JP5022206B2 - Method for producing polylactic acid composition - Google Patents

Description

  The present invention relates to a method for producing a polylactic acid composition. More specifically, the present invention relates to a method for producing a polylactic acid composition having an excellent hue without using a metal polymerization catalyst.

  Many petroleum-derived plastics are light and tough, have excellent durability, can be easily and arbitrarily molded, and have been mass-produced to support our lives. However, when these plastics are disposed in the environment, they accumulate without being easily decomposed. Incineration also releases a large amount of carbon dioxide, spurring global warming.

  In view of the current situation, resins made from non-petroleum raw materials, so-called plant-derived resins, have been actively studied. Polylactic acid, which is under active investigation, is obtained by fermenting corn and other cereals into lactic acid, dehydrating and condensing it, and then subjecting it to cyclic dimerization, followed by ring-opening polymerization. In the ring-opening polymerization, a tin compound is used as a polymerization catalyst and an alcohol compound is used as a polymerization initiator, so that a resin having high molecular weight and excellent mechanical properties is obtained.

  Polylactic acid has an ester group of aliphatic carboxylic acid, is easily decomposed by microorganisms, and has attracted attention as a biodegradable resin. On the other hand, thermal stability is poor, and molecular weight reduction or hue deterioration is serious in molding processes exposed to high temperatures such as melt spinning, injection molding, and melt film formation. Such molecular weight reduction and hue deterioration are caused by the metal polymerization catalyst remaining in the polylactic acid, depolymerization by the hydroxy terminal, hydrolysis by moisture in the air, and in the molten state, pyrubin which is the cause of coloring components Accelerates acid generation.

  As a catalyst, ring-opening polymerization of lactide using a thiourea derivative has been reported (see Non-Patent Document 1), but it takes a long time of one day or more to reach a molecular weight that can be used as a resin. Not suitable for industrial production.

Further, it is taught that ring-opening polymerization of lactide is possible with 1,5,7-triazabicyclo [4,4,0] -5-decene and a hydroxy compound (see Non-Patent Document 2). Such a guanidine-based compound causes a serious coloring during the melt processing of polylactic acid. When removing guanidine-based compounds to avoid this, cleaning with an organic solvent such as acetone is necessary. However, in industrial implementation, recovery and drying of the organic solvent are required, complicating the manufacturing process. It will be a thing.
As described above, a method for producing polylactic acid having excellent hue from production to processing without using a metal polymerization catalyst has not been known yet.

Journal of American Society 2005, Vol. 127, 13798-13799 Journal of American Society 2006, Vol. 128, 4556-4557

  An object of the present invention is to provide a method for producing a polylactic acid composition having an excellent hue without using a metal polymerization catalyst and solving the problems of the conventional techniques.

As a result of intensive studies in view of the prior art, the present inventors have found that ring-opening polymerization can be initiated by an alcoholate ion generated by contacting an amidine compound and a hydroxy compound, and results of further intensive studies The present invention has been completed. That is, the object of the present invention is to
After contacting the amidine compound, the hydroxy compound and the first lactide to initiate ring-opening polymerization of the first lactide to obtain polylactic acid, the first lactide has chirality at the reactive end group of the polylactic acid. This can be achieved by a method for producing a polylactic acid composition, in which a polylactic acid composition is obtained by contacting a different second lactide.

