WO2010038860A1 - Polylactic acid composition and method for producing same - Google Patents

Abstract

Provided are: a polylactic acid composition having extremely good molding processability; and a method for producing the same.  A polylactic acid composition comprising poly-L-lactic acid and a polylactic acid block copolymer in which the mass ratio of an L-lactic acid unit to a D-lactic acid unit is from 50/50 to 91/9 (L-lactic acid unit/D-lactic acid unit); a polylactic acid composition comprising poly-D-lactic acid and a polylactic acid block copolymer in which the mass ratio of an L-lactic acid unit to a D-lactic acid unit is from 49/51 to 9/91 (L-lactic acid unit/D-lactic acid unit); and a method for producing the same.

Description

Polylactic acid composition and method for producing the same

The present invention relates to a polylactic acid composition and a method for producing the same, and more particularly to a polylactic acid composition advantageous for improving moldability and productivity in molding and a method for producing the same.

Polylactic acid is a bio-based polymer starting from renewable resources such as starch and sugar, and has excellent mechanical properties. However, a low crystallization rate and a low melt tension are problems in molding. Therefore, the present condition is that higher moldability is required.

The flow of polymer melt during molding is roughly divided into two types: shear flow that prevails when flowing through a tube, and elongation flow that prevails when having a free surface. In particular, in a molding process in which elongational flow having a free surface such as spinning, film, and blow molding is dominant, the elongational rheological property, that is, strain hardening property greatly affects the moldability. Accordingly, there is an increasing demand for improving this strain hardening property.

Non-Patent Documents 1 and 2 show that the addition of a small amount of poly-D-lactic acid (PDLA) to poly-L-lactic acid (PLLA) improves the crystallization speed and melt tension of poly-L-lactic acid. It is reported that it can be done. The high melting point stereocomplex polylactic acid formed by the PLLA chain and the PDLA chain becomes a crystal nucleus, and the crystallization speed is remarkably improved. Further, long chain branching is introduced into PLLA using a stereo complex dispersed in the PLLA melt as a crosslinking point, and as a result, the melt tension is improved. Furthermore, it has been clarified that the above-mentioned effect is remarkably exhibited by addition of higher PDLA.

H. Yamane and K.K. Sasai, Polymer, vol. 44,569-2575 (2003) H. Yamane, K .; Sasai, M .; Takano, and M.M. Takahashi, J. et al. Rheol. , 48 (3), 599-609 (2004)

However, the technique of adding a small amount of poly-D-lactic acid to poly-L-lactic acid described in Non-Patent Documents 1 and 2 does not provide sufficient improvement in strain hardening and also increases the shear viscosity at the same time. For this reason, the productivity of the molding process may be reduced. Therefore, there is a strong demand for a technique for improving strain hardening while suppressing an increase in shear viscosity.

Therefore, an object of the present invention is to provide a polylactic acid composition that is low in cost and has improved strain-hardening properties while suppressing an increase in shear viscosity and a method for producing the same.

As a result of intensive studies in view of the above prior art, the present inventors have found a method for achieving the above object and have completed the present invention.

As a result of studying without being bound by conventional techniques, the present inventors have surprisingly found that the composition ratio (mass ratio) in which the L-lactic acid unit (L component) and the D-lactic acid unit (D component) are biased. The composition obtained by mixing a polylactic acid block copolymer and poly-L-lactic acid or poly-D-lactic acid has an excellent strain hardening property while suppressing an increase in shear viscosity. I found it.
For example, by using a polylactic acid block copolymer having a biased composition ratio (mass ratio) in which the number of L-lactic acid units (L component) is larger than that of D-lactic acid units (D component), D-lactide is obtained. It has been found that the use amount of can be suppressed, and that it can lead to the solution of a problem that has been considered unsolvable, which is to reduce the production cost of stereocomplex polylactic acid.

That is, the present invention relates to a polylactic acid block copolymer (A1) in which the mass ratio of L-lactic acid units to D-lactic acid units is L-lactic acid units / D-lactic acid units = 50/50 to 91/9, A polylactic acid composition comprising poly-L-lactic acid (B).

The present invention also provides a polylactic acid block copolymer (A2) in which the mass ratio of L-lactic acid units to D-lactic acid units is L-lactic acid units / D-lactic acid units = 49/51 to 9/91; A polylactic acid composition comprising poly-D-lactic acid (C).

Further, the present invention is a method for producing the polylactic acid composition.

According to the polylactic acid composition of the present invention, the composition (mass ratio) of the L component (poly-L-lactic acid or L-lactide) to be used and the D component (poly-D-lactic acid or D-lactide) is greatly increased. Even if it is biased, a polylactic acid composition having a very high content of stereocomplex crystals can be obtained. Therefore, when there is a manufacturing cost and / or price difference between the L component and the D component in the manufacturing stage, the polylactic acid having a very low cost and high molding processability is used by using more inexpensive ones. Compositions and molded articles can be provided.

In addition to the above effects, according to the present invention, it is possible to provide a polylactic acid composition having improved strain hardening while suppressing an increase in shear viscosity.

It is a graph which shows the frequency dependence of dynamic viscosity | η ^* | and storage elastic modulus G ′ measured at 190 ° C. of PLLA to which PDLA is added. It is a graph which shows the frequency dependence of dynamic viscosity | η ^* | and storage elastic modulus G ′ measured at 190 ° C. of PLLA to which a polylactic acid block copolymer (50/50) is added. It is a graph which shows the frequency dependence of dynamic viscosity | η ^* | and storage elastic modulus G ′ measured at 190 ° C. of PLLA to which a polylactic acid block copolymer (30/70, 20/80) is added. It is a graph which shows the time dependence of the biaxial extensional viscosity measured by various extension speeds of the sample which added PDLA (150,000, 330,000) to PLLA. It is a graph which shows the time dependence of the biaxial extension viscosity measured at various extension speeds of the sample which added the polylactic acid block copolymer (50/50) to PLLA. It is a graph which shows the time dependence of the biaxial extensional viscosity measured by the various extension rate of the sample which added the polylactic acid block copolymer (30/70, 20/80) with respect to PLLA. It is a graph which shows the time dependence of the biaxial extensional viscosity measured by the various extension rate of the sample which added the polylactic acid block copolymer (70/30, 80/20) with respect to PLLA. It is the table | surface and graph which show the result of having calculated the strain hardening coefficient from FIG. It is the table | surface and graph which show the result of having calculated the strain hardening coefficient from FIG. 4A. It is the table | surface and graph which show the result of having calculated the strain hardening coefficient from FIG. 4A. It is the table | surface and graph which show the result of having calculated the strain hardening coefficient from FIG. 4B. It is the table | surface and graph which show the result of having calculated the strain hardening coefficient from FIG. 4B. It is the table | surface and graph which show the result of having calculated the strain hardening coefficient from FIG. 4C. It is the table | surface and graph which show the result of having calculated the strain hardening coefficient from FIG. 4C.

The first of the present invention is a polylactic acid block copolymer (A1) in which the mass ratio of L-lactic acid units to D-lactic acid units is L-lactic acid units / D-lactic acid units = 50/50 to 91/9. And a poly-L-lactic acid (B).

The second of the present invention is a polylactic acid block copolymer (A2) in which the mass ratio of L-lactic acid units to D-lactic acid units is L-lactic acid units / D-lactic acid units = 49/51 to 9/91. ) And poly-D-lactic acid (C).

The polylactic acid composition of the present invention is excellent in moldability because it suppresses an increase in shear viscosity and has excellent strain hardening properties. For example, in the case of foam molding, by adding a specific amount of the polylactic acid composition of the present invention, the strain hardening property of the extension viscosity can be controlled and the stability of the cell can be improved. For this reason, the polylactic acid composition of the present invention is excellent in foam moldability. In the case of blow molding or vacuum molding, many flow processes having a free surface are included. Changes in the shear viscosity and speed may make it difficult to control the thickness of the extruded barison. However, by adding a specific amount of the polylactic acid composition of the present invention, the thickness of the product is constant, and the speed of the process can be increased only by increasing the amount of extrusion.

