JPH0940761A - Polylactic acid block copolymer, production thereof and molded article made therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polylactic acid block copolymer excellent in crystallinity, heat resistance, flexibility and toughness by forming a block copolymer consisting of crystalline segments and amorphous segments of lactic acid. SOLUTION: This polylactic acid block copolymer is one in which crystalline segments comprising a substantial homopolymer of poly-L-lactic acid or poly-D- lactic acid are combined with amorphous segments composed mainly of L-lactic acid and D-lactic acid. The heat absorption on melting of the crystal of the copolymer is preferably at least 5J/g. This copolymer is obtained by reacting an amorphous polymer composed mainly of L-lactic acid and D-lactic acid and having a hydroxyl group at least on one end with L-lactide or D-lactide, or reacting a substantial homopolymer or L-lactic acid or D-lactic acid having a hydroxyl group at least on one end with L-lactide, D-lactide and/or LD-lactide.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to crystallinity, heat resistance,
The present invention relates to a novel polylactic acid block copolymer having excellent flexibility and toughness, a method for producing the same, and a molded product 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. Among them, polylactic acid is excellent in cost and performance using agricultural products as raw materials, and is expected as the most practical biodegradable polymer. However, since polylactic acid has a rigid molecular structure and high crystallinity, it has the drawback that molded products are hard and brittle. Therefore, it has been attempted to suppress crystallinity by copolymerization and improve flexibility and toughness. As one of the methods, copolymerization of L-lactic acid and D-lactic acid is considered.

[0003]

However, the L / D-lactic acid copolymerization that has been conducted so far is a random copolymerization, and although the flexibility and toughness are improved, the crystallinity is lost and the heat resistance is remarkably increased. Only the inferior is obtained. The present inventors have earnestly studied to improve flexibility and toughness while maintaining preferable crystallinity and heat resistance of polylactic acid, and arrived at the present invention.

[0004]

The above object of the present invention is to provide a crystalline segment (A) comprising a substantially homopolymer of poly-L-lactic acid or poly-D-lactic acid, and L-lactic acid and D-lactic acid.
It is achieved by a novel polylactic acid block copolymer in which an amorphous segment (B) containing lactic acid as a main component is bound.

Here, the segment means a part of a polymer molecular chain. The substantially homopolymer of poly L-lactic acid or poly D-lactic acid forming the segment (A) is poly L-lactic acid.
-Lactic acid homopolymer, poly D-lactic acid homopolymer, and those obtained by copolymerizing them with a small amount of other components such that the melting point and crystallinity are not significantly impaired. For example, even if about 2-3 wt% of D-lactic acid component is copolymerized with poly L-lactic acid homopolymer (melting point 170 to 180 ° C.), the melting point is slightly decreased (10 ° C. or less), and Are considered to be homopolymers. The same applies when another ester bond-forming component is copolymerized as a small amount of another component. However, when the D-lactic acid component is copolymerized with poly L-lactic acid in an amount of, for example, more than 5%, the melting point is lowered by 20 ° C. or more, and it cannot be said to be substantially a homopolymer. Even if such a small amount of the second component is mixed, the heat resistance of the product tends to be impaired, and it should be avoided as much as possible. That is, segment (A)
Is preferably of high purity. Therefore, it is preferable to increase the purity of the polymerization raw material, to keep the polymerization reaction at a temperature as low as possible and to prevent racemization during the reaction.

The amorphous polymer mainly composed of L-lactic acid and D-lactic acid forming the segment (B) is (1) L
/ D-lactic acid copolymer, and (2) L / D-lactic acid copolymer having an ester bond-forming third component (one or more)
Of 50% by weight or less and is not crystalline. Whether the polymer is crystalline or not is determined as a fiber or a film, sufficiently stretched and heat treated, and then tested by a scanning differential calorimeter (hereinafter referred to as DSC) to determine whether an endothermic peak of melting of the crystal is present. Alternatively, it can be easily determined by conducting an X-ray diffraction test on a stretch-oriented fiber or film. In the case of a random copolymer of L / D-lactic acid, the L / D ratio is 94/6 to 6/94, especially 9
The range of 0/10 to 10/90 is often amorphous.

