JP3471109B2 - Polylactic acid copolymer and molded product thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a plasticized polylactic acid copolymer suitable for fibers, films and other molded articles and molded articles thereof.

[0002]

2. Description of the Related Art Polymers that are biodegradable or decompose in a natural environment have been attracting attention from the viewpoint of environmental protection. In particular, polylactic acid is most expected because it is resource-friendly because it uses agricultural products as raw materials, and it is also excellent in melt moldability and heat resistance. However, since the polylactic acid homopolymer, which is an unmodified product, has high crystallinity, it is hard and brittle, and the molded product is easily damaged. Therefore, improvement in impact resistance and toughness is required. Further, depending on the application, for example, a part for a film or a molded product is required to have high flexibility and biodegradability.

The present invention is a novel polylactic acid which suppresses the crystallinity and can be adjusted to have impact resistance, toughness, flexibility, biodegradability, etc. according to the purpose and application, and which is cost-effective. It is intended to provide a copolymer.

[0004]

In order to solve the above-mentioned problems, the polylactic acid copolymer of the present invention comprises lactic acid, an aliphatic and / or aromatic dicarboxylic acid, and a polymer having hydroxyl groups at both ends. Degree 10 or less (excluding polymerization degree 3 or less)
Of oligoalkylene oxide, wherein the weight ratio of the lactic acid component is 50% or more.

Lactic acid includes L-lactic acid and D-lactic acid, which are polymerized to produce poly L-lactic acid, poly D-lactic acid, and poly L-lactic acid.
/ D-copolymerized lactic acid is obtained. The copolymer according to the present invention is obtained by copolymerizing these lactic acid or polylactic acid with an aliphatic or / and aromatic dicarboxylic acid and an alkylene oxide oligomer having hydroxyl groups at both ends.

Alkylene oxide polymers such as polyethylene oxide (glycol) and polypropylene oxide (glycol) are well known as copolymers with polylactic acid. However, these are unstable substances, and the molded products obtained from them are inferior in heat resistance and light resistance. Further, it tends to lower the glass transition temperature and is not suitable for applications requiring heat resistance.

Alkylene oxide oligomers such as those of the present invention, for example, those having a degree of polymerization of 10 or less and particularly having a molecular weight of 3
A copolymer of less than 00 and polylactic acid is not known. Even if an alkylene oxide oligomer, that is, an oligoalkylene oxide (glycol) is to be copolymerized with polylactic acid, a high molecular weight copolymer cannot be obtained, and its practicality is hardly achieved. However, the present inventor, as a result of diligent studies, obtained a wide range of improved properties by combining an oligoalkylene oxide having hydroxyl groups at both ends and a dicarboxylic acid in such a manner that they are approximately equimolar and copolymerized with polylactic acid. It was found that a high molecular weight polylactic acid copolymer having the above can be obtained, and the present invention was completed.

The oligoalkylene oxide suitable for the purpose of the present invention has a degree of polymerization of 10 or less (excluding the degree of polymerization of 3 or less) , and examples thereof include oligoethylene oxide, oligopropylene oxide, oligobutylene oxide, and copolymers thereof. (For example, oligoethylene / propylene oxide, oligoethylene / butylene oxide and the like).

The degree of polymerization of the copolymerization oligomer referred to herein is represented by the number of moles of constitutional units forming one molecule,
For example, one consisting of 1 mol of ethylene oxide and 1 mol of propylene oxide (glycol) has a degree of polymerization of 2,
A polymer composed of 2 mol of ethylene oxide and 1 mol of propylene oxide (glycol) has a degree of polymerization of 3.

A dimer of ethylene oxide, that is, diethylene glycol, can be obtained by adding 1 mol of ethylene oxide to ethylene glycol, and a trimer, ie, triethylene glycol can be obtained by adding 2 mol of ethylene oxide. Similarly, an oligoethylene / propylene oxide (glycol) copolymerized oligomer can be obtained by adding ethylene oxide to propylene glycol or propylene oxide to ethylene glycol. Similarly, various copolymerized oligomers can be obtained by adding ethylene oxide or propylene oxide to butanediol or hexanediol and can be applied to the present invention.

Thus, by adding ethylene oxide or propylene oxide to glycols, oligomers suitable for the present invention can be obtained easily and inexpensively. However, in general, such an addition reaction is not always carried out uniformly, and the obtained reaction product is a mixture having different degrees of polymerization. In such a mixed oligomer, a high molecular weight polyester can be obtained by investigating the amount of terminal hydroxyl group and reacting it with an approximately equimolar amount of dicarboxylic acid. It is also possible to separate this mixture using a method such as distillation or ultrafiltration to obtain a highly pure oligomer, and then to react it with a dicarboxylic acid.

