JPH08245866A - Plasticized polylactic acid composition and its molded item - Google Patents

Abstract

PURPOSE: To obtain an improved polylactic acid compsn. which has a reduced crystallinity, is excellent in impact resistance, softness, biodegradability, flexibility, and clarity suitable for various puposes and applications, and hardly exhibits surface staining due to plasticizer exudation and to obtain a molded item from the compsn. CONSTITUTION: This plasticized polylactic acid compsn. is obtd. by compounding a polymer obtained mainly from lactic acid with an aliph. polyester plasticizer obtained mainly from an aliph. dicarboxylic acid and linear-chain diol. The affinity between the polymer and the plasticizer is enhanced by introducing closely similar structural units into both the polymer and the plasticizer, thereby the surface staining of the compsn. due to plasticizer exudation and the loss of clarity and gloss of molded items obtd. from the compsn. can be prevented.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a plasticized biodegradable polylactic acid composition and a molded article 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 resource-friendly because it uses agricultural products as raw materials,
It is also most expected because it has excellent melt moldability and heat resistance. However, the polylactic acid homopolymer, which is an unmodified product, has high crystallinity and a rigid molecular structure, and thus is hard and brittle, and the molded product is easily damaged. Therefore, improvement in flexibility is required. Further, depending on the application, for example, a part for film or a molded product is required to have high flexibility.

Therefore, conventionally, the third component has been copolymerized or mixed to enhance flexibility and improve brittleness.

[0004]

However, according to the copolymerization method, there arises a problem that the melting point and the heat resistance decrease with the decrease in crystallinity. According to the method of mixing plasticizers,
Since the plasticizer and the matrix polylactic acid have a low affinity, problems such as leaching of the plasticizer to stain the surface of the composition and deterioration of the transparency and gloss of the molded product occur.

The present invention is improved in that it has excellent flexibility, flexibility, transparency and luster without excessively impairing crystallinity and heat resistance, and has little surface stain due to leaching of the plasticizer. The present invention provides a polylactic acid composition and its application products.

[0006]

In order to achieve the above-mentioned object of the present invention, the polylactic acid composition of the present invention comprises a copolymer containing lactic acid as a main component, an aliphatic dicarboxylic acid and a chain molecule. A mixed composition comprising a plasticizer of an aliphatic polyester containing diol (hereinafter referred to as a chain) as a main component, wherein the weight ratio of the plasticizer is less than 50%.

The term "lactic acid-based copolymer" as used herein means polylactic acid homopolymers such as poly-L-lactic acid and poly-D-lactic acid, poly-L / D-lactic acid copolymers, and ester bond formation thereof. A polylactic acid copolymer obtained by copolymerizing a polymerizable polymer material and having a lactic acid-derived component weight ratio of 50% or more in the copolymer.

Examples of the ester bond-forming polymerization material copolymerizable with polylactic acid include hydroxyalkylcarboxylic acids such as glycolic acid and hydroxybutylcarboxylic acid; lactones such as glycolide, butyrolactone and ε-caprolactone; Examples thereof include aromatic dicarboxylic acid, aliphatic diol, hydroxyl group-terminated polyalkylene ether and its oligomer, polyalkylene carbonate and its oligomer (diol), and the like.

The aliphatic dicarboxylic acid is preferably a dicarboxylic acid having 4 to 20 carbon atoms such as succinic acid, adipic acid, sebacic acid, decanedicarboxylic acid and dodecanedicarboxylic acid. As the aromatic dicarboxylic acid, phthalic acid, isophthalic acid, 5-sulfoisophthalic acid and its metal (Na, K etc.) salts, terephthalic acid, naphthalenedicarboxylic acid and the like are preferable.

As the aliphatic diol, ethylene glycol, propylene glycol, butanediol,
Hexane diol, octane diol, decane diol, dodecane diol and the like having 2 to 20 carbon atoms are preferable.

