JP2009249460A - Polylactic acid composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid composition becoming a molded article excellent in dynamic physical properties such as impact resistance, tensile strength, elongation at break, modulus, etc. <P>SOLUTION: This polylactic acid composition comprises a polylactic acid (A) having a melting point of ≥190°C, the polylactic acid (B) having a melting point of <190°C and a coupling agent (E). The method for producing the same and its molded article are also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polylactic acid composition. More particularly, the present invention relates to a polylactic acid composition having improved elongation at break.

From the viewpoint of resource conservation and environmental protection, bio-based polymers have attracted attention. Especially, polylactic acid is said to have high rigidity because L-lactic acid, which is a raw material, has been produced in large quantities at low cost by fermentation. It is expected to expand its field of use due to its excellent characteristics. However, polylactic acid still has physical properties problems for practical use as compared with conventional polymers made from petroleum resources. In particular, improvements in heat resistance, chemical resistance, impact resistance and the like are desired.
Conventional polylactic acid is poly-L lactic acid whose main raw material is L-lactic acid, but stereocomplex polylactic acid containing poly-L lactic acid and poly-D lactic acid as raw materials is known (see Non-Patent Document 1). ). Stereocomplex polylactic acid is a crystalline resin having a remarkably higher melting point than conventional poly-L lactic acid, and can be expected to have characteristics superior to those of conventional poly-L lactic acid. However, a technique for highly expressing a stereocomplex crystal with high reproducibility has not yet been completed.
Under these circumstances, attempts have been made to develop a resin material having both characteristics by blending polylactic acid and other resins. In order to improve the elongation at break, polylactic acid, polyolefin and a compatibilizing agent are added. A resin composition obtained by blending has been proposed (for example, see Patent Document 1). However, this resin composition is limited in compatibility between polylactic acid and polyolefin, and has a drawback of having an effect only in a region where the polylactic acid content is low.
JP 2008-038142 A Macromolecules 1987, 20, 904-906.

  Accordingly, an object of the present invention is to provide a polylactic acid composition that is a molded product having excellent mechanical properties such as impact resistance, tensile strength, breaking elongation, and modulus. Another object of the present invention is to provide a molded article comprising the polylactic acid composition. Furthermore, the objective of this invention is providing the manufacturing method of this polylactic acid composition.

  The inventor has intensively studied to improve the mechanical properties such as impact resistance, tensile strength, elongation at break and modulus of a molded article made of a polylactic acid composition. As a result, a molded product comprising a composition obtained by adding poly-L lactic acid or poly-D lactic acid and a coupling agent to stereocomplex polylactic acid having excellent heat resistance has excellent mechanical strength such as impact resistance. As a result, the present invention has been completed.

  That is, the present invention is a polylactic acid composition comprising polylactic acid (A) having a melting point of 190 ° C. or higher, polylactic acid (B) having a melting point of less than 190 ° C., and a coupling agent (E). Moreover, this invention is a molded article which consists of this polylactic acid composition. Furthermore, the present invention provides a polylactic acid composition characterized by melt-kneading polylactic acid (A) having a melting point of 190 ° C. or higher, polylactic acid (B) having a melting point of less than 190 ° C., and a coupling agent (E). Includes methods.

  The polylactic acid composition of the present invention is a molded article having excellent mechanical properties such as impact resistance, tensile strength, breaking elongation, and modulus. According to the production method of the present invention, it is possible to provide a polylactic acid composition that becomes a molded article having excellent mechanical properties such as impact resistance, tensile strength, elongation at break, and modulus.

  Hereinafter, the present invention will be described in detail.

<Polylactic acid (A)>
The polylactic acid (A) used in the present invention is a polylactic acid having a melting point of 190 ° C. or higher, and a crystalline polylactic acid such as stereocomplex polylactic acid can be suitably used. Stereocomplex polylactic acid is formed from poly-L lactic acid and poly-D lactic acid, and poly-L lactic acid and poly-D lactic acid are substantially composed of L-lactic acid units and D-lactic acid units represented by the following formula (1), respectively.

