JPH04168150A - Biodegradable plastic - Google Patents

Abstract

PURPOSE:To obtain the title plastic having high mechanical strength when being in normal service, degradable, after disposed of, rapidly by the activity of environmental microbes, thus useful for garbage bags for incineration, tablewares, polymeric containers, etc., by incorporating a base polymer with a microbial medium component. CONSTITUTION:The objective plastic can be obtained by incorporating (A) 100 pts.wt. of a base polymer, pref. a hydrolyzable polymer with a molecular weight of 1X10<4>-300X10<4> [e.g. oxyacid (co)polymer], more pref. polylactic acid (esp. poly-L-lactic acid) with (B) 10-0.01 pts.wt. of a microbial medium component (e.g. yeast extract, peptone, starch, glucose). The present plastic can be produced through the following process: the component A is dissolved in a solvent such as chloroform or THF, and the component B is added to the resulting solution, and the solution is cast on a plate followed by evaporation of the solvent into a film; alternatively, the components A and B are mixed in a powdery state followed by compression molding. The present plastic has high mechanical strength when being in service, and after disposed of, will degrade rapidly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to biodegradable plastics. In particular, it relates to biodegradable plastics used as consumer goods such as garbage incineration bags, tableware, and plastic containers.

[Prior art and its challenges] In recent years, biodegradable plastics have been in the spotlight due to the growing need and awareness of environmental conservation.

Biodegradable plastics are generally defined as used plastics that are broken down into carbon dioxide and water by the action of microorganisms in soil or water and returned to the natural environment. Although such biodegradable plastics are attracting attention worldwide,
Development has just begun, and various materials are currently being developed.

The properties required of biodegradable plastics are that they have hydrolyzability and high material strength. However, these are generally contradictory properties since hydrolyzability decreases with increasing molecular weight, while material strength increases with increasing molecular weight. This tendency is particularly strong in polyester resins bonded by ester groups.

In order to solve these problems, conventional methods have been used to elongate the material by stretching or other processing methods to improve the tensile strength, but this inevitably increases costs. Additionally, methods have been proposed in which polymers are decomposed and treated using external energy such as ultraviolet irradiation, but such treatment methods are difficult to implement in ordinary households.

An object of the present invention is to provide a biodegradable plastic that has high strength during normal use, but is quickly decomposed when discarded when no longer needed, and does not pose a risk of destroying the global environment.

[Means for Solving the Problems] The present invention provides a biodegradable plastic characterized by blending a culture medium component into a base polymer.

Examples of the medium components to be added to the base polymer include microorganism medium components such as yeast extract, peptone, starch, and glucose. If the amount of the medium component is large, it will decompose quickly, and if it is a small amount, the decomposition will be slow, so the decomposition time should be controlled by adjusting it depending on the use and purpose. Usually, it is 10 to 0.01 m per 100 parts of plastic. If the amount of the medium component is less than this range, sufficient biodegradability cannot be obtained, while if it is more than this range, the effect will not be improved.

Specifically, if the polymer molecular weight is several hundred thousand or less, it can be decomposed in water within about one month.

Furthermore, the base polymer used in the present invention is preferably a hydrolyzable polymer, such as lactic acid, malic acid,
Polymers of oxyacids such as gelcholic acid or copolymers thereof can be mentioned. The molecular weight of these polymers is lXl
0' to 300xlO' is preferred.

Among these, polylactic acid, particularly poly-L-lactic acid, is preferred.

Since poly-L-lactic acid is hydrolyzed to become L-lactic acid, it has high biosafety, and in recent years has been actively researched as a medical material, and some of it has been put into practical use. In addition, monolactic acid, which is a monomer, is generally produced by lactic acid bacteria through fermentation, but it is also used in pharmaceuticals,
It is also used in food, and its metabolic pathway in vivo is also clear. Therefore, polylactic acid has extremely high biosafety after decomposition. When poly-L-lactic acid has a molecular weight of 1000, it decomposes in physiological saline within about two weeks, and the material strength is low, making it impractical. On the other hand, when the molecular weight is over 100,000, it is difficult to decompose, and when the molecular weight is over 1 million, it remains unchanged for about 1 year or more.
The material strength is also high, equal to or higher than polystyrene.

To prepare biodegradable plastic from the above ingredients,
A hydrolyzable resin such as high molecular weight poly-L-lactic acid is dissolved in an appropriate solvent such as chloroform or THP, medium components are added to this solution, and after casting into a plate shape, the solvent is evaporated to form a film.

Alternatively, a homogeneous molded body may be obtained by mixing the hydrolyzable resin and the medium component in powder form and compression molding the mixture.

The biodegradable plastic of the present invention may contain a plasticizer such as lactic acid ester or octylic acid, or an additive.

[Function] The plastic of the present invention has high strength under normal usage conditions, but if it is disposed of in an environment where microorganisms are active, such as underground or in a river, the microbial culture medium components contained in the plastic will deteriorate. actively promotes the decomposition of plastic by environmental microorganisms, and the decomposed products are utilized, resulting in rapid decomposition.

[Example code] Next, the present invention will be explained in more detail with reference to Examples.

10g of polylactic acid (molecular weight approximately 100,000) in chloroform 40g
1 g each of peptone, yeast extract, and starch were added thereto and cast into a glass plate shape. When the membranes were buried in soil in the garden after the solvent had evaporated, they were destroyed within about three months.

[Effects of the Invention] The biodegradable plastic of the present invention has high strength during normal use, and is quickly decomposed by environmental microorganisms after disposal.

Patent applicant: Shimadzu Corporation

Claims (3)

[Claims] (1) A biodegradable plastic characterized by blending a microbial culture medium component with a base polymer. (2) The biodegradable plastic according to claim 1, wherein the medium component is at least one medium component selected from yeast extract, peptone, starch, and glucose. (3) The biodegradable plastic according to claim 1, wherein the base polymer is a hydrolyzable polymer.