The combination form of the segments (A) and (B) is not particularly limited. For example, AB type in which one (A) and one (B) are bound, BAB type in which two (B) are bound to one (A), the opposite ABA type, a plurality of ( It is arbitrary such as ABABA type in which A) and a plurality of (B) are combined. However, AB type, ABA type, and BAB type are preferable from the viewpoint of easy production and excellent physical properties (crystallinity and heat resistance).

As the bond between the segments (A) and (B), an ester bond is most widely used, but it may be bonded by another "joint". For example, a polymer for the segment (A) and a polymer for the segment (B), both of which have a hydroxyl group at the terminal, can be reacted with a dicarboxylic acid anhydride or a dicarboxylic acid chloride to bond them. Similarly, a diisocyanate compound can be reacted to bond both. That is, a well-known chemical bond such as an ester bond, a urethane bond, a urea bond, an amide bond, a carbonate bond or the like can be applied as the "joint".

The molecular weights of the segments (A) and (B) are not particularly limited. The molecular weight of each of the segments (A) and (B) may be selected depending on the weight ratio and the desired physical properties. However, in general, if the molecular weight is too small,
The block (segment) copolymer has unsatisfactory features, which is not preferable. The molecular weight of the segment is preferably 2000 or more, particularly preferably 5000 or more, and in many cases 10,000 to 3
Widely used is 00000, especially 30,000 to 200,000.

If the weight ratio of the segments (A) and (B) is too small, the effect is poor. For example, the weight ratio A / B is in the range of about 20/80 to 85/15, particularly 30/70 to 80 /. The range of 20 is preferable and 40/6
The range 0-75 / 25 is most widely used. The segment (A) is, so to speak, a hard segment, and the more it is, the higher the melting point and the softening point and the better the heat resistance. Conversely, the more the segment (B) is the soft segment, the more the flexibility,
Excellent impact resistance and elastic recovery. In the conventional random copolymerization, the copolymer is non-crystalline and the heat resistance is remarkably inferior in a wide range of the copolymerization ratio, but according to the present invention, a crystalline product having improved heat resistance can be obtained. The molecular weight of the copolymer of the present invention is not particularly limited, but is often 5
0000 or more is preferable, 80,000 or more is particularly preferable, and the range of 100,000 to 300,000 is most widely used. As a few examples of preferable molecular structures, poly L-lactic acid (homopolymer) having a molecular weight of 150,000 as the segment (A) and a molecular weight of 50 as the segment (B).
000 L-lactic acid / D-lactic acid 90/10 random copolymer as a component AB type block copolymer (molecular weight 20
0000), also BAB type (molecular weight 250,000),
Similarly, there is an ABA type (molecular weight 250,000) of A having a molecular weight of 100,000 and B having a molecular weight of 50,000. The copolymer of the present invention does not have to have the same molecular structure (structure of block copolymer) of all molecules, and may be an aggregate of various molecular structures.
In the actual polymerization process, various molecular aggregates (for example, Gaussian distribution) are obtained due to statistical variations. However, the component and molecular weight of each block (segment) can be represented by an average value, and that is practically sufficient.

FIG. 1 is an explanatory view showing the relationship between the copolymerization ratio of poly L-lactic acid and poly D-lactic acid and the melting point. In the figure, curve 1 shows an example of a block copolymer according to the present invention, and curve 2 shows an example of a random copolymer. In random copolymerization, the homopolymer is copolymerized with 5 to 6% of optical isomers, whereby the crystallinity is lost and the melting point becomes unclear. The solid line of the curve 2 indicates the region where the melting point of the crystal is observed by the DSC method, and the dotted line indicates the temperature at which the melting point of the polymer starts without the melting point being observed by the DSC method. Of course, this flow starting point also varies depending on the molecular weight of the polymer, so it cannot be uniquely shown, and the figure shows only an example. Similarly, the melting point of the block copolymer also changes depending on the molecular structure and molecular weight of the segment, the method of connecting the segments and the molecular weight of the entire molecule, and thus the curve 1 is only an example. However, in the block copolymer according to the present invention, the crystallinity and the melting point can be maintained over the entire region of the L / D ratio, and as a result, the melting point and the heat resistance higher than those of the random copolymer can be obtained. It will be appreciated that, in essence, this is distinct from random copolymerization.

