JPH10176038A - Polylactic acid composition, its production and molded product from the composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polylactic acid composition having high molecular weight and excellent heat stability with a small lowering of molecular weight in molding and capable of giving a molded product having high strength by compounding a polylactic acid with tris(acetylacetonato)aluminum at a specific ratio. SOLUTION: This composition contains (A) a poylactic acid composed of L- and/or D-lactic acid and (B) tris(acetylacetonato)aluminum Al(Acac)3 } in an amount of 0.075-2.0mol% based on a lactic acid unit of the component A. A method for using Al(Acac)3 as a catalyst in an amount of 0.15-4.0mol% based on lactide as a cyclic dimer of lactic acid in performing melt ring-opening polymerization of the lactide is exemplified to obtain the component A. By this method, the objective composition can be provided without requiring a post-treatment after the melt ring-opening polymerization of the lactide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to powders, fibers and films which can be used for clothing, daily life, pharmaceutical materials, medical materials, and industrial materials such as agriculture, fisheries, industry, construction and civil engineering. And a polylactic acid composition suitable as a molding material, a method for producing the composition, and a molded article from the composition.

[0002]

2. Description of the Related Art For synthetic polymers derived from fossil raw materials,
Polylactic acid, which uses lactic acid obtained by fermenting grains as a raw material, is receiving attention from the viewpoint of protecting global resources. Also,
Polylactic acid is easily hydrolyzed in soil, water and living organisms, is widely found in nature and is harmless to animals and plants, and is eventually decomposed into carbon dioxide and water by metabolism or microbial degradation , Has also attracted attention as a biodegradable material. Furthermore, in recent years, applications to the medical and medical fields have been vigorously performed, particularly because of its high safety for living organisms.

As a method for synthesizing polylactic acid, there is known a method in which lactic acid is oligomerized, depolymerized to isolate lactide, which is a cyclic dimer, and obtained by subjecting the lactide to melt ring-opening polymerization. I have. This method is a very useful method because high-molecular-weight polylactic acid can be obtained relatively easily if lactide is sufficiently purified.

Various metal compounds have been reported as catalysts for the lactide melt ring-opening polymerization. Among them, tin compounds, particularly tin octylate (hereinafter abbreviated as Sn (Oct) ₂ ) have high catalytic activity. Therefore, it is preferably used because a high-molecular-weight polylactic acid can be obtained in a short polymerization time.

[0005]

The problem to be solved by the present invention is to improve the thermal stability of polylactic acid.
The second is to reduce residual lactide in polylactic acid for the purpose of preventing the surrounding environment from being contaminated by volatile components during molding.

First, the first problem will be described in detail. Polylactic acid, like other thermoplastics, can be molded by heating and melting. However, polylactic acid produced using Sn (Oct) ₂ as a catalyst has a problem that the molecular weight is remarkably reduced in a molding process, and a molded article having sufficient strength cannot be obtained. The cause is due to hydrolysis, depolymerization and cyclic oligomerization, and intra- and intermolecular transesterification, and it is known that tin compounds remaining in polylactic acid are involved in such a reaction.

Several solutions have been proposed as solutions to this problem. For example, a polylactic acid polymerization product is dissolved in an organic solvent immiscible with water, and then contacted with an aqueous phase or water containing an inorganic acid, a water-soluble organic acid, or a water-soluble complexing agent, and the organic phase is dried. A method of removing the catalyst by separating polylactic acid by a known method after separation (Japanese Patent Application Laid-Open No. 63-145327).
), A method of removing the catalyst by bringing the polymerization product into contact with an acidic substance in the presence of a hydrophilic organic solvent (JP-A-7-102553), or adding a boron compound to the polymerization product to form a catalyst. For improving thermal stability by deactivating (Japanese Patent Application Laid-Open No. 7-62213).

However, the first and second methods are disadvantageous in terms of cost because they require a large amount of solvent, labor and equipment, and it is difficult to completely remove the solvent permeated into polylactic acid. There are many problems on the surface. Further, in the third method, it is very difficult to uniformly disperse a trace amount of additive in a polymer chip which is a polymerization product, and when a solvent is used for this dispersion, there is a problem in removing the solvent. , And the second method.