Oligoalkylene oxide (glycol)
The dicarboxylic acid to be combined with may be aliphatic or aromatic, and both may be used in combination. Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid and the like, having 4 to 20 carbon atoms.
The dicarboxylic acids of are preferred. As the aromatic dicarboxylic acid, (ortho) phthalic acid, isophthalic acid, 5-sulfoisophthalic acid and its metal (Na, K etc.) salts, terephthalic acid, naphthalenedicarboxylic acid and the like are preferable, and those having a diphenyl group are also preferable. It is useful.

Generally, a dicarboxylic acid having an aromatic group,
Polyester ethers obtained from oligoalkylene oxides (glycols) tend to have higher melting points and glass transition points than those using aliphatic dicarboxylic acid components. An excellent copolymer is obtained. However, if the melting point of this polyester ether is too high, melt copolymerization with polylactic acid becomes difficult, and the melt moldability of the obtained copolymer becomes poor. Therefore, when an aromatic dicarboxylic acid is used, pay attention to the melting point of the polyester ether obtained from the aromatic dicarboxylic acid and the oligoalkylene oxide (glycol). For example, the melting point is 200 ° C or lower, particularly 180 ° C or lower, and most preferably 170 ° C or lower. It is desirable to adjust the ingredients. Reducing the melting point of this polyester ether can be extremely easily realized by using an oligoalkylene oxide (glycol) having a long chain length or by using (mixing) an aliphatic dicarboxylic acid together. Similarly, when a compound having low symmetry such as isophthalic acid is used, crystallinity is lowered and melting point is lowered. On the other hand, when a highly symmetric compound such as terephthalic acid or a compound having a large molecular weight component such as a naphthalene nucleus is used, the melting point and heat resistance are increased.

The copolymerization of polylactic acid (or lactic acid) with a polyester ether composed of an aliphatic or / and aromatic dicarboxylic acid and an oligoalkylene oxide (glycol) can be easily carried out. For example, the above-mentioned dicarboxylic acid and glycol are polymerized in substantially equimolar amounts to obtain a polyester ether having a hydroxyl group at the terminal, and then the terminal hydroxyl group of this polyester ether is used as a polymerization initiation point to obtain a lactide which is a cyclic dimer of lactic acid. By performing ring-opening polymerization,
A block copolymer of a polylactic acid segment (block A) and a polyester ether (block B) is obtained.
When one end of the polyester ether is a hydroxyl group, an A / B type block copolymer is obtained, and when both ends are a hydroxyl group, an A / B / A type block copolymer is obtained. To be

If the oligoalkylene oxide (glycol) and dicarboxylic acid are equimolar, one end group of the polyester ether will be a hydroxyl group and the other will be a carboxyl group. With a slight excess of oligoalkylene oxide,
Both terminal groups of the polyester ether become hydroxyl groups. For example, by completely reacting 101 mol of oligoalkylene oxide (glycol) with 100 mol of dicarboxylic acid, a polyester ether having a degree of polymerization of about 101 can be obtained. That is, the molecular weight and end groups of the polyester ether can be controlled by adjusting the molar ratio of the dicarboxylic acid component and the glycol component. Monofunctional compound,
For example, when a small amount of monoalcohol or monocarboxylic acid is added, it functions as a polymerization terminator and a polyester ether having a blocked end is obtained. Of course, for copolymerization with lactide, it is necessary that at least one end of the polyester ether has a hydroxyl group, the polymerization terminator is limited to monoalcohol, and monocarboxylic acid is not used.

In this way, a block copolymer can be easily obtained by reacting (polymerizing) a polyester ether composed of a dicarboxylic acid and an oligoalkylene oxide (glycol) with a lactide. The block copolymer can improve toughness, plasticity, flexibility, dyeability, glass transition point, etc., without significantly lowering the crystallinity or melting point of polylactic acid, which is the main component, and the object of the present invention. Is particularly preferred. On the other hand, the random copolymer can be obtained by preparing lactic acid, dicarboxylic acid and oligoalkylene oxide (glycol) so that the carboxyl group and the hydroxyl group are almost equimolar and dehydrating and condensing in a solvent or in a molten state. it can. This random copolymer has low crystallinity and becomes amorphous when the copolymerization ratio is high,
Although it is inferior in heat resistance, it can be improved in toughness, plasticity and flexibility, so it can be used in applications where heat resistance is not required so much.