As described above, the amorphous segment (B) constituting the block copolymer of the present invention contains other polymerization raw materials (constituents) for polyester other than lactic acid within the range of 50% by weight or less. It can be copolymerized. The purpose of copolymerization is hydrophilicity, water repellency, dyeability, antioxidant property, flexibility, elastic recovery property, impact resistance, heat resistance, gas barrier property, glass transition temperature, decomposability, smoothness, releasability, Improving moldability and cost reduction. Examples of copolymerizable components or raw materials include (1) hydroxy acids such as glycolic acid, hydroxybutylcarboxylic acid and hydroxybenzoic acid, (2) aliphatic lactones such as glycolide, butyrolactone and caprolactone, and (3) ethylene glycol. C2-20 diols such as propylene glycol, butanediol and hexanediol, (3) succinic acid, adipic acid, sebacic acid, decanedicarboxylic acid, phthalic acid, isophthalic acid, sulfoisophthalic acid (alkali metal salt), terephthalate Acids, naphthalene dicarboxylic acid and other aliphatic and aromatic dicarboxylic acids, and further as polymers or oligomers having a hydroxyl group at the molecular end, (4) polyalkylene ethers such as polyethylene glycol, polypropylene glycol and polybutylene ether, and These copolymers or oligomers, (5) poly hexane carbonates, polyalkylene carbonates, such as octane carbonate, (6) dimethylsiloxane, diethyl siloxane, such as polyorganosiloxanes, such as diphenyl siloxane.

For example, a compound having a sulfone group or an ether bond for improving hydrophilicity and degradability, a silicon compound for improving water repellency, and a compound having a glass transition temperature of room temperature or lower for improving flexibility and toughness (polyalkylene). Copolymerization of lactam, polyalkylene alkylate, polyalkylene ether, polyalkylene carbonate, etc.) and those having a high glass transition point (aromatic compounds etc.) are effective for improving heat resistance.

The block copolymer of the present invention is characterized in that it is crystalline and has better heat resistance than an amorphous one. The degree of crystallinity can be evaluated by DSC analysis as described above. The larger the melting (melting) endothermic amount of the crystal by DSC analysis, the higher the crystallinity. For the purpose of the present invention, the melt endothermic amount of the crystal of the block copolymer is preferably 5 Joule (J) / g or more, particularly preferably 10 J / g or more, most preferably 15 J / g or more. Poly L-
The melting endotherm of lactic acid homopolymer crystals is 40-50 J /
g, melting point (peak value) is about 170 to 180 ° C. The melting point of the block copolymer of the present invention is preferably 130 ° C or higher, particularly preferably 140 ° C or higher, and 150 ° C or higher is most widely used.

In general, polylactic acid includes direct polymerization of lactic acid (dehydration condensation), condensation of lactic acid ester (methyl ester, ethyl ester, etc.) (dealcoholization), and cyclic lactic acid 2
It is polymerized by ring-opening polymerization of lactide which is a monomer. The copolymer of the present invention can be easily obtained by ring-opening polymerization of lactide. In the direct polymerization (dehydration condensation) of lactic acid or the condensation method of lactic acid ester, random copolymerization is likely to occur and block copolymerization is often extremely difficult. Lactide is an L-lactic acid dimer, LL-lactide (referred to as L-lactide), and D-lactic acid dimer, DD-lactide (D-lactide).
Lactide) and L / D-lactide (also called mesolactide) containing L-lactic acid and D-lactic acid as components. For the polymerization of the crystalline segment (A), it is preferable to use L-lactide or D-lactide, and for the polymerization of the amorphous segment (B), the above-mentioned three lactides are mixed to obtain a desired L / D ratio. Can be polymerized.