That is, it is industrially ideal to use the polymerization product as it is in the next molding step without post-treatment, but this is achieved by lactide melt ring-opening polymerization using a Sn (Oct) ₂ catalyst. Is difficult to achieve.

On the other hand, many studies have been made on polylactic acid polymerization using a catalyst other than Sn (Oct) ₂ , but there is no example of examining a catalyst from the viewpoint of the thermal stability of the obtained polymerization product.

The fact that the trisacetylacetonatoaluminum (hereinafter abbreviated as Al (Acac) ₃ ) used in the present invention has a catalytic action in the ring-opening polymerization of lactide is disclosed in Makromol. Chem. , 1991, 2
287-2296, (1996). According to the document, 0.1 mol% of Al based on lactide is used.
(Acac) ₃ was polymerized at 150 ° C. for 50 hours to obtain polylactic acid having a weight average molecular weight (Mw) of 171,000 (number average molecular weight (Mn) of 90,000, calculated from Mw / Mn = 1.9). Have been obtained.

The problem that arises when the above example is industrialized is that, first of all, the polymerization time is too long. A method that can be easily considered as a means for solving this problem is to increase the polymerization temperature and increase the amount of the catalyst. However, in the case of polylactic acid polymerization by lactide melt ring-opening polymerization, there is a polymerization equilibrium between lactide and polylactic acid, and the higher the temperature, the more the equilibrium is on the lactide side. It is known that climbing is difficult. Regarding the amount of catalyst, as a result of research on tin compounds and other catalysts, it is common knowledge among those skilled in the art that the higher the amount, the lower the degree of polymerization. Therefore, for the polymerization conditions of the above example, when performing an operation such as raising the polymerization temperature or increasing the amount of the catalyst, the molecular weight of the resulting polylactic acid is considered to be even lower than the value of the above example. I was These are Al (A
This is because it was determined that cac) ₃ was not suitable for industrial use as a lactide melt ring-opening polymerization catalyst for obtaining high molecular weight polylactic acid.

Next, the second problem will be described in detail. When polylactic acid is produced by melt ring-opening polymerization of lactide, it cannot be avoided that lactide remains in the polymerization product.
This residual lactide is vaporized during the molding process, causing contamination of the surrounding environment, contamination of the molding die, and reduction in strength due to the formation of voids in the molded product. The reason that lactide remains in polylactic acid is that the monomer does not become 0 at 150 ° C. or higher due to polymerization equilibrium between the monomer (lactide) and the polymer.

As a method proposed for removing this lactide from a polymerization product, Japanese Patent Application Laid-Open No. 3-14829 has been proposed.
The method described in Japanese Unexamined Patent Publication (Kokai) No. HEI 9-205 (1994) is exemplified. In this method, the pressure is reduced while maintaining the polymerization product in a molten state in the second half of the production of the bioabsorbable polyester by ring-opening polymerization of lactide or after the reaction, and the remaining lactide is removed from the system.

Although the above publication does not specify the catalyst used in the ring-opening polymerization and the amount of the catalyst, it is described in Examples that Sn (Oct) ₂ is used and the amount used is based on lactide. It is in the range of 0.00086 to 0.0032 mol%. However, it is difficult to complete the polymerization in a commercially reasonable time with the catalyst amount in the above range. For example, Example 9 of the publication discloses an example using 0.0024 mol% of Sn (Oct) ₂ with respect to L-lactide.
It requires a very long polymerization time of 200 hours at 200 ° C. under normal pressure and 2 hours under reduced pressure.

On the other hand, when the amount of Sn (Oct) ₂ is increased, the polymerization rate increases, but at the same time, the depolymerization rate also increases.
Even if lactide is removed by reducing the pressure, the lactide is immediately re-produced, so that the amount of the remaining lactide does not decrease, and if the pressure is kept reduced, the polymer yield decreases.

Therefore, in the polymerization of polylactic acid using a Sn (Oct) ₂ catalyst, it has been difficult to remove lactide under reduced pressure under conditions that can be carried out industrially.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances. The first object of the present invention is to provide a high-strength molded article having a high molecular weight and excellent thermal stability, so that a decrease in molecular weight during molding is small. , A novel method for producing a polylactic acid composition having a high molecular weight and excellent thermal stability that does not require post-polymerization in lactide melt ring-opening polymerization, and molding comprising the polylactic acid composition The purpose is to provide goods.