Further, according to this onset Ming manufacturing method, simultaneously satisfying the following requirements (a) to (g), it is possible to provide a polylactic acid composition.
(A) The polylactic acid composition has a weight average molecular weight (Mw) of 50,000 or more and less than 300,000.
(A) The polylactic acid composition forms a stereocomplex crystal, and its melting point is 200 ° C. or higher and lower than 250 ° C.
(C) The stereocomplex crystal content (S) is 80% or more.
(D) In the differential scanning calorimeter (DSC) measurement, even if the program consisting of a temperature rising process of 20 to 250 ° C. and a quenching process of 250 to 20 ° C. is repeated three times, the requirements (A) and (C) are satisfied. To do.
(E) The lactide content of the polylactic acid composition is 1 ppm or more and less than 5000 ppm.
(F) The randomization rate (R) is greater than 0 and less than 2.5%.
The stereocomplex crystal content (S) is a numerical value calculated from the following formula.
[Equation 1]
S = ΔHmsc / (ΔHmh + ΔHmsc) × 100 (%)
[In the formula, ΔHmh and ΔHmsc are the melting enthalpy (ΔHmh) of the crystal melting point appearing at 150 ° C. or more and less than 190 ° C. and the crystal melting point appearing at 190 ° C. or more and less than 250 ° C., respectively, in the temperature rising process of the differential scanning calorimeter (DSC). Melting enthalpy (ΔHmsc) is shown. ]
The randomization rate (R) is a numerical value represented by the following formula.
[Equation 2]
R = {1- (P1 / P2)} × 100 (%)
[Wherein P1 and P2 are homonuclear decoupling ¹ H− measured in a mixed solution of 10 wt% deuterated chloroform / 1,1,1,2,2,2-hexafluoro-2-propanol = 9/1 of polylactic acid. In NMR, the total intensity of the III quadruple peak with a chemical shift of 5.175 ppm and the sum of four quadruples (SIS, SII, IIS, III, ISI) of the methine proton peak appearing at a chemical shift of 5.250 to 5.150 ppm, respectively. Integral intensity. The quadruple S indicates a syndiotactic diad, and I indicates an isotactic diad. ]
(G) Yellowness (YI) is 0 or more and less than 1.0.

  According to the production method of the present invention, a polylactic acid composition containing no metal polymerization catalyst can be produced, and a polylactic acid composition excellent in hue can be provided. Moreover, since the amidine compound used for the polymerization can be easily removed, the hue of the polylactic acid composition is not deteriorated even in the melt processing step. Therefore, it can be suitably used as a raw material for optical use and food packaging films.

Hereinafter, the present invention will be described in detail.
In the production method of the present invention, ring-opening polymerization is carried out by contacting an amidine compound, a hydroxy compound and a first lactide to obtain polylactic acid.

  As the ring-opening polymerization method, a conventionally known production apparatus for producing polylactic acid may be used. For example, a vertical reaction vessel equipped with a stirring blade and capable of replacing the inside with an inert gas atmosphere is used. Can do. For the ring-opening polymerization, an organic solvent capable of dissolving the amidine compound, the hydroxy compound and the first lactide is used. Examples of such organic solvents include halogenated hydrocarbons such as dichloromethane, chloroform and dichloroethane, and aprotic polar solvents such as N-methylpyrrolidone, N, N′-dimethylformamide and dimethyl sulfoxide. In view of the ease of post-treatment, dichloromethane and dichloroethane are most preferred. The addition amount of the organic solvent may be an amount that can completely dissolve the reaction substrate such as lactide, and is usually preferably 1 to 10 times the weight of the first lactide.

  Although there is no restriction | limiting in ring-opening polymerization temperature, Preferably it is 0 to 150 degreeC, More preferably, it is 25 to 120 degreeC. When the polymerization is carried out at less than 0 ° C., the polymerization rate becomes extremely slow, and when the polymerization is carried out at 150 ° C. or more, the amidine compound itself decomposes and efficient polymerization does not proceed. When a high molecular weight polylactic acid composition is to be obtained, the polymerization atmosphere is preferably carried out in an inert gas atmosphere such as nitrogen or argon that is well dried so that moisture does not become an initiator. The second lactide is added after the polymerization of the first lactide, and the polymerization is performed under the same conditions as the first lactide.

  The 1st lactide and 2nd lactide used by this invention refer to L-lactide or D-lactide with high optical purity. Specifically, if it is L-lactide, the content of D-lactide and DL-lactide is less than 1%, preferably less than 0.5%, and if it is D-lactide, L-lactide and DL-lactide Is less than 1%, preferably less than 0.5%. In addition, when lactide with low optical purity is used, the crystal melting point and crystallinity of the polylactic acid composition finally obtained are lowered, leading to extreme deterioration of heat resistance.