The block copolymer of the present invention comprises first producing (1) a crystalline substantially homopolymer of poly (L-lactic acid) or a substantially homopolymer of poly (D-lactic acid), that is, a polymer forming the segment (A). , (2) L-lactide, D-lactide L / D lactide, and optionally other ester bond-forming raw materials are mixed and reacted to form the amorphous segment (B) 2
It can be obtained by the process method. For this purpose, one or both of the molecular ends of the segment (A) -forming polymer produced in the first step must be hydroxyl groups. Such polylactic acid homopolymer can be obtained by using a monoalcohol or a polyhydric alcohol (for example, diol or triol) as a polymerization initiator.

Similarly, the block copolymer of the present invention comprises (1) L-lactide (or L-lactic acid), D-lactide (or D-lactic acid), L / D lactide and, if necessary, other ester. A bond-forming raw material is mixed and reacted (polymerized) to produce an amorphous polymer that forms the segment (B), and (2) L-lactide or D-lactide is reacted (polymerized) with the crystalline to form a crystalline polymer. It can also be manufactured by forming the segment (A).
Also in this case, a monoalcohol or a polyhydric alcohol can be used because a hydroxyl group is introduced into the molecular terminal (one or both) of the polymer produced in the first step. By these two methods, AB, ABA or BAB type block copolymers can be produced fairly accurately. The above two steps can be performed continuously or / and batchwise.

As another method for producing the block copolymer of the present invention, first, (1) a polymer for a crystalline segment (A) having a hydroxyl group (or other functional group) at one or both molecular ends, Making both of the polymers for the amorphous segment (B), (2) reacting them with a polyfunctional compound such as diisocyanate, dicarboxylic acid anhydride or dicarboxylic acid halide, dicarboxylic acid,
There is a method of joining the segments (A) and (B) using a polyfunctional compound as a joint. This method is AB type,
In addition to ABA type and BAB type, ABAB, ABABA, BA
BAB and various other types, and a mixture of various types can be manufactured. This method can also be carried out continuously or / and batchwise.

The block copolymer of the present invention contains stabilizers, antioxidants, ultraviolet absorbers, pigments, colorants, various inorganic particles, various fillers, water repellents as secondary additives depending on the purpose of use. Agents, hydrophilic agents, release agents, plasticizers, bioactive agents, antibacterial agents, preservatives and the like can be added. The block copolymer of the present invention includes fibers, sheets, films, plates, rods,
It can be suitably applied to applications such as cylinders, containers and various molded products.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In the following examples,% and parts are weight ratios unless otherwise specified. The molecular weight of the aliphatic polyester is the weight average value of the dispersion of the polymer component excluding the component having a molecular weight of 1000 or less in GPC analysis of a 0.1% chloroform solution of the sample. The DSC analysis was performed with a sample of 10 mg in a nitrogen atmosphere and a temperature rising rate of 10 ° C./m.
went in. In addition, the impact strength was measured according to JIS K
7110 Measured by the Izod impact test method.

(Example 1) L having an optical purity of 99.5% or more
100 parts of lactide, 100 ppm of tin octylate as a polymerization catalyst, 0.07 parts of octyl alcohol as a polymerization initiator, 0.1 part of Ciba Geigy Irganox 1010 as an antioxidant, and a reaction with a stirrer Prepolymer PP1 was obtained by reacting for 12 minutes at 185 ° C. in a container under a nitrogen atmosphere. The prepolymer PP1 is a polylactic acid homopolymer (crystalline) having a molecular weight of 156000 and a hydroxyl group at most one end.