In addition to the above, the polylactic acid composition of the present invention can be produced at a very low cost by using more inexpensive ones according to the production costs of the L component and D component which are raw materials in the production stage. .

Hereinafter, the polylactic acid block copolymers (A1) and (A2), poly-L-lactic acid (B), and poly-D-lactic acid (C) contained in the polylactic acid composition of the present invention will be described in detail.

<Polylactic acid block copolymer (A1) or (A2)>
In the polylactic acid block copolymer (A1) contained in the polylactic acid composition of the present invention, the mass ratio of D-lactic acid units to L-lactic acid units is such that L-lactic acid units / D-lactic acid units = 50/50 to 91/9. The polylactic acid block copolymer (A2) contained in the polylactic acid composition of the present invention has a mass ratio of L-lactic acid units to D-lactic acid units of L-lactic acid units / D-lactic acid units = 49 / 51-9 / 91.

The polylactic acid block copolymer (A2) comprises (i) ring-opening of D-lactide (D-lactic acid unit component or D component) in the presence of poly-L-lactic acid (L-lactic acid unit component or L component). It can manufacture by performing superposition | polymerization. The polylactic acid block copolymer (A1) is subjected to (ii) ring-opening polymerization of L-lactide (L-lactic acid unit component) in the presence of poly-D-lactic acid (D-lactic acid unit component). Can be manufactured. Hereinafter, the polylactic acid block copolymer (A1) or (A2) will be described in more detail.

(I) Poly-L-lactic acid (PLLA) or (ii) Poly-D-lactic acid (PDLA)
The poly-L-lactic acid (PLLA) of (i) or the poly-D-lactic acid (PDLA) of (ii) is substantially composed of an L-lactic acid unit or a D-lactic acid unit represented by the following chemical formula (1). Configured. Here, poly-L-lactic acid (PLLA) can also be used as poly-L-lactic acid (B) according to the present invention. Similarly, poly-D-lactic acid (PDLA) can be used as poly-D-lactic acid (C) according to the present invention.

The PLLA or PDLA is not particularly limited in its composition and molecular weight as long as it has a structure substantially composed of L-lactic acid units or D-lactic acid units.

The PLLA is composed of L-lactic acid units, preferably 90 to 100 mol%, more preferably 92 to 100 mol%, and still more preferably 95 to 100 mol%, with all the structural units in PLLA as 100 mol%. The If the L-lactic acid unit in the PLLA is less than 90 mol%, the final melting point of the polylactic acid block copolymer (A1) or (A2) may be difficult to increase.

The PLLA may contain a structural unit other than the L-lactic acid unit. The content of structural units other than the L-lactic acid unit is preferably 10 to 0 mol%, more preferably 8 to 0 mol%, still more preferably 5 to 0 mol, with all the structural units in PLLA as 100 mol%. %. Examples of structural units other than L-lactic acid units that can be contained in PLLA include D-lactic acid units, structural units derived from compounds other than lactic acid, and the like.

The PDLA is composed of 90 to 100 mol%, more preferably 92 to 100 mol%, and still more preferably 95 to 100 mol% of D-lactic acid units, with all the structural units in the PDLA being 100 mol%. The If the D-lactic acid unit in the PDLA is less than 90 mol%, the final melting point of the polylactic acid block copolymer (A1) or (A2) may be difficult to increase.

The PDLA may contain a structural unit other than the D-lactic acid unit. The content of structural units other than D-lactic acid units is preferably 10 to 0 mol%, more preferably 8 to 0 mol%, still more preferably 5 to 0 mol, with 100 mol% of all structural units in PDLA. %. Examples of structural units other than D-lactic acid units that can be contained in PDLA include L-lactic acid units, structural units derived from compounds other than lactic acid, and the like.

Examples of structural units derived from compounds other than lactic acid that can be contained in the PLLA or the PDLA include, for example, dicarboxylic acid-derived units, polyhydric alcohol-derived units, hydroxycarboxylic acid-derived units, or lactone-derived units. Preferred examples include units, units derived from polyesters obtained from these structural units, units derived from polyethers, units derived from polycarbonate, and the like. However, it is not limited to these.

Preferred examples of the dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the polyhydric alcohol include, for example, ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, octanediol, glycerin, sorbitan, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, or polypropylene glycol. Preferred examples include aliphatic polyhydric alcohols or aromatic polyhydric alcohols obtained by adding ethylene oxide to bisphenol. Preferred examples of the hydroxycarboxylic acid include glycolic acid and hydroxybutyric acid. Preferable examples of the lactone include glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, and δ-valerolactone.

From the viewpoint of obtaining a polymer having a higher melting point, the mass ratio of the L-lactic acid unit to the D-lactic acid unit in the PLLA is L-lactic acid unit / D-lactic acid unit = 95/5 to 100/0. The mass ratio of the D-lactic acid unit and the L-lactic acid unit in the PDLA is preferably in the range of D-lactic acid unit / L-lactic acid unit = 95/5 to 100/0. .

The weight average molecular weight of the PLLA or the PDLA is preferably 7,000 to 1,500,000, more preferably 30,000 to 1,400,000, still more preferably 80,000 to 1,250,000, even more preferably 100,000 to 1.1 million, It is preferably 120,000 to 500,000. When the weight average molecular weight of the PLLA and the PDLA is out of the range, the content of the stereocomplex crystal in the polylactic acid block copolymer (A1) or (A2) produced using these PDLA or PLLA, It may be difficult to be 80% by weight or more. In the present invention, as the weight average molecular weight, a polystyrene equivalent value measured by a GPC (Gel Permeation Chromatography) method is adopted. More specifically, the weight average molecular weight is a value measured by the method described in the following examples.

The method for obtaining the PLLA or the PDLA is not particularly limited, and includes, for example, a method of dehydrating condensation (condensation polymerization) of L-lactic acid or D-lactic acid, a method of ring-opening polymerization of L-lactide or D-lactide, etc. Is mentioned. The production method of PLLA or PDLA by dehydration condensation (condensation polymerization) of L-lactic acid or D-lactic acid is not particularly limited, and a known method such as the method described in JP-A-9-31180 can be used. Further, the production method of PLLA or PDLA by ring-opening polymerization of L-lactide or D-lactide is not particularly limited, and examples thereof include methods described in JP-A Nos. 7-118259 and 7-138253, etc. Known methods can be used. Among these, the method of ring-opening polymerization of L-lactide or D-lactide is preferable because it is easy to obtain a high molecular weight product and the molecular weight can be easily controlled. Hereinafter, a method for producing PLLA or PDLA by ring-opening polymerization of L-lactide or D-lactide will be described in detail.

The purity of L-lactide or D-lactide used for obtaining the PLLA or the PDLA is not particularly limited, but from the viewpoint of obtaining a polymer having a high molecular weight, the purity of the LLA-lactide or D-lactide is not limited in the L-lactide or the D-lactide. The compound other than lactic acid such as free acid contained is preferably 10% by weight or less, more preferably 1% by weight or less, based on 100% by weight of the L-lactide or D-lactide. More preferably, it is 15% by weight or less, and particularly preferably 0.05% by weight or less. If the free acid in the L-lactide or the D-lactide exceeds 10% by weight, the ring-opening polymerization reaction may not proceed. A method for purifying the L-lactide or the D-lactide is not particularly limited. For example, a conventionally known method such as crystallization or distillation, a method described in JP-A No. 2004-149418, or JP-A No. 2004-149419 is used. The method described in the publication can be appropriately selected and employed.

The ring-opening polymerization can be performed in the presence of an organic solvent and a polymerization catalyst. The polymerization catalyst is not particularly limited as long as it causes a polymerization reaction to proceed. For example, the polymerization catalyst is selected from the group consisting of Group 2 elements, rare earth metals, transition metals in the fourth period, aluminum, germanium, tin, and antimony. Preferred examples include compounds containing at least one metal element. Examples of the Group 2 element include magnesium, calcium, and strontium. Examples of the rare earth element include scandium, yttrium, lanthanum, and cerium. Examples of the transition metal in the fourth period include iron, cobalt, nickel, zinc, and titanium.