Further, the second object is to provide a polylactic acid composition which does not contaminate the surrounding environment at the time of molding, a method for efficiently producing a polylactic acid composition having a small amount of residual lactide in a short time, and the polylactic acid composition. It is intended to provide a molded article comprising the composition.

[0020]

Means for Solving the Problems The present invention for achieving the first object is a polylactic acid comprising L- and / or D-lactic acid, and a polylactic acid having a content of 0.075 to lactic acid unit of the polylactic acid.
A polylactic acid composition comprising 2.0 mol% of Al (Acac) ₃ is characterized.

Another invention is a method for producing a polylactic acid by subjecting lactide, which is a cyclic dimer of lactic acid, to melt-opening polymerization to produce polylactic acid.
A method for producing a polylactic acid composition, comprising using mol% of Al (Acac) ₃ .

Another invention relates to a polylactic acid comprising L- and / or D-lactic acid, and 0.075 to 2.0 mol% of Al (Acac) based on lactic acid units of the polylactic acid.
₃ is a molded article characterized by comprising the the comprising at polylactic acid composition.

The present invention for achieving the second object is a polylactic acid comprising L- and / or D-lactic acid and having a lactide content of less than 1%, and a lactic acid unit of the polylactic acid. 0.075 to 2.0 mol% of Al (Acac)
_{3. A} polylactic acid composition comprising ( ₃ ).

Another invention is a method for producing polylactic acid by subjecting lactide, which is a cyclic dimer of lactic acid, to melt-opening polymerization to produce polylactic acid, wherein the lactide is used as a catalyst in an amount of 0.15 to 4.0.
A first step of using a mole% of Al (Acac) ₃ to advance the polymerization reaction until the amount of residual lactide in the polymerization system becomes 30 to 5%, and placing the polymerization product of the step in a molten state under reduced pressure. A method for producing a polylactic acid composition, comprising a second step of completing polymerization.

Further, another invention relates to L- and / or
Or, a polylactic acid composed of D-lactic acid and having a lactide content of less than 1%, and 0.0
A molded article characterized by comprising a polylactic acid composition containing 75 to 2.0 mol% of Al (Acac) ₃ .

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Lactide used in the present invention is a cyclic dimer of lactic acid obtained by oligomerizing lactic acid and then depolymerizing as described above. L for lactic acid
-Lactic acid and D-lactic acid are present, and lactide is accompanied by L-lactide, D-lactide, D, L-lactide, and racemic lactide. Although the optical purity of lactide used in the present invention is not particularly limited, the melting point of the obtained high molecular weight polylactic acid is determined by the optical purity of the polylactic acid, and the higher the purity, the higher the melting point of the polylactic acid. Therefore, if polylactic acid having higher heat resistance is desired, it is preferable to use lactide having high optical purity.

In the melt ring-opening polymerization of lactide, since the compound having a hydroxyl group functions as a polymerization initiator, the molecular weight of the resulting polylactic acid is determined by the hydroxyl group concentration in the raw material. For example, in the case of a homopolymer, in order to obtain polylactic acid having a weight average molecular weight of 200,000 or more, the water content in the raw material needs to be within a range of 5 ppm to 60 ppm.

As described above, if the amount of Al (Acac) ₃ used in the present invention is 0.1 mol% based on lactide, polylactic acid having a sufficient molecular weight cannot be obtained. However, the present inventors have found that, contrary to the common knowledge of those skilled in the art, the molecular weight of polylactic acid obtained by increasing the amount of Al (Acac) ₃ increases. A in the present invention
l (Acac) ₃ is used in an amount of 0.1 to lactide.
5 to 4.0 mol% (0.075 to 2.0 mol% for the lactic acid unit of the polylactic acid). If the amount is less than 0.15 mol%, the molecular weight of the obtained polylactic acid is not sufficient, and if the amount used is increased, the molecular weight of the obtained polylactic acid becomes large. Rather, the molecular weight decreases. Also, Al (Acac) ₃
The thermal stability of the obtained polylactic acid tends to decrease with an increase in the amount of used, and the use of more than 4.0 mol% is disadvantageous from the viewpoint of thermal stability.