Almost the same as the prepolymer PP1, except that 0.07% of triethylene glycol was used as a polymerization initiator.
Was used to obtain a prepolymer PP2. Prepolymer P
P2 is a polylactic acid homopolymer (crystalline) having hydroxyl groups at most of both ends and a molecular weight of 162000.

To a twin-screw kneading extruder having a diameter of 30 mm, the molten prepolymer PP1 and an 8/2 mixture of L-lactide and D-lactide were continuously fed at a weight ratio of 70/30,
At the same time, polymerization catalyst tin octylate 100p for lactide
pm was added, and the mixture was polymerized at 190 ° C. for 7 minutes on average. After the polymerization, the product was extruded from a nozzle, cooled with water, cut into chips, dried, and then treated in nitrogen at 140 ° C. for 6 hours (solid phase polymerization) to obtain a block copolymer BP1. BP1 is an AB type block copolymer of a poly L-lactic acid (crystalline) segment (A) having a molecular weight of 223,000 and a molecular weight of 156000 and a poly L / D-copolymerized lactic acid (amorphous) segment (B) having a molecular weight of 67,000. It is united.

Block copolymer BP2 was obtained in substantially the same manner as block copolymer BP1, but using prepolymer PP2. BP2 is a BAB type block copolymer of a poly L- (crystalline) lactic acid segment (A) having a molecular weight of 216000 and a molecular weight of 156000 and a poly L / D copolymerized lactic acid (amorphous) segment (B) having a molecular weight of 30,000. Is.

For comparison, poly L-having a molecular weight of 235,000 obtained by polymerizing in substantially the same manner as prepolymer PP1 except that a polymerization initiator was not used, and then solid-phase polymerizing in a chip form.
Let lactic acid homopolymer be HP1. In addition, 8/2 of L-lactide and D-lactide having an optical purity of 99.5% or more, respectively.
Polymerization was carried out in the same manner as in the prepolymer PP1 below without using a polymerization initiator, and then solid-state polymerization was carried out in a chip form to obtain a poly L / D-lactic acid copolymer having a molecular weight of 228,000 as a polymer AP1. To do.

Table 1 shows the melting point, melting endotherm and impact strength of each polymer. The polymer AP1 has a softening temperature because it is amorphous and its melting point is unclear by the DSC method. As seen in Table 1, the polymers BP1 and BP2 of the invention
Has a high melting point and melting endotherm, excellent crystallinity, and impact resistance. On the other hand, poly L-lactic acid homopolymer HP1 is excellent in crystallinity but inferior in impact resistance.
It is clear that the / D-lactic acid copolymer AP1 is excellent in impact resistance but inferior in heat resistance.

[0027]

[Table 1] Example 2 A crystalline polymer having a molecular weight of 107,000 obtained by adding 0.12% of a polymerization initiator was prepared in substantially the same manner as in the prepolymer PP2 of the prepolymer PP3.
And Similar to Prepolymer PP2 of Example 1,
However, 80 parts of L-lactide having an optical purity of 99.5% or more, 20 parts of D-lactide having an optical purity of 99.5% or more, and 0.17% of triethylene glycol were used to obtain a molecular weight of 7200.
0 amorphous prepolymer PP4 was obtained. Prepolymer P
P3 (107 parts), PP4 (72 parts) and terephthalic acid dichloride (0.36 parts) were mixed, reacted using the same twin-screw kneading extruder as in Example 1 at 190 ° C. for 6 minutes and then extruded from a nozzle to form a cooling chip. After heat treatment for 4 hours in nitrogen at ℃, washed with acetone containing 3% of water and dried to obtain a block copolymer BP3. The molecular weight of BP3 is 2520
At 00, it is assumed to be a mixture of AB type, ABA type, BAB type, ABAB type and the like.