Examples of the polyalkylene ether (glycol) include polyethylene glycol, polypropylene glycol, polybutylene ether, and copolymers thereof, such as polyethylene / propylene glycol and polyethylene / butylene ether.
Further, these oligomers, particularly those having a molecular weight of less than 2000, preferably 1000 or less, for example, diethylene glycol and triethylene glycol are most preferable.
As the copolymerized alkylene ether, for example, 1 mol of polypropylene glycol can be subjected to an addition reaction with 2 mols of ethylene oxide to obtain ethylene / propylene ether glycol having an average degree of polymerization of 3, and 3 mols of ethylene oxide can be added to 1 mol of butanediol. If reacted, ethylene / butylene ether glycol having an average degree of polymerization of 4 can be obtained. Similarly, a propylene ether copolymerized glycol can be obtained by addition-reacting propylene oxide with a diol.

The diol and the dicarboxylic acid are combined so as to be approximately equimolar to form a copolymerization component. For example, when equimolar ethylene glycol and adipic acid are reacted, polyethylene adipate having a hydroxyl group at one end and a carboxyl group at the other end is obtained, and the molar ratio is 101/100.
When the reaction is carried out with 1, a polyethylene adipate having hydroxyl groups at both ends is obtained with a degree of polymerization of 101, and both can be copolymerized with lactide to obtain a good polylactic acid / polyethylene adipate block copolymer.

Such a copolymer component accounts for less than 50% by weight of the copolymer (A) containing lactic acid as a main component. The more the copolymerization component is, the more the copolymer (A) is modified, the crystallinity and the heat resistance are lowered, and the decomposability is increased. The copolymerization ratio may be arbitrarily selected depending on the purpose and application, but in many cases it is 1
~ 40%, especially 3 ~ 30% is often used, and 2 ~ 20% is most widely used.

Generally, copolymerizing an aliphatic component has the effect of improving flexibility and impact resistance, but tends to lower the glass transition point and heat resistance. Further, the glass transition point and heat resistance tend to be improved by the copolymerization of the aromatic component. However, a copolymerization component having a too high melting point (for example, a polyester composed of an aromatic dicarboxylic acid and a diol) has a problem from the viewpoint of the copolymerization operation and melt moldability, and as a copolymerization component, an appropriate melting point such as a melting point is used. 200
It is desirable to select a temperature below ℃, especially below 180 ℃.

Both random copolymerization and block copolymerization can be used for the copolymerization of such a copolymerization component with lactic acid or polylactic acid. However, block copolymerization is particularly preferable in order to minimize the crystallinity, melting point, heat resistance, etc. due to the copolymerization. Block copolymerization can be carried out by, for example, preliminarily polymerizing a copolymerization component into a polymer or oligomer having a hydroxyl group at the molecular end, and then polymerizing a lactide with the terminal hydroxyl group as a polymerization initiation point to copolymerize with a polylactic acid segment (block). Polymer (polyester)
It is possible to obtain a block copolymer in which segments are bonded. Further, polylactic acid having a hydroxyl group or a carboxyl group at the molecular end, and polyester which is a copolymerization component also having a functional group at the end are used for dicarboxylic acid, dicarboxylic acid anhydride, dicarboxylic acid halide, diisocyanate, diamine and the like. A block copolymer can be obtained by reacting and linking with a bifunctional compound.

The matrix (matrix) polymer of the composition of the present invention is a polymer (A) containing lactic acid as a main component, and a polymer plasticizer (B) containing an aliphatic polyester (containing an oligomer) as a main component. It is characterized by being mixed.

The plasticizer (B) contains an aliphatic dicarboxylic acid and a chain diol as main components. That is, 50% by weight or more of the constituent components of the plasticizer (polymer) are derived from these aliphatic dicarboxylic acids and chain diols.

Examples of the aliphatic dicarboxylic acid which is one of the constituents of the plasticizer (B) include succinic acid, adipic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid and the like, which have 4 to 50 carbon atoms, especially carbon atoms. The number 4 to 20 linear dicarboxylic acid is preferable, but those having a side chain or a double bond can also be used.