  In the production method of the present invention, the first lactide and the second lactide have different chiralities. That is, when the first lactide is L-lactide, the second lactide is D-lactide, and when the first lactide is D-lactide, the second lactide is L-lactide.

  Examples of amidine compounds include 1,8-diazabicyclo [5,4,0] undec-7-ene (hereinafter sometimes abbreviated as DBU), 1,5-diazabicyclo [4,3,0] non-. Examples include 5-ene (hereinafter sometimes abbreviated as DBN), N′-tert-butyl-N, N-dimethylformamidine, and the like, but can be easily removed by decompression after the completion of polymerization. Has a boiling point of less than 150 ° C., more preferably less than 100 ° C. at 133.32 Pa (1.0 mmHg).

  The addition amount of the amidine-based compound is 1 or more and less than 10, preferably 2 or more and less than 5, in molar ratio to the hydroxy compound. When the addition amount is out of the above range, the polymerization time is prolonged, or it becomes a cause of off-flavor and coloring in the processing step.

  Examples of the hydroxy compounds include aliphatic primary alcohols or phenolic compounds, aliphatic primary alcohols having 1 to 20 carbon atoms, aliphatic primary diols having 2 to 20 carbon atoms, phenol, p-cresol, p-tert-butylphenol, Hydroquinone and the like are preferable. Considering the steric hindrance and the acidity of the hydroxyl group, the aliphatic primary alcohol having 1 to 20 carbon atoms and phenol are preferable among the above examples.

The amount of the hydroxy compound added is 5 × 10 ⁻⁴ or more and less than 0.01, preferably 7 × 10 ⁻⁴ or more and less than 0.001 in terms of the molar ratio to the first lactide. When the addition amount is out of the above range, the yield of the finally obtained polylactic acid composition is lowered, or the molecular weight of the obtained polylactic acid composition is lowered.

  The reaction time for the first lactide is 15 minutes to less than 3 hours, preferably 30 minutes to less than 2 hours, 30 minutes to less than 5 hours, preferably 1 hour to less than 3 hours after the addition of the second lactide.

The atmosphere for addition is not particularly limited, but it is preferably carried out under an inert gas stream such as nitrogen or argon.
A method of simultaneously removing the first lactide and / or the second lactide that have not been reacted in the reaction system during the decompression operation can also be exemplified as a preferred embodiment.

The specific polymerization steps of the polylactic acid composition of the present invention are summarized as follows.
(1) The first lactide (L-lactide), amidine compound and hydroxy compound are contacted in an organic solvent to polymerize poly-L-lactic acid.
(2) The second lactide (D-lactide) is added to the mixture of (1) and brought into contact with the reactive end group of poly L-lactic acid to polymerize the polylactic acid composition.
(3) The organic solvent, residual lactide and amidine compound are removed under reduced pressure.
Or
(1 ′) The first lactide (D-lactide), the amidine compound and the hydroxy compound are contacted in an organic solvent to polymerize poly-D-lactic acid.
(2 ′) The second lactide (L-lactide) is added to the mixture of (1 ′) and brought into contact with the reactive end group of poly D-lactic acid to polymerize the polylactic acid composition.
(3 ′) The organic solvent, residual lactide and amidine compound are removed under reduced pressure.

  By adopting such a method, a block copolymer in which poly D-lactic acid is linked to the reactive end group of poly L-lactic acid or poly L-lactic acid is linked to the reactive end group of poly D-lactic acid is produced. A polylactic acid composition excellent in hue from the production intended for the invention to the processing steps can be obtained.

