JPH09202825A - Production of crosslinked material of polyaspartic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply and inexpensively obtain the subject new crosslinked material usable as a thicknening agent, a water-absorbing resin, etc., high in biodegradability, by irradiating a solution of a polyaspartic acid with radiation. SOLUTION: A polyaspartic acid is dissolved in a solvent and the prepared solution is irradiated with radiation to give the objective crosslinked material having an absorption ability of 200 times as much as the weight of the crosslinked material by a tea bag method. For example, the neutralization degree of the polyaspartic acid is 50-100%, and a mixture of water as a main component with a water-soluble liquid such as methyl alcohol is used as the solvent. The radiation is γ-rays and the γ-ray absorbed dose is preferably 10-500kGy.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a novel polyaspartic acid crosslinked product. More specifically, the present invention relates to a crosslinked product derived from polyaspartic acid, which has biodegradability and can be used as a thickener or a water absorbent resin, and a method for producing the same. The polyaspartic acid cross-linked product obtained by the present invention has biodegradability and its use is not particularly limited over a wide variety, and examples thereof include various polymer emulsions, thickeners such as latex, water-stopping agents, It can be used as a soil conditioner, a water retention agent for gardening, disposable diapers, disposable sanitary materials such as sanitary products, surface treatment agents, and sealing agents.

[0002]

2. Description of the Related Art As water-absorbent resins, polyvinyl alcohol, polyethylene oxide, sodium polyacrylate and the like have hitherto been known. Examples of crosslinked products include carboxymethyl cellulose crosslinked products, polyethylene oxide partially crosslinked products, hydrolyzates of starch-acrylonitrile graft copolymers, vinyl alcohol-acrylic acid salt copolymers, and the like.

However, none of these resins have sufficient performance, have low biodegradability or hydrolyzability, and remain in the natural environment when discarded or left after use, which adversely affects the surrounding environment. Or the water absorbability and the water retention capacity under pressure were low even though the biodegradability was high. Therefore, in recent years, studies have been conducted to obtain highly water-absorbing crosslinked products from biodegradable or hydrolyzable polyamino acids, for example, side chains of acidic amino acid-based resins such as polyaspartic acid and polyglutamic acid. A technique for producing a water-absorbent resin by crosslinking an esterified resin with a diamine and then carboxylating the ester residue or a salt thereof (Japanese Patent Publication No. 52-413).
No. 09), and a technique of producing a polyaspartic acid-based water-absorbing resin by crosslinking polysuccinimide with a diamine and then hydrolyzing it (JP-A-7-224163).

However, these manufacturing methods industrially require complicated operations, the raw material costs are high, and there is a cost problem. On the other hand, irradiating a poly (γ-glutamic acid) solution with γ-rays (Polymer Papers, Vol. 50, No. 10, 75)
5 (1993)) and poly (ε-lysine) with γ-rays (Journal of the Textile Society, Vol. 51, No. 3, 137 (199).
5)) has reported a technique for producing a biodegradable superabsorbent.

However, the above-mentioned method requires the use of expensive amino acids in the raw material, and further, in order to obtain the polymer, it is expensive to use a microorganism or a monomer N-carboxyanhydride. It is necessary to use various methods.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide a highly water-absorbing crosslinked product from polyaspartic acid, which is a biodegradable polyamino acid, simply and inexpensively. To do.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a novel polyaspartic acid crosslinked product can be simply and inexpensively irradiated by irradiating a polyaspartic acid solution with radiation. The inventors have found that they can be obtained and have solved the present invention. That is, the gist of the present invention is:
A method for producing a crosslinked polyaspartic acid, which comprises irradiating a solution obtained by dissolving polyaspartic acid in a solvent to obtain a crosslinked polyaspartic acid.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The method for producing polyaspartic acid used in the present invention is not particularly limited, but for example, polysuccinimide can be obtained by heating aspartic acid in the presence of phosphoric acid or in the absence of a catalyst, and subjecting it to dehydration condensation. (Japanese Patent Publication No. 48-20638). Further, the reaction of hydrolyzing polysuccinimide to obtain polyaspartic acid is known, and thus polyaspartic acid can be produced.

The weight average molecular weight of polysuccinimide is
Although it depends on the temperature of thermal condensation, the type of catalyst (phosphoric acid, polyphosphoric acid or other dehydrating agent) and the amount added, the pressure in the reaction system (pressure reduction degree), etc., generally a weight average molecular weight of 1,000 or higher However, in order to obtain a water-insoluble cross-linked product, a high molecular weight product is advantageous, preferably 10,000 or more, more preferably 20,000 or more, and most preferably 300.
00 or more.