The poly-L lactic acid is preferably composed of 90 to 100 mol%, more preferably 95 to 100 mol%, and still more preferably 99 to 100 mol% L lactic acid units. Examples of other units include D lactic acid units and units other than lactic acid. The D lactic acid unit and the units other than lactic acid are preferably 0 to 10 mol%, more preferably 0 to 5 mol%, still more preferably 0 to 1 mol%.
The poly-D lactic acid is preferably composed of 90 to 100 mol%, more preferably 95 to 100 mol%, still more preferably 99 to 100 mol% of D lactic acid units. Examples of other units include L-lactic acid units and units other than lactic acid. The L lactic acid unit and the units other than lactic acid are 0 to 10 mol%, preferably 0 to 5 mol%, more preferably 0 to 1 mol%.
Units other than lactic acid are units derived from dicarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, lactones and the like having functional groups capable of forming two or more ester bonds, and various polyesters, various polyethers composed of these various components, Examples are derived from various polycarbonates and the like.

  Examples of the dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Polyhydric alcohols include ethylene glycol, propylene glycol, propanediol, butanediol, pentanediol, hexanediol, octanediol, glycerin, sorbitan, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polyteoramethylene glycol. Aliphatic polyhydric alcohols such as aliphatic polyhydric alcohols, and aromatic polyhydric alcohols obtained by adding ethylene oxide to bisphenol. Examples of the hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, 4-hydroxybenzoic acid and the like. Examples of the lactone include glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, δ-valerolactone, and the like.

Stereocomplex polylactic acid is a mixture of poly L lactic acid and poly D lactic acid and can form stereocomplex crystals. The weight average molecular weight of poly L lactic acid is preferably 150,000 to 250,000. The weight average molecular weight of poly-D lactic acid is preferably 130,000 to 160,000. Thus, by making a difference in the weight average molecular weight, it becomes easy to form a stereo complex, and it becomes easier to form a stereo complex having a higher molecular weight.
Poly L lactic acid and poly D lactic acid can be produced by a known method. For example, L- or D-lactide can be produced by heating and ring-opening polymerization in the presence of a metal polymerization catalyst. Moreover, after crystallizing low molecular weight polylactic acid containing a metal polymerization catalyst, it can be produced by solid phase polymerization by heating under reduced pressure or in an inert gas stream. Further, it can be produced by a direct polymerization method in which lactic acid is subjected to dehydration condensation in the presence / absence of an organic solvent.

The polymerization reaction can be carried out in a conventionally known reaction vessel. For example, a vertical reactor or a horizontal reactor equipped with a stirring blade for high viscosity, such as a helical ribbon blade, can be used alone or in parallel. Moreover, any of a batch type, a continuous type, a semibatch type may be sufficient, and these may be combined.
Alcohol may be used as a polymerization initiator. Such alcohol is preferably non-volatile without inhibiting the polymerization of polylactic acid. For example, decanol, dodecanol, tetradecanol, hexadecanol, octadecanol and the like can be suitably used.

  In the solid phase polymerization method, a relatively low molecular weight lactic acid polyester obtained by the above-described ring-opening polymerization method or lactic acid direct polymerization method is used as a prepolymer. It can be said that the prepolymer is preferably crystallized in advance in the temperature range of the glass transition temperature (Tg) or higher and lower than the melting point (Tm) from the viewpoint of preventing fusion. The crystallized prepolymer is filled in a fixed vertical or horizontal reaction vessel, or a reaction vessel (rotary kiln, etc.) where the vessel itself rotates like a tumbler or kiln, and the prepolymer glass transition temperature (Tg) or higher. Heated to a temperature range below the melting point (Tm). There is no problem even if the polymerization temperature is raised stepwise as the polymerization proceeds. In addition, for the purpose of efficiently removing water generated during solid phase polymerization, a method of reducing the pressure inside the reaction vessels or circulating a heated inert gas stream is also preferably used.