The polymerization temperature in the present invention is not particularly limited, but is preferably from 180 to 200 ° C. If the temperature is lower than 180 ° C., it takes a long time for polymerization, and the temperature is lower than the melting point of the obtained polylactic acid. If the temperature is higher than 200 ° C., the equilibrium between lactide and polylactic acid is too close to the lactide side, so that the degree of polymerization is hardly increased, and the production amount of lactide increases, so that the yield of polylactic acid decreases.

As a means for reducing the residual lactide in the polymerization product, it is desirable to carry out the first step of proceeding the polymerization to a certain extent and the second step of removing lactide from the polymerization product by reducing the pressure. The end point of the first step is that the residual lactide content in the polymerization product is 30 to 5%.
Is reached. When the first step is terminated when the amount of the remaining lactide is more than 30%, the remaining lactide is removed in the second step, so that the polymer yield is 70%.
It is smaller and uneconomical. If the residual lactide amount at the end of the first step is less than 5%, lactide is not sufficiently removed in the second step. This is believed to be due to the residual lactide acting as a plasticizer in the polymerization product, helping to volatilize itself under reduced pressure.

The time required for the first step is usually 60-60.
Although it is 0 minutes, it depends on the amount of the catalyst used, the polymerization temperature, the amount of water in the system, and the like. Therefore, the amount of residual lactide in the system may be checked and the time may be appropriately selected. Further, the polymerization apparatus for performing the first step is not particularly limited, for example, a batch type reaction vessel equipped with a stirring device and a heating mechanism, or an extruder type continuous reaction device and the like. it can. However, as described above, since the degree of polymerization of the generated polylactic acid depends on the amount of water in the system in this reaction, the reaction system is desirably under an anhydrous atmosphere, and under an inert gas atmosphere such as nitrogen or argon. It is desirable to polymerize with.

The method of transferring the polymerization product obtained in the first step to the second step is not particularly limited, but the polymerization product is preferably kept under an anhydrous atmosphere during that time. Therefore, for example, when the first step is performed in a batch-type reaction vessel sealed with an inert gas, it is better to carry out the second step by reducing the pressure of the system without removing the polymerization product to the outside of the reaction vessel. desirable. When the first step is carried out in a continuous reaction apparatus, it is directly transferred from the outlet to the second step under an anhydrous atmosphere, or is taken out and stored in an anhydrous atmosphere, and then is returned to the second step. Transfer method.

The second step of the present invention is a step of reducing the residual lactide in the polymerization product obtained in the first step,
The end point is preferably selected when the amount of the remaining lactide becomes less than 1%. It is essential that the temperature conditions in the second step be higher than the melting point of the polymerization product. For example,
In the case of a poly-L-lactic acid homopolymer, the temperature must be 180 ° C. or higher. The upper limit is 20 as described above.
It is preferable that the temperature is 0 ° C. or lower. If the temperature is higher than 200 ° C., the rate of depolymerization of polylactic acid increases, and even if lactide is removed by reducing the pressure, the end point may not be reached due to lactide reproduction. The conditions for the pressure reduction are not particularly limited, but the lower the degree of the pressure reduction, the shorter the time required to reach the end point.
Hg or less, more preferably 5 mmHg or less.

The molded article of the present invention is a molded article obtained by melt-molding the polylactic acid composition of the present invention as described above. Examples of the molded product include various molded products such as injection and extrusion, films, sheets, unstretched or stretch-oriented fibers, and fiber structures (knits, woven fabrics,
Non-woven fabric, paper, string, tape, rope, net, etc.), and a composite of the film or sheet and fiber such as synthetic leather, but is not limited thereto.