As the chain diol which is the other main component of the plasticizer (B), those having 2 to 20 carbon atoms such as ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, decanediol and dodecanediol are used. , And polyalkylene ethers such as polyethylene glycol, polypropylene glycol and polybutylene ether, copolymers thereof and oligomers thereof, and polyalkylene carbonates and oligomers thereof. As the oligomer of polyalkylene ether and polyalkylene carbonate, those having a molecular weight of less than 2000, particularly preferably 1000 or less are preferable.

The main components of the plasticizer (B) are the above-mentioned aliphatic dicarboxylic acids and chain diols, but components other than these may be contained secondarily. As the secondary component, for example, lactic acid, glycols, hydroxyalkylcarboxylic acid such as hydroxybutylcarboxylic acid, butyrolactone, lactone such as ε-caprolactone, diamine, diisocyanate and the like can be applied.

The degree of polymerization and the molecular weight of the plasticizer (B) are not particularly limited, but generally, the smaller the molecular weight, the greater the plasticizing effect, but the lower the stability and the more easily the surface of the molded product is liable to be contaminated by leaching. Become. In many cases, the plasticizer (B) has a molecular weight of 500 or more, particularly preferably 1000 or more,
3000 or more is more preferable, and 5000 to 200,000 is most widely used.

One of the characteristics of the plasticizer in the present invention is that it has a low glass transition point and has a great plasticizing effect because it contains an aliphatic polyester as a main component, and it has high flexibility and impact resistance in molded products. Give sex. In addition, if necessary, it can be a high molecular weight plasticizer, less leaching to the surface of the molded product, sustaining a stable effect, and minimizing the decrease in strength due to plasticization. be able to. Such an effect as a polymer plasticizer is clearly exhibited when the molecular weight is 3000 or more, and is particularly remarkable when the molecular weight is 10,000 or more.

The end of the plasticizer (B) may be a carboxyl group, a hydroxyl group, or the like, or may be blocked with a compound having an alkyl group, an allyl group, an alkylallyl group, or another functional group. When the terminal has a carboxyl group or a hydroxyl group, it has a high affinity with the base polymer (A), but on the contrary, it is unstable from the viewpoint of stability and reacts with the base polymer (A), It tends to absorb water and accelerate the decomposition of the base polymer (A). The terminal functional group of the plasticizer may be arbitrarily selected depending on the purpose of use of the composition, but the blocked functional group is preferable from the viewpoint of stability of the composition described above. For example, by blocking both terminals with a higher alkyl group such as stearyl group, the plasticizing effect of the higher alkyl group itself is added, and a composition having both excellent stability and plasticizing effect can be obtained.

Further, in the present invention, a component which is the same as or similar to the aliphatic dicarboxylic acid and the chain diol which are the constituents of the plasticizer (B) is used as a copolymerization component of the base polymer (A), whereby The closeness of the molecular structures of the polymer (A) and the plasticizer (B) can be increased.

The approximation of the molecular structures of the polymers can be represented by the approximation of the number of carbon atoms and the number of oxygen atoms of the constituent units (dicarboxylic acid, diol, hydroxycarboxylic acid, etc.) constituting the main chain. For example, if the difference in the number of carbon atoms and the number of oxygen atoms of the two types of structural units is 4 or less, the closeness is recognized, and if the difference is 2 or less, the closeness is considerably high, and if they are the same, the closeness is highest. For example, ethylene adipate, ethylene sebacate, butylene adipate, butylene sebacate, etc. have high mutual resemblance. Similarly, the polyester ether of diethylene glycol and adipic acid is highly similar to polybutylene adipate.

The number of atoms in the repeating unit of the main chain of polylactic acid is 2 carbons and 1 of oxygen, and the number of atoms in the repeating unit of polyglycolic acid is exactly the same as that of polylactic acid. high. Similarly, that of hydroxybutyl carboxylic acid is also quite similar to lactic acid. A polyester composed of a dicarboxylic acid and a diol, which has a small number of atoms in a repeating unit is ethylene succinate, which has carbon 6 and oxygen 2, but since it contains two ester bonds, In terms of the average number of atoms between ester bonds, carbon 3 and oxygen 1 can be said to be quite close to polylactic acid. That is, a polyester composed of a dicarboxylic acid or diol having 6 or less carbon atoms, particularly 4 or less, shows a high degree of approximation to polylactic acid.

