose derivative content is ≥50 wt.%; (2) the polymerization degree of the cellulose or the cellulose derivative is 80-1,800; (3) the saline- and seawater-absorbing capacities are ≥50 g/g and ≥30 g/g, respectively. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a superabsorbent resin and a method for producing the same. More specifically, the present invention relates to a physiological saline that can be effectively used as an activated sludge treatment agent, a soil water retention agent, a garbage disposal aid, a superabsorbent resin excellent in water absorption performance and biodegradability for seawater, and a method for producing the same.

  Superabsorbent resins are used in sanitary materials such as paper diapers and sanitary products, medical fields such as poultices and body fluid absorbents, agricultural and horticultural fields such as activated sludge treatment agents and soil water retention agents, and food fields such as freshness retaining materials. It is used in a wide variety of fields such as civil engineering and construction fields such as sealing materials and anti-condensation materials, and other fields such as electrical and electronic materials and paints and adhesives. In particular, in recent years, there has been an increasing need for activated sludge treatment agents, soil water retention agents, and garbage disposal aids due to the use of large amounts of energy in activated sludge treatment, desertification by deforestation, and waste disposal. ing.

In order to use it as an activated sludge treatment agent, soil water retention agent, and garbage disposal aid, it is necessary to have a high water absorption performance with respect to a high salt concentration aqueous solution. Although the water absorption performance in pure water is excellent, the water absorption performance decreases at a stretch as the salt concentration in water increases. Furthermore, polyacrylic acid-based superabsorbent resins do not have biodegradability. Therefore, the polyacrylic acid-based superabsorbent resin cannot be used as an activated sludge treatment agent, a soil water retention agent, or a garbage disposal aid.
On the other hand, Patent Document 1 discloses a mixed cross-linked product of carboxymethyl cellulose and polyvinyl alcohol as a highly water-absorbing resin with improved biodegradability. However, the water absorption performance of the mixed crosslinked body with respect to physiological saline is about 20 g / g, and the problem of low water absorption performance with respect to an aqueous solution having a high salt concentration has not been improved.

JP 2004-10634 A

  The present invention provides a physiological saline that can be effectively used as an activated sludge treatment agent, a soil water retention agent, and a garbage disposal aid, a superabsorbent resin excellent in water absorption performance and biodegradability for seawater, and a method for producing the same. It is in.

The inventors of the present invention have made extensive studies to solve the above problems, and as a result, have found that a superabsorbent resin satisfying specific requirements can solve the above problems, and have completed the present invention.
That is, the present invention is a superabsorbent resin characterized by satisfying the following requirements (1) to (3).
(1) The content of cellulose or cellulose derivative is 50 wt% or more.
(2) The degree of polymerization of the cellulose or cellulose derivative is 80 to 1800.
(3) The water absorption with respect to physiological saline is 50 g / g or more, and the water absorption with respect to seawater is 30 g / g or more.

  ADVANTAGE OF THE INVENTION By this invention, the water absorbing resin excellent in the water absorption performance with respect to physiological saline and seawater, and biodegradability, and its manufacturing method can be provided.

The superabsorbent resin of the present invention needs to have a cellulose or cellulose derivative content of 50 wt% or more, preferably 70 wt% or more. When the content of cellulose or cellulose derivative is less than 50 wt%, the water absorption performance is lowered.
The superabsorbent resin of the present invention is required to have a water absorption performance of 50 g / g or more for physiological saline and a water absorption performance of 30 g / g or more for seawater. When the water absorption performance with respect to physiological saline is less than 50 g / g and the water absorption performance with respect to seawater is less than 30 g / g, for example, when used as an activated sludge treatment agent, a high water absorption of 20 wt% or more with respect to the activated sludge dry weight. When the activated sludge is used as a soil conditioner, the effect cannot be expressed. It is also disadvantageous in terms of cost.
The water-absorbing performance of the superabsorbent resin with respect to physiological saline and seawater is preferably 100 g / g or more with respect to physiological saline and 80 g / g or more with respect to seawater, from the viewpoint of suppressing the amount of superabsorbent resin used. . Although there is no upper limit in particular in the water absorption performance with respect to physiological saline and seawater, both are preferably 2000 g / g or less from the viewpoint of maintaining the water absorption gel strength.

  The cellulose used in the present invention is not particularly limited, and examples thereof include pulp, purified cellulose, cellulose derivatives, alkali metal salts such as sodium salts and potassium salts, ammonium salts, and the like. Examples of the cellulose derivative include cellulose derivatives having an acidic group such as carboxymethyl cellulose, cellulose sulfate, and cellulose phosphate; hydroxyalkylated cellulose derivatives such as hydroxyethyl cellulose and hydroxypropyl cellulose; alkyls such as methyl cellulose, ethyl cellulose, and methyl ethyl cellulose. The cellulose derivative which was made into is mentioned.