Obtained by the onset Ming manufacturing method, polylactic acid composition of the present invention are those satisfying the following requirements (a) to (g) at the same time.
(A) The polylactic acid composition has a weight average molecular weight (Mw) of 50,000 or more and less than 300,000.
(A) The polylactic acid composition forms a stereocomplex crystal, and its melting point is 200 ° C. or higher and lower than 250 ° C.
(C) The stereocomplex crystal content (S) is 80% or more.
(D) In the differential scanning calorimeter (DSC) measurement, even if the program consisting of a temperature rising process of 20 to 250 ° C. and a quenching process of 250 to 20 ° C. is repeated three times, the requirements (A) and (C) are satisfied. To do.
(E) The lactide content of the polylactic acid composition is 1 ppm or more and less than 5000 ppm.
(F) The randomization rate (R) is greater than 0 and less than 2.5%.
The stereocomplex crystal content (S) is a numerical value calculated from the following formula.
[Equation 3]
S = ΔHmsc / (ΔHmh + ΔHmsc) × 100 (%)
[In the formula, ΔHmh and ΔHmsc are the melting enthalpy (ΔHmh) of the crystal melting point appearing at 150 ° C. or more and less than 190 ° C. and the crystal melting point appearing at 190 ° C. or more and less than 250 ° C., respectively, in the temperature rising process of the differential scanning calorimeter (DSC). Melting enthalpy (ΔHmsc) is shown. ]
The randomization rate (R) is a numerical value represented by the following formula.
[Equation 4]
R = {1- (P1 / P2)} × 100 (%)
[Wherein P1 and P2 are homonuclear decoupling ¹ H− measured in a mixed solution of 10 wt% deuterated chloroform / 1,1,1,2,2,2-hexafluoro-2-propanol = 9/1 of polylactic acid. In NMR, the total intensity of the III quadruple peak with a chemical shift of 5.175 ppm and the sum of four quadruples (SIS, SII, IIS, III, ISI) of the methine proton peak appearing at a chemical shift of 5.250 to 5.150 ppm, respectively. Integral intensity. The quadruple S indicates a syndiotactic diad, and I indicates an isotactic diad. ]
(G) Yellowness (YI) is 0 or more and less than 1.0.

Hereafter, each said requirement which the polylactic acid composition of this invention satisfies is demonstrated.
Polylactic acid composition of the present invention is its weight average molecular weight is less than 50,000 300,000 (requirements a). In order to increase mechanical properties such as the strength of the molded product, it is preferable that the molecular weight is high, but if the molecular weight exceeds the above range, the moldability is deteriorated, especially the melt molding becomes difficult, and the quality of the molded product is deteriorated. There is. On the other hand, if the molecular weight is smaller than the above range, mechanical properties such as the strength of the molded product may not reach a practical level. From the above viewpoint, the weight average molecular weight is preferably in the range of 80,000 to 300,000, more preferably 100,000 to 200,000.

The polylactic acid composition of the present invention forms a stereocomplex crystal and has a melting point of 200 ° C. or higher and lower than 250 ° C. (Requirement A).
When the crystal melting point is less than 200 ° C., the heat resistance of the molded product or the like is lowered. On the other hand, when it is 250 ° C. or higher, the molecular weight is significantly reduced at the processing temperature, and the mechanical properties of molded articles and the like are deteriorated.

  The polylactic acid composition of the present invention has a stereocomplex crystal content (S) of 80% or more. When the stereocomplex crystal content is less than 80%, desired heat resistance is not exhibited.

Even if the polylactic acid composition of the present invention repeats a program consisting of a temperature rising process of 20 to 250 ° C. and a cooling process of 250 to 20 ° C. three times in a DSC (differential scanning calorimeter), the polylactic acid composition is A stereocomplex crystal is formed, the melting point is 200 ° C. or higher and lower than 250 ° C., and the stereocomplex crystal content (S) is 80% or more (requirement d).
This requirement means that a stereocomplex crystal grows even if the polylactic acid composition is repeatedly melted and crystallized.

The polylactic acid composition of the present invention has a lactide content of 1 ppm or more and less than 5000 ppm (requirement e).
If the lactide content is less than 1 ppm, it takes a long time to remove the lactide, leading to a decrease in molecular weight. On the other hand, if it is 5000 ppm or more, the heat-and-moisture resistance and melt stability of the product deteriorate.