As described above, by introducing into the base polymer (A) and the plasticizer (B) having a high molecular structure, excellent miscibility, plasticizing effect and transparency can be realized. it can. Further, the higher the degree of similarity between the molecular structures of the base polymer (A) and the plasticizer (B), the better the action and effect, and the most remarkable effect when both have the same constituent components. For example, if at least one of the copolymerization components in the base polymer (A) is the same as the aliphatic dicarboxylic acid or chain diol that is a constituent of the plasticizer (B), the affinity between the two is extremely high. The highest affinity is achieved if both the acid and diol components are the same.
That is, by using the same type of polyester composed of the same aliphatic dicarboxylic acid / chain diol as the copolymerization component in the base polymer (A) and as the main component of the plasticizer (B), the highest affinity is obtained. Which is most suitable for the purpose of the present invention. Of course, the aliphatic polyester (segment) shared by the base polymer (A) and the plasticizer (B)
Is sufficient if the constituent diol and dicarboxylic acid are the same, and the degrees of polymerization thereof may be different.

The mixing ratio of the plasticizer (B) to the base polymer (A) varies depending on the purpose, but generally, the larger the mixing ratio, the more remarkable the plasticization. In order to impart impact resistance without impairing the heat resistance of the molded product, the mixing ratio of the plasticizer is 1
About 15%, especially about 3-10% is often used. On the contrary, when high flexibility is required, the mixing ratio of the plasticizer is often about 10 to 50%, particularly about 15 to 40%.
Since the copolymerization component in the base polymer (A) also acts as a plasticizer, the mixing ratio of the plasticizer (B) may be relatively small when the copolymerization component is large. In many cases, the sum of the weight fractions of the copolymerization component and the plasticizer (B) in the composition as a whole is
2 to 70%, especially 5 to 50%, most often 8 to 40% are preferred.

The plasticizer (B) is often mixed after the polymerization of the base polymer (A). It is not impossible to mix the raw material of the base polymer (A) during the polymerization process or the polymerization step, but the desired mixing ratio and the plasticizing effect can be obtained without copolymerization with the base polymer by the transesterification reaction or decomposition of the plasticizer. In order to realize the above-mentioned character, it is preferable to mix the base polymer after the polymerization and before the molding or in the molding step.

The mixing method is arbitrary, but the materials may be mixed in a molten state or a solution by mechanical stirring or a static mixer, or may be mixed in the form of powder or particles and melted or dissolved. The composition of the present invention has a high affinity for the base polymer (A) and the plasticizer (B), and can be easily and uniformly mixed.

In the composition of the present invention, in addition to the main polymer (A) and the plasticizer (B) which are main components, other components may be secondarily added. Examples of secondary additives include stabilizers, antioxidants, ultraviolet absorbers, pigments, colorants, various inorganic particles, various fillers, water repellents, hydrophilic agents, antistatic agents, release agents, plasticizers. , Physiologically active substances, preservatives, fragrances, antibacterial agents, foaming agents and the like.

In the following examples, parts and% are shown by weight unless otherwise specified. The molecular weight of the polylactic acid and the polylactic acid copolymer is the weight average value of the dispersion of the polymer excluding those having a molecular weight of 500 or less in terms of polystyrene by GPC analysis of a 0.1% chloroform solution of the sample.