  These celluloses or cellulose derivatives may be used alone or in combination of two or more. Moreover, if content of a cellulose and a cellulose derivative is 50 wt% or more, you may mix biodegradable polymers, such as polyvinyl alcohol, for example. Among the cellulose derivatives, carboxymethyl cellulose and alkali metal salts such as sodium salt and potassium salt thereof and ammonium salts are preferable from the viewpoint of obtaining high water absorption performance.

The degree of substitution of the cellulose derivative is in the range of 0.2 to 1.5, preferably in the range of 0.4 to 1.0. When the degree of substitution is less than 0.2, the water-absorbing performance of the resulting highly water-absorbent resin is lowered. Moreover, when substitution degree exceeds 1.5, the fall of the biodegradation rate of the superabsorbent resin obtained and the fall of crosslinking efficiency will arise.
The degree of polymerization of the cellulose or cellulose derivative is in the range of 80-1800. When the polymerization degree of cellulose or a cellulose derivative is less than 80, the water absorbing performance of the resulting superabsorbent resin is lowered. On the other hand, when the degree of polymerization exceeds 1800, the dissolution efficiency is lowered due to an increase in the solution viscosity of the cellulose derivative, resulting in non-uniform cross-linking reaction and reduced water absorption performance. Preferably it is the range of 150-1500, More preferably, it is the range of 300-1000.

The biodegradation rate of the superabsorbent resin of the present invention is preferably 15% or more. If it is less than 15%, soil may be contaminated during landfill by waste disposal.
Furthermore, the amount of the superabsorbent resin of the present invention dissolved in physiological saline and seawater is preferably 30% or less. When the dissolved amount exceeds 30%, sufficient gel strength and stability cannot be maintained.
The superabsorbent resin of the present invention can be produced by mixing cellulose or a cellulose derivative and a crosslinking agent. Examples of the mixing method include a method of mixing in a powder state, a method of mixing in a slurry state, a method of mixing in a solution state, and the like. From the viewpoint of uniform crosslinking, a method of mixing in a solution state is preferable.

The solvent used in the method of mixing in the solution state includes water.
When making a cellulose derivative into a uniform solution, the density | concentration of the solution is 0.1-20 wt%, Preferably it is 1-10 wt%. When the concentration is less than 0.1 wt%, the production efficiency is lowered due to an increase in the amount of the solution and a decrease in the crosslinking efficiency with the crosslinking agent. On the other hand, when the concentration exceeds 20 wt%, the solution viscosity becomes high, and it becomes difficult to mix uniformly and sufficiently.

In the present invention, at least one crosslinking agent selected from the group of divinyl sulfone, epichlorohydrin, and polyfunctional epoxy compounds is used.
Examples of the polyfunctional epoxy compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol diglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythric ether. Examples include tall diglycidyl ether, trimethylolpropane polyglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether. From the viewpoints of high water solubility, water absorption performance, and gel strength, divinyl sulfone and ethylene glycol diglycidyl ether, glycerol polyglycidyl ether, and polyglycerol polyglycidyl ether are preferred.
The amount of the crosslinking agent used is 0.1 to 50 mol%, preferably 1 to 20 mol%, based on the number of moles of functional groups capable of reacting with the crosslinking agent, such as hydroxyl groups and carboxylic acids in cellulose or cellulose derivatives. It is a range. When the usage-amount of a crosslinking agent is less than 0.1 mol%, the melt | dissolution content of the obtained superabsorbent resin will increase, and gel strength will fall. Moreover, when the usage-amount of a crosslinking agent exceeds 50 mol%, the water absorption performance of the highly water-absorbing resin obtained will fall.

The crosslinking reaction of the present invention is performed under alkaline conditions of pH 8 or higher. The alkaline medium is not particularly limited, and examples thereof include alkali metal hydroxides such as sodium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide, and amine compounds such as triethylamine. It is done.
The temperature at the time of crosslinking is 0 to 100 ° C. When temperature is less than 0 degreeC, a crosslinking reaction rate becomes slow and manufacturing efficiency falls. When temperature exceeds 100 degreeC, a crosslinking agent reacts with water and alcohol which are solvents, and crosslinking efficiency falls. Preferably it is 20-80 degreeC.
The time for the crosslinking reaction is not particularly limited, and may be appropriately set according to the reaction temperature and the physical properties of the water-absorbent resin, but is usually about 5 minutes to 48 hours.
The post-treatment method of the obtained crosslinked product is not particularly limited, but it is immersed and re-precipitated in a hydrophilic organic solvent such as methanol, and after completely removing moisture or remaining solvent using a vacuum dryer or the like, it is pulverized. Thus, a highly water-absorbing resin can be produced.