The weight ratio of poly L lactic acid to poly D lactic acid in the stereocomplex polylactic acid is in the range of 90:10 to 10:90. It is preferably in the range of 75:25 to 25:75, more preferably in the range of 60:40 to 40:60, and preferably as close to 50:50 as possible.
The weight average molecular weight of the stereocomplex polylactic acid is preferably 100,000 to 500,000, more preferably 100,000 to 300,000. The weight average molecular weight is a standard polystyrene equivalent weight average molecular weight value measured by gel permeation chromatography (GPC) using chloroform as an eluent.

The stereocomplex polylactic acid is preferably composed of poly-L lactic acid and poly-D lactic acid to form a stereocomplex crystal. The content of stereocomplex crystals is preferably 80 to 100%, more preferably 95 to 100%. The stereocomplex polylactic acid referred to in the present invention has a melting peak at 195 ° C. or higher, preferably 80% or higher, more preferably 90% or higher, in the melting peak in the temperature rising process in the differential scanning calorimeter (DSC) measurement. More preferably, it is 95% or more. The melting point is in the range of 195 to 250 ° C, more preferably in the range of 200 to 220 ° C. The melting enthalpy is 20 J / g or more, preferably 30 J / g or more. Specifically, in the differential scanning calorimeter (DSC) measurement, the ratio of the melting peak at 195 ° C. or higher in the melting peak in the temperature rising process is 90% or higher, and the melting point is in the range of 195 to 250 ° C. It is preferable that the melting enthalpy is 20 J / g or more.
Stereocomplex polylactic acid can be produced by coexisting and mixing poly L lactic acid and poly D lactic acid in a predetermined weight ratio. The polylactic acid (A) is preferably composed of poly L lactic acid having a weight average molecular weight of 150,000 to 250,000 and poly D lactic acid having a weight average molecular weight of 130,000 to 160,000.

Mixing can be performed in the presence of a solvent. The solvent is not particularly limited as long as it dissolves poly L lactic acid and poly D lactic acid. For example, chloroform, methylene chloride, dichloroethane, tetrachloroethane, phenol, tetrahydrofuran, N-methylpyrrolidone, N, N-dimethylformamide, butyrolactone, trioxane, hexafluoroisopropanol or the like alone or in combination of two or more are preferred.
The mixing can be performed in the absence of a solvent. That is, a method of melt kneading after mixing a predetermined amount of poly L lactic acid and poly D lactic acid, and a method of adding and kneading one of them after melting one of them can be employed.

  Alternatively, stereoblock polylactic acid in which a poly L lactic acid segment and a poly D lactic acid segment are bonded can also be suitably used for the polylactic acid component of the present invention. Stereoblock polylactic acid is a block polymer in which a poly L lactic acid segment and a poly D lactic acid segment are bonded in the molecule. Such a block polymer can be produced by, for example, a method of producing by sequential ring-opening polymerization, a method of polymerizing poly L lactic acid and poly D lactic acid, and then binding them with a chain exchange reaction or a chain extender, poly L lactic acid. A block copolymer having the above-mentioned basic structure, such as a method of polymerizing poly-D-lactic acid, blending and then solid-phase polymerization to extend the chain, a method of producing from racemic lactide using a stereoselective ring-opening polymerization catalyst If so, it can be used regardless of the production method. However, it is more preferable from the viewpoint of ease of production to use a high-melting stereoblock polymer obtained by sequential ring-opening polymerization and a polymer obtained by a solid phase polymerization method.

The stereocomplex polylactic acid and stereoblock polylactic acid used in the present invention preferably have a stereogenicity (S) of 90% or more, more preferably 100%. The degree of stereoification can be determined by the following formula (A) by comparing the enthalpies of the melting point in DSC measurement.
S = [(ΔHms / ΔHms0) / (ΔHmh / ΔHmh0 + ΔHms / ΔHms0)] (A)
(However, ΔHms0 = 203.4 J / g, ΔHmh0 = 142 J / g, ΔHms = melting enthalpy of stereocomplex melting point, ΔHmh = melting enthalpy of homocrystal)
It is preferable to add a specific additive to the polylactic acid used in the present invention in order to improve the degree of stereoization. A preferable example of such an additive is a metal phosphate represented by the following formula (2).

