JP2005336226A - Easy-degradable polylactic acid stereocomplex and biodegradable polymer material containing the same - Google Patents

Abstract

An easily degradable polylactic acid stereocomplex and a biodegradable material containing the same are provided.
SOLUTION: It contains poly D-lactic acid and poly L-lactic acid in a ratio of 10:90 to 45:55, which has excellent heat resistance and can be easily decomposed by enzymes such as proteinase K, subtilisin, α-chymotrypsin, etc. Polylactic acid stereocomplex and biodegradable material containing the same.
[Selection figure] None

Description

  The present invention relates to an easily decomposable stereocomplex and a biodegradable polymer material containing the same.

  Polylactic acid is expected as a biodegradable polymer, but it is more biodegradable in the environment than other industrially produced biodegradable plastics such as polyhydroxybutyric acid, polycaprolactone, polybutylene succinate, etc. It is known that there is a very low difficulty (Non-patent Document 1).

  In addition, poly L-lactic acid, which is one of polylactic acids, is degraded by proteinase K, which is a protease derived from the filamentous fungus Trichiacum album (Non-patent Document 2). It is reported that Bacillus licheniformis (Non-patent Document 3) and further α-chymotrypsin (Patent Document 1).

  However, although poly L-lactic acid has a relatively high melting point of 175 ° C., it has a problem that it is still low in heat resistance and impact resistance compared to general-purpose plastics such as ABS and PET, and cannot be used in a wide range of applications.

On the other hand, it has been reported that when poly-D-lactide is mixed with poly-L-lactide, a stereocomplex is formed and the melting point thereof increases by about 50 ° C. (Non-patent Document 4).
However, the optimal formation ratio of D-form and L-form in these stereocomplex bodies has not been elucidated, and the specific biodegradation characteristics have not been elucidated yet.

JP 2003-252966 A Appl. Envir. Microbiol. 63, 4,1637-1640 (1997) Eng. Med. 10, 5-7 (1981) J. Poly. Environ. 8, 1, 29-32 (2000) Macromolecules, 20, 904-906 (1987)

  The main object of the present invention is an easily decomposable polylactic acid stereocomplex which is easily obtained from poly-D-lactic acid and poly-L-lactic acid, has a melting point of 200 ° C. or higher, and is excellent in biodegradability, and It is to provide a degradable polymer material.

As a result of intensive studies to solve the above problems, the present inventors have found that a polylactic acid stereocomplex containing poly D-lactic acid and poly L-lactic acid in a specific ratio has excellent heat resistance and extremely excellent biodegradation. As a result, the present invention has been completed.
That is, according to the present invention, the following inventions are provided.
(1) An easily decomposable polylactic acid stereocomplex having a weight ratio of poly D-lactic acid to poly L-lactic acid of 10:90 to 45:55.
(2) The number average molecular weight of poly D-lactic acid is 1 × 10 ³ to 1 × 10 ⁴ and the number average molecular weight of poly L-lactic acid is 1 × 10 ^{4 to} 5 × 10 ^5. Degradable polylactic acid stereocomplex.
(3) A biodegradable polymer material comprising the easily decomposable polylactic acid stereocomplex described in (1) or (2) above.
(4) The biodegradable polymer material according to (3), wherein the biodegradable polymer material is decomposed by at least one enzyme selected from the enzymes of proteinase K, subtilisin and α-chymotrypsin.
(5) At least one or more selected from among microorganisms belonging to the genus Actinomycete genus Polendria, genus Lenzea, saccharolyticus, and genus Amycolatopsis and having the ability to degrade poly (L-lactic acid) and microorganisms of the filamentous fungus Trichiacum album The biodegradable polymer material according to (3), which is degraded by microorganisms.

The readily degradable polylactic acid stereocomplex of the present invention and biodegradable polymer materials such as films and fibers containing the same are used for clothing and biocompatibility that require rapid biodegradability and heat resistance in the natural environment. It can be used for sexual materials, simple tableware, garbage bags, diapers, vegetation nets, sandbags, piles, and multi-films.
In addition, an easily degradable polylactic acid stereocomplex and a biodegradable polymer material including the same easily recover monomers without using a long time process such as the growth of microorganisms by the action of the enzyme described above. Can be used for any industrial process.
Furthermore, the use of enzymes in industrial processes is not limited to the recycling of readily degradable polylactic acid stereocomplexes and biodegradable materials containing them, and the use of yarns, fabrics, and the plastics themselves formed from these materials. It is also suitable for the use of surface treatment such as texture treatment.

