JP3339601B2 - Polylactic acid based polyester block copolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biodegradable polylactic acid-based polyester block copolymer having a high melting point. More specifically, the present invention relates to AB-type and ABA-type complete block copolymers.

[0002]

2. Description of the Related Art In recent years, due to the problem of environmental destruction caused by plastic waste, research and development of biodegradable plastics decomposed by enzymes and microorganisms have been actively conducted. Among them, aliphatic polyesters have attracted attention. ing. As the biodegradable polyester, poly [(R) -3]
-Hydroxybutyrate], polycaprolactone, or polyesters comprising glycols such as ethylene glycol and 1,4-butanediol and carboxylic acids such as succinic acid and adipic acid. Poly [(R) -3-hydroxybutyrate] -based polyesters are expensive because they are mainly produced by microbial synthesis. Further, other polyesters have a problem that their melting points are low and their use is difficult to expand.

[0003] On the other hand, polylactic acid has a melting point around 180 ° C and is economically advantageous because it is produced by chemical synthesis. Other mechanical properties, transparency, etc. are also attracting attention, but have the disadvantage that the rate of decomposition by microorganisms is slow.
Generally, polymers having a high melting point have a rigid main chain, and thus tend to have a low rate of microbial degradation. In the case of polylactic acid, it is necessary to increase the rate of microbial degradation.

In order to solve the problems of polylactic acid as described above, copolymerization of the second component has been attempted (for example, Polymer Bulletin, 25, 335, 1991). No copolymer was obtained, and the melting point was significantly reduced due to randomization in part.
Although attempts have been made to synthesize block copolymers,
(For example, JP-A-5-320323), the melting point of the block copolymer obtained by this method is 40 to 100 ° C., which is not sufficient for the purpose.

[0005]

As described above, a copolymer having a high melting point and improved biodegradability has not yet been obtained. For these reasons, an object of the present invention is to provide a polylactic acid-based polyester copolymer having a high melting point and exhibiting good biodegradability.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to obtain a polylactic acid-based polyester copolymer having a high melting point and good biodegradability.
It has been found that the object can be achieved by synthesizing a BA type complete block copolymer, and the present invention has finally been completed.

That is, the present invention is characterized by being represented by the following general formula (I) and having a melting point of 120 ° C. or more.
The present invention relates to a polylactic acid-based polyester block copolymer for molding .

Embedded image (In the formula, R ₁ represents an aliphatic alkylene group having 1 to 20 carbon atoms, and R ₂ represents an aliphatic hydrocarbon group having 2 to 20 carbon atoms. X represents a hydrogen atom or 1 to 2 carbon atoms. −
Represents an acyl group. l represents a positive integer of 1 or more, and m and n are positive integers satisfying the following formula (II).

[0008]

(Equation 2)

[0009] The present block copolymer is, for example,
_A ring-opening polymerization of a lactone giving R ₁ is carried out by using an alcohol giving _two residues as an initiator, and an oxyacid giving R ₁ is polycondensed in the presence of an alcohol giving R ₂ residue to form a terminal hydroxyl group. Is produced by synthesizing an oligomer represented by the following formula (III), further adding lactide and subjecting it to ring-opening polymerization.

Embedded image

[0010] In some cases, it is possible to block the hydroxyl group in order to impart thermal stability at the time of melting, but as a method, when polymerizing lactide, an aliphatic compound giving X in the formula (I) is used. The block copolymer may be produced by polymerization in the presence of a carboxylic acid, or the unblocked hydroxyl group-terminated polymer may be blocked by a post-treatment using an aliphatic carboxylic acid anhydride. Also, these two methods may be used in combination.

R ₁ represents an aliphatic alkylene group having 1 to 20 carbon atoms. Specific examples of cyclic lactones that provide this are β-butyrolactone, γ-butyrolactone, ε-caprolactone, propiolactone, δ. -Valerolactone, 4-valerolactone, and the like, but are not limited thereto. Among them, β-butyrolactone and ε-caprolactone are particularly preferred.

One or more of these cyclic lactones can be used in combination. In addition, the rate of decomposition of the present block copolymer by microorganisms varies depending on the lactone used, and it is necessary to use the block copolymer properly according to the purpose. Generally, β-butyrolactone and ε-caprolactone are preferred. It is important that the composition ratio of lactide and these lactones satisfies the formula (II), and if it exceeds this range, the desired performance will not be exhibited.

R ₂ represents an aliphatic hydrocarbon group having 2 or more and 20 or less carbon atoms. Specific examples of alcohols that provide this are methanol, ethanol, propanol, isopropanol, butanol, pentanol, nonanol,
Monoalcohols such as decanol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, methyl lactate, ethyl lactate and butyl lactate, and dialcohols such as ethylene glycol, propanediol, butanediol, hexamethylene glycol, nonanediol, and tetramethylene glycol Glycerol, sorbitol, xylitol, ribitol, erythritol and the like, but are not limited thereto. One or more of these alcohols can be used in combination. When the boiling point of the alcohol used is lower than the polymerization temperature, it is necessary to carry out the reaction under pressure.

X is a hydrogen atom or a 1-acyl group having 2 to 50 carbon atoms. Specific examples of the aliphatic carboxylic acid which provides a 1-acyl group having 2 to 50 carbon atoms include acetic acid and propionic acid. , Butyric acid, valeric acid, caproic acid, capric acid, pelargonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, argidic acid, behenic acid, linoleic acid, oleic acid, succinic acid, adipic acid, suberic acid, azelaic acid , Sebacic acid, undecandioic acid, dimer acid, fumaric acid and the like, but are not limited thereto. Further, these acid anhydrides may be added. One or more of these aliphatic acids can be used in combination.