The polylactic acid composition of the present invention has a randomization rate (R) of more than 0 and less than 2.5% (requirement f).
When the randomization rate is 0, the composition is nothing but a mixture of substantially poly (L-lactic acid) and poly (D-lactic acid), and does not satisfy the requirement (d) in three repeated measurements in DSC. On the other hand, if it is 2.5% or more, the crystal melting point of the stereocomplex crystal becomes less than 200 ° C., and the requirement (A) described in claim 9 is not satisfied.

The polylactic acid composition of the present invention has a yellowness (YI) of 0 or more and less than 1.0 (requirement key).
Here, yellowness (YI) means an ideal white color (complete diffuse reflection surface) of 0, and means a distance from this white color. The color difference from white to yellow is plus, and the color difference in blue is minus. It is expressed. Therefore, when it is 0 or less (a negative value), bluishness increases, and when it is 1.0 or more, yellowishness increases, both of which cause hue deterioration.

  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, fillers, antibacterial / antifungal agents, nucleating agents, dyes, colorants including pigments, and the like can be included as desired.

  Optical use film using the polylactic acid composition of the present invention, film for food packaging, sheet nonwoven fabric, fiber, cloth, composite with other materials, agricultural materials, fishery materials, civil engineering / building materials, stationery, Medical articles or other molded articles can be obtained, and molding can be carried out by conventional methods.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples. In the examples, the physical properties of the compositions were measured by the following methods.

(1) Measurement of weight average molecular weight (Mw):
For the weight average molecular weight (Mw), GPC-11 manufactured by Shodex was used, 50 mg of the composition was dissolved in 5 ml of chloroform, and developed with chloroform at 40 ° C. The weight average molecular weight (Mw) was calculated as a polystyrene equivalent value.

(2) Crystal melting peak temperature, crystal melting heat and stereogenic rate S:
A 10 mg sample piece was placed in a dedicated aluminum pan and measured using a differential scanning calorimeter (DSC2920) manufactured by TA Instruments. The measurement conditions were as follows, and the crystal melting enthalpy was calculated by the area of the region surrounded by the crystal melting peak and the base line appearing on the DSC chart.
10 mg of sample was heated from 30 ° C. to 250 ° C. at a temperature increase rate of 20 ° C./min at 1st RUN in a nitrogen atmosphere, and low and high temperature crystal melting peak temperatures (° C.), Tmh, Tmsc, low temperature and high temperature crystal fusion Antipyretic (J / g), ΔHmh, ΔHmsc were measured.
The stereo ratio (S) was obtained from the following equation using the low-temperature phase crystal heat of fusion of 190 ° C. or lower, ΔHmh, the high-temperature phase crystal heat of fusion of 190 ° C. or higher, and ΔHmsc.
[Equation 5]
S = ΔHmsc / (ΔHmh + ΔHmsc) × 100

(3) Randomization rate (R):
The randomization rate (R) is a numerical value represented by the following formula.
[Equation 6]
R = {1- (P1 / P2)} × 100 (%)
[Wherein P1 and P2 are homonuclear decoupling ¹ H− measured in a mixed solution of 10 wt% deuterated chloroform / 1,1,1,2,2,2-hexafluoro-2-propanol = 9/1 of polylactic acid. In NMR, the total intensity of the III quadruple peak with a chemical shift of 5.175 ppm and the sum of four quadruples (SIS, SII, IIS, III, ISI) of the methine proton peak appearing at a chemical shift of 5.250 to 5.150 ppm, respectively. Integral intensity. The quadruple S indicates a syndiotactic diad, and I indicates an isotactic diad. ]

(4) DSC three times repeated measurement:
A sample piece of 5 mg was placed in a dedicated aluminum pan and measured using a differential scanning calorimeter (DSC2920) manufactured by TA Instruments. The measurement conditions were as follows. The crystal melting enthalpy was calculated from the area of the region surrounded by the crystal melting peak appearing on the DSC chart and the baseline, and the stereocomplex crystal content (S) was determined. The crystal melting point was also measured.
(A) The temperature is raised from 20 to 250 ° C. at 20 ° C./min.
(B) After reaching 250 ° C., rapidly dry to 20 ° C. at 45 ° C. per second using dry ice.
(C) Repeat the above (a) and (b) three times.