In the formula, R ₁ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group. R ₂ and R ₃ may be the same or different and each represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, and an octyl group.
M ₁ represents an alkali metal atom, an alkaline earth metal atom, a zinc atom or an aluminum atom. Examples of M ₁ include Na, K, Al, Mg, and Ca. In particular, K, Na, and Al can be preferably used. n represents 0 when M ₁ is an alkali metal atom, an alkaline earth metal atom, or a zinc atom, and represents 1 or 2 when M ₁ is an aluminum atom.

These metal phosphates are preferably used in an amount of 10 ppm to 2 wt%, more preferably 50 ppm to 0.5 wt%, and still more preferably 100 ppm to 0.3 wt% with respect to the polylactic acid component. When the amount is too small, the effect of improving the degree of stereoization is small, and when too large, the resin itself is deteriorated, which is not preferable.
Moreover, in order to improve the heat resistance of the polylactic acid composition, it is preferable to further add calcium silicate. As calcium silicate, what contains a hexagonal crystal can be used, for example, and the one where the particle diameter is low is preferable. For example, when the average primary particle diameter is in the range of 0.2 to 0.05 μm, the polylactic acid composition is appropriately dispersed in the polylactic acid composition, so that the heat resistance of the polylactic acid composition is good. Further, the addition amount is preferably in the range of 0.01 to 1 wt% based on the polylactic acid composition, and more preferably in the range of 0.05 to 0.5 wt%. If the amount is too large, the appearance tends to deteriorate, and if the amount is too small, no particular effect is exhibited, which is not preferable.

  In the present invention, the carboxyl end group concentration of polylactic acid in the polylactic acid composition is preferably 15 eq / ton or less. When it is within this range, a composition having good melt stability and wet heat durability can be obtained. In the case of 15 eq / ton or less, specifically, any of the known methods for reducing the carboxyl end group concentration in the polyester can be employed. For example, addition of a terminal blocking agent, specifically, oxazoline Ester, amidation with alcohol or amine without addition of condensing agents such as monocarbodiimides, dicarbodiimides, polycarbodiimides, or end-capping agents or condensing agents. You can also.

<Polylactic acid (B)>
The polylactic acid (B) having a melting point of less than 190 ° C. used in the present invention consists essentially of L lactic acid units or D lactic acid units represented by the above formula (1).
When the polylactic acid (B) is poly-L-lactic acid, the content of the L-lactic acid unit is preferably 90 to 100 mol%, more preferably 95 to 100 mol%, still more preferably 99 to 100 mol%. . Examples of other units include D lactic acid units and units other than lactic acid. The D lactic acid unit and the units other than lactic acid are preferably 0 to 10 mol%, more preferably 0 to 5 mol%, still more preferably 0 to 1 mol%.
When polylactic acid (B) is poly-D-lactic acid, the content of D-lactic acid units is preferably 90 to 100 mol%, more preferably 95 to 100 mol%, and even more preferably 99 to 100 mol%. . Examples of other units include L-lactic acid units and units other than lactic acid. The content of other units is preferably 0 to 10 mol%, more preferably 0 to 5 mol%, still more preferably 0 to 1 mol%.
Other units include units derived from dicarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, lactones, etc. having functional groups capable of forming two or more ester bonds, and various polyesters, various polyethers, various types of these various constituent components. Examples are units derived from polycarbonate and the like.

Examples of the dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Polyhydric alcohols include ethylene glycol, propylene glycol, propanediol, butanediol, pentanediol, hexanediol, octanediol, glycerin, sorbitan, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polyteoramethylene glycol. Aliphatic polyhydric alcohols such as aliphatic polyhydric alcohols, and aromatic polyhydric alcohols obtained by adding ethylene oxide to bisphenol. Examples of the hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, 4-hydroxybenzoic acid and the like. Examples of the lactone include glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, δ-valerolactone, and the like.
These poly-L lactic acid and poly-D lactic acid can be produced by employing a known method as described in the section of polylactic acid (A) having a melting point of 190 ° C. or higher. The polylactic acid (B) is preferably poly L lactic acid having a weight average molecular weight of 150,000 to 250,000. The polylactic acid (B) is preferably poly-D lactic acid having a weight average molecular weight of 150,000 to 250,000.

