JPH04335060A - Degradable thermoplastic polymer composition - Google Patents

Abstract

PURPOSE:To obtain a thermoplastic polymer composition which can be degraded under natural environmental conditions and can be used as a packaging material or a medical material. CONSTITUTION:A degradable thermoplastic polymer composition mainly consisting of polylactic acid, a copolymer of lactic acid with a hydroxycarboxylic acid or a mixture of polylactic acid with polyhydroxycarboxylic acid each of which is plasticized and is flexible.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a degradable thermoplastic resin used for packaging materials and the like. More specifically, flexible L-lactide containing plasticizer, D
- Thermoplastic degradable polymers obtained from lactide, D,L-lactide or mixtures thereof. These thermoplastic degradable polymers have recently attracted attention as packaging materials and medical materials.

0002

BACKGROUND OF THE INVENTION In recent years, the amount of packaging plastic used has increased due to problems with the aesthetics, hygiene, and packaging and transportation of prizes. Along with this, the amount of garbage being discarded from households and factories is rapidly increasing, and the lack of land to bury the garbage has become a serious problem in areas surrounding major cities.

Conventionally, polyethylene, polypropylene, polystyrene, polyethylene terephthalate, vinyl chloride, etc. have been used as such packaging plastics. However, when these are disposed of in the natural environment, they remain undecomposed due to their stability, causing problems such as damaging the landscape and contaminating the living environment of marine organisms.

Much research and development has been carried out to use degradable polymers as packaging materials that do not suffer from these problems. For example, attempts have been made to impart degradability to materials such as polyethylene, polypropylene, and polystyrene by blending them with starch.

[0005] However, in this method, although the starch decomposes and the resin itself collapses, the non-degradable polymer itself remains intact, which is said to cause further environmental pollution.

As a thermoplastic and degradable polymer,
Lactic acid and its copolymers are known. This lactic acid polymer biodegrades 100% within an animal's body within a few months to a year. Furthermore, if placed in soil or seawater, it will begin to decompose in a few weeks in a humid environment, and will disappear in about a year. The decomposition products are lactic acid, carbon dioxide, and water, all of which are harmless.

[0007] The raw material, lactic acid, can be obtained from the fermentation of inexpensive raw materials such as corn starch and corn syrup, and can also be obtained from petrochemical raw materials such as ethylene.

US Pat. No. 1,995,970, 2,362
, 511, 2,683,136 contains lactic acid, lactide,
or a manufacturing method for polymerizing a mixture thereof. Polymers of lactic acid are commonly synthesized from cyclic dimers of lactic acid called lactides. If a polymer is synthesized directly from lactic acid by dehydration condensation, a high molecular weight polymer cannot be obtained even over a long period of time. On the other hand, linear polyester synthesized by ring-opening polymerization using lactide as a raw material has a high molecular weight.

[0009] The lactic acid polymer thus obtained is
It is processed into threads and molded products and used in biomedical sustained release materials, bone plates, screws, etc. However, these applications require strong and hard polymer physical properties, but not flexibility.

However, when a lactide polymer is used as a film raw material, it lacks flexibility and is therefore brittle and hard, making it difficult to use.

US Pat. Nos. 3,736,646 and 3,982
, 543 discloses the use of volatile solvents as plasticizers to obtain flexibility in lactide copolymers. However, when a solvent is used as a plasticizer, the solvent gradually evaporates while a product such as a film is stored or used, and its effectiveness is lost. Furthermore, there are problems with the safety of these solvents for products for food and medical purposes.

[0012] In PCT International Application No. 9001521, L-
lactide, D-lactide, meso-lactide,
A method has been shown in which, when polymerizing in the presence of a catalyst, the polymerization is stopped until a small amount of lactide remains, and the remaining lactide, lactide oligomer, and lactic acid oligomer act as plasticizers and give flexibility to the polymer. . This patent also describes a method for adding lactide, lactic acid oligomers, and lactide oligomers after the polymerization is complete.