Examples of the polymerization catalyst containing a metal element as described above include the metal carboxylates exemplified above, the alkyl carboxylates exemplified above, the metal alkoxides exemplified above, and the metals exemplified above. Preferred examples include aryl oxides and enolates of metal β-diketones exemplified above, and these can be used alone or in combination of two or more. In consideration of polymerization activity and hue, the polymerization catalyst containing the metal element is selected from the group consisting of tin 2-ethylhexanoate (tin octylate), titanium tetraisopropoxide, and aluminum triisopropoxide. At least one is more preferable.

The amount of the polymerization catalyst containing the metal element is preferably 0.001 to 0.5 parts by mass, more preferably 0.001 to 0.1 parts per 100 parts by mass of the L-lactide or the D-lactide. Part by mass, more preferably 0.003 to 0.01 part by mass. When the amount of the polymerization catalyst containing the metal element is less than 0.001 part by mass with respect to 100 parts by mass of the L-lactide or D-lactide, the reaction proceeds slowly and the L component (poly-L -Lactic acid or L-lactide) and the polylactic acid block copolymer (A1) used in the present invention, which is produced with an uneven composition ratio (mass ratio) of D component (poly-D-lactic acid or D-lactide) Or the effect which reduces the manufacturing cost of (A2) may not be acquired. On the other hand, when the amount of the polymerization catalyst containing the metal element exceeds 0.5 parts by mass with respect to 100 parts by mass of the L-lactide or the D-lactide, it becomes difficult to control the reaction and the racemization is performed. In some cases, the degree of dispersion may increase, and coloring of the obtained polymer may become remarkable, and the use of the obtained polymer may be limited.

When performing ring-opening polymerization in the presence of a polymerization catalyst containing the metal element, a molecular weight modifier (polymerization initiator) may be used. Examples of the molecular weight regulator (polymerization initiator) include alcohol compounds. The alcohol compound preferably does not inhibit the polymerization of polylactic acid and is non-volatile. Specific examples include, for example, decanol, dodecanol, tetradecanol, hexadecanol, octadecanol, or lauryl alcohol, and these can be used alone or in combination of two or more.

The amount used when the molecular weight modifier (polymerization initiator) is used can be appropriately selected depending on the desired molecular weight of the target polylactic acid. In order to obtain polylactic acid having a weight average molecular weight as described above, the amount of the molecular weight modifier (polymerization initiator) used is preferably 0.1 with respect to 100 parts by mass of the L-lactide or the D-lactide. To 20 parts by mass, more preferably 0.1 to 15 parts by mass. When the amount of the polymerization initiator used exceeds 20 parts by mass with respect to 100 parts by mass of the L-lactide or the D-lactide, it may be difficult to obtain a polymer having a target molecular weight.

The atmosphere of the ring-opening polymerization of the L-lactide or the D-lactide in the presence of the polymerization catalyst containing the metal element is not particularly limited, but for reasons such as suppressing the coloring of the product, An inert gas atmosphere such as nitrogen gas or argon gas is preferred.

The reaction time for the ring-opening polymerization of the L-lactide or the D-lactide in the presence of the polymerization catalyst containing the metal element is preferably 15 minutes to 7 hours, more preferably 30 minutes to 5 hours. If the reaction time is less than 15 minutes, the target polymer may not be obtained due to insufficient reaction, and if it exceeds 5 hours, the resulting polymer may be colored or increased in degree of dispersion. There is a case.

The reaction temperature of the ring-opening polymerization of the L-lactide or the D-lactide in the presence of the polymerization catalyst containing the metal element is preferably 100 ° C. to 250 ° C., more preferably 150 ° C. to 230 ° C., further preferably 170 ° C to 230 ° C. When the reaction temperature is less than 100 ° C., the progress of the reaction is slow, and the L component (poly-L-lactic acid or L-lactide) and D component (poly-D-lactic acid or D-lactide) in the obtained polymer are slow. In some cases, the effect of reducing the production cost of the polylactic acid block copolymer (A1) or (A2) used in the present invention, which is produced with a significantly biased composition ratio (mass ratio), may not be obtained. When the reaction temperature exceeds 250 ° C., it becomes difficult to control the reaction, there is a possibility that racemization or an increase in dispersibility may occur, and there is a possibility that coloring of the resulting polymer may become remarkable. There is a possibility that the use of the is limited.

The reaction pressure of the ring-opening polymerization of the L-lactide or the D-lactide in the presence of the polymerization catalyst containing the metal element is not particularly limited as long as it is within a range in which the ring-opening polymerization can proceed in the solution. However, it may be performed under atmospheric pressure, reduced pressure, or increased pressure. It is preferable to carry out under atmospheric pressure from the standpoint that a pressure-resistant manufacturing apparatus is unnecessary and it can contribute to reduction in manufacturing cost.

The ring-opening polymerization of the L-lactide or the D-lactide in the presence of the polymerization catalyst containing the metal element is a vertical reaction equipped with a conventionally known production apparatus, for example, a high-viscosity stirring blade such as a helical ribbon blade. It can be performed using a container or the like.

It is preferable that the PLLA is obtained by removing excess lactide after ring-opening polymerization of L-lactide. Similarly, it is preferable that the PDLA is obtained by removing excess lactide after ring-opening polymerization of D-lactide. It is preferable to remove the excess lactide from the PLLA or the PDLA because the final melting point of the polylactic acid block copolymer (A1) or (A2) can be increased.

The method for removing the excess lactide is not particularly limited, and can be performed, for example, by reducing the pressure in the reaction system, washing with organic solvent (purification), or the like. It is preferable to do so.

The pressure reduction conditions are not particularly limited, but the temperature in the system after the completion of the polymerization reaction is preferably 130 to 250 ° C., more preferably 150 to 230 ° C., and the pressure in the system is It is preferably 70 kPa or less, more preferably 15 kPa (112 mmHg) or less. When the temperature is lower than 130 ° C., the apparatus may become difficult to operate due to an increase in viscosity in the system or solidification of the system. On the other hand, when it exceeds 250 ° C., the depolymerization reaction of lactide proceeds, and the degree of dispersion of the resulting PLLA or PDLA may increase. Moreover, when the system internal pressure exceeds 70 kPa, the removal of lactide may be insufficient.

The atmosphere during decompression is not particularly limited, but is preferably an inert gas atmosphere such as nitrogen gas or argon gas from the viewpoint of suppressing decomposition of residual lactide and coloring of the polymer.

In addition, since the melting point of the finally obtained polylactic acid block copolymer (A1) or (A2) may be lowered when the residual amount of lactide in the PLLA or the PDLA is large, as described above. Regardless of whether or not the excessive lactide is removed, it is preferable that the PLLA or the PDLA has a low content of L-lactide or D-lactide. That is, the content of L-lactide in the poly-L-lactic acid before the ring-opening polymerization of D-lactide in the presence of poly-L-lactic acid is based on the mass of the poly-L-lactic acid. It is preferably 0 to 5% by weight, more preferably 0 to 1% by weight, still more preferably 0 to 0.5% by weight, and particularly preferably 0 to 0.1% by weight. . The content of D-lactide in the poly-D-lactic acid before the ring-opening polymerization of L-lactide in the presence of poly-D-lactic acid is based on the mass of the poly-D-lactic acid. It is preferably 0 to 5% by weight, more preferably 0 to 1% by weight, still more preferably 0 to 0.5% by weight, and particularly preferably 0 to 0.1% by weight. . When the content of L-lactide in the poly-L-lactic acid or the content of D-lactide in the poly-D-lactic acid exceeds 5% by weight, the finally obtained polylactic acid block copolymer (A1 ) Or (A2) may decrease in melting point.