(5) Hue:
The polylactic acid (A) composition was made into a 1 wt% dichloromethane solution, and the YI value was measured with an ultraviolet-visible spectrometer UV-2400PC manufactured by Shimadzu Corporation. The YI value was calculated from the tristimulus values X, Y, and Z by the following formula.
[Equation 7]
YI value = 100 (1.28X-1.06Z)

[Reference Example 1] Pre-drying of dichloromethane:
Dichloromethane used as the organic solvent was 1 W of reagent grade manufactured by Wako Pure Chemicals, 1 g of calcium hydride was added and stirred at room temperature for 12 hours, and the dehydrated product was distilled under atmospheric pressure in a nitrogen stream. . (Boiling point 39 ° C)

[Reference Example 2] Purification of 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) and 1,5-diazabicyclo [4,3,0] non-5-ene (DBN):
In each case, a barium oxide powder is added to a product with a purity of 98% manufactured by Aldrich, and the temperature is 66-66 Pa (0.5 mmHg), 80-82 ° C. (DBU), 1 kPa (7.5 mmHg), 95-98 ° C. (DBN). And distilled under reduced pressure.

[Example 1]
A reactor equipped with a three-way valve was charged with 20 parts by weight of L-lactide (optical purity 100%) manufactured by Musashino Chemical Laboratory, and a nitrogen cylinder and piping connected to a vacuum pump were connected to the three-way valve. The inside of the reaction apparatus was purged with nitrogen three times, and 60 parts by weight of dichloromethane was added to dissolve lactide. 1-octadecanol 0.03 weight part and DBU 0.03 weight part were added here and superposition | polymerization was started. After continuing polymerization at 25 ° C. for 1 hour, 20 parts by weight of D-lactide (optical purity 100%) manufactured by Musashino Chemical Laboratory was added to the reaction solution to form a block polymer.
After completion of the polymerization, dichloromethane was distilled from the reaction vessel, and then the temperature in the reactor was raised to 100 ° C., and the degree of vacuum was 133.32 Pa (1.0 mmHg) to remove excess lactide and DBU.
Table 1 shows the number average molecular weight (Mn), weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), and yellow index (YI) of the obtained polylactic acid composition. Table 2 shows the low temperature and high temperature crystal melting peak temperatures Tmh, Tmsc, low temperature crystal melting heat and high temperature crystal melting heat (J / g), ΔHmh, ΔHmsc, stereoization rate S, and randomization rate R in DSC.

[Example 2]
In Example 1, the polylactic acid composition was polymerized in the same manner except that 0.03 part by weight of DBU was changed to 0.025 part by weight of DBN.
Table 1 shows the number average molecular weight (Mn), weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), and yellow index (YI) of the obtained polylactic acid composition. Table 2 shows the low temperature and high temperature crystal melting peak temperatures Tmh, Tmsc, the low temperature crystal melting heat and the high temperature crystal melting heat (J / g), ΔHmh, ΔHmsc, stereoization rate S, and randomization rate R in DSC.

[Comparative Example 1]
A polylactic acid composition was prepared in the same manner as in Example 1, except that 0.03 part by weight of DBU was changed to 0.027 part by weight of 1,5,7-triazabicyclo [4.4.0] -5-decene. Got.
1,5,7-triazabicyclo [4.4.0] -5-decene had a melting point of 127 ° C. and could not be removed under reduced pressure, and the polylactic acid composition was slightly colored yellow.
Table 1 shows the number average molecular weight (Mn), weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), and yellow index (YI) of the obtained polylactic acid composition. Table 2 shows low temperature and high temperature crystal melting peak temperatures Tmh, Tmsc, low temperature crystal melting heat and high temperature crystal melting heat (J / g), ΔHmh, ΔHmsc, stereoization rate S, and randomization rate R in DSC.