The superabsorbent resin of the present invention can be used particularly as an activated sludge treatment agent or a soil water retention agent.
In that case, the superabsorbent resin content in the soil is preferably in the range of 0.01 to 1 wt%. When the superabsorbent resin content in the soil is less than 0.01 wt%, a sufficient water retention effect does not appear in the soil. When the superabsorbent resin content in the soil is 1 wt% or more, it is disadvantageous in terms of cost.

The highly water-absorbing resin of the present invention is a sanitary field such as paper diapers and sanitary products, a medical field such as a poultice and a body fluid water absorbent, a sludge gelling agent, a sealing material, and a dew condensation prevention material for preventing mud loss in the muddy water shield method Civil engineering / architecture field, etc., food field such as freshness-keeping materials such as vegetables, meat and fish, agricultural / horticultural fields such as soil water retention agents and seed coating agents for agriculture, cosmetics, cold insulation materials, fragrances and deodorants To be used in various fields such as cosmetics and toiletries such as miscellaneous goods, electrical / electronic materials, paints / adhesives, and oil / water separators, waste liquid absorbers, anti-vibration materials, soundproof materials, toys, etc. Can do. In particular, the applications requiring water absorption performance for the high salt concentration aqueous solution of the superabsorbent resin of the present invention include activated sludge treatment agents, soil water retention agents, garbage disposal aids, and the like. Resin can also be used for such applications.

EXAMPLES Hereinafter, although an Example etc. demonstrate this invention further in detail, this invention is not limited at all by these Examples. The measurement method in the present invention is shown below.
(1) Water absorption performance (g / g)
0.2 g of the superabsorbent resin was placed in a nylon tea bag, immersed in an excess of 0.9% aqueous sodium chloride solution or in seawater, and allowed to stand for 24 hours. After water absorption, the weight A (g) with the tea bag and the weight B (g) after water absorption of the tea bag not containing the superabsorbent resin were measured, and the water absorption performance (g / g) was calculated by the following equation.
Water absorption capacity (g / g) = (A−B) /0.2

(2) Biodegradation rate According to JIS-K-6951, anhydrous potassium dihydrogen phosphate 8.5 g, anhydrous dipotassium hydrogen phosphate 21.75 g, disodium hydrogen phosphate 33.4 g, and ammonium chloride 0.5 g were distilled water. 80 mg of a superabsorbent resin was added to 400 ml of a standard test culture solution dissolved in 1000 ml, and then added so that the standard activated sludge was 30 ppm. The culture was stirred for 28 days at 25 ° C. with stirring. 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 not added with the superabsorbent resin was similarly determined. Furthermore, from the calculated value C (mg) of the amount of carbon dioxide generated when the superabsorbent resin was completely decomposed, the biodegradation rate (%) was determined by the following equation.
Biodegradation rate (%) = (A−B) / C × 100

(3) Dissolved content 0.5 g of a superabsorbent resin was placed in 150 ml of 0.9% saline and sufficiently swollen. Next, the superabsorbent resin was filtered off with a 200-mesh metal sieve, and 50 ml of the filtrate was collected in a beaker having a weight A (g) and dried with a hot air dryer. The weight B (g) for each beaker after drying was measured, and the dissolved content was calculated by the following formula.
Dissolved content (%) = [(B−A) /50×150−150×0.009] × 100
(4) Twenty-day radish growth test (germination rate)
100 kg of radish seeds were sown in 1 kg of soil. Watering was performed once every two days, and a three-week growth test was conducted. The number of seeds germinated after 3 weeks was counted, and the germination rate was calculated by the following formula.
Germination rate (%) = (number of germinated seeds / number of seeds sown) × 100

Example 1
20 g of a 3% aqueous solution of carboxymethylcellulose (substitution degree 0.7, polymerization degree 800) and 0.1 g divinylsulfone (10 mol% based on the number of moles of functional groups of the cellulose derivative) were stirred and mixed at room temperature. To this mixed solution, 5.2 g of 1M aqueous sodium hydroxide solution was added to adjust the mixed solution to pH 13, and then allowed to stand at 25 ° C. for 24 hours to advance the crosslinking reaction. The obtained gel-like fixed matter was precipitated with 400 g of methanol, and the obtained precipitate was dried with a vacuum dryer. The obtained dried product was pulverized with a pulverizer to obtain a highly water-absorbent resin. The resulting superabsorbent resin had a biodegradation rate of 20% and a dissolved content of 27%.