(D-lactide or L-lactide ring-opening polymerization)
After obtaining the poly-L-lactic acid or the poly-D-lactic acid, (i) ring-opening polymerization of D-lactide in the presence of the poly-L-lactic acid, or (ii) the poly-D -Ring-opening polymerization of L-lactide in the presence of lactic acid. Under the present circumstances, according to said (i), the polylactic acid block copolymer (A1) based on this invention is manufactured. Moreover, according to said (ii), the polylactic acid block copolymer (A2) based on this invention is manufactured. Here, after obtaining the poly-L-lactic acid or the poly-D-lactic acid, the ring-opening of D-lactide or L-lactide in the presence of the poly-L-lactic acid or the poly-D-lactic acid The polymerization will be described.

The purity of the D-lactide is preferably 90 to 100 mol%, more preferably 92 to 100 mol%, still more preferably 95 to 100 mol%, where the total number of moles of D-lactide is 100 mol%. The content of components other than D-lactide is preferably 10 to 0 mol%, more preferably 8 to 0 mol%, still more preferably 5 to 0 mol%. When the purity of the D-lactide is less than 90 mol%, the content of stereocomplex crystals in the polylactic acid block copolymer (A1) or (A2) may not easily be 80% by weight or more. Examples of other components that can be contained in the D-lactide include L-lactide, L-lactic acid, dicarboxylic acid, polyhydric alcohol, hydroxycarboxylic acid, or lactone. Since specific examples of the dicarboxylic acid, the polyhydric alcohol, the hydroxycarboxylic acid, or the lactone are as described above, the description thereof is omitted here.

The purity of the L-lactide is preferably 90 to 100 mol%, more preferably 92 to 100 mol%, still more preferably 95 to 100 mol%, where the total number of moles of L-lactide is 100 mol%. The content of components other than L-lactide is preferably 10 to 0 mol%, more preferably 8 to 0 mol%, still more preferably 5 to 0 mol%. When the purity of the L-lactide is less than 90 mol%, the content of stereocomplex crystals in the polylactic acid block copolymer (A1) or (A2) may not easily be 80% by weight or more. Examples of other components that can be contained in the L-lactide include D-lactide, D-lactic acid, dicarboxylic acid, polyhydric alcohol, hydroxycarboxylic acid, or lactone. Since specific examples of the dicarboxylic acid, the polyhydric alcohol, the hydroxycarboxylic acid, or the lactone are as described above, the description thereof is omitted here.

The free acid content in the D-lactide or the L-lactide is preferably 10% by weight or less, more preferably 1% by weight or less, and preferably 0.15% by weight or less. More preferably, it is particularly preferably 0.05% by weight or less. When the content of the free acid exceeds 10% by weight, the finally obtained polymer is unlikely to have a high molecular weight, and the use of the obtained polymer may be limited.

From the viewpoint of obtaining a copolymer having a higher melting point, the optical purity of the D-lactide or the L-lactide is preferably 90 to 100% ee, more preferably 95 to 100% ee, and 98 to 100% ee. Is more preferable. When the optical purity is less than 90% ee, the melting point and crystal melting enthalpy of the resulting polymer may be lowered. In the present specification, the value measured by the method described below is adopted as the optical purity.

<Measurement method of optical purity>
The optical purity is determined from the constituent ratio of L-lactic acid and D-lactic acid constituting polylactic acid. To 0.1 g of the sample, 5 ml of 5N sodium hydroxide and 2.5 ml of isopropanol were added, and the mixture was hydrolyzed while heating and stirring at 30 ° C., and then neutralized with 1M sulfuric acid. 1 ml of the resulting neutralized solution was diluted 25 times to adjust the concentration. This was injected into a high performance liquid chromatograph (HPLC), and the peak areas of L-lactic acid and D-lactic acid detected with ultraviolet light (wavelength 254 nm) were calculated. The measurement conditions of HPLC are shown in the table below. Further, from the mass ratio [L] (%) of L-lactic acid calculated from the peak area and the mass ratio [D] (%) of D-lactic acid, the optical purity (% ee) is expressed by the following formula (1). Calculated by

The ring-opening polymerization of the D-lactide or the ring-opening polymerization of the L-lactide is the above-mentioned “poly-L-lactic acid (PLLA) of (i) or poly-D-lactic acid (PDLA) of (ii)”. It can be performed by a method similar to the method described in the section. That is, the type and purity of raw material lactide to be subjected to ring-opening polymerization, the type and amount of various additives such as polymerization catalyst and polymerization initiator, reaction conditions (temperature, time, pressure, atmosphere, etc.), reactor, surplus after polymerization The removal of lactide in the above is as described in the above-mentioned section of “(i) poly-L-lactic acid (PLLA) or (ii) poly-D-lactic acid (PDLA)”. Omitted.

Regarding the reaction temperature among the above reaction conditions, the same conditions as those used in the production of the above-mentioned poly-L-lactic acid or poly-D-lactic acid can be employed. Depending on the melting point of the union (A1) or (A2) and the residual amount of lactide in the poly-L-lactic acid or the poly-D-lactic acid, a polymerization method by melt polymerization, solid phase polymerization, or a combination thereof is appropriately selected. It is preferable to do so. Further, in the present ring-opening polymerization after the production of PLLA or PDLA, further addition of a polymerization catalyst may or may not be performed.

The amount of D-lactide or L-lactide added in the ring-opening polymerization of D-lactide or L-lactide after obtaining the poly-L-lactic acid or the poly-D-lactic acid depends on the polylactic acid finally obtained. In the block copolymer (A1) or (A2), the mass ratio of L-lactic acid units to D-lactic acid units (L-lactic acid units / D-lactic acid units), or D-lactic acid units and L-lactic acid units, The mass ratio (D-lactic acid unit / L-lactic acid unit) may be determined to be within the range described later. That is, the amount of D-lactide or L-lactide added in this ring-opening polymerization is such that when the polylactic acid block copolymer (A1) is produced, the mass ratio of L component to D component (feeding ratio) is: L component / D component = 50/50 to 91/9, or L component / D component = 49/51 to 9/91 when producing the polylactic acid block copolymer (A2) Is preferred. From the viewpoint of increasing the crystal melting enthalpy of the finally obtained polylactic acid block copolymer (A1) or (A2) and improving the heat resistance, when producing the polylactic acid block copolymer (A1), The mass ratio of the L component to the D component is such that the L component / D component is preferably 50/50 to 90/10, more preferably 50/50 to 85/15, and even more preferably 65/35 to 85. / 15, particularly 70/30 to 80/20; when the polylactic acid block copolymer (A2) is produced, the mass ratio of the L component to the D component is such that the L component / D component is It is preferably 40/60 to 10/90, more preferably 35/65 to 15/85, particularly 30/70 to 20/80. When the polylactic acid block copolymer (A1) is produced, which is out of the above range, particularly when the mass ratio of the L component and the D component is 9/91 <L component / D component, or the polylactic acid block In the case of producing the copolymer (A2), when the mass ratio of the L component and the D component is 9/91> L component / D component, the stereocomplex crystal content is 80% by weight or more. It may be difficult to produce a polylactic acid block copolymer that is, and it may be difficult to produce a polylactic acid block copolymer having a higher melting point.

The atmosphere of the polymerization reaction is preferably an inert gas atmosphere such as nitrogen gas or argon gas from the viewpoint of suppressing coloring of the resulting polymer.

By adopting the method as described above, a polylactic acid block copolymer (A1) or (A2) having a high molecular weight and in which only a stereocomplex crystal grows even when melting and crystallization are repeated is obtained. be able to. At this time, from the viewpoint of obtaining a polymer having a higher molecular weight, it is preferable to perform ring-opening polymerization of L-lactide (L-lactic acid unit component) in the presence of poly-D-lactic acid (D-lactic acid unit component). .

The polylactic acid block copolymer (A1) or (A2) used in the present invention described above preferably has a weight average molecular weight of 7,000 to 1,500,000, more preferably 30,000 to 1,400,000, and even more preferably 80,000. 1.25 million, even more preferably 100,000 to 1.1 million, and particularly preferably 120,000 to 500,000. When the weight average molecular weight is within the above range, a polylactic acid block copolymer (A1) or (A2) excellent in mechanical strength and molding processability can be obtained.