The uses of these molded articles include insect-proof, heat-retaining, frost-proof, light-shielding, weed-proof films, sheets, textile structures, etc., agricultural uses, vehicle interiors and electric products, industrial uses, etc. Applications include civil engineering applications such as sheets and fiber structures for slope revegetation protection, architectural applications such as floors and wall materials, disposable equipment, disposable clothing, daily necessities including shoes and bags, toys and game machines. Examples include, but are not limited to, sanitary and medical applications including playground equipment, sanitary goods, and the like, and fishing applications such as fishing nets, fishing lines, various aquaculture ropes, and nets.

[0036]

The present invention will be described below in detail with reference to examples. Before that, the method of measuring various characteristic values in this specification will be described.

<Weight average molecular weight> The weight average molecular weight (M) of the polymer part in the polylactic acid composition was determined by GPC (gel permeation chromatography) using chloroform as an eluent.
w) was measured. In addition, the molecular weight calibration curve was created using polystyrene.

<Amount of Residual Lactide> From the area of the polymer part and the monomer (lactide) part in the above-described GPC measurement, a value obtained by the following equation was defined as the amount of residual lactide in the polymerization product.

Residual lactide amount (%) = Area of monomer part / (Area of polymer part + Area of monomer part) × 100

<Bending strength> 24 hours at room temperature in the presence of phosphorus pentoxide.
The polylactic acid composition dried under reduced pressure for hours was compression molded at 200 ° C. for 5 minutes to obtain a molded plate having a thickness of about 1.6 mm. From this, a test piece having a width of 15 mm and a length of 80 mm was cut out, and the bending strength was measured under the conditions of a distance between supporting points of 26 mm and a test speed of 0.8 mm / min.

<Stability of Physical Properties> The stability as physical properties of a molded article was examined in terms of molding stability as follows. That is, the polylactic acid composition (after polymerization) before molding was molded (after molding) by the compression molding method described above. The weight average molecular weight (Mw) of the polylactic acid composition after polymerization and after molding was measured, and the molding stability was determined by the following formula.

Molding stability (%) = polylactic acid composition Mw
(After molding) / polylactic acid composition Mw (after polymerization) × 100

The stability of the molded article was represented by the thermal stability by the following method instead of performing the molding operation. That is, about 3 g of the polylactic acid composition (after polymerization) before the melt treatment,
Heat at 180 ° C for 1 hour under nitrogen in test tube (melting process)
Then, the obtained polylactic acid composition (after melting) was obtained. The weight average molecular weight (Mw) of the polylactic acid composition after polymerization and after melting was measured by the method described above, and the thermal stability was determined by the following equation.

Thermal stability (%) = polylactic acid composition Mw (after melting) / polylactic acid composition Mw (after polymerization) × 100

<Yield> From the weight of lactide as a raw material for polymerization and the weight of a polylactic acid composition as a polymerization product, the yield of a polymerization reaction was determined by the following formula.

Yield (%) = weight of polylactic acid composition / weight of raw material × 100

Example 1 L-lactide (moisture ratio 31 p)
pm, manufactured by PURAC) 120 g (833 mmol) and 2.70 g (8.33 mmol) of Al (Acac) ₃
Into a reaction vessel equipped with a stirrer and a nitrogen inlet tube,
After the replacement with nitrogen, the mixture was heated to 180 ° C. in a nitrogen stream to perform melt ring-opening polymerization. At this time, the catalyst Al (Acac) ₃
Was 1.0 mol% with respect to the raw material L-lactide and 0.5 mol% with respect to the lactic acid units of the resulting polylactic acid composition. The reaction was terminated when the increase in the molecular weight was saturated, and the polymerization product was taken out of the system. Table 1 shows the properties of the obtained polylactic acid composition and the molded plate obtained by molding the same.
Was as shown in FIG. The weight-average molecular weight of the polylactic acid composition after polymerization is as large as 432,000, and after molding, the polylactic acid composition maintains a high molecular weight of 3240 (molding stability 75.0%). Has a bending strength of 998kgf / cm
^{It was 2} and very big. This is because Sn
The bending strength of the polylactic acid composition molded plate obtained using (Oct) ₂ was about 1.6 times the bending strength (Comparative Example 1).