The molecular weight of the polylactic acid copolymer of the present invention needs to be large to some extent from the practical viewpoint of strength and processability. For fibers, films and many molded products, a molecular weight of 50,000 or more is required, preferably 70,000 to 500,000, and 1
Most commonly used is from 0,000 to 300,000. In order to obtain such a high molecular weight block copolymer, it is necessary that the polyester ether composed of a dicarboxylic acid and an oligoalkylene oxide (glycol) has a relatively high molecular weight. If the molecular weight of this polyester ether is small,
It is difficult to obtain a sufficient modifying effect by increasing the copolymerization ratio (polymerization fraction) and obtain a high molecular weight block copolymer. From this point of view, the molecular weight of the polyester ether (block B) is preferably 5,000 or more, particularly preferably 8,000 or more, most preferably 10,000 to 100,000. That is, an excellent polylactic acid copolymer can be obtained by preparing such a high molecular weight polyester ether and block-copolymerizing it with lactide.

In the copolymer of the present invention, the main component, polylactic acid or polylactic acid segment (block A), has sufficiently high crystallinity and gives a molded product high heat resistance. on the other hand,
The polyester ether segment (block B) obtained from a dicarboxylic acid and an oligoalkylene oxide (glycol), which is a copolymer component, is preferably amorphous from the viewpoint of impact resistance and flexibility. For that purpose, it is preferable that one or both of dicarboxylic acids and glycols constituting the polyester ether segment are not used alone but one or both of them are used (a certain kind of copolymer). For example, as a glycol component, it is useful to mix diethylene glycol and triethylene glycol, mix diethylene glycol and tripropylene glycol, and use a copolymer oligomer of ethylene oxide and propylene glycol. Similarly, mixing adipic acid and sebacic acid, mixing adipic acid and terephthalic acid or isophthalic acid, mixing adipic acid and naphthalenedicarboxylic acid, and the like are also useful.

In the copolymer of the present invention, the larger the copolymerization ratio of the copolymerization component composed of dicarboxylic acid and oligoalkylene oxide (polymerization fraction in the copolymer), the stronger the polylactic acid copolymer obtained. Be denatured. Therefore, the purpose
A suitable copolymerization ratio may be selected according to the application, but in many cases, the copolymerization ratio is in the range of 2 to 40%, particularly 3 to 30%, and 5 to 20% is most widely used.

The main components in the copolymer of the present invention are lactic acid, aliphatic and / or aromatic dicarboxylic acid, and oligoalkylene oxide (glycol).
However, a component other than these, such as an aliphatic glycol having 2 to 20 carbon atoms, may be added as a secondary component. However,
The main component (50% by weight or more) in the glycol component is oligoalkylene oxide.

Similarly, the copolymer of the present invention can be modified in various ways by adding a secondary additive. Examples of secondary additives include stabilizers, antioxidants, UV absorbers,
Pigments, colorants, various inorganic particles, various fillers, volatilizers,
Examples include hydrophilic agents, antistatic agents, release agents, plasticizers, physiologically active substances, preservatives, fragrances, antibacterial agents, foaming agents, and the like.

In the present invention and the following examples, parts,%
Unless otherwise specified, weight ratios and weight fractions are shown. The molecular weight of the polymer containing lactic acid as the main component is the weight average value of the dispersion of the polymer excluding the molecular weight of 500 or less in terms of polystyrene by GPC analysis of a 0.1% chloroform solution of the sample.

[0023]

[Example] Diethylene glycol, triethylene glycol, and adipic acid were mixed at a molar ratio of 50/50/98, and 0.05% of tetrabutyl titanate was added to the mixture, and the mixture was stirred at 220 ° C in nitrogen for 2 hours. The reaction was carried out, and the pressure was further reduced and the reaction was carried out at 1 Torr for 2 hours to obtain a high-viscosity starch syrup-like polyester ether P1. P1 has hydroxyl groups at both ends and has a molecular weight of about 18,000.

7 parts of polyester ether P1 was melt-mixed with 93 parts of L-lactide having an optical purity of 99% or more, tin octylate 0.03%, and Ciba Geigy Irganox 1010 (antioxidant) 0.5% based on the total polymerization system. And 0.1% of titanium oxide particles (crystal nucleating agent) with a diameter of 0.05 μm are mixed, and the mixture is melted with two screws in a continuous melt mixer.
Mix and react for an average of 30 minutes at ℃, then tin octylate
Mixing 0.1%, consisting of screw groups that mesh with each other and oval (2-flight type) stirring element groups that mesh with each other 2
Polymerization was carried out at 190 ° C. for 17 minutes using a shaft kneader, then extruded from a die, cooled and solidified with water, and cut to obtain a polylactic acid copolymer chip C1.

Chip C1 was treated in nitrogen at 120 ° C. and a pressure of 1.5 kg / cm ² for 12 hours, and then heat-treated (solid phase polymerization) at 160 ° C. and normal pressure for 48 hours to obtain chip C2. Chip C2 has an average molecular weight of 181,000 and residual monomer (lactide) of 0.2
%Met.