The polylactic acid block copolymer (A1) or (A2) used in the present invention has a program comprising a temperature rising process of 20 to 250 ° C. and a cooling process of 250 to 20 ° C. in differential scanning calorimetry (DSC). Repeating three times, the melting point of the stereocomplex crystal observed in the temperature rising process is preferably 190 to 250 ° C, more preferably 195 to 250 ° C, and further preferably 200 to 250 ° C.

Further, the content of the stereocomplex crystal of the polylactic acid block copolymer (A1) or (A2) used in the present invention is preferably 80 to 100% by weight, more preferably 90 to 100% by weight, still more preferably. Is 95 to 100% by weight. Further, the melting enthalpy (ΔH _ms ) of the stereocomplex crystal appearing at 190 to 250 ° C. of the polylactic acid block copolymer (A1) or (A2) used in the present invention is preferably 10 J / g or more, more preferably 20 J / g or more, more preferably 30 J / g or more. If the program as described above is repeated three times and the crystal melting point of the stereocomplex crystal is within the above range, it means that only the stereocomplex crystal grows even if melting and crystallization are repeated. In the process of repeating the above melting and crystallization program three times, if the crystalline melting point observed in the temperature rising process is less than 190 ° C, the performance as a polylactic acid block copolymer forming a stereocomplex is reduced. There is a case. On the other hand, when the temperature exceeds 250 ° C., the molecular weight is lowered due to thermal decomposition of the polylactic acid block copolymer during molding, and the mechanical properties and the like of the polylactic acid composition of the present invention may be impaired.

In order for the polylactic acid composition of the present invention to exhibit excellent heat resistance, the content of stereocomplex crystals of the polylactic acid block copolymer (A1) or (A2), the polylactic acid block copolymer (A1) Alternatively, the melting point of the stereocomplex crystal (A2) and the melting enthalpy of the stereocomplex crystal are preferably in the above numerical range.

The mass ratio of L-lactic acid units to D-lactic acid units in the polylactic acid block copolymer (A1) used in the present invention is L-lactic acid units / D-lactic acid units = 50/50 to 91/9. . Preferably, L-lactic acid unit / D-lactic acid unit = 50/50 to 90/10, more preferably L-lactic acid unit / D-lactic acid unit = 50/50 to 85/15, and even more preferably L -Lactic acid unit / D-lactic acid unit = 65/35 to 85/15, particularly preferably 70/30 to 80/20. When the mass ratio of the L-lactic acid unit to the D-lactic acid unit is 91/9 <L-lactic acid unit / D-lactic acid unit, a stereocomplex crystal in the resulting polylactic acid block copolymer (A1) In some cases, the content of is significantly reduced.

The mass ratio of L-lactic acid units to D-lactic acid units in the polylactic acid block copolymer (A2) used in the present invention is L-lactic acid units / D-lactic acid units = 49/51 to 9/91. It may be. In this case, L-lactic acid unit / D-lactic acid unit = 40/60 to 10/90 is preferable, L-lactic acid unit / D-lactic acid unit = 35/65 to 15/85 is particularly preferable. L-lactic acid unit / D-lactic acid unit = 30/70 to 20/80. When the mass ratio of the L-lactic acid unit to the D-lactic acid unit is 9/91> L-lactic acid unit / D-lactic acid unit, the stereocomplex crystal in the polylactic acid block copolymer (A2) to be obtained In some cases, the content of is significantly reduced.

<Poly-L-lactic acid (B) or poly-D-lactic acid (C)>
The polylactic acid composition of the present invention contains poly-L-lactic acid (B) or poly-D-lactic acid (C) in addition to the polylactic acid block copolymer (A1) or (A2).

Regarding the structural unit, production method and the like in the poly-L-lactic acid (B) or poly-D-lactic acid (C), the above-mentioned “(i) poly-L-lactic acid (PLLA) or poly (ii) Since it is the same as that described in the section “-D-lactic acid (PDLA)”, the description thereof is omitted here.

The weight average molecular weight of the poly-L-lactic acid (B) mixed with the polylactic acid block copolymer (A1) is not particularly limited, but is preferably 7,000 to 1,500,000, more preferably 30,000 to 140. It is 10,000, more preferably 80,000 to 1,250,000, still more preferably 100,000 to 1.1 million, and particularly preferably 120,000 to 500,000. When the weight average molecular weight is within the above range, a large strain hardening improvement effect can be obtained.

The weight average molecular weight of the poly-D-lactic acid (C) mixed with the polylactic acid block copolymer (A2) is not particularly limited, but is preferably 7,000 to 1,500,000, more preferably 30,000. To 1.4 million, more preferably 80,000 to 1,250,000, even more preferably 100,000 to 1.1 million, and particularly preferably 120,000 to 500,000. When the weight average molecular weight is within the above range, a large strain hardening improvement effect can be obtained.

A polylactic acid block copolymer (A1) in which the mass ratio of L-lactic acid units to D-lactic acid units is L-lactic acid units / D-lactic acid units = 50/50 to 91/9, and poly-L-lactic acid ( B) and the content of the polylactic acid block copolymer (A1) in the polylactic acid composition of the present invention containing 0.1 to 30 parts by mass with respect to 100 parts by mass of the poly-L-lactic acid (B). The amount is preferably part by mass, more preferably 0.2 to 20 parts by mass, and still more preferably 0.2 to 10 parts by mass. When content of the said polylactic acid block copolymer is less than 0.1 weight%, the improvement effect of the dimensional stability derived from strain hardening may not be acquired. On the other hand, when it exceeds 30% by weight, the melting point of the polylactic acid composition is increased, and the moldability may be lowered.

Further, a polylactic acid block copolymer (A2) in which the mass ratio of the L-lactic acid unit to the D-lactic acid unit is L-lactic acid unit / D-lactic acid unit = 49/51 to 9/91; -D-lactic acid (C), and the content of the polylactic acid block copolymer (A2) in the polylactic acid composition of the present invention is 100 parts by mass of the poly-D-lactic acid (C). The amount is preferably 0.1 to 30 parts by mass, more preferably 0.2 to 20 parts by mass, and still more preferably 0.2 to 10 parts by mass. When content of the said polylactic acid block copolymer (A2) is less than 0.1 weight%, the improvement effect of the dimensional stability derived from strain hardening may not be acquired. On the other hand, when it exceeds 30% by weight, the melting point of the polylactic acid composition is increased, and the moldability may be lowered.

In the polylactic acid composition of the present invention, the polylactic acid block copolymer (A1) or (A2) and poly-L-lactic acid (B) or poly-D-lactic acid (C) are melt-mixed or solution-mixed. Can be manufactured.

Hereinafter, the melt mixing and the solution mixing will be described.

<Melt mixing>
The melt mixing is a method in which the polylactic acid block copolymer (A1) or (A2) and poly-L-lactic acid (B) or poly-D-lactic acid (C) are mixed in a molten state.

The melting temperature may be any temperature at which the polylactic acid block copolymer (A1) or (A2) and poly-L-lactic acid (B) or poly-D-lactic acid (C) are melted. In order to suppress the decomposition reaction, it is preferable to make it as low as possible so that the molten mixture does not solidify. Therefore, the higher melting point of the polylactic acid block copolymer (A1) or (A2) and poly-L-lactic acid (B) or poly-D-lactic acid (C) is set as the lower limit temperature, It is preferable that the melting be performed within a range in which the temperature is preferably 10 to 50 ° C., more preferably 10 to 30 ° C., and particularly preferably 10 to 20 ° C. higher than the lower limit temperature. More specifically, it is preferable to perform melt mixing at 150 ° C. to 220 ° C.

The atmosphere at the time of melt mixing is not particularly limited, and can be performed under normal pressure or reduced pressure. In the case of normal pressure, it is preferably carried out under a flow of an inert gas such as nitrogen gas or argon gas. Moreover, in order to remove the monomer which decomposes | disassembles at the time of melting, it is preferable to carry out under reduced pressure.

