JP3273821B2 - Purification method of polyhydroxycarboxylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying polyhydroxycarboxylic acid. More specifically, the present invention relates to a method for converting a catalyst into a chloride form by removing polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid in an organic solvent with hydrogen chloride gas to remove the catalyst.

[0002]

2. Description of the Related Art Polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid (hereinafter abbreviated as a lactic acid-based polymer) is known as a biodegradable polymer of a thermoplastic resin. These polymers are 100% biodegradable in the body of animals in months to one year, and when placed in soil or seawater, begin to degrade in weeks in moist environments and disappear in one to several years. Further, the decomposition product has the property of becoming lactic acid, carbon dioxide, and water that are harmless to the human body.

[0003] Polylactic acid is synthesized from a cyclic dimer of lactic acid, usually called lactide.
SP1,995,970, USP2,362,511,
No. 2,683,136. In addition, copolymers of lactic acid and other hydroxycarboxylic acids are synthesized from lactide, which is a cyclic dimer of lactic acid, and a cyclic ester intermediate of hydroxycarboxylic acid (glycolide, which is a dimer of glycolic acid). Regarding the production method, USP 3,636,956 and USP 3,795
7,499. However, these methods have a disadvantage that the used catalyst remains in the polymer because pelletization is performed as it is after the melt polymerization. In this case, even if the polymer is decomposed, the catalyst remains, so that the use of the polymer is restricted depending on the toxicity of the catalyst. Further, when a catalyst is present in the polymer, there is a problem that the polymer is likely to undergo a depolymerization reaction by heating during the subsequent processing and molding, whereby the molecular weight of the polymer is reduced and physical properties are deteriorated. A method of removing the catalyst after the polymerization reaction is also conceivable. However, in the case of tin octoate used in this reaction, it is difficult to remove it by a reprecipitation purification method or the like.

Accordingly, in order to obtain a lactic acid-based polymer having a sufficiently high molecular weight and containing no catalyst, it is necessary to remove the catalyst by purification. In JP-A-63-145327, a polymer containing a catalyst is dissolved in an organic solvent immiscible with water, and then dissolved in an aqueous phase or water containing an inorganic acid, a water-soluble organic acid or a water-soluble complexing agent. A method for contacting to remove the catalyst is disclosed. However, in this method, when the polymer solution becomes viscous, the efficiency of contact with the aqueous phase becomes poor, and thus the efficiency of removing the catalyst is reduced.
There is a problem that the treatment must be performed with a dilute solution such as 5 to 4.0% by weight, and a problem that the liquid separation property after mixing the organic solvent solution and the aqueous phase is poor. JP-A-63-
No. 254128 discloses a method for purifying a polymer solution by adding a precipitant in a turbulent shear field, but the catalyst removal efficiency and the catalyst removal efficiency are poor because the removal of the catalyst and the precipitation of the polymer proceed simultaneously. There was a problem in performing it industrially, such as requiring special equipment.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for industrially inexpensively and easily removing a catalyst in a lactic acid-based polymer.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by bringing a lactic acid-based polymer into contact with hydrogen chloride gas in an organic solvent, the catalyst in the polymer was reduced. The present invention has been completed by finding that it can be converted into chloride form and removed.

That is, the present invention is characterized in that a polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid is treated with hydrogen chloride gas in an organic solvent and then mixed with a precipitant to precipitate a polymer. This is a method for purifying an acid.

