JPH1017757A - Polylactic acid composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition having faster decomposition rate under natural circumference by mixing an aliphatic polyester consisting essentially of lactic acid with polyether having an alkyl group and a surfactant having sulfone group at a specific ratio. SOLUTION: This composition improved in decomposition rate is obtained by mixing (A) an aliphatic polyester composed mainly of lactic acid in an amount of 99-60wt.% based on total weight with (B) polyether having a 2-4C alkyl in an amount of 0.5-35wt.% based on the total weight and (C) a surfactant having sulfone group in an amount of 0.5-25wt.% based on the total weight. Furthermore, weight ratio of sulfone group of the component C is preferably 0.1-5wt.%. It can be expected to enable free change of decomposition rate in a wide range, widen use of polylactic acid and distribute to protection of natural circumference by changing a mixing ratio of the components B/C which are active ingredients.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to novel polylactic acid-based compositions having faster degradation rates.

[0002]

2. Description of the Related Art At present, synthetic resins, which are consumed in large quantities as fibers, films and various molded products, have a very low decomposition rate under a natural environment, generate a large amount of heat when incinerated, and damage the furnace and cause carbon dioxide in the atmosphere. There are problems such as increasing gas, and it is necessary to review it from the viewpoint of protecting the natural environment.
Aliphatic polyesters are generally spontaneously degradable, but low-melting aliphatic polyesters having a melting point of 150 ° C. or less have a problem in practicality in terms of heat resistance. On the other hand, high-melting aliphatic polyesters having a melting point of 150 ° C. or higher include polyglycolic acid (melting point of about 230 ° C.), polylactic acid (melting point of about 175 ° C.), polyhydroxybutyrate (melting point of about 180 ° C.), and those containing these as main components. Copolymers and the like are known, and among them, polylactic acid is a raw material of agricultural products, so it has little adverse effect on the environment and has many excellent physical properties. However, polylactic acid, particularly a homopolymer, has a problem that the decomposition rate in a natural environment is low because of high crystallinity and glass transition point and low decomposability by enzymes.
A low decomposition rate is suitable for applications requiring a long life, but depending on the application, it is necessary to decompose quickly. That is, polymers that can have various decomposition rates are desired depending on the application. However, at present, technology for controlling the decomposition rate of polylactic acid has not been developed.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved novel polylactic acid composition having a higher decomposition rate in a natural environment.

[0004]

An object of the present invention is to provide an aliphatic polyester (A) containing lactic acid as a main component, and having 2 carbon atoms.
A composition comprising a mixture of a polyether (B) having an alkyl group of 4 to 4 and a surfactant (C) having a sulfone group, wherein the ratio of the polyester (A) to the total weight is 99 to 60%. Wherein the ratio of the polyether (B) is 0.5 to 35% and the ratio of the surfactant (C) is 0.5 to 25%. This is achieved by a lactic acid composition.

[0005] Here, the aliphatic polyester (A) containing lactic acid as a main component is one in which the component derived from lactic acid occupies 50% by weight or more in the polymer. For example, (1) polylactic acid homopolymer, (2) ) Polylactic acid obtained by copolymerizing other polyester-forming raw materials in a small amount (50% or less) (block or random copolymerization), and (3) those obtained by mixing small amounts (50% or less) of other components with them .

Examples of aliphatic polyester-forming raw materials that can be copolymerized with polylactic acid include (a) aliphatic hydroxycarboxylic acids such as glycolic acid and hydroxybutyl carboxylic acid, and (b) glycolide, butyrolactone, and caprolactone. Aliphatic lactones, (c) aliphatic diols such as ethylene glycol, propylene glycol, butanediol, hexanediol, etc., (d) diethylene glycol, triethylene glycol, ethylpropyl ether glycol, bishydroxyethylpropane, bishydroxypropylbutane, Aliphatic polyether glycols such as polyethylene glycol, polypropylene glycol, polybutylene ether, copolymers and oligomers thereof, (e) dihydroxybutyl Sulfonates, dihydroxy hexyl carbonate, polybutylene carbonate (glycol)
Examples thereof include aliphatic polycarbonate glycols such as polyhexane carbonate (same as above) and polyoctane carbonate (same as above), copolymers and oligomers thereof, and (f) aliphatic dicarboxylic acids such as succinic acid, adipic acid and sebacic acid.