1/1 mixture of polyhexane adipate having hydroxyl groups at both ends and a molecular weight of 20000 and polybutylene adipate having hydroxyl groups at both ends and a molecular weight of 20000 3
100 parts of tin octylate was mixed with 0 parts, 50 parts of L-lactide having an optical purity of 99.5% or more and 20 parts of D-lactide having an optical purity of 99.5% or more, and the following Example 1 was used.
Prepolymer P1 is polymerized in the same manner as Prepolymer PP1
P5 was obtained. The prepolymer PP5 has a molecular weight of 63,000 and has hydroxyl groups at both ends.

The molten prepolymer PP5 and L-lactide were continuously fed to a biaxial kneading extruder at a weight ratio of 1/2,
At the same time, 100 ppm of tin octylate was added to lactide, and a block copolymer BP4 was obtained in the same manner as in the block copolymer BP1 of Example 1 below. BP4 has a molecular weight of 1
87,000 is an ABA type block copolymer of an amorphous segment (B) containing a polybutylene / hexane adipate component and a crystalline segment (A) composed of poly L-lactic acid. Table 2 shows the physical properties of BP3 and BP4. Table 2
As can be seen, BP3 and BP4 have excellent crystallinity and impact resistance. Particularly, BP4 is excellent in impact resistance because it contains the components of polybutylene adipate and polyhexane adipate having a low glass transition point.

[0030]

[Table 2]

[0031]

Industrial Applicability According to the present invention, the drawback of polylactic acid homopolymer, which is hard and brittle, is effectively improved while suppressing the deterioration of heat resistance and crystallinity, and it has both toughness and heat resistance, which is suitable for various applications. It has become possible to provide a new, naturally degradable polymer. The block copolymer of the present invention has higher crystallinity and heat resistance than a random copolymer, and by having two phases of a hard segment and a soft segment, rubber elastic properties are expressed and flexibility, It is possible to obtain a material having excellent toughness and elastic recovery rate. Further, the copolymer of the present invention tends to have a faster decomposition rate than a homopolymer, and is suitable for applications where the homopolymer decomposes too slowly. Similarly, the copolymer of the present invention is more easily dissolved in a solvent than a homopolymer, and is easy to produce a film by a solvent method or to coat a cloth or the like. Furthermore, the copolymer of the present invention can change its properties in a very wide range by changing the molecular weight and the weight ratio of each crystalline and amorphous segment, and has an extremely wide range of applications. There is a feature.

The polymers of the present invention can be used in fibers, knits, fabrics,
Non-woven fabric, paper, net, rope, string, sheet, film, board,
It can be used for rods, tubes, containers, bags, plates, dishes, various parts, and other various molded products.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a relationship between an L / D ratio of a poly L / D-lactic acid copolymer and a melting point.

[Explanation of symbols]

1: Example of relationship between L / D ratio and melting point of block copolymer of the present invention 2: Example of relationship between L / D ratio and melting point of conventional random copolymer

Claims (4)

[Claims] 1. A crystalline segment (A) comprising a substantially homopolymer of poly L-lactic acid or poly D-lactic acid, and L-
A polylactic acid block copolymer obtained by bonding lactic acid and an amorphous segment (B) containing D-lactic acid as a main component. 2. The melting endotherm of the crystal measured by a scanning differential calorimeter in a sufficiently crystallized and / or oriented state is
The copolymer according to claim 1, which has 5 joules or more per 1 g of the polymer. (1) L-lactide or D-lactide is reacted with an amorphous polymer having L-lactic acid and D-lactic acid as main components having a hydroxyl group at at least one terminal, or (2) For L-lactic acid or a substantially homopolymer of L-lactic acid or D-lactic acid having a hydroxyl group at at least one terminal, L-lactide, D-lactide or / and L
The reaction with D-lactide is characterized in that
2) The method for producing the copolymer according to 2). 4. A fiber, a knitted fabric, a woven fabric, a non-woven fabric, a paper, a felt, a cord, a rope, a sheet, a film, a rod, a cylinder, a plate, which comprises the copolymer according to any one of claims 1 to 2 as at least a part thereof.
Plates, tableware, containers, various parts and other molded products.