The order in which the polylactic acid block copolymer (A1) or (A2) and poly-L-lactic acid (B) or poly-D-lactic acid (C) are charged into the apparatus or the like during melt mixing is not particularly limited. For example, the polylactic acid block copolymer (A1) or (A2), and poly-L-lactic acid (B) or poly-D-lactic acid (C) may be charged simultaneously into the mixing apparatus. After the coalescence (A1) or (A2) is melted, poly-L-lactic acid (B) or poly-D-lactic acid (C) may be charged and mixed, or poly-L-lactic acid (B) or poly After melting -D-lactic acid (C), polylactic acid block copolymer (A1) or (A2) may be charged and mixed. At this time, each component may have any shape such as powder, granule, or pellet. Examples of the apparatus that can be used for melt mixing include, for example, a mill roll, a mixer, a single or twin screw extruder, or a batch container that can be heated.

The mixing time during melt mixing is preferably 1 to 60 minutes, more preferably 1 to 10 minutes.

<Solution mixing>
In the solution mixing, the polylactic acid block copolymer (A1) or (A2) and poly-L-lactic acid (B) or poly-D-lactic acid (C) are dissolved in a solvent and mixed, and then the solvent is mixed. It is a method of removing.

In this case, the solvent to be used is not particularly limited as long as the polylactic acid block copolymer (A1) or (A2) and poly-L-lactic acid (B) or poly-D-lactic acid (C) are dissolved. It is not limited. Specific examples include chloroform, methylene chloride, dichloroethane, tetrachloroethane, phenol, tetrahydrofuran, N-methylpyrrolidone, N, N-dimethylformamide, butyrolactone, trioxane, hexafluoroisopropanol, and the like. They can be used alone or in combination of two or more.

At this time, the content of the polylactic acid block copolymer (A1) or (A2), and poly-L-lactic acid (A) or poly-D-lactic acid (C) in the solution is 100 parts by mass of the solvent. One or both of the polylactic acid block copolymer (A1) or (A2) and the poly-L-lactic acid (B) or the poly-D-lactic acid (C) are preferably 1 to 30 parts by mass, more preferably Is in the range of 1 to 10 parts by mass.

The mixing may be carried out by dissolving the polylactic acid block copolymer and poly-L-lactic acid or poly-D-lactic acid in a solvent and mixing them, or the polylactic acid block copolymer (A1) or ( A2) and either one of poly-L-lactic acid (B) or poly-D-lactic acid (C) may be dissolved in a solvent, and then the other may be added and mixed. The solvent used in the solution can be removed by heating, distillation under reduced pressure, extraction, or a combination thereof.

The mixing temperature at the time of mixing the solution is preferably 10 to 110 ° C., more preferably 10 to 30 ° C. The mixing time is preferably 1 to 60 minutes, more preferably 1 to 10 minutes.

In addition, the polylactic acid block copolymer (A1) or (A2), and the poly-L-lactic acid (B) or poly-D-lactic acid (C) are used with various end-cappings. May be. The polylactic acid block copolymer (A1) or (A2) and the poly-L-lactic acid (B) or poly-D-lactic acid (C) contained in a reactive terminal and a terminal block such as a carboxy group and a hydroxy group Hydrolysis resistance and melt stability can be improved by reacting with an agent to perform end-capping. Examples of the terminal blocking group include an acetyl group, an ester group, an ether group, an amide group, or a urethane group. Examples of the terminal blocking agent include carboxylic acids such as acetic acid and anhydrides thereof, aliphatic alcohols, carbodiimide compounds, oxazoline compounds, oxazine compounds, and epoxy compounds.

The content of stereocomplex crystals in the polylactic acid composition of the present invention is preferably 80 to 100% by weight, more preferably 90 to 100% by weight, and still more preferably 95 to 100% by weight. Further, the melting enthalpy (ΔH _ms ) of the stereocomplex crystal appearing at 190 to 250 ° C. of the polylactic acid composition of the present invention is preferably 15 J / g or more, more preferably 25 J / g or more, and further preferably 35 J / g. That's it.

The strain hardening coefficient of the polylactic acid composition of the present invention is preferably 2 to 40, more preferably 2.05 to 30, and still more preferably 2.1 to 20. In this specification, the “strain hardening coefficient” is an index indicating molding processability, and is a time-extension viscosity curve (elongation time and biaxial extension viscosity) obtained by performing biaxial extensional viscosity measurement at 190 ° C. In the logarithmic plot of (2), the strain hardening coefficient (a2 / a1) expressed by the ratio of the slope (a1) of the linear region at the initial stage of elongation until the inflection point appears and the slope (a2) of the later stage of elongation after the inflection point. It is. When the inclination at the initial stage of elongation is hardly recognized (a1 = about 0), the slope at the latter stage of elongation itself is taken as the strain hardening coefficient. That is, in this specification, the “strain hardening coefficient” is a value calculated by the slope of the later stage of inflection after the inflection point in the time-extension viscosity curve obtained by measuring the biaxial extensional viscosity measurement at 190 ° C. adopt.

Here, when the strain hardening coefficient is high, a resin with a high foaming rate can be produced when the foamed resin is produced. Further, when performing bottle molding, which is a kind of blow molding, when the strain hardening coefficient is high, a portion called a shoulder of the bottle is difficult to be thinned, and a bottle having a uniform thickness can be obtained. Therefore, the strain hardening coefficient and the formability are in a proportional relationship, and a high strain hardening coefficient can achieve improvement in formability. That is, if the strain hardening coefficient is within the above range, moldability and productivity, particularly moldability can be improved. The strain hardening coefficient can be controlled by adjusting the addition amount of the polylactic acid block copolymer.

If the strain hardening coefficient is less than 2, the thickness of the molded product may be uneven. On the other hand, if the strain hardening coefficient exceeds 40, gelation of the composition may occur during molding.

The polylactic acid composition of the present invention may be added to conventional additives such as plasticizers, antioxidants, light stabilizers, ultraviolet absorbers, heat stabilizers, lubricants, release agents, and the like within the range not impairing the object of the present invention. Shapers, various fillers, antistatic agents, flame retardants, foaming agents, antibacterial / antifungal agents, nucleating agents, dyes, coloring agents containing pigments, and the like can be added as desired.

The polylactic acid composition of the present invention can be molded by a conventionally known method such as injection molding, extrusion molding, blow molding, foam molding, pressure molding, or vacuum molding. That is, this invention is a molded article containing the said polylactic acid composition. Examples of molded articles obtained by the molding method as described above include, for example, films, sheets, fibers, cloths, non-woven fabrics, agricultural materials, horticultural materials, fishery materials, civil engineering / building materials, stationery, and medical supplies. Or electrical / electronic parts.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

1. Samples Samples are PLLA and PDLA synthesized by the ring-opening polymerization method of L- or D-lactide as summarized in Table 2, and polylactic acid block copolymers synthesized by the solid phase polymerization method.

That is, PLLA and PDLA, which are polylactic acids, have tin octylate as a polymerization catalyst for raw materials L-lactide (optical purity: 100% ee) and D-lactide (optical purity: 100% ee), respectively. A fixed amount (0.005% by weight based on L- or D-lactide) was added, and then melt-kneaded and polymerized. Under the present circumstances, the molecular weight of the said polylactic acid was controlled by adjusting the addition amount of the dodecanol which is a molecular weight regulator. In the polymerization (melt kneading), the standard temperature is about 180 ° C. to 200 ° C., and the time is about 2 to 5 hours. The amount of catalyst (tin octylate) is 0.005% by weight with respect to lactide. As a guideline for the addition amount of the molecular weight modifier, when synthesizing polylactic acid having a weight average molecular weight of 100,000, it is about 0.5% by weight with respect to lactide, and when synthesizing polylactic acid having a weight average molecular weight of 200,000. Is about 0.26% by weight with respect to lactide, and when synthesizing polylactic acid with a weight average molecular weight of 300,000, polylactic acid with a weight average molecular weight of 1,000,000 is about 0.18% by weight with respect to lactide. When synthesized, it is about 0.06% by weight with respect to lactide. The weight average molecular weights of the polylactic acids (PLLA and PDLA) thus obtained are shown in Table 2 below.

In addition, the weight average molecular weight of polylactic acid (PLLA and PDLA) synthesized in this way was measured by GPC under the following conditions.