In the easily degradable polylactic acid stereocomplex of the present invention, poly D-lactic acid and poly L-lactic acid are in a weight ratio of 10:90 to 45:55, preferably 20:80 to 45:55, more preferably 30:70 to 40: It is characterized by being contained at a weight ratio of 60.
When the content of poly-D-lactic acid is smaller than the above range, the melting point becomes 200 ° C. or less, and when it is larger, separation by enzymes and microorganisms is not recognized, and the intended purpose of the present invention cannot be achieved.
The readily degradable polylactic acid stereocomplex according to the present invention usually has a melting point in the range of 201 to 215 ° C., is excellent in heat resistance, and, as will be apparent from the examples described later, as compared with conventionally known polylactic acid stereocomplexes. Its biodegradability is extremely excellent.

There is no special restriction | limiting in poly D-lactic acid and poly L-lactic acid used as a raw material, Any conventionally well-known thing can be used.
The poly D-lactic acid has a number average molecular weight of 1 × 10 ³ to 1 × 10 ^4, preferably 1 × 10 ^{3 to} 5 × 10 ³ , more preferably 1 × 10 ^{3 to} 3 × 10 ³ . used. The number-average molecular weight of the poly D- lactic acid tends to decompose if 1 × 10 ⁴ or less, also has an advantage capable of forming prepare stereocomplex in a short time, 1 × 10 ³ In the following, melting point 200 ° C. or more stereo It becomes difficult to obtain a complex.

Poly L-lactic acid having a number average molecular weight of 1 × 10 ^{4 to} 5 × 10 ⁵ , preferably 1 × 10 ^{5 to} 3 × 10 ^{5, more} preferably 2 × 10 ^{5 to} 3 × 10 ⁵ is used. The When the number average molecular weight of poly-L-lactic acid is 1 × 10 ⁴ or less, mechanical strength such as tensile strength is weak and it cannot be used for films and fibers. Further, when the number average molecular weight of poly L-lactic acid is 5 × 10 ⁵ or more, synthesis is difficult and impractical.

  In addition, the easily degradable polylactic acid stereocomplex of the present invention has a pigment, a heat stabilizer, an antioxidant, a weathering agent, a flame retardant, a plasticizer, a lubricant, a release agent, a charge, as long as the characteristics are not significantly impaired. It is also possible to add an inhibitor, a filler or the like. As the heat stabilizer or antioxidant, for example, hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, alkali metal halides, or mixtures thereof can be used. Inorganic fillers include talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon, carbon black, Examples thereof include zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fiber, metal whisker, ceramic whisker, potassium titanate, boron nitride, graphite, glass fiber, and carbon fiber. Examples of the organic filler include naturally occurring polymers such as starch, cellulose fine particles, wood powder, okara, silk powder, fir shell, and bran, and modified products thereof.

  The method for producing the easily decomposable polylactic acid stereocomplex of the present invention is not particularly limited as long as a product having a specific blending ratio as described above is obtained. For example, poly D-lactic acid and poly L- It can be easily synthesized by a method in which lactic acid is mixed in a desired ratio in a solvent such as chloroform and preferably heated appropriately.

  The easily decomposable polylactic acid stereocomplex body according to the present invention includes, for example, a protein belonging to the genus Protenas K, subtilisin, α-chymotrypsin, actinomycetes, genus sporadine, lentea, saccharolyticus, and amicolatopsis. It can be easily degraded by microorganisms having L-lactic acid degrading ability and microorganisms of the filamentous fungus Trichiacum album. The protease to be used is preferably a purified product, but it may be a crude product obtained by homogenizing an animal organ, a microorganism culture solution or the like, or an industrial enzyme containing a stabilizer.

  Therefore, the readily degradable polylactic acid stereocomplex according to the present invention is required to be rapidly biodegradable and heat resistant in natural environment, such as fibers, various container clothes, biocompatible materials, simple tableware, garbage bags, It can be effectively used as a material for biodegradable polymer materials such as diapers, vegetation nets, sandbags, piles, and multi-films.

Hereinafter, the present invention will be described in more detail with reference to examples.
The poly-D-lactic acid used in the synthesis was obtained by adding 0.28 g of tin octylate (Nacalai) to 10 g of Purac D-lactide and heating at 130 ° C. for 1 hour. An average molecular weight Mn = 1.76 × 10 ³ ) was used. Further, as poly L-lactic acid, Lacty # 1012 (number average molecular weight Mn = 1.8 × 10 ⁵ ) manufactured by Shimadzu Corporation was used.

Example 1
[Synthesis of readily degradable polylactic acid stereocomplex (mixing ratio 90:10)]
1.8 g of poly L-lactic acid (lacty # 1012, number average molecular weight Mn = 1.8 × 10 ⁵ ) and 0.2 g of poly D-lactic acid (number average molecular weight Mn = 1.76 × 10 ³ ) are dissolved in 50 ml of chloroform and stirred for 30 minutes. did. The precipitate was precipitated in 500 ml of methanol, and the precipitate was filtered through No. 2 filter paper and dried under reduced pressure at room temperature (yield 1.8 g, yield 90%, melting point 207.5 ° C.).

