JPH11240941A - Production of hydrolyzable and biodegradable polyhydroxycarboxylic acid copolymer resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily producing a hydrolyzable and/or biodegradable polyhydroxycarboxylic copolymer resin, useful as a material for agriculture/horticulture, fishery, medical equipment and medicaments which are difficult to recover, and eventually decomposed into carbon dioxide and water by hydrolysis or by the actions of microorganisms in the soil, when discarded, to cause no environmental problems. SOLUTION: This copolymer resin is obtained by reacting 100 pts.wt. of a monofunctional hydroxycarboxylic acid (e.g. lactic acid and glycolic acid) with 0.001 to 20 pts.wt. of a multifunctional hydroxycarboxylic acid (e.g. tartaric acid, citric acid and malic acid) in the presence of a polymerization catalyst (e.g. 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane) for dehydration/copolymerization under heating and a vacuum with stirring. The polyhydroxycarboxylic copolymer resin thus produced has characteristics, e.g. higher in weight-average molecular weight and melt viscosity than the homopolymer of a monofunctional hydroxycarboxylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a hydrolyzable and biodegradable polyhydroxycarboxylic acid copolymer resin.

[0002]

2. Description of the Related Art
Various resin moldings are used as agricultural and horticultural materials (for example, polyvinyl chloride film) and fishing materials (for example, fishing nets made of polyethylene fiber), and any of these materials is discarded. Therefore, there is a demand for a resin that does not become a source of pollution even when discarded, and is hydrolyzed over time or biodegraded by microorganisms in the soil. The present invention can be used for such agricultural and horticultural materials, fishery materials, binders, and the like. Another object is to provide a method for easily producing a biodegradable polyhydroxycarboxylic acid copolymer resin.

[0003]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and have found that a monofunctional hydroxycarboxylic acid and a polyfunctional hydroxycarboxylic acid can be used to form a hydrolyzable and biodegradable polyhydroxycarboxylic acid. They have found that a carboxylic acid copolymer resin can be produced, and have completed the present invention.

That is, according to the present invention, a polymerization catalyst is added to a mixture of at least one or more monofunctional hydroxycarboxylic acids and at least one or more polyfunctional hydroxycarboxylic acids, and the mixture is heated and stirred under reduced pressure to carry out dehydration copolymerization. By performing the above, a hydrolyzable and biodegradable polyhydroxycarboxylic acid copolymer resin is produced.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION As the monofunctional hydroxycarboxylic acid used in the present invention, any of lactic acid, glycolic acid and the like may be used, but lactic acid is particularly preferably used in terms of availability. preferable.

As the polyfunctional hydroxycarboxylic acid used in the present invention, tartaric acid, citric acid, malic acid and the like are particularly preferably used from the viewpoint of inexpensiveness.

The amount of the polyfunctional hydroxycarboxylic acid is as follows:
0.1 parts by weight per 100 parts by weight of monofunctional hydroxycarboxylic acid.
001 to 20 parts by weight are preferred. When the amount is less than 0.001 part by weight, a remarkable molecular weight increasing effect cannot be obtained,
On the other hand, when the compounding amount exceeds 20 parts by weight, the obtained polyhydroxycarboxylic acid copolymer resin has a reduced weight average molecular weight and is colored black.

In the present invention, the polymerization catalyst used for the copolymerization reaction between the monofunctional hydroxycarboxylic acid and the polyfunctional hydroxycarboxylic acid includes 1,3-substituted-1,1,3,3.
3-Tetraorganodistanoxane can be mentioned. Here, the organo group bonded to the tin atom may be any of a methyl group, an ethyl group, a propyl group, a butyl group, an octyl group, an allyl group, a benzyl group, and a phenyl group.
Considering the solubility and cost, a butyl group is preferred. The substituent at the 1,3-position may be any of a halogen, a thiocyano group, a hydroxyl group, an alkoxy group, and a carboxyl group. Particularly preferred polymerization catalysts include 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane.

[0009]

According to the above-mentioned means, a hydrolyzable and biodegradable polyhydroxycarboxylic acid copolymer resin can be easily and efficiently produced in one pot. Compared to a carboxylic acid homopolymer resin, it has properties such as a large weight average molecular weight and a large melt viscosity. And even if these resins are discarded, they are hydrolyzed and / or decomposed into carbon dioxide and water by microorganisms in the soil with the passage of time.

[0010]

EXAMPLES Example 1 (Copolymer resin of lactic acid and tartaric acid) 1 mol (100 g) of 90% L-lactic acid and 1 mmol of tartaric acid
l (0.15 g) and 1,3-dichloro-1,1,3,3
-0.1 mmol of tetrabutyldistannoxane (50 m
g) was placed in a 500 ml reactor and heated and stirred at 180 ° C. under reduced pressure for 24 hours. The weight average molecular weight (Mw) of the obtained polylactic acid copolymer was 42,000. The melt viscosity at 160 ° C. was 9.5 × 10 ⁴ poise.