[0033]

【Example】

<< Example 1 >> To 95 parts of L-lactide having an optical purity of 99% or more, 5 parts of polyethylene adipate having hydroxyl groups at both ends and a molecular weight of 9000 as copolymerization components, and titanium oxide particles (crystal nucleating agent) having a diameter of 0.05 μm 0.5% , Tin octylate 0.05%, Ciba-Geigy Irganox 1010 (antioxidant) 0.2% are mixed, and it is a twin-screw mixing liquid feeder in which two screws mesh.
React continuously in nitrogen atmosphere at 180 ℃ for 30 minutes on average (preliminary)
Polymerization, followed by the addition of 0.1% tin octylate, using a twin-screw kneader consisting of a screw group that meshes with each other and an elliptical (2-flight type) stirring element group that meshes with each other at 190 ° C.
After polymerizing for 15 minutes on average, 5% of the plasticizer P1 which was melted and had a water content of 10 ppm or less was supplied from the final vent hole and mixed, and further passed through a cylinder containing 60 static mixing elements of Kenix Co., Ltd. After that, it was extruded from the die, cooled and solidified with water, and cut to obtain a chip C1.

The plasticizer P1 is a polyethylene adipate having a molecular weight of about 4000 and having both terminal hydroxyl groups esterified with stearic acid and blocked, and has a molecular weight of about 4500. In addition, 0.3% of triethylene glycol was mixed as a solid phase polymerization initiator. It is a thing.

Chip C1 was heat-treated in nitrogen at 120 ° C. and a pressure of 1.5 kg / cm ² for 12 hours, and then heat-treated (solid-state polymerization) at 160 ° C. and normal pressure for 48 hours to obtain chip C2. Chip C2
Has an average molecular weight of 162,000 and the residual monomer (lactide) is
It was 0.2%.

Using the chip C2, injection molding it into V
An impact test piece with a letter notch was created. Similarly, chip C2 was melted at 210 ° C with a screw extruder, extruded from the slit of the T-shaped die, cooled, and then vertically oriented at 90 ° C
The film was stretched 3.1 times and 2.9 times in the transverse direction to form a film with a thickness of 50 μm.

Chip C3 was prepared in substantially the same manner as chip C2, except that 5% of plasticizer P1 was added to and mixed with polylactic acid homopolymer obtained without adding a copolymerization component during lactide polymerization. Chip C3 had a molecular weight of 163,000 and a residual monomer amount of 0.2%. From chip C3 to chip C
An impact test piece and a stretched film were prepared in the same manner as in 2.

Chip C4 was obtained in substantially the same manner as chip C2, but without adding a plasticizer to the polylactic acid homopolymer obtained without adding a copolymerization component during lactide polymerization. Chip C4 had a molecular weight of 169,000 and the amount of residual monomer was 0.2%. An impact test piece and a stretched film were prepared from the chip C4 in the same manner as the chip C2.

Chip C5 was obtained in substantially the same manner as chip C2, except that poly ε-caprolactone having a molecular weight of about 4500 was added and mixed in place of the plasticizer P1 and solid phase polymerization was similarly carried out. Chip C5 had a molecular weight of 153,000 and a residual monomer amount of 0.3%. An impact test piece and a stretched film were prepared from the chip C5 in the same manner as the chip C2.

In substantially the same manner as the chip C2, except that no copolymerization component was added during the lactide polymerization, polyε-caprolactone having a molecular weight of about 4500 was added and mixed in place of the plasticizer P1, and the solid phase polymerization was repeated in the same manner. The result obtained is a chip C6
And The molecular weight of Chip C6 was 154,000 and the amount of residual monomer was 0.3%. An impact test piece and a stretched film were prepared from the chip C6 in the same manner as the chip C2.

The impact strength of each of the test pieces obtained from the chips C2 to C6 was measured. In addition, the transparency of each stretched film was visually evaluated. Table 1 shows the results. As shown in Table 1, the impact strength and the transparency of the composition of the present invention are superior to those of the comparative examples, and particularly, the one obtained from the chip C2 in which the base polymer and the plasticizer have the same copolymerization component has the best performance. Is shown.