Example 2-4, Comparative Example 1-3
Table 1 shows the results of synthesis yield, synthesis yield, and melting point of the easily decomposable polylactic acid stereocomplex with various blending ratios adjusted in the same manner as in Example 1. In addition, the film of the degradable material containing a polylactic acid stereocomplex body was manufactured by the casting method. The melting point was measured with a differential scanning calorimeter DSC220C manufactured by Seiko Denshi Kogyo.

Example 5
[Degradation of readily degradable polylactic acid stereocomplex by enzyme]
10 mg of easily degradable polylactic acid stereocomplex (poly L-lactide: poly D-lactide = 90: 10) powder 1 ml of proteinase K enzyme solution (1 mg / ml) manufactured by ICN Biomedical, 1 ml of 0.05% octylglucoside solution, pH 7 Was added to the reaction solution consisting of 4 ml of the phosphate buffer and reacted at 37 ° C. with stirring. After 14 hours, the water-soluble organic carbon produced by the enzyme reaction was measured with a total organic carbon analyzer (TOC5000A manufactured by Shimadzu Corporation). The amount of water-soluble organic carbon produced was 158 ppm.

Example 6-16, Comparative Example 3-8
Table 2 shows the degradability of readily degradable polylactic acid stereocomplexes by various enzymes at various blending ratios. The reaction method was the same as in Example 4. For subtilisin and α-chymotrypsin, Sigma products were used.

Example 17
[Degradation of readily degradable polylactic acid stereocomplex by polylactic acid-degrading bacteria 1]
Ciderosporandium aridam received from RIKEN Microbial System Storage Facility was cultured in a basic medium containing 0.1% gelatin for 5 days at 30 ° C. After adjusting the pH of the culture to 7.0, 50 ml of culture broth 100 mg of an easily decomposable polylactic acid stereocomplex (poly L-lactide: poly D-lactide = 90: 10) powder was added to the mixture and reacted at 30 ° C. with stirring. After 14 hours, the water-soluble organic carbon produced by the microbial decomposition reaction was measured with a total organic carbon analyzer (TOC5000A manufactured by Shimadzu Corporation). As a result, the amount of water-soluble organic carbon produced was 320 ppm.
Table 3 shows the basic medium.

Examples 18-28, Comparative Examples 9-14
Tables 4 and 5 show the degradability of cast films as biodegradable materials from readily degradable polylactic acid stereocomplexes and easily degradable polylactic acid stereocomplexes by various enzymes at various blending ratios. The reaction method was the same as in Example 17. Kiderosporandium Aridam, Saccharos Rix Australian cis and Lenzea albidcapiratta were ordered from the Institute of Physical and Chemical Research Microbiology System.

Example 29
[Degradation of readily degradable polylactic acid stereocomplex by polylactic acid-degrading bacteria 2]
Amycolatopsis orientus obtained from the Institute for Microbial Strains of RIKEN is cultured in a basic medium containing 0.1% silk fibroin at 30 ° C for 5 days, and an easily degradable polylactic acid stereocomplex (50 ml of culture solution) (Poly L-lactide: poly D-lactide = 90: 10) 100 mg of powder was added and reacted at 30 ° C. with stirring. After 14 hours, the water-soluble organic carbon produced by the microbial decomposition reaction was measured with a total organic carbon analyzer (TOC5000A manufactured by Shimadzu Corporation). The amount of water-soluble organic carbon produced was 349 ppm.

Examples 30-32, Comparative Examples 15 and 16
Table 6 shows the degradability of readily degradable polylactic acid stereocomplexes by various enzymes at various blending ratios. The reaction method was the same as in Example 13.

Claims (5)

An easily decomposable polylactic acid stereocomplex having a weight ratio of poly D-lactic acid to poly L-lactic acid of 10:90 to 45:55. 2. The easily degradable polylactic acid according to claim 1, wherein the number average molecular weight of poly-D-lactic acid is 1 × 10 ³ to 1 × 10 ⁴ and the number average molecular weight of poly-L-lactic acid is 1 × 10 ^{4 to} 5 × 10 ^5. Stereo complex body. A biodegradable polymer material comprising the easily decomposable polylactic acid stereocomplex according to claim 1 or 2. The biodegradable polymer material according to claim 3, wherein the biodegradable polymer material is decomposed by at least one enzyme selected from enzymes of proteinase K, subtilisin and α-chymotrypsin. At least one microorganism selected from among the microorganisms belonging to the actinomycetes of the genus Kiderosporandium, Lenzea, Saccharus Rix, Amicolatopsis and poly L-lactic acid, and the microorganisms of the filamentous fungus Trichiacum album The biodegradable polymer material according to claim 3, which undergoes decomposition.