The molecular weight of the obtained polyhydroxycarboxylic acid resin was measured by using a gel filtration chromatograph (GPC). The solvent used was chloroform and the temperature was 40
At 100C, the flow rate is 1.0 ml / min. The GPC apparatus is a high pressure pump (Model 510 for high performance liquid chromatography) manufactured by Nippon Millipore Limited, a differential refractive index detector (Showex RI-71) manufactured by Showa Denko KK, and a column G.
PCK806M. The molecular weight is a value obtained by converting polystyrene as a standard sample. The melt viscosity was measured by Shimadzu Flow Tester CFT-500 manufactured by Shimadzu Corporation.
According to C.

Example 2 (Copolymer resin of lactic acid and citric acid) 1 mol (100 g) of 90% L-lactic acid and 1 mm of citric acid
ol (0.19 g) and 1,3-dichloro-1,1,3,
0.1 mmol of 3-tetrabutyldistannoxane (50
mg)) in a 500 ml reactor and
Heating and stirring were performed under reduced pressure for a time. The weight average molecular weight (Mw) of the obtained polylactic acid copolymer was 38,000. The melt viscosity at 160 ° C. is 9.3 × 10 ⁴
Poise.

Comparative Example (Homopolymerized Resin of Lactic Acid) 1 mol (100 g) of 90% L-lactic acid and 1,3-dichloro-1,1,3,3-tetrabutyldistanoxane 0.1 mol.
1 mmol (50 mg) was placed in a 500 ml reactor, and heated and stirred at 180 ° C. for 24 hours under reduced pressure. The weight average molecular weight (Mw) of the obtained polylactic acid (lactic acid homopolymer) was 20,000. The melt viscosity at 160 ° C. was 1.5 × 10 ⁴ poise.

(Evaluation of Biodegradability by Hydrolysis Acceleration Test) In general, biodegradation of a biodegradable resin by microorganisms first occurs after hydrolysis and a reduction in the molecular weight of the resin occurs.
It is known that degradation by microorganisms occurs. Therefore, as for the biodegradable resin, the evaluation of the easily hydrolyzable property can be directly employed as one of the methods for evaluating the biodegradability. Then, in order to evaluate the hydrolyzability of the polyhydroxycarboxylic acid resin, 2 mm of the polylactic acid copolymer obtained in Examples 1 and 2 and the lactic acid homopolymer obtained in Comparative Example in a 0.1 N NaOH aqueous solution were used. Soak the sheet 4
The weight loss after days was measured. Lactic acid homopolymer was reduced to 96 when the initial weight was 100, whereas
The polylactic acid copolymer was reduced to 92. From this, it has been found that the polyhydroxycarboxylic acid copolymer resin obtained according to the present invention has a higher biodegradation rate than the polyhydroxycarboxylic acid homopolymer.

[0015]

As described above, according to the present invention, a hydrolyzable and biodegradable polyhydroxycarboxylic acid copolymer resin can be easily and efficiently produced in one pot, and the resulting polyhydroxycarboxylic acid can be produced. The acid copolymer resin has properties such as a higher weight average molecular weight and a higher melt viscosity than a homopolymer resin of a monofunctional hydroxycarboxylic acid. These resins can be used as binders, and their molded products can be used as agricultural and horticultural materials and fishery materials that are difficult to recover, as medical tools and medical materials, and even if they are discarded over time. It does not become a source of environmental pollution because it is hydrolyzed or decomposed into carbon dioxide and water by soil microorganisms.

Claims (5)

[Claims] (1) at least one kind of monofunctional hydroxycarboxylic acid and at least one kind of polyfunctional hydroxycarboxylic acid;
A method for producing a hydrolyzable and biodegradable polyhydroxycarboxylic acid copolymer resin, comprising adding a polymerization catalyst to a mixture of at least one species and heating and stirring under reduced pressure to carry out dehydration copolymerization. 2. The mixing ratio of the monofunctional hydroxycarboxylic acid and the polyfunctional hydroxycarboxylic acid is 0.001 to 20 parts by weight of the polyfunctional hydroxycarboxylic acid per 100 parts by weight of the monofunctional hydroxycarboxylic acid. The method for producing a hydrolyzable and biodegradable polyhydroxycarboxylic acid copolymer resin according to claim 1. 3. The method according to claim 1, wherein the monofunctional hydroxycarboxylic acid is lactic acid or glycolic acid.
A method for producing the hydrolyzable and biodegradable polyhydroxycarboxylic acid copolymer resin described in the above. 4. The method according to claim 1, wherein the polyfunctional hydroxycarboxylic acid is tartaric acid, citric acid or malic acid.
Or the method for producing a hydrolyzable and biodegradable polyhydroxycarboxylic acid copolymer resin according to 2 or 3. 5. A polymerization catalyst comprising 1,3-substituted-1,1,3,3
3. The method for producing a hydrolyzable and biodegradable polyhydroxycarboxylic acid copolymer resin according to claim 1, wherein the resin is a tetraorganodistanoxane.