The degree of neutralization of the polyaspartic acid used in the present invention is not particularly limited, but if the degree of neutralization (the state where all carboxylic acids are carboxylic acids is 0) is too low, the water absorption ability is increased. It is preferably 20 to 100%, more preferably 30 to 100%, most preferably 50 to 50%, because it causes a decrease or the decomposition reaction during irradiation is likely to proceed.
100%, after hydrolysis of polysuccinimide, if necessary, by using mineral acids such as hydrochloric acid, sulfuric acid, etc., organic acids such as formic acid, acetic acid, etc., particularly preferably inexpensive and easy to handle. A polyaspartic acid solution with a degree of neutralization can be obtained.

In the present invention, the solvent for mixing and dissolving polyaspartic acid is usually water, but it is also possible to use a mixture of water and a water-soluble liquid. The water-soluble liquid referred to here is not particularly limited, but examples include methyl alcohol,
Examples thereof include alcohols such as ethyl alcohol and isopropanol, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and esters such as methyl acetate and ethyl acetate. The mixing ratio of water to the water-soluble liquid differs depending on the water-soluble liquid used, but it is preferable to adjust the amount of the water-soluble solvent containing water as the main component so that the polyaspartic acid can be dissolved.

The concentration of polyaspartic acid in the above solution is preferably 0.1 to 50% by weight, more preferably 1 to 25% by weight. The container used when irradiating the solution obtained by mixing and dissolving the polyaspartic acid in the solvent in the present invention is not particularly limited as long as it is a radiation permeable container, such as a glass sealable bottle. Preferred examples include:

The radiation used in the present invention is preferably α rays, β rays, γ rays, electron rays, neutron rays, X rays, and charged particle rays, and more preferably γ rays.
Further, when the target product is produced in the form of a film or sheet, it is preferable to use α rays, β rays, or electron beams having a small penetrating power. When using γ-rays for the radiation, the γ-ray absorption amount is preferably 1 to 500 kGy, more preferably 5 to 5 kGy.
00 kGy, most preferably 10-500 kG
y, and crosslinking generally proceeds at room temperature and atmospheric pressure. Also,
Regarding the atmosphere in the system, the crosslinking proceeds even in the presence of air, but since the degree of crosslinking is difficult to increase, it is more preferable that the atmosphere is an inert gas such as nitrogen or argon.

The gamma ray is not particularly limited,
For example, one generated by an irradiation device or the like using cobalt 60 as a radiation source can be used. The water absorption capacity of the crosslinked product in the present invention was determined by the Teaback method. In the present invention, the tea-back method is to put distilled water in a beaker,
Nylon Net (NBC Industry Co., Ltd., N-255H
A bag made of D, 250 mesh (depth 20 cm x width 1)
(0 cm) is immersed in the sample, left to stand in a cool dark place for one day, taken out of the bag, hung at room temperature for 15 minutes, and drained to measure. That is, the amount of water absorption is the value obtained by subtracting the weight of the crosslinked product and the weight of the bag from the final weight divided by the weight of the crosslinked product. The water absorption amount is not particularly limited, but considering practicality as a water absorbent resin, it is preferably 200 times by weight or more, more preferably 300 times by weight or more, and most preferably 500 times by weight or more.

The crude polyaspartic acid cross-linked product thus obtained is usually a colorless and transparent gel, which can be used as it is as a water-absorbing material, but if necessary, dipping, dialysis, or reprecipitation. It can be purified by usual methods such as filtration, washing, and drying. The resulting polyaspartic acid crosslinked product is a water-insoluble and water-absorbing white or yellow solid, which is usually swollen or insoluble in an organic solvent and does not melt even when heated.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0017]

EXAMPLES The polyaspartic acid used in the present invention was analyzed by the following measuring method. 1) Weight average molecular weight The weight average molecular weight of polysuccinimide is calculated from Tosoh Corporation.
"TSKgel""GMHHR-M" + "TSKg"
It is a polystyrene conversion value obtained by gel permeation chromatography (differential refractometer) using an el "" G2000HHR "column and a 10 mM lithium bromide dimethylformamide solution as an eluent.

The weight average molecular weight of polyaspartic acid is
Tosoh Corporation "TSKgel""G6000PWX"
It is a polyethylene glycol conversion value obtained by a gel permeation chromatograph (differential refractometer) using an L "+" TSKgel "" G3000PWXL "column and a 0.4 M sodium nitrate aqueous solution as an eluent.

2) Water absorption capacity The gel obtained by irradiation with radiation is immersed in distilled water to remove water-soluble substances such as uncrosslinked polymers and decomposition products, and then filtered and dried to form a crosslinked body. Obtained. Using 0.1 g of the particles (30 to 180 mesh) of each crosslinked product, the water absorption capacity was determined by the tea bag method.