(Example 2)
In Example 1, except that divinyl sulfone as a crosslinking agent was changed to ethylene glycol diglycidyl ether (10 mol% with respect to the number of moles of functional groups of the cellulose derivative), and the crosslinking reaction was carried out at 40 ° C. for 5 hours. In the same manner as in Example 1, a highly water-absorbent resin was obtained.
(Example 3)
In Example 1, except that it was changed to a mixed solution (cellulose content 70%) of 3 g aqueous solution of 14% 3% aqueous solution of carboxymethyl cellulose and 6 g of 3% aqueous solution of polyvinyl alcohol (molecular weight 3500, saponification degree 86% or more). In the same manner as above, a highly water-absorbent resin was obtained.

Example 4
In Example 1, a highly water-absorbent resin was obtained in the same manner as in Example 1 except that carboxymethyl cellulose was changed to one having a polymerization degree of 300.
(Example 5)
In Example 1, a superabsorbent resin was obtained in the same manner as in Example 1 except that carboxymethylcellulose was changed to one having a polymerization degree of 1500 and the crosslinking reaction was carried out at 25 ° C. for 48 hours.

(Comparative Example 1)
In Example 1, a superabsorbent resin was obtained in the same manner as in Example 1 except that it was changed to a mixed solution of 6 g of 3% aqueous solution of carboxymethylcellulose and 14 g of 3% aqueous solution of polyvinyl alcohol (molecular weight 3500, saponification degree 86% or more). 0.6 g was obtained.
(Comparative Example 2)
In Example 1, a superabsorbent resin was obtained in the same manner as in Example 1 except that carboxymethylcellulose was changed to one having a polymerization degree of 50.
(Comparative Example 3)
In Example 1, a superabsorbent resin was obtained in the same manner as in Example 1 except that the amount of divinyl sulfone was changed to 0.7 g (70 mol% with respect to the number of moles of functional groups of the cellulose derivative).
Table 1 shows the water absorption amounts of the superabsorbent resins obtained in Examples 1 to 5 and Comparative Examples 1 to 3 with respect to physiological saline and seawater.

From Table 1, it can be seen that the highly water-absorbent resins of Examples 1 to 3 are excellent in water absorption performance for physiological saline and seawater. On the other hand, the ratio of the cellulose derivative of Comparative Example 1 to polyvinyl alcohol is 3
: Superabsorbent resin produced by mixing in No. 7, superabsorbent resin produced using carboxymethylcellulose having a polymerization degree of less than 150 in Comparative Example 2, and produced by adding the crosslinking agent in Comparative Example 3 in excess. In addition, the water-absorbing performance of all the highly water-absorbing resins decreased.

(Example 6)
0.3 g of the superabsorbent resin of Example 1 was mixed with 500 g of activated sludge having a concentration of 20%, and left at room temperature for 24 hours. 50 g of the mixture of the obtained activated sludge and the superabsorbent resin was mixed with 950 g of red clay, and a growth test for radish was performed. Watering was performed once every two days. The germination results are shown in Table 2.
(Comparative Example 4)
950 g of red bean clay and 50 g of activated sludge having a concentration of 20% were mixed, and a radish growth test was conducted in the same manner as in Example 7. The germination results are shown in Table 2.
(Comparative Example 5)
A 20-day radish growth test was conducted on 1 kg of red corn soil. The germination results are shown in Table 2.

  From Table 2, the soil containing the activated sludge of Example 7 and the superabsorbent resin showed a high germination rate. The soil mixed with the activated sludge of Comparative Example 4 showed a higher germination rate than that of the soil not mixed with the activated sludge of Comparative Example 5, but did not reach the germination rate of the soil of Example 7.

  The superabsorbent resin of the present invention can be effectively used as an activated sludge treatment agent, a soil water retention agent, and a garbage disposal aid.

Claims (4)

A superabsorbent resin characterized by satisfying the following requirements (1) to (3).
(1) The content of cellulose or cellulose derivative is 50 wt% or more.
(2) The degree of polymerization of the cellulose or cellulose derivative is 80 to 1800.
(3) The water absorption with respect to physiological saline is 50 g / g or more, and the water absorption with respect to seawater is 30 g / g or more.   The superabsorbent resin according to claim 1, wherein the biodegradation rate is 15% or more. It is a manufacturing method of the superabsorbent resin of Claim 1 or 2, Comprising: The manufacturing method of superabsorbent resin characterized by including the process of following (1)-(3) at least.
(1) Cellulose or cellulose derivative is dissolved in water at a concentration of 0.1 to 20 wt%.
(2) In the solution of (1) above, at least one cross-linking agent selected from the group of divinyl sulfone, epichlorohydrin, and polyfunctional epoxy compound is used with respect to the number of moles of functional groups of cellulose or cellulose derivative. Add 0.1-50 mol%.
(3) The crosslinking reaction is performed at 0 to 100 ° C. for 5 minutes to 48 hours under alkaline conditions of pH 8 or higher.   A soil comprising 0.001 to 1 wt% of the superabsorbent resin according to claim 1 or 2.