(Comparative Example 1) Al (Ac) in Example 1
Melt ring-opening polymerization was carried out in the same manner as in Example 1 except that 0.1 mol% of Sn (Oct) ₂ with respect to the lactide was used as a catalyst instead of ac) ₃ . The properties of the obtained polylactic acid composition and the molded plate obtained by molding the same were as shown in Table 1. The weight average molecular weight of the polylactic acid composition after polymerization was a high molecular weight of 4560,000 as in Example 1, but the molecular weight was greatly reduced to 1240,000 (molding stability: 27.2%) by molding. However, the bending strength of the formed plate was only 625 kgf / cm ² , which was much smaller than that of Example 1.

[0049]

[Table 1]

Table 2 shows the weight average molecular weights of the polylactic acid compositions according to Example 1 and Comparative Example 1 before and after the melt treatment. As in the case of the stability of the molded article, the one according to Example 1 has a high molecular weight of 36.5 million and a thermal stability of 84.5.
%, Whereas the sample according to Comparative Example 1 had a remarkably reduced molecular weight of 78,000 and a low thermal stability of 17.3%. This result also indicates the high thermal stability of the polylactic acid composition using the Al (Acac) ₃ catalyst. It also shows that this process is appropriate as a simulation for molding.

(Embodiments 2 to 6) Al in Embodiment 1
Melt ring-opening polymerization was carried out in the same manner as in Example 1 except that the amount of (Acac) ₃ catalyst was as shown in Table 2. The characteristic values of the obtained polylactic acid composition are as shown in Table 2.
From all of these, a polylactic acid having a large weight average molecular weight can be obtained, and a polylactic acid composition having a high heat stability having a weight average molecular weight of 200,000 or more (thermal stability of 60% or more) even after the melting treatment can be obtained. Was done.

Comparative Example 2 Melt ring-opening polymerization was carried out in the same manner as in Example 1 except that the amount of Al (Acac) ₃ catalyst was changed to 0.270 g (0.833 mmol). At this time, Al (Acac) ₃ is 0.1 mol% with respect to the raw material L-lactide, and 0.05 mol% with respect to the lactic acid unit of the produced polylactic acid composition. The characteristic values of the obtained polymerization product are as shown in Table 2, and the weight average molecular weight is 2
As low as 100,000 or less, the method of the present invention (Examples 1-6)
Was smaller than that obtained by

Comparative Example 3 Melt ring-opening polymerization was carried out in the same manner as in Example 1 except that the amount of Al (Acac) ₃ catalyst was changed to 13.5 g (41.6 mmol). At this time,
Al (Acac) ₃ is 5.0 mol% based on the raw material L-lactide, and 2.5 mol% based on the lactic acid unit of the polylactic acid composition produced. The characteristic values of the obtained polymerization product are as shown in Table 2. The weight average molecular weight after the melt treatment was 200,000 or less, and the thermal stability was as low as 51.9%. It was smaller than that obtained by Examples 1-6).

[0054]

[Table 2]

Example 7 L-lactide (moisture 11p)
pm, PURAC) 60 g (416 mmol) and A
0.675 g (2.08 mmol) of l (Acac) ₃
Was charged into a reaction vessel equipped with a stirrer and a nitrogen inlet tube. At this time, the amount of Al (Acac) ₃ as a catalyst is
It was 0.5 mol% with respect to the raw material L-lactide. After the replacement with nitrogen, as a first step, the mixture was heated to 180 ° C. under a nitrogen stream to carry out melt ring opening polymerization. When the amount of residual lactide became about 15%, as a second step, the pressure of the system was reduced to 3 mmHg, and the system was heated and polymerized at 180 ° C. The reaction was terminated when the increase in the molecular weight was saturated, and the polymerization product was taken out of the system. The properties of the obtained polylactic acid composition are as shown in Table 3, and 48.2 g of polylactic acid composition having a very small Mw of 36,000 and a residual lactide amount of 0.1% (yield: 80.80 g) was obtained.
3%). Further, the Mw after melting treatment at 180 ° C. for 1 hour was 324,000, which was a high molecular weight retention rate, and the thermal stability was as excellent as 90%.

Example 8 In Example 7, after completion of the first step, the polymerization product was once taken out of the system under nitrogen, cooled, pulverized, returned to the reaction vessel, and subjected to the second step. The properties of the obtained polymerization product are as shown in Table 3. As in Example 7, a polylactic acid composition having a high degree of polymerization and excellent thermal stability of 88% was obtained.