However, with this method, it is difficult to stop the polymerization reaction at a degree of polymerization that exhibits the desired physical properties of the polymer, and requires special technology from an industrial perspective. If the content of lactide, lactic acid oligomer, lactide oligomer, etc. is increased, the lactide will crystallize and lose transparency over time after being formed into a film or the like.

[0014] Thus, until now, there has been no known flexible polymer composition containing polylactic acid as a main component that can be used for films, threads, packaging materials, etc., especially for food packaging agents or medical applications. .

[0015]

SUMMARY OF THE INVENTION Accordingly, the present invention provides films, threads, packaging materials, etc., which overcome the above-mentioned drawbacks, and which have flexibility and are mainly composed of polylactic acid, which can be used particularly for food packaging agents or medical applications. The object of the present invention is to provide a polymer composition that has the following properties.

[0016]

[Means for Solving the Problems] As a result of intensive studies to solve the above problems, the present inventors have found that L-lactic acid, D
- Dehydration condensation of lactic acid or mixtures thereof, or L-lactide (L-LTD), D-lactide (D
-LTD), D,L-lactide (DL-LTD), m
After ring-opening polymerization of eso-lactide (meso-LTD) or mixtures thereof, flexibility can be imparted to the polymer by adding a plasticizer, and the amount added can be increased by an amount that provides sufficient flexibility. The present invention was completed based on the discovery that a transparent polymer molded article could be obtained even when the polymer was used.

The polymer used in the present invention is a mixture of polylactic acid and other hydroxycarboxylic acid polymers, or a copolymer of lactic acid and other hydroxycarboxylic acids. As other hydroxycarboxylic acids, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid, etc. are used.

These polymers may be synthesized by direct dehydration polycondensation from lactic acid or other hydroxycarboxylic acids, or may be synthesized from lactide, glycolide (GLD), ε-caprolactone (CL), or their like. A product obtained by ring-opening polymerization of a mixture may also be used. It may also be a copolymer synthesized by transesterifying a polymer of polylactic acid and another hydroxycarboxylic acid at high temperature. The lactic acid constituting the polymer may be L-lactic acid, D-lactic acid, or a mixture thereof.

The polymerization method may be a method using a solvent or a method not using a solvent, but due to problems such as recovery of the solvent,
Industrially, bulk polymerization without using a solvent is preferred.

[0020] The catalyst for ring-opening polymerization is generally a chloride or carboxylate of zinc or tin, but is not particularly limited. When used in biocompatible materials or food-related applications, toxicity must be considered.

[0021] The polymerization temperature varies depending on the catalyst, but is usually carried out at 95 to 180°C. The polymerization time is determined by the type of catalyst and temperature, and can be determined while measuring the amount of lactide remaining during the reaction.

[0022] The end point of polymerization is the point when the remaining raw material lactide monomer becomes 5% or less, and if more lactide remains, it will affect the physical properties of the obtained thermoplastic resin, so the method of the present invention It becomes difficult to obtain desired physical properties along these lines.

[0023] The polymerization degree of the polymer is 150 to 20,00
0 is preferred. If the degree of polymerization is lower than this, the strength when molded into a film or the like is low and it is not suitable for practical use.

[0024] If the degree of polymerization is higher than this, the viscosity in a hot molten state will be high and the moldability will be poor.

The plasticizer to be added is preferably one that is safe for use in food packaging containers, etc., but examples include phthalate esters such as diethyl phthalate, dioctyl phthalate, and dicyclohexyl phthalate, and di-i-adipate. Aliphatic dibasic acid esters such as butyl, di-n-octyl adipate, di-n-butyl sebacate, di-2-ethylhexyl azelaate, diphenyl-2-ethylhexyl phosphate, diphenyl octyl phosphate, etc. Phosphate esters, hydroxy polyhydric carboxylic acid esters such as tributyl acetyl citrate, tri-2-ethylhexyl acetyl citrate, tributyl citrate, fatty acid esters such as methyl acetyl ricinolate, amyl stearate, glycerin triacetate, triethylene Examples include polyhydric alcohol esters such as glycol dicaprylate, epoxidized soybean oil, epoxy plasticizers such as epoxy octyl stearate, and polyester plasticizers such as polypropylene glycol adipate and polypropylene glycol sebacate. It will be done.