The lactic acid-based polymer is directly dehydrated and polycondensed from lactic acid or lactic acid and another hydroxycarboxylic acid, or is a cyclic dimer of lactic acid or a cyclic ester intermediate of hydroxycarboxylic acid such as dimer of glycolic acid. Ring-opening polymerization may be carried out in the presence of a catalyst using a copolymerizable monomer such as glycolide (GLD), which is a body, and ε-caprolactone (CL), which is a cyclic ester of 6-hydroxycaproic acid. In the case of direct dehydration polycondensation, lactic acid or lactic acid and another hydroxycarboxylic acid are azeotropically dehydrated and condensed, preferably in an organic solvent, in the presence of a catalyst, particularly in the presence of a phenyl ether solvent, and particularly preferably azeotropically. Polymerization can be carried out by removing water from the distilled solvent and returning the substantially anhydrous solvent to the reaction system. Lactic acid as a raw material is L-lactic acid or D-lactic acid,
Or a mixture thereof, and other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid,
5-hydroxyvaleric acid, 6-hydroxycaproic acid and the like are used.

Catalysts usually used in the reaction of the present invention include metals such as zinc, tin, iron and aluminum, metal oxides such as zinc oxide, tin oxide, iron oxide and aluminum oxide, zinc carbonate, magnesium carbonate and the like. Organic carbonates such as carbonate, zinc oxide, tin acetate, tin lactate, tin octoate, and aluminum acetate are exemplified. Its usage is
0.0001 to 10% by weight of the hydroxycarboxylic acid or oligomers used.

[0010] The solid or solution polymer prepared by the known method is dissolved in a suitable organic solvent. The solvent to be used should just dissolve the lactic acid-based polymer,
For example, hydrocarbon solvents such as benzene and toluene, ketone solvents such as acetone, methyl ethyl ketone and acetophenone, halogenated hydrocarbon solvents such as methylene chloride and chloroform, and non-solvents such as N, N-dimethylformamide, dimethylacetamide and dimethylsulfoxide. It may be a protic polar solvent, an ether solvent such as diphenyl ether or anisole, or a mixture of various organic solvents. The concentration of the polymer to be dissolved is usually 3 to 50% by weight, but the concentration is not particularly limited as long as the polymer solution can be stirred. When an organic solvent is used at the time of polymerization, the reaction solution can be used as it is without taking out the polymer after completion of the polymerization reaction.

Next, the lactic acid-based polymer solution is brought into contact with hydrogen chloride gas. The method of bringing the lactic acid-based polymer into contact with hydrogen chloride gas may be a method in which hydrochloric acid gas is directly blown into a solution of the lactic acid polymer, or a method in which a solution in which hydrogen chloride gas is dissolved is mixed. The lactic acid-based polymer is brought into contact with hydrogen chloride gas, and stirring is continued for a time sufficient for the catalyst to be converted into chloride. The amount of the hydrogen chloride gas to be brought into contact may be an amount sufficient to produce the catalyst and the chloride. The temperature at the time of treatment with hydrogen chloride gas is not particularly limited, but is usually 0 to 10
It is carried out at 0 ° C., preferably 10 to 60 ° C. If the temperature is low, the conversion rate to chloride is slow, and if it is too high, the polymer is deteriorated.

Examples of the precipitant mixed with the solution after contact with hydrogen chloride gas include water, methanol, ethanol, isopropanol and tert-butanol. In order to improve the dispersibility of the polymer solution in the precipitant, the polymer can be precipitated with sufficient stirring.
It is preferable that the temperature at the time of mixing is lower because the decomposition of the polymer can be suppressed, and the temperature is usually 30 ° C. or lower.

[0013]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Production Example 1 10 kg of L-lactide and 0.1% by weight of tin octoate
And 2% by weight of lauryl alcohol were sealed in a thick cylindrical stainless steel polymerization vessel equipped with a stirrer, degassed under vacuum for 2 hours, and then replaced with nitrogen gas. The mixture was heated at 180 ° C. for 3 hours with stirring under a nitrogen atmosphere. While maintaining the temperature as it is, the inside of the reaction vessel was gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver to 3 mmHg.
The pressure was reduced to. One hour after the start of degassing, the distillation of the monomer and low-molecular-weight volatile components disappeared. Therefore, the inside of the container was replaced with nitrogen, and the polymer was drawn out from the lower part of the container in a string form and pelletized to obtain poly L-lactic acid. The average molecular weight of this polymer was about 80,000, and the Sn content was 500 ppm.