[0042]

[Table 1] << Example 2 >> In substantially the same manner as the chip C2 of Example 1, except that a polyester ether obtained by polymerizing diethylene glycol and adipic acid during lactide polymerization had a molecular weight of about 900.
0, a polyester ether obtained by copolymerizing 5% of both ends with a hydroxyl group and then polymerizing diethylene glycol and adipic acid in place of the plasticizer P1 and esterifying both ends with lauric acid to block the molecular weight of about 6000 Things
5% was added, and thereafter, chip C7 was obtained by similarly performing chip formation and solid phase polymerization. Chip C7 has a molecular weight of 17
The residual monomer amount was 1,000 and 0.1%. The impact strength of the test piece obtained from the chip C7 was 6.3 kg · cm / cm 2, and the transparency of the stretched film was equivalent to that of the film obtained from the chip C2, which was extremely excellent.

[0043]

INDUSTRIAL APPLICABILITY According to the present invention, a wide variety of compositions of the base polymer (A) and the plasticizer (B) can be combined, and various plasticized polylactic acid compositions can be obtained according to the purpose and application. . In particular, by combining the base polymer with a plasticizer having a high affinity, a molded product having excellent flexibility, impact resistance, and transparency can be obtained, and stains due to surface leaching of the plasticizer can be suppressed. Similarly, by using a plasticizer having a high molecular weight, it is possible to obtain a molded product having excellent durability and stability of the plasticizing effect and less surface contamination.
These excellent effects become more remarkable by introducing the components (A) and the plasticizer (B), which have lactic acid as a main component as a main component, and are highly similar to each other. The most remarkable effect is obtained by introducing.

Further, the aliphatic dicarboxylic acid and the aliphatic diol are excellent in decomposability, the aliphatic polyesters obtained from them are also excellent in decomposability, and the base polymer (A) and the plasticizer (B) into which they are introduced are also decomposable. Excellent in. Generally, when the number of carbon atoms of the alkyl group contained in the aliphatic dicarboxylic acid or the aliphatic diol is increased, the water repellency is increased, and the decomposability of the base polymer (A) or the plasticizer (B) containing them as a constituent is suppressed. By way of trend, these compositions have a long life and are suitable for applications requiring low degradability.

When a polyalkylene ether, particularly an oligomer thereof, such as diethylene glycol, triethylene glycol, low-molecular-weight polyethylene glycol, polypropylene glycol, etc. is applied, a molded product excellent in plasticizing effect, particularly flexibility is obtained. In addition, biodegradability is also fully recognized, which is effective for environmental protection and the like.

Further, by adjusting the addition amount of the plasticizer, the degradability and physical properties of the molded product can be greatly changed, and it can be suitably used for a wide range of applications. Especially when a high molecular weight plasticizer is used, even if a large amount of plasticizer is mixed,
Compared with a low molecular weight plasticizer, the characteristics (strength, etc.) are less deteriorated, and an excellent flexible product can be obtained.

The composition of the present invention comprises fibers, knits, woven fabrics, non-woven fabrics, papers, felts, nets, ropes, films, sheets,
Plates, rods, tubes, porous molded products, various containers, various parts, various composite materials, and other various molded products, etc. can be used by improving them to the optimum properties according to their respective applications. it can.

Claims (4)

[Claims] 1. A mixed composition comprising a copolymer containing lactic acid as a main component and a plasticizer for an aliphatic polyester containing an aliphatic dicarboxylic acid and a chain molecular diol as a main component. A polylactic acid composition having a weight ratio of less than 50%. 2. The copolymer containing lactic acid as a main component is a block copolymer of polylactic acid and an aliphatic polyester containing an aliphatic dicarboxylic acid and a chain molecule diol as a component. The polylactic acid composition described. 3. The aliphatic polyester as a copolymerization component constituting a polymer containing lactic acid as a main component is the same or similar to the aliphatic polyester as a main component of the plasticizer. Polylactic acid composition. 4. Fibers, knitted fabrics, woven fabrics, non-woven fabrics, papers, felts, nets, ropes, films, sheets, plates, rods, tubes, porous molded articles made of the polylactic acid composition according to claim 1. , Various containers, various parts, and other molded products.