[0026] Additives are usually added to the polymer composition in an amount of 5.
~50% by weight is used. Particularly preferably, it is 5 to 20% by weight. These plasticizers may be added to polylactic acid in a state dissolved in a solvent, or may be added in a molten state.

In addition to the plasticizer, the polymer composition of the present invention may also contain other additives such as stabilizers, antioxidants, ultraviolet absorbers, and colorants.

The plasticized polymer composition can be processed by, for example, injecting it into an extrusion mold while heating. Alternatively, a method such as dissolving it in a solvent and making it into a membrane to form a film can also be used. In order to use molded products such as films processed in this way as packaging materials, it is necessary that they have an appropriate modulus of elasticity. Usually, this value is preferably 10 to 100 kg/mm2. If it is larger than this, it is hard and tends to crack due to external force. If it is smaller than this, it is easily deformed by a small force and is not practical.

[0029]

EXAMPLES The method of the present invention will be specifically explained below using Examples and Comparative Examples.

Examples 1 to 7 Monomers were charged in a glass polymerization tube, and 150 mg of stannous octoate was added as a catalyst. A degassing cock was attached to this polymerization tube, and after degassing and drying for several hours, the cock was closed and the polymerization tube was sealed while maintaining a vacuum. Next, at 180℃ 2
Polymerization was carried out for 0 hours to obtain a resin composition as a reaction product. After stopping the polymerization reaction, the reaction product is dissolved in methylene chloride,
The residual monomer was quantified by gas chromatography.

Further, the polymer was dissolved in chloroform, and the weight average molecular weight was calculated by gel permeation chromatography (GPC).

The obtained resin composition was dissolved in chloroform (concentration: 5% by weight), and additives were added. These were cast onto a Teflon flat petri dish, and the solvent was slowly evaporated at room temperature to create a film. Further reduced pressure (3
The film was dried at 50° C. for 24 hours under (mmHg), and it was confirmed that there was no solvent remaining in the film by measuring the infrared absorption spectrum of the film.

A test piece with a width of 10 mm and a length of 50 mm was prepared from the obtained film, and measured using a tensile tester at a chuck width of 20 mm and a tensile speed of 50 mm/min. Further, Table 1 shows the results of a hydrolysis test in 60°C warm water.

[0034] The obtained results are summarized (Table 1) and (Table 2)
), (Table 3) shown in Table 1. Both films had good flexibility.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

Comparative Examples 1 to 4 Films were prepared in the same manner as in Examples 1 to 4 without adding any additives to the reaction products obtained. These were clearly less flexible than those containing additives.

[0039]

[Effects of the Invention] According to the present invention, a thermoplastic resin composition containing polylactic acid as a main component and having good flexibility and hydrolyzability can be obtained.

Claims (4)

[Claims] 1. A thermoplastic degradable polymer composition containing a plasticizer and based on highly flexible polylactic acid, a copolymer of lactic acid and hydroxycarboxylic acid, or a mixture of a polymer of polylactic acid and hydroxycarboxylic acid. [Claim 2] The plasticizer is a phthalate ester, an aliphatic dibasic acid ester, a phosphoric acid ester, a hydroxy polycarboxylic acid ester, a fatty acid ester, a polyhydric alcohol ester, an epoxy plasticizer, a polyester plasticizer, or the like. The composition according to claim 1, which is a mixture of. 3. The composition according to claim 1, wherein the polylactic acid is obtained from L-lactic acid, D-lactic acid, or a mixture thereof. 4. The composition according to claim 1, wherein the hydroxycarboxylic acid is glycolic acid, 3-hydroxybutyric acid, 3-hydroxyvaleric acid, or 6-hydroxycaproic acid.