  Since the polylactic acid of the present invention is excellent in hue, it can be suitably used as an optical use film.

Claims (9)

  After contacting the amidine compound, the hydroxy compound and the first lactide to initiate ring-opening polymerization of the first lactide to obtain polylactic acid, the first lactide has chirality at the reactive end group of the polylactic acid. A method for producing a polylactic acid composition, which comprises contacting a different second lactide to obtain a polylactic acid composition.   The production method according to claim 1, wherein the amidine-based compound is 1,5-diazabicyclo [4,3,0] -5-nonene or 1,8-diazabicyclo [5,4,0] -7-undecene. .   The production method according to claim 1, wherein the hydroxy compound is an aliphatic primary alcohol or a phenol compound.   The manufacturing method of Claim 1 whose reactive terminal group is a hydroxyl group or a carboxyl group. The manufacturing method of Claim 1 whose molar ratio of the amidine type compound with respect to a 1st lactide is 5 * 10 < ^-4 > or more and less than 5 * 10 < ^-3 >. The production method according to claim 1, wherein the molar ratio of the hydroxy compound to the first lactide is 5 × 10 ⁻⁴ or more and less than 0.01.   The method according to claim 1, wherein the boiling point of the amidine compound is less than 150 ° C. under a reduced pressure of 133.32 Pa (1.0 mmHg).   The production method according to any one of claims 1 to 6, wherein after the second lactide is brought into contact and polymerized, the amidine compound and the residual lactide in the reaction system are simultaneously removed under reduced pressure. To claim 1 obtained by the manufacturing method described, satisfying the lower SL requirements (a) to (g) at the same time, the polylactic acid composition.
(A) The polylactic acid composition has a weight average molecular weight (Mw) of 50,000 or more and less than 300,000.
(A) The polylactic acid composition forms a stereocomplex crystal, and its melting point is 200 ° C. or higher and lower than 250 ° C.
(C) The stereocomplex crystal content (S) is 80% or more.
(D) In the differential scanning calorimeter (DSC) measurement, even if the program consisting of a temperature rising process of 20 to 250 ° C. and a quenching process of 250 to 20 ° C. is repeated three times, the requirements (A) and (C) are satisfied. To do.
(E) The lactide content of the polylactic acid composition is 1 ppm or more and less than 5000 ppm.
(F) The randomization rate (R) is greater than 0 and less than 2.5%.
The stereocomplex crystal content (S) is a numerical value calculated from the following formula.
[Equation 1]
S = ΔHmsc / (ΔHmh + ΔHmsc) × 100 (%)
[In the formula, ΔHmh and ΔHmsc are the melting enthalpy (ΔHmh) of the crystal melting point appearing at 150 ° C. or more and less than 190 ° C. and the crystal melting point appearing at 190 ° C. or more and less than 250 ° C., respectively, in the temperature rising process of the differential scanning calorimeter (DSC). Melting enthalpy (ΔHmsc) is shown. ]
The randomization rate (R) is a numerical value represented by the following formula.
[Equation 2]
R = {1- (P1 / P2)} × 100 (%)
[Wherein P1 and P2 are homonuclear decoupling ¹ H− measured in a mixed solution of 10 wt% deuterated chloroform / 1,1,1,2,2,2-hexafluoro-2-propanol = 9/1 of polylactic acid. In NMR, the total intensity of the III quadruple peak with a chemical shift of 5.175 ppm and the sum of four quadruples (SIS, SII, IIS, III, ISI) of the methine proton peak appearing at a chemical shift of 5.250 to 5.150 ppm, respectively. Integral intensity. The quadruple S indicates a syndiotactic diad, and I indicates an isotactic diad. ]
(G) Yellowness (YI) is 0 or more and less than 1.0.