Next, using the polylactic acid synthesized as described above, a polylactic acid block copolymer (A1) or (A2) was synthesized according to the following method. The optical purity of D, L-lactide was measured according to the above method.

First, a polylactic acid block copolymer (A1) was synthesized according to the following method. In other words, the PDLA synthesized as described above is mixed with a predetermined amount of L-lactic acid so that the mass ratio (D component / L component) of the D-lactic acid unit and the L-lactic acid unit is as shown in Table 2 below. Lactide (optical purity: 100% ee) was added to initiate ring-opening polymerization. The ring-opening polymerization was carried out at 190 ° C. for 5 hours using 0.01 wt% tin octylate based on L-lactide as a polymerization catalyst. As a result, sb-PLA (1) to (4) were obtained as polylactic acid block copolymers (A1) (stereoblock polylactic acid of L-form Rich) as shown in Table 2. Here, PDLA was determined based on the molecular weight determined by sb-PLA, and the molecular weight of the base PDLA was determined, and PDLA having that molecular weight was synthesized. That is, in order to produce the following sb-PLA (1), a weight average molecular weight (Mw) = 4.5 × 10 ⁴ PDLA; to produce the following sb-PLA (2), a weight average molecular weight (Mw) = 9.9 × 10 ⁴ PDLA; to produce the following sb-PLA (3), the weight average molecular weight (Mw) = 4.0 × 10 ⁴ PDLA; and the following sb-PLA In order to produce (4), PDLA having a weight average molecular weight (Mw) = 4.9 × 10 ⁴ was synthesized. These PDLA production methods are the same as described above except that the amount of D-lactide used is appropriately changed in accordance with the weight average molecular weight.

Separately, a polylactic acid block copolymer (A2) was synthesized according to the following method. That is, the PLLA synthesized as described above is mixed with a predetermined amount of D− so that the mass ratio (D component / L component) of the D-lactic acid unit and the L-lactic acid unit is as shown in Table 2 below. Lactide (optical purity: 99.9% ee) was added to initiate ring-opening polymerization. Here, PLLA determined the molecular weight of the base PLLA based on the molecular weight required by sb-PLA, and synthesized PLLA of that molecular weight. As a result, sb-PLA (5) and (6) were obtained as polylactic acid block copolymer (A2) (stereoblock polylactic acid of D-form Rich) as shown in Table 2. Here, PLLA determined the molecular weight of the base PLLA based on the molecular weight required by sb-PLA, and synthesized PLLA of that molecular weight. That is, to produce the following sb-PLA (5), a weight average molecular weight (Mw) = 3.9 × 10 ⁴ PLLA; and to produce the following sb-PLA (6), a weight average PLLA having a molecular weight (Mw) = 4.8 × 10 ⁴ was synthesized. These PLLA production methods are the same as described above except that the amount of L-lactide used is appropriately changed in accordance with the weight average molecular weight.

The mass ratio (D component / L component) and weight average molecular weight of D-lactic acid units and L-lactic acid units of the polylactic acid block copolymer thus obtained are shown in Table 2 below. The weight average molecular weight was measured by the GPC method. “D component / L component” in each sb-PLA is a mass ratio of L-lactic acid units to D-lactic acid units in the polylactic acid block copolymer.

PLLA (1), PDLA (1) to (3) and polylactic acid block copolymer sb-PLA (1) to (6) were each mixed with 5% by weight of hexafluoroisopropanol (HFIP) / chloroform (CHCl). ₃ ) Dissolved in the mixed solution to prepare PLLA (1) solution, PDLA (1) to (3) solution, and polylactic acid block copolymer solution sb-PLA (1) to (6) solution, respectively. These PDLA solutions or sb-PLA (1) to (4) solutions, which are polylactic acid block copolymer solutions, have a mass fraction (0, 1, 2, 5 wt%) with respect to PLLA. Mixed with PPLA solution. Similarly, the sb-PLA (5), (6) solution, which is a PLLA solution or a polylactic acid block copolymer solution, has a mass fraction (0, 1, 2, 5% by weight) with respect to PDLA. And mixed with PDLA solution. By adding 5% by weight of acetic anhydride to these mixed solutions, the hydroxyl group ends were sealed. Then, it reprecipitated in diethyl ether, and various blend samples (blend products) were obtained by filtration and vacuum drying.

2. Measurement Samples for measuring the dynamic viscoelasticity and biaxial elongational flow of the melt were prepared by melt compression molding at 200 ° C. For the thermal measurement, a differential scanning calorimeter (model number: DSC3100SA, manufactured by Bruker AXS Co., Ltd.) was used, and the temperature was raised to 200 ° C. or 240 ° C. (1st-Heating) at 10 ° C./min in a nitrogen atmosphere. Later, the crystallization behavior in the cooling process at 2 ° C./min was examined. Dynamic viscoelasticity was measured using a parallel disk viscometer (MR-300, manufactured by Rheology) at 190 ° C., angular frequency range ω = 10 ⁻² to 10 ² (s ⁻¹ ), and gap 1.0 mm. The biaxial elongational flow was measured at 190 ° C. by the lubricating compression flow method (BE-100, manufactured by Iwamoto Manufacturing). The elongation rate range was ε _β = 0.01 to 0.06 (s ⁻¹ ), and silicone oil was used as the lubricant.

3. Result 3-1. Crystallization behavior As detailed in 3-3 below, In the biaxial elongational flow behavior experiment, the biaxial elongational flow experiment was conducted at a considerably slow speed of 0.01 to 0.06 / s. Generally, the strain hardening property appears when the elongation rate is increased, but it hardly appears when the elongation rate is small. When the polylactic acid composition of the present invention is used, strain hardening is exhibited even when the elongation rate is low. Therefore, the addition of the polylactic acid block copolymer of the present invention is also effective as a crystal nucleating agent for PLLA. It is suggested. From this result, when the polylactic acid block copolymer of the present invention is used, it leads to excellent foamability and moldability of the molded resin even in molding at a low elongation rate, shortening molding and improving productivity. Can be expected.

3-2. Dynamic Viscoelasticity FIGS. 1 to 2B show the frequency dependence of the dynamic viscosity | η ^* | (painted in the figure) and the storage elastic modulus G ′ (white in the figure) measured at 190 ° C. . The upper graph in FIG. 1 shows the results of using the PDLA (1) solution as the PDLA solution; the lower left graph in FIG. 1 shows the results of using the PDLA (2) solution as the PDLA solution. The lower right graph of FIG. 1 shows the result of using the PDLA (3) solution as the PDLA solution. Also, in FIG. 1, the red symbol is the result regarding the solution in which the PDLA solution is mixed with the PPLA solution so that the mass fraction is 5% by weight with respect to the PLLA; the green symbol is the result of the PDLA solution being the PLLA. Is the result for the solution mixed with the PPLA solution so that the mass fraction is 2% by weight; the blue symbol indicates that the PDLA solution is 1% by weight with respect to PLLA. Results for solutions mixed with PPLA solution; and black symbols are results for PPLA solution with no PDLA solution added (mass fraction 0% by weight of PLLA).

Similarly, the upper graph of FIG. 2A shows the result of using the sb-PLA (2) solution as the sb-PLA solution; the lower left graph of FIG. 2A shows the sb-PLA solution as the sb-PLA solution. FIG. 2A shows the result of using the PLA (4) solution; the lower right graph of FIG. 2A shows the result of using the sb-PLA (3) solution as the sb-PLA solution.

Similarly, the left graph of FIG. 2B shows the results of using the sb-PLA (6) solution as the sb-PLA solution; the right graph of FIG. 2A shows the sb-PLA solution as the sb-PLA solution. (5) The result of using the solution is shown.

From FIG. 1 to FIG. 2B, it can be seen that when PDLA is added, the values of | η ^* | and G ′ increase as the addition amount increases. In the sample to which 5% by weight of PDLA (3) was added, the Newton region was not observed in the measurement range, and G ′ also showed a remarkably high value in the low frequency region, which seems to have formed a network structure throughout the entire system. It is. On the other hand, as shown in FIGS. 2A and 2B, also in the case of the polylactic acid composition of the present invention to which a polylactic acid block copolymer is added, although | η ^* | and G ′ increase, the degree is moderate. is there. This is because the polylactic acid block copolymer has a short PDLA chain, so that a single molecular chain cannot form a stereocomplex with many PLLA chains, and there are few crosslinking points and the increase in entanglement is small. I think that the.