(Comparative Example 4) Polymerization was carried out in the same manner as in Example 7 except that the first step was repeated until the increase in the molecular weight of the polylactic acid composition was saturated, and the second step was not performed. Was. Table 3 shows the properties of the obtained polymerization products.
And the residual lactide amount was as high as 3.5%.

Comparative Example 5 Al (Ac) in Example 7
Polymerization was carried out in the same manner as in Example 7 except that 0.1 mol% of Sn (Oct) _{2 based} on the lactide was used instead of ac) ₃ . Table 3 shows the properties of the obtained polylactic acid composition.
The residual lactide content was as high as 1.8% and the thermal stability was as low as 21%.

[0059]

[Table 3]

Examples 9 and 10 Polymerization was carried out in the same manner as in Example 7 except that the first step in Example 7 was repeated until the residual lactide became 28.3% and 6.4%. The properties of the obtained polymerization product are as shown in Table 4. In each case, a polylactic acid composition having a high degree of polymerization and a low residual lactide amount was obtained in high yield.

Comparative Example 6 Polymerization was carried out in the same manner as in Example 7, except that the first step in Example 7 was repeated until the residual lactide content became 39.1%. The properties of the obtained polymerization product are as shown in Table 4. Since the amount of residual lactide after the first step was large, a polymerization product having a high degree of polymerization and a low residual lactide amount was obtained. Was as low as 55.2%.

Comparative Example 7 Polymerization was carried out in the same manner as in Example 7 except that the first step in Example 7 was repeated until the residual lactide amount became 4.3%. The properties of the obtained polymerization product are as shown in Table 4, and the amount of lactide remaining in the second step was too small after the completion of the first step. 0.3%
Became

[0063]

[Table 4]

[0064]

The polylactic acid composition of the present invention has high thermal stability, so that the molecular weight at the time of molding is maintained at 200,000 or more.
A high-strength molded product is obtained. In addition, the method of the present invention does not require post-treatment after lactide melt-ring-opening polymerization, and can obtain a polylactic acid composition having a high molecular weight and excellent thermal stability, and thus has a very high industrial value. . In addition, since a safer aluminum compound is used as a catalyst instead of the conventional tin compound, the safety is high even when used in biomedical materials or food-related products. Further, the polylactic acid composition of the present invention has a small amount of residual lactide, so that lactide does not volatilize during the molding process and does not pollute the surrounding environment. A molded product having no parts can be obtained. In addition, the method of the present invention does not use a method that requires a solvent removal step such as reprecipitation or washing to remove residual lactide in polylactic acid, and the time required for polymerization is short. Furthermore, since the molded article of the present invention has high strength, powders and fibers used for clothing, daily life, pharmaceutical materials, medical materials, and industrial materials such as agriculture, fisheries, industry, construction, civil engineering, etc. , A film, and a molding material.

Claims (6)

[Claims] 1. A polylactic acid comprising L- and / or D-lactic acid, and 0.075 to 2.75 to lactic acid unit of the polylactic acid.
A polylactic acid composition comprising 0 mol% aluminum trisacetylacetonato. 2. The polylactic acid composition according to claim 1, wherein the content of lactide in the polylactic acid is less than 1%. 3. A lactide, which is a cyclic dimer of lactic acid, is melt-opened and polymerized to produce polylactic acid. As a catalyst, 0.15 to 4.0 mol% of trisacetylacetonatoaluminum based on lactide is used as a catalyst. A method for producing a polylactic acid composition, characterized by using: 4. The amount of residual lactide in the polymerization system is 30 to 5%.
4. The polylactic acid composition according to claim 3, comprising a first step of allowing the polymerization reaction to proceed until the polymerization reaction reaches a temperature, and a second step of completing the polymerization by placing the polymerization product in the molten state under reduced pressure in a molten state. Method of manufacturing a product. 5. The method for producing a polylactic acid composition according to claim 4, wherein the degree of reduced pressure in the second step is 10 mmHg or less. 6. A molded article comprising the polylactic acid composition according to claim 1.