Polymers obtained from the above polyester raw materials, for example, polycaprolactone, polyglycolic acid, polyethylene adipate, polyethylene sebacate, polybutylene succinate, polybutylene adipate, polybutylene sebacate, polyhexane adipate, polyhexane sebacate, etc. Block copolymerization with polylactic acid is easy. In addition, for example, phthalic acid, terephthalic acid, isophthalic acid, and other aromatic polyester raw materials other than the aliphatic raw materials can be copolymerized in a small amount (for example, 20% or less). Similarly, a small amount (50% or less) of the aliphatic polyester obtained from the above raw materials can be mixed with polylactic acid.

The purpose of modifying polylactic acid by copolymerization or mixing is to lower the crystallinity, lower the melting point (lower the polymerization temperature, molding temperature, and processing temperature), melt fluidity, toughness, flexibility and elastic recovery. Improvement or reduction of friction coefficient, surface roughness, adhesion, mixing, heat resistance and glass transition temperature, improvement of gas barrier properties, moisture permeability, improvement of hydrophilicity and water repellency, improvement of dyeability, improvement of decomposability In addition, modified polylactic acid can be applied to the present invention according to the purpose. For example, polylactic acid obtained by block copolymerizing a small amount (about 1 to 10%) of polyether is excellent in miscibility (miscibility) with polyether and is particularly suitable for the purpose of the present invention.

Polyester containing lactic acid as a main component (A)
Is a major component of the composition of the present invention. The higher the ratio of the polyester (A) in the composition, the lower the spontaneous decomposition rate of the composition and a molded article using the composition. In order to improve (increase) the decomposition rate, the weight ratio of the polyester (A) in the composition needs to be 99% or less. On the other hand, the larger the ratio of the polyether (B) and the surfactant (C) is, the more the physical properties such as heat resistance of the composition and the molded article tend to be remarkable. Therefore, the ratio of the polyester (A) in the composition is as follows: 60
%, And for many applications a range of 97-70% is preferred, with a range of 95-80% being especially preferred.

The polyether (B) having an alkyl group having 2 to 4 carbon atoms used in the present invention includes polyethylene glycol, polypropylene glycol, polybutylene ether, copolymers thereof, and aliphatic or aromatic compounds at their molecular terminals. Derivatives in which the components are bound and blocked are included.

The surfactant (C) having a sulfone group used in the present invention has an alkyl group, an alkylaryl group and other lipophilic components and a sulfonic acid group having a molecular weight of about 1,000 or less, particularly about 500 or less. Alkyl benzene sulfonic acid metal salts (Na, K, Li salts, etc.) are preferred. Usually, the sulfonic acid group is neutralized with an alkali metal and used as a salt, but can be used without neutralization. For the purpose of the present invention, those having a highly biodegradable lipophilic group, such as alkyl groups contained in natural fats and oils, such as octyl, nonyl, decyl, lauryl, dodecyl,
Those having a group such as linoleyl, stearyl, oleyl and the like are particularly preferred.

Similarly, an alkyl obtained by reacting a vinyl monomer having a sulfone group such as sulfonated styrene (Na salt) or sodium methallylsulfonate with an unsaturated aliphatic compound such as an unsaturated alcohol or an unsaturated carboxylic acid. Surfactants having groups and sulfone groups are also useful in the present invention.

In the present invention, a polyether and a surfactant having a sulfone group (hereinafter sometimes referred to as a sulfone compound) act as an accelerator for decomposing polylactic acid.
Although the mechanism of action is not necessarily clear, it is presumed that water is adsorbed or absorbed on the surface or inside of the polylactic acid by the hydrophilic component or polar group, thereby promoting hydrolysis. In addition, the decrease in the crystallinity of polylactic acid due to the mixing of these components may be one of the reasons for accelerating the decomposability. In general, the degradation of polylactic acid in a natural environment is presumed to be caused by a chemical hydrolysis that causes a reduction in molecular weight or a monomer, followed by a degradation process by a monomer or an organism. It appears that the rate of both initial hydrolysis and subsequent biodegradation is often enhanced.

In the present invention, both the polyether and the sulfone compound have a decomposition promoting action. In particular, the sulfone compound has a high water absorption and has a remarkable promoting effect. But,
Since the sulfone compound has a high water absorption and a low melt fluidity, it is extremely difficult to directly melt-mix it with polylactic acid. However, it is relatively easy to melt-mix the sulfone compound with the polyether, and it is also easy to dehydrate the molten mixture, for example, by reducing the pressure, and to convert the dehydrated polyether / sulfone compound mixture into a molten polylactic acid-based mixture. It is easy to mix with the polymer. That is, the polyether not only functions as a decomposition accelerator but also has an important function as an admixture or a solvent for mixing a sulfone compound with polylactic acid.