<Coupling agent (E)>
As long as the coupling agent of this invention is an ethylene acrylate copolymer, all can be employ | adopted, Specifically, Biomax100,120 of DuPont, Surlyn 1652E, PC-100, Fusbond A ME0-556 etc. Can be illustrated. The ethylene acrylate copolymer has the following conditions:
(i) an acrylate content of 20% by weight or more,
(ii) ethylene acrylate content of 90% or more,
(iii) A melt index at 190 ° C. and a 21.2N load condition is 10 g / 10 min or more,
Those satisfying one or more of these are preferred.

<Composition ratio>
The content of polylactic acid (B) is preferably 5 to 800 parts by weight, more preferably 20 to 200 parts by weight, and still more preferably 40 to 100 parts by weight with respect to 100 parts by weight of polylactic acid (A). The content of the coupling agent (E) is preferably 5 to 300 parts by weight, more preferably 10 to 100 parts by weight, and further preferably 15 to 50 parts by weight with respect to 100 parts by weight of the polylactic acid (A). Therefore, the polylactic acid composition of the present invention preferably contains 5 to 800 parts by weight of polylactic acid (B) and 5 to 300 parts by weight of coupling agent (E) with respect to 100 parts by weight of polylactic acid (A). .
When polylactic acid (B) exceeds 800 parts by weight with respect to 100 parts by weight of polylactic acid (A), the heat resistance is poor. If the amount is less than 5 parts by weight, the effect of improving impact resistance is small. If the coupling agent (E) exceeds 300 parts by weight with respect to 100 parts by weight of the polylactic acid (A), the modulus decreases, and if it is less than 5 parts by weight, the effect of addition is small.

  In producing the polylactic acid composition of the present invention, the polylactic acid (A), the polylactic acid (B), and the coupling agent (E) may be mixed uniformly, such as melt blending and solution blending. If possible, it can be blended by any method. In particular, it is preferable to knead in a molten state in a kneader, a single-screw kneader, a twin-screw kneader, a melt reactor, or the like. In the case of melt-kneading, the temperature may be a temperature at which both lactic acid components are melted, but a range of 190 ° C. to 250 ° C. is preferable considering the stability of the resin.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In addition, each value in a present Example was calculated | required according to the following method.

(1) Impact resistance:
According to ISO 179-1, the Charpy impact strength of a 4 mm pressure notched strip-shaped molded product was measured.
(2) Tensile strength, elongation at break and modulus:
According to ISO 527, the tensile strength, elongation at break and modulus of the 4 mm thick strip-shaped molded product were measured.
The following were used as polylactic acid (A), polylactic acid (B), and coupling agent (E).
(1) Polylactic acid (A)
The stereocomplex polylactic acid (A1) obtained in Synthesis Example 2 was used.
(2) Polylactic acid (B)
Poly-L lactic acid (4042D manufactured by Nature Works, optical purity 95% or more, weight average molecular weight 210,000, melting point 150 ° C.) was used.
(3) Coupling agent (E)
BioPont Strong 120 from DuPont with 99% or more ethylene-acrylate copolymer and less than 0.4% normal butyl acrylate was used.

[Synthesis Example 1] Preparation of poly-D lactic acid 0.006 parts by weight of octylate and 0.37 parts by weight of octadecyl alcohol with respect to 100 parts by weight of D-lactide (manufactured by Musashino Chemical Laboratory, Inc., optical purity 99% or more) The reaction was carried out in a reactor equipped with a stirring blade under a nitrogen atmosphere at 190 ° C. for 2 hours, and then 0.01 parts by weight of a transesterification inhibitor (dihexylphosphonoethyl acetate DHPA) was added, and the pressure was reduced. The remaining lactide was removed and chipped to obtain poly-D lactic acid. The resulting poly-D lactic acid had a weight average molecular weight of 130,000, a glass transition point (Tg) of 60 ° C., and a melting point of 170 ° C.