3-3. Biaxial Elongation Flow Behavior FIGS. 3A and B and FIGS. 4A-4C show the time dependence of biaxial elongational viscosity measured at various elongation rates. In FIGS. 3A and B and FIGS. 4A to 4C, black squares (□) indicate biaxial extensional viscosity changes when the extension rate is 0.01 (s ⁻¹ ); blue diamonds (◇) indicate extension rate Is the biaxial elongational viscosity change when 0.02 (s ⁻¹ ); the green triangle (Δ) is the biaxial elongational viscosity change when the elongation rate is 0.04 (s ⁻¹ ); and Red circles (O) represent biaxial elongational viscosity changes when the elongation rate is 0.06 (s ⁻¹ ), respectively. FIG. 3A and FIG. 3B are graphs showing the time dependence of the biaxial elongational viscosity measured at various elongation rates for a sample in which PDLA is added to PLLA. FIG. 3A and FIG. 3B are the results regarding the solution obtained by mixing the PDLA (1) and (2) solutions with the PPLA (1) solution so that the mass fraction thereof is 5% by weight with respect to PLLA, respectively. The result of calculating the strain hardening coefficient from FIG. 3A is shown in FIG. From FIG. 5, it can be seen that it is difficult to keep the strain hardening coefficient at 2 or more by simply blending PLLA and PDLA.

FIGS. 4A to 4C are graphs showing the time dependence of the biaxial elongational viscosity measured at various elongation rates of a sample in which a polylactic acid block copolymer is added to PLLA.

The left figure of FIG. 4A is the result regarding the solution which mixed sb-PLA (1) solution with PPLA (1) solution so that the mass fraction might be 0, 1, 2, 5 weight% with respect to PLLA; The right figure of FIG. 4A is the result regarding the solution which mixed the sb-PLA (2) solution with the PPLA (1) solution so that the mass fraction is 0, 1, 2, 5 wt% with respect to PLLA; The left figure of FIG. 4B is the result regarding the solution which mixed sb-PLA (4) solution with PPLA (1) solution so that the mass fraction might be 0, 1, 2, 5 weight% with respect to PLLA; The right figure of FIG. 4B is the result regarding the solution which mixed the sb-PLA (3) solution with the PPLA (1) solution so that the mass fraction is 0, 1, 2, 5 wt% with respect to PLLA; The left figure of FIG. 4C shows sb-PLA (6) solution as PDLA (1). FIG. 4C shows the result for the solution mixed with the PDLA (1) solution so that the mass fraction becomes 0, 1, 2, 5% by weight; FIG. 4C shows the sb-PLA (5) solution in the PDLA ( It is the result regarding the solution mixed with the PDLA (1) solution so that the mass fraction becomes 0, 1, 2, 5% by weight with respect to 1). The results of calculating the strain hardening coefficient from FIG. 4A are shown in FIGS. 6A-1 and 6A-2, the results of calculating the strain hardening coefficient from FIG. 4B are shown in FIGS. 6B-1 and 6B-2, and from FIG. 4C. The results of calculating the strain hardening coefficient are shown in FIGS. 6C-1 and 6C-2, respectively.

3 to 6, even with PLLA alone, a slight strain hardening phenomenon was observed on the long time side, but in the sample to which PDLA was added, the rising of the extensional viscosity was more remarkable as the molecular weight was higher. The strongest strain hardening phenomenon is shown when 1% by weight is added. Similarly to the result of dynamic viscoelasticity, in the sample to which 5% by weight of PDLA (3) was added, the extensional viscosity was remarkably increased, suggesting the existence of the entire network. On the other hand, as shown in FIGS. 4A to 6C, in the polylactic acid composition sample of the present invention to which the polylactic acid block copolymer was added, the change in dynamic viscoelasticity was small, whereas the low polylactic acid block copolymer was used. A strong strain hardening phenomenon is shown by the addition amount of the polymer. This is because the PDLA chain of the polylactic acid block copolymer, which is an AB type block copolymer of PLLA and PDLA, forms a stereocomplex microcrystal, and the PLLA chain linked to it plays the role of long chain branching effectively. It seems to be because.

Claims (14)

A polylactic acid block copolymer (A1) in which the mass ratio of L-lactic acid units to D-lactic acid units is L-lactic acid units / D-lactic acid units = 50/50 to 91/9;
Poly-L-lactic acid (B);
A polylactic acid composition comprising: The content of the polylactic acid block copolymer (A1) is 0.1 to 30 parts by mass with respect to 100 parts by mass of the poly-L-lactic acid (B). Polylactic acid composition. 3. The polylactic acid composition according to claim 1 or 2, wherein the strain hardening coefficient is 2 to 40. The mass ratio of the L-lactic acid unit to the D-lactic acid unit in the polylactic acid block copolymer (A1) is L-lactic acid unit / D-lactic acid unit = 60/40 to 91/9. The polylactic acid composition according to any one of claims 1 to 3, wherein the composition is a polylactic acid composition. The mass ratio of the L-lactic acid unit to the D-lactic acid unit in the polylactic acid block copolymer (A1) is L-lactic acid unit / D-lactic acid unit = 71/29 to 91/9. 5. The polylactic acid composition according to claim 4, characterized in that A polylactic acid block copolymer (A2) in which the mass ratio of L-lactic acid units to D-lactic acid units is L-lactic acid units / D-lactic acid units = 49/51 to 9/91;
Poly-D-lactic acid (C);
A polylactic acid composition comprising: The content of the polylactic acid block copolymer (A2) is 0.1 to 30 parts by mass with respect to 100 parts by mass of the poly-D-lactic acid (C). The polylactic acid composition as described. The polylactic acid composition according to claim 6 or 7, wherein the strain hardening coefficient is 2 to 40. The mass ratio of the L-lactic acid unit to the D-lactic acid unit in the polylactic acid block copolymer (A2) is L-lactic acid unit / D-lactic acid unit = 40/60 to 9/91. The polylactic acid composition according to any one of claims 6 to 8, which is characterized by the following. The mass ratio of the L-lactic acid unit to the D-lactic acid unit in the polylactic acid block copolymer (A2) is L-lactic acid unit / D-lactic acid unit = 29/71 to 9/91. The polylactic acid composition according to claim 9, characterized in that The polylactic acid according to any one of claims 1 to 10, wherein the polylactic acid block copolymer (A1) or (A2) has a weight average molecular weight (Mw) of 80,000 to 1,100,000. Composition. A polylactic acid block copolymer (A1) obtained by ring-opening polymerization of L-lactide (L-lactic acid unit) in the presence of poly-D-lactic acid (D-lactic acid unit), the D-lactic acid A polylactic acid block copolymer (A1) in which the mass ratio of the unit to the L-lactic acid unit is L-lactic acid unit / D-lactic acid unit = 50/50 to 91/9;
A polylactic acid composition comprising a step of melt-mixing or solution-mixing poly-L-lactic acid (B) obtained by ring-opening polymerization of L-lactide or condensation polymerization of L-lactic acid. Production method. A polylactic acid block copolymer (A2) obtained by ring-opening polymerization of D-lactide (D-lactic acid unit) in the presence of poly-L-lactic acid (L-lactic acid unit), the L-lactic acid A polylactic acid block copolymer (A2) in which the mass ratio of the unit to the D-lactic acid unit is L-lactic acid unit / D-lactic acid unit = 49/51 to 9/91;
A polylactic acid composition comprising a step of melt-mixing or solution-mixing poly-D-lactic acid (C) obtained by ring-opening polymerization of D-lactide or condensation polymerization of D-lactic acid. Production method. A molded article comprising the polylactic acid composition according to any one of claims 1 to 11 or the polylactic acid composition obtained by the production method according to claim 12 or 13.

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