As the mixing ratio of the polyether (B) and the sulfone compound (C) increases, the decomposition rate of the resulting composition tends to increase. That is, by adjusting the mixing ratio according to the purpose and application, it is possible to obtain compositions and molded articles having various decomposition rates. However, if the mixing ratio is too large, the physical properties of the composition are significantly deteriorated.
Should be in the range of 0.5-35%, and 2-3
0% is preferable, and a range of 3 to 20% is particularly preferable.
The range of ~ 15% is most widely used. Similarly, the mixing ratio of the sulfone compound (C) needs to be in the range of 0.5 to 25%, preferably 1 to 20%, and the range of 1 to 15% is most widely used. The decomposition promoting effect of polyether is
Polyethylene glycol is the strongest, followed by polypropylene glycol, and polybutylene ether the lowest. However, all are effective as admixtures. on the other hand,
Since the effect of the sulfone compound depends on the sulfone group, the weight ratio of the sulfone group in the whole composition is important, and the content of the sulfone group (calculated by molecular weight SO3 = 80) of the composition is 0.05 to 10%. Is preferred, 0.1 to 5% is particularly preferred, and the range of 0.2 to 3% is most widely used.

The molecular weight of the aliphatic polyester (A) containing lactic acid as a main component is not particularly limited, but is preferably 50,000 or more, particularly preferably 70,000 to 300,000, and more preferably 80,000 to 200,000 in view of the strength of a molded product. The range is most widely used. Similarly, the molecular weight of the polyether (B) is not particularly limited, but is preferably 3,000 or more, more preferably about 5,000 to 500,000, particularly preferably 7000 to 300,000, and 8,000.
The range of ~ 200,000 is most widely used.

The method of mixing the components (A), (B) and (C) is not particularly limited, but the polyether (B) and the sulfone compound (C) are first melt-mixed as described above, and the mixture is mixed with the mixture. The polyester (A) may be mixed by mechanical stirring such as a screw extruder, a twin-screw kneading extruder, a kneader, a gear pump, a kneading roll, a tank having a stirrer, and the like. A repeating static mixer may be applied, or they may be used in combination. Mixing may be a batch method or a continuous method, but of course, a continuous method such as a screw extruder, a twin-screw kneading extruder,
A static mixer or the like is preferred for high efficiency. The mixing may be performed, for example, in the polymerization step (particularly in the latter half), or may be performed after the polymerization step, before the molding step, or during the molding step.

The composition of the present invention may contain, if necessary, a coloring agent such as a pigment or a dye, a filler such as inorganic or organic particles, glass fiber, whisker, mica, a nucleating agent, an antioxidant, Stabilizers such as UV absorbers, lubricants, release agents,
Water repellents, plasticizers, antibacterial agents and other secondary additives can be incorporated. In particular, polyethers have poor stability. Therefore, hindered phenols, hindered amines and other antioxidants are used, for example, in an amount of 0.01% or more, particularly 0.05 to 0.05%.
It is desirable to mix about 5%.

The composition of the present invention can be used as various molded products such as fibers, yarns, ropes, knits, woven fabrics, nonwoven fabrics, papers, films, sheets, tubes, plates, bars, containers, bags, parts and the like.
It can be suitably used in agriculture, fishing, forestry, horticulture, medicine, sanitary goods, clothing, non-clothing, packaging, and other fields.

[0020]

EXAMPLES In the following examples,% and parts are by weight unless otherwise specified. The molecular weight of the aliphatic polyester is
In GPC analysis of a 0.1% chloroform solution of a sample, it is a weight average value of dispersion of a high molecular component excluding components having a molecular weight of 500 or less. In the decomposition test in soil, the sample fiber is buried in ordinary field soil at a depth of 10 cm, taken out every month for one year and every three months after one year, and the strength is measured. Was estimated by the interpolation method or the extrapolation method, and it was defined as the (practical) life.

Example 1 100 parts of L-lactide having an optical purity of 99.5% or more and 100 ppm of a tin octylate polymerization catalyst were continuously supplied to a twin-screw kneading extruder and reacted at 188 ° C. for an average of 8 minutes. After extruding, cooling in water, cutting and drying, chip C1
I got Further, the chip C1 was placed in a nitrogen stream at 140 ° C. for 4 hours.
After heating (solid-state polymerization) for a time, polymer P1 was obtained. The polymer P1 is poly L-lactic acid having a molecular weight of 193,000 and a melting point of 1
At 76 ° C., the residual monomer amount was 0.1%.

Approximately as for polymer P1, except that L
-A mixture of lactide with a molecular weight of 12000, 3% of polyethylene glycol having a hydroxyl group at both ends (hereinafter referred to as PEG), and 0.1% of an antioxidant Irganox 1010 manufactured by Ciba-Geigy Co., Ltd. Obtained. The polymer P2 was obtained by block copolymerization of poly L-lactic acid with about 3% of polyethylene glycol, and had a molecular weight of 178,000, a melting point of 175 ° C., and a residual monomer amount of 0.1%.