[Synthesis Example 2] Preparation of stereocomplex polylactic acid (A1) Poly D lactic acid (weight average molecular weight 130,000) obtained in Synthesis Example 1 and poly L lactic acid (4042D manufactured by Nature Works, optical purity of 95% or more, A weight average molecular weight of 210,000) was melt kneaded using a 32 mm diameter twin screw extruder (manufactured by Coperion, ZSK 32) under the conditions of a cylinder temperature of 200 ° C. to 250 ° C. and a rotation speed of 200 rpm, and stereocomplex polylactic acid ( A1) was obtained. Stereocomplex polylactic acid (A1) had a melting point of 213 ° C., a stereogenicity of 100%, and a weight average molecular weight of 160,000.

[Comparative Example 1]
The stereocomplex polylactic acid (A1) obtained in Synthesis Example 2 was injection molded at a cylinder temperature of 200 ° C. to 230 ° C. and a mold temperature of 120 ° C. using an injection molding machine (ES200 / 60 HLST manufactured by ENGEL) for various evaluations. A molded product was obtained.

[Comparative Example 2]
Poly L-lactic acid (4042D manufactured by Nature Works, optical purity 95% or more, weight average molecular weight 210,000, melting point 150 ° C.) was used with a 32 mm diameter twin screw extruder (Coperion ZSK 32), and cylinder temperature 200 ° C. to 250 ° C. Melt kneading was performed under the conditions of 200 ° C. and a rotational speed of 200 rpm to obtain polylactic acid (B). The obtained polylactic acid (B) was injection molded at a cylinder temperature of 200 ° C. to 230 ° C. and a mold temperature of 30 ° C. using an injection molding machine (ES200 / 60 HLST manufactured by ENGEL) to obtain molded products for various evaluations.

[Examples 1 to 4, Comparative Example 3]
As shown in Table 1, the raw materials were blended and melt kneaded using a 32-mm twin screw extruder (ZSK 32, manufactured by Coperion) at a cylinder temperature of 200 ° C. to 250 ° C. under a rotation speed of 200 rpm. Obtained.
The obtained polylactic acid composition was injection molded at a cylinder temperature of 200 ° C. to 230 ° C. and a mold temperature of 30 ° C. or 120 ° C. using an injection molding machine (ES200 / 60 HLST manufactured by ENGEL) to produce molded products for various evaluations. Obtained. These results are summarized in Table 1.

Claims (10)

A polylactic acid composition comprising polylactic acid (A) having a melting point of 190 ° C. or higher, polylactic acid (B) having a melting point of less than 190 ° C., and a coupling agent (E). The polylactic acid composition according to claim 1, wherein the polylactic acid (A) forms a stereocomplex crystal. The polylactic acid composition according to claim 2, wherein the degree of stereoification of the polylactic acid (A) is 90% or more. The polylactic acid composition according to claim 1, wherein the polylactic acid (A) comprises poly L-lactic acid having a weight average molecular weight of 150,000 to 250,000 and poly D lactic acid having a weight average molecular weight of 130,000 to 160,000. The polylactic acid composition according to claim 1, wherein the polylactic acid (B) is poly-L lactic acid having a weight average molecular weight of 150,000 to 250,000. The polylactic acid composition according to claim 1, wherein the polylactic acid (B) is poly-D lactic acid having a weight average molecular weight of 150,000 to 250,000. The polylactic acid composition according to claim 1, wherein the coupling agent (E) is an ethylene acrylate copolymer. The polylactic acid composition according to claim 1, comprising 5 to 800 parts by weight of polylactic acid (B) and 5 to 300 parts by weight of a coupling agent (E) with respect to 100 parts by weight of polylactic acid (A). A molded article comprising the polylactic acid composition according to claim 1. A method for producing a polylactic acid composition, comprising melting and kneading polylactic acid (A) having a melting point of 190 ° C. or higher, polylactic acid (B) having a melting point of less than 190 ° C., and a coupling agent (E).