The average molecular weight (weight average molecular weight) of the polymer was measured by gel permeation chromatography using polystyrene as a standard under the following conditions. Apparatus: Shimadzu LC-10AD Detector: Shimadzu RID-6A Column: Hitachi Chemical GL-S350DT-5 + GL-S3
70DT-5 Solvent: chloroform Concentration: 1% Injection volume: 20 μl Flow rate: 1.0 ml / min The Sn content in the polymer was measured by X-ray fluorescence analysis.

Production Example 2 10 kg of L-lactide, 8 kg of L-lactide and D
Pelletization was carried out in the same manner as in Production Example 1 except that L-lactide was changed to 2 kg to obtain poly-DL-lactic acid. The average molecular weight of this polymer was about 70,000, and the Sn content was 550 ppm.

Production Example 3 Pelletization was carried out in the same manner as in Production Example 1 except that 10 kg of L-lactide was changed to 8 kg of L-lactide and 2 kg of glycolide to obtain a copolymer of L-lactide and glycolide. The average molecular weight of this polymer was about 60,000, and the Sn content was 600 ppm.

Production Example 4 10 kg of 90% by weight L-lactic acid was added at 150 ° C./50 mmHg.
After distilling water while stirring for 3 hours, 6.2 g of tin powder was obtained.
Was added, and the mixture was further stirred at 150 ° C./30 mmHg for 2 hours to oligomerize. To this oligomer were added 28.8 g of tin powder and 21.1 kg of diphenyl ether, and added at 150 ° C./35
An azeotropic dehydration reaction was performed at mmHg, and the distilled water and the solvent were separated by a water separator, and only the solvent was returned to the reactor. Two hours later, the organic solvent to be returned to the reactor was passed through a column packed with 4.6 kg of molecular sieve 3A, and then returned to the reactor. A polylactic acid solution having a molecular weight of about 110,000 was obtained. The Sn content in this polymer was 1800 ppm.

Production Example 5 5 kg of 90% by weight L-lactic acid and 0.6 kg of 70% by weight glycolic acid were stirred at 140 ° C./50 mmHg for 3 hours to distill water, and then 15 g of tin powder was added.
The mixture was further stirred at 50 mmHg for 3 hours to be oligomerized.
62 g of tin powder and 6 k of diphenyl ether are added to this oligomer.
g was added, and the solvent was returned to the reactor through a column packed with molecular sieve 3A (2 kg).
Reflux was performed at 50 ° C./25 mmHg for 50 hours to obtain a copolymer solution having an average molecular weight of about 70,000. The Sn content in this polymer was 5,400 ppm.

Example 1 4 kg of the poly L-lactic acid obtained in Production Example 1 was dissolved in 36 kg of methylene chloride, and 0.8 kg of methylene chloride in which 1% by weight of hydrogen chloride gas was dissolved was added thereto. Stirred. Next, the polymer solution was dropped into methanol stirred at 20 ° C., and the precipitated polymer was filtered, washed with hexane, and then dried in a vacuum dryer at about 60 ° C. The average molecular weight of this polymer is about 80,000,
The Sn content was 20 ppm. The obtained polymer was treated with a pelletizer to produce pellets having an average molecular weight of about 80,000.

Example 2 2 kg of the poly DL-lactic acid obtained in Production Example 2 was dissolved in 18 kg of N, N-dimethylformamide, and hydrogen chloride gas was bubbled into the solution to dissolve 2 g of hydrogen chloride. The solution was stirred at 40 ° C. for 2 hours and then reprecipitated with methanol at 20 ° C. to obtain a polymer having an average molecular weight of about 70,000 and a Sn content of 25 ppm. This polymer is again converted to N,
As a result of dissolving in N-dimethylformamide and treating in the same manner, a polymer having an average molecular weight of about 70,000 and an Sn content of 10 ppm or less was obtained.

Example 3 A copolymer having