Specifically, in a 500 ml beaker containing 400 ml of distilled water, a bag (depth 20 cm x width 10 cm) made of nylon net (NBC industry Co., Ltd., N-255HD, 250 mesh) was placed in the above. The sample was put and dipped, and allowed to stand still overnight in a cool dark place, then taken out of the bag, hung at room temperature for 15 minutes, and drained, and then weighed. The value obtained by subtracting the weight of the crosslinked product (0.1 g) and the bag weight from the weight was divided by the weight of the crosslinked product (0.1 g) to obtain the water absorption (g-
Water / g-polymer-).

[Reference Example 1] Synthesis of polysuccinimide (molecular weight 100,000) 100 g of L-aspartic acid and 50 g of phosphoric acid were placed in a 2 L eggplant-shaped flask, and the pressure was reduced to about 5 mm at 180 ° C.
After reacting for 3.5 hours while rotating using a rotary evaporator under the condition of Hg, 400 ml of dimethylformamide was added to an eggplant-shaped flask, and 120
The product was homogeneously dissolved at ° C. 1.5 L of this solution with pure water
The resulting slurry was pulverized with a mixer and then filtered under reduced pressure. This was suspended and washed with pure water until the filtrate became neutral, and the obtained cake was dried with hot air at 150 ° C. for 24 hours,
A white powder was obtained. This polysuccinimide has a weight average molecular weight of 100,000 and a conversion rate to a polymer of 97.8.
%Met.

Reference Example 2 Synthesis of polysuccinimide (molecular weight 70,000) 200 equipped with a cooler, thermometer, stirrer and water separator
25 ml of aspartic acid, 8 g
2.5 g of 5% phosphoric acid, 56 g of mesitylene and 24 g of sulfolane were charged. Then, polycondensation was carried out under normal pressure and under reflux of mesitylene (162 ° C.) for 4.5 hours. Water generated during the reaction was distilled out of the system together with a part of mesitylene. After completion of the reaction, the product was filtered off, and the product was washed 4 times with 100 g of pure water and once with 100 g of methanol. Next, this was dried under reduced pressure at 80 ° C. for 24 hours to obtain a yellow-white powder. This polysuccinimide has a weight average molecular weight of 70,
000, conversion to polymer was 98%.

[Reference Example 3] Synthesis of polysuccinimide (molecular weight 40,000) The same procedure as in Reference Example 2 was performed except that 0.92 g of cyclohexylamine was added together with aspartic acid and the like. The polysuccinimide had a weight average molecular weight of 40,000 and a conversion rate to a polymer of 95%. [Reference Example 4] Polysuccinimide (molecular weight 24,000)
Synthesis of 0) Reference example 2 except that the phosphoric acid was changed from 2.5 g to 0.18 g
I went the same way. The polysuccinimide had a weight average molecular weight of 24,000 and a conversion rate to polymer of 59%.

Reference Example 5 Synthesis of Polyaspartic Acid An equimolar amount of an aqueous NaOH solution was added dropwise to a liquid prepared by suspending the polysuccinimide obtained in Reference Example 1, 2, 3, 4 or 5 in water. , 1N if necessary after completing hydrolysis
The degree of neutralization was adjusted with a hydrochloric acid aqueous solution. The obtained polyaspartic acid aqueous solution was dropped into a large amount of methanol, and this was filtered under pressure, washed and dried to obtain polyaspartic acid. The results are shown in Table 1.

[0025]

[Table 1] [Examples 1 to 37] The polyaspartic acid obtained in Reference Example 6 was used to examine the conditions for forming crosslinked products and changes in water absorption capacity when the molecular weight, the degree of neutralization and the like were changed. That is, 1 to 50% aqueous solution of the polyaspartic acid was prepared and
After 2 ml each was dispensed into a glass sample bottle for ml, the container was sealed and irradiated with γ rays at 20 ° C. Cobalt 60
Gamma rays were irradiated using a gamma ray irradiation device (manufactured by Mitsubishi Heavy Industries, Ltd.) equipped with (110TBq) as a radiation source. The results are shown in Table 2.

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

[0029]

EFFECTS OF THE INVENTION According to the present invention, an inexpensive and novel polyaspartic acid crosslinked product having high biodegradability, which can be used as a thickener, a water absorbent resin, and the like and is expected to have various industrial applications. Is obtained.

Claims (2)

[Claims] 1. A method for producing a crosslinked polyaspartic acid, which comprises irradiating a solution obtained by dissolving polyaspartic acid in a solvent to obtain a crosslinked polyaspartic acid. 2. The method for producing a polyaspartic acid crosslinked product according to claim 1, wherein the water absorption capacity of the polyaspartic acid crosslinked product by the tea bag method is 200 times or more the weight of the crosslinked product.