In particular, stearic acid, palmitic acid, myristic acid, linoleic acid and oleic acid are flavorants, emulsifiers,
Vitamin fortifiers, fumaric acid, succinic acid, and adipic acid are also included in food additives as seasonings, acidulants, or raw materials thereof, and are preferred because safety has been established. More preferably, stearic acid, which is a raw material of calcium stearate used as an auxiliary for baking, is exemplified. When the boiling point of the aliphatic acid used is lower than the polymerization temperature, it is necessary to carry out the reaction under pressure.

The lactide for providing the polylactic acid segment in the present invention may be any of L-lactide, D-lactide, DL-lactide and meso-lactide, and may be used alone or in combination of two or more.

The production of the block copolymer is carried out by known solution polymerization or melt polymerization, in which a catalyst is generally used. All known catalysts can be used for these. Specific examples include tin, antimony, zinc, titanium, iron, and aluminum compounds, but are not limited thereto.

The block copolymer of the present invention may be added with additives such as a pigment, an antioxidant, an anti-deterioration agent, a plasticizer, a matting agent, an antistatic agent and an ultraviolet absorber, if necessary. Absent. In the case of adding, it is preferable to add the compound after reducing the low molecular weight compound from the amount remaining in the polymer.

The polylactic acid-based resin of the present invention can be formed into fibers, films, sheets and various molded articles from a molten / solution state, and has better hydrolysis resistance than conventional ones. Can be used over a wide range. Specifically, in the case of fibers and non-woven fabrics, fishing lines, fishing nets, non-woven fabrics for root winding of plant trees, non-woven fabrics for nursery beds, mulching materials, non-woven fabrics for agricultural and horticultural purposes such as grass-proof sheets, etc. , Shopping bags, garbage bags, tapes, fertilizer bags, separation membranes, etc. For molded products, bottles for drinks and cosmetics, disposable cups, trays, knives, forks, spoons and other tableware, flowerpots for agricultural and horticultural use, nursery beds And building materials such as pipes that need not be dug and temporary fixing materials.

[0020]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. In addition, the characteristic value in an Example was measured by the following method. Reduced specific viscosity (η _SP / C) Dissolve 0.5 g of polymer in 100 ml of chloroform,
It was measured at 25 ° C. The blocking ratio (B) was calculated from the measurement result of ¹ H-NMR using the following formula.

[0021]

(Equation 3) Melting point (Tm) DSC was measured at a rate of temperature rise of 10 ° C./min.

Example 1 An oligomer having a number average molecular weight of 10,000 was synthesized by ring-opening polymerization of ε-caprolactone using ethylene glycol as an initiator, and 7.0 g of this oligomer was added to L-lactide 2
0.0 g, stearic acid 114 mg and tin octylate 6
mg of the toluene solution was placed in a polymerization tube equipped with a stirrer and a nitrogen inlet tube, dried under vacuum for 2 hours, and replaced with nitrogen.
Ring-opening polymerization was carried out at 190 ° C. for 1 hour under a nitrogen stream. Thereafter, the polymer was dissolved in chloroform and poured into methanol to reprecipitate and purify the polymer. The reduced viscosity of the polymer obtained by drying under reduced pressure at 50 ° C. for 24 hours is 0.70 d.
L / g. As a result of 1 H-NMR measurement, it was confirmed that the copolymer was a complete block copolymer. This polymer showed a melting point at 170 ° C. as a result of DSC measurement.

Examples 2 to 11 Polymers were produced in the same manner as in Example 1 except for the conditions shown in Table 1. Table 1 also shows the evaluation results of the obtained polymer.

Comparative Example 1 A toluene solution of 17.0 g of L-lactide, 3.0 g of ε-caprolactone and 6 mg of tin octylate was placed in a polymerization tube equipped with a stirrer and a nitrogen inlet tube, and dried under vacuum for 2 hours and replaced with nitrogen. After that, ring-opening polymerization was performed at 190 ° C. for 1 hour under a nitrogen stream. Thereafter, the polymer was dissolved in chloroform and poured into methanol to reprecipitate and purify the polymer. The polymer was dried under reduced pressure at 50 ° C. for 24 hours to obtain a polymer. Table 2 shows the polymer evaluation results.

Comparative Examples 2 and 3 Polymers were produced in the same manner as in Comparative Example 1 except for the conditions shown in Table 1. Table 2 also shows the evaluation results of the obtained polymer.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

As is clear from the above examples, the polylactic acid-based polyester block copolymer of the present invention has a high melting point and an improved biodegradability.
Therefore, it can be expected to be used in a wide range of applications, and greatly contributes to solving the industrial and environmental problems.

Continuing from the front page (72) Inventor Kiyoshi Hotta 2-1-1 Katata, Otsu-shi, Shiga Toyo Spinning Co., Ltd. (72) Inventor Minako Arichi 2-1-1 Katata, Otsu-shi, Shiga Toyo Spinning (56) References JP-A-2-84431 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (2)

(57) [Claims] 1. A polylactic acid-based polyester block copolymer for molding, which is represented by the following general formula (I) and has a melting point of 120 ° C. or higher . Embedded image (In the formula, R ₁ represents an aliphatic alkylene group having 1 to 20 carbon atoms, and R ₂ represents an aliphatic hydrocarbon group having 2 to 20 carbon atoms. X represents a hydrogen atom or 1 to 2 carbon atoms. −
Represents an acyl group. l represents a positive integer of 1 or more, and m and n are positive numbers satisfying the following formula (II). ) (Equation 1) 2. The polylactic acid-based polyester block copolymer according to claim ₁ , wherein in the general formula (I), the compound providing R ₁ is β-butyrolactone and / or ε-caprolactone.