Approximately the same as the chip C2, except that diethylene glycol as a polyester ether was polymerized with isophthalic acid.
A chip of polylactic acid copolymer having a molecular weight of 183,000 obtained by copolymerizing 7% of 6,000 and a melting point of about 130 ° C is designated as C3. On the other hand, for comparison, a chip of poly L-lactic acid (homopolymer) having a molecular weight of 183,000 obtained without copolymerizing polyester ether is designated as C4. Using chips C2 to C4, injection molding was performed to prepare test pieces with V-shaped notches, and the impact strengths were measured. Table 1 shows the impact strength of the chips used and the test pieces obtained therefrom. As seen in Table 1, the molded products obtained from the chips C2 and C3 of the present invention have higher impact strength and superior impact resistance as compared with the comparative examples.

[0027]

[Table 1]

[0028]

According to the present invention, a novel polylactic acid copolymer which is internally plasticized and has improved impact resistance and flexibility can be obtained easily and at low cost. By adjusting the weight ratio of the oligoalkylene oxide as the copolymerization component and the polyester ether obtained from the aliphatic or / and aromatic dicarboxylic acid, a polymer having a wide range of impact resistance and flexibility can be obtained. It can be applied to various purposes.

Furthermore, the copolymer of the present invention has a high affinity for many plasticizers, for example, a plasticizer having an aliphatic or / and aromatic dicarboxylic acid component, particularly the same dicarboxylic acid as the copolymerization component of the present invention. To obtain a composition having a high affinity for a low molecular weight type or high molecular weight type plasticizer having a component or a glycol component, capable of being mixed easily and uniformly, and having excellent transparency, flexibility and impact resistance. Therefore, it can be applied to a wide variety of applications.

Further, it is recognized that the biodegradability and the spontaneous disintegration tend to be increased with the decrease in crystallinity due to the copolymerization of oligoalkylene oxide and dicarboxylic acid, and the decomposition rate of unmodified polylactic acid (homopolymer) is slow. Suitable for too many uses. For the purpose of enhancing biodegradability, those using an aliphatic dicarboxylic acid are preferable. Generally, polyalkylene oxide is also biodegradable, but the alkylene oxide oligomer used in the present invention is particularly excellent in degradability. In general, polyalkylene oxides are apt to be oxidized by heating, ultraviolet rays, etc. and tend to be inferior in stability, but the oligomer (oligoalkylene oxide) used in the present invention is superior in stability and reliability to the polymer. Highly molded products can be obtained.

The copolymer of the present invention and the composition in which the plasticizer is added to the copolymer of the present invention can be improved so as to have a wide range of properties. Molded products, that is, fibers, knits, woven fabrics, non-woven fabrics, Suitable for paper, felt, net, rope, film, sheet, plate, rod, tube, various containers, various parts, various molded products, etc. Can be used for.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masakazu Kobayashi Masakazu Kobayashi, No. 1, Kuwahara-cho, Nishinokyo, Nakagyo-ku, Kyoto Shimadzu Corporation Sanjo Factory (56) Reference JP-A-7-233245 (JP, A) JP-A-7- 173266 (JP, A) JP-A-8-165339 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (7)

(57) [Claims] 1. A lactic acid, an aliphatic and / or aromatic dicarboxylic acid, and a polymerization degree of 10 or less having hydroxyl groups at both ends (however,
Of the lactic acid component is 50% by weight.
The polylactic acid copolymer is characterized by the above. 2. The aliphatic dicarboxylic acid has 4 to 2 carbon atoms.
The polylactic acid copolymer according to claim 1, which is 0. 3. The aromatic dicarboxylic acid is at least one selected from phthalic acid, isophthalic acid, 5-sulfoisophthalic acid and metal salts thereof, terephthalic acid, and naphthalenedicarboxylic acid . The polylactic acid copolymer according to any one of claims. 4. The oligoalkylene oxide is an oligomer of ethylene oxide, propylene oxide, butylene oxide or a copolymerization oligomer thereof, and has a molecular weight of 3
The polylactic acid copolymer according to any one of claims 1 to 3 , which is less than 00. 5. The polylactic acid copolymer according to claim 1, wherein the weight ratio of the lactic acid component is 70 to 97%. 6. A polylactic acid segment (block A),
A polylactic acid copolymer according to any one of claims 1 to 5 , which is a block copolymer having a polyester ether segment (block B) of an aliphatic and / or aromatic dicarboxylic acid component and an oligoalkylene oxide (glycol) component. Polymer. 7. A molded article comprising the polylactic acid copolymer according to any one of claims 1 to 6.