100 parts of PEG having a molecular weight of 20,000 and high-purity sodium dodecylbenzenesulfonate (hereinafter referred to as DBS-Na)
30 parts of the powder and 0.5 part of the above Irganox were melt-mixed at 200 ° C. using a tank equipped with a stirrer, decompressed gradually for 30 minutes, kept at 1 Torr for 30 minutes, and dehydrated. While the polymer P1 was melted at 220 ° C. with a screw extruder, 5% of the dehydrated PEG / DBS-Na mixture was continuously mixed and passed through a Kenix-type static mixer having 30 elements. 2m, spun from orifice at 226 ° C, cooled in air and oiled while 1500m /
The yarn was wound at a speed of min and further stretched 4.5 times at 80 ° C. to obtain a yarn F1 of 75 denier / 24 filament.
The yarn F1 had a strength of 4.8 g / d (gram / denier) and an elongation of 29%.

In the same manner as the yarn F1, except that the polymer P1
Is used in place of the polymer P2, and a yarn obtained in the same manner is hereinafter referred to as F2. The yarn F2 has a strength of 4.6 g / d and an elongation of 2
8%.

For comparison, only the polymer P2 was used (P
Hereinafter, a yarn having a strength of 4.8 G / d and an elongation of 29% obtained in the same manner as the yarn F1 is referred to as F3. Similarly, for comparison, only 4% of PEG was mixed with the polymer, and a yarn having a strength of 4.7 G / d and an elongation of 29%, which was obtained in the same manner as the yarn F1, was designated as F4. When only the polymer P1 was used, a sample was not collected because the yarn was easily cut in the stretching step.

Each yarn is buried in the soil and subjected to a decomposition test.
Table 1 shows the results obtained for the life. The PEG mixing ratio in the table indicates the mixed PEG, and does not include the copolymerized PEG. As shown in Table 1, the yarn F using the composition of the present invention
1 and F2 have a considerably shorter life than the yarns F3 and F4 of the comparative example, and the effect of the sulfone group is apparent.

Although this embodiment shows an example of a fiber having a large surface area, a thick molded product such as a film, a sheet, and a bottle generally has a much longer life than this example, but the decomposition promoting effect is not significant. This is almost the same as the embodiment. Table 1 Sample PEG mixing ratio Sulfone group content Lifetime Remark F1 3.7% 0.26% 7.2 months Present invention F2 3.7 0.26 6.1 Present invention F30027 Comparative example F4 4.00 22 Comparative Example Example 2 A block copolymer P5 was obtained in the same manner as in the polymer P2 of Example 1, except that polybutylene succinate having a molecular weight of 125,000 and having a hydroxyl group at a terminal was used instead of PEG. Polymer P5 has a molecular weight of 1490,000 and a melting point of 174 ° C.
Met. Using the polymer P5, the yarn F1 of Example 1
In the same manner as in the above, a yarn F5 was obtained. The strength of the yarn F5 is 4.6 g
/ D, elongation was 29%. The life span of the thread F5 in the soil was 6.6 months.

[0028]

According to the present invention, the problem of polylactic acid having a low decomposition rate in a natural environment is improved, and a polylactic acid having a higher decomposition rate can be obtained depending on the purpose of use. By changing the mixing ratio of the polyether and the sulfone compound, which are the active ingredients, the decomposition rate can be changed over a wide range and freely, and it is expected that the use of polylactic acid will expand and contribute to the protection of the natural environment. The present invention has the feature that it can be easily carried out at a relatively low cost, and when the mixing ratio of the active ingredient is, for example, 3% or more, particularly 5% or more, the flexibility and antistatic property of the obtained product are improved. There is also a side effect that it does. The composition of the present invention has high utility as fibers, films, sheets and other various general-purpose molded articles, and also has high utility in special fields such as medical and hygiene products.

Claims (2)

[Claims] 1. An aliphatic polyester containing lactic acid as a main component (A), a polyether having an alkyl group having 2 to 4 carbon atoms (B), and a surfactant having a sulfone group (C) are mixed. A composition, wherein the ratio of the polyester (A) to the total weight is 99 to 60%, the ratio of the polyether (B) is 0.5 to 35%, and the ratio of the surfactant (C) is also A polylactic acid composition having an improved decomposition rate, which is 0.5 to 25%. 2. The polylactic acid composition according to claim 1, wherein the weight ratio of the sulfone group to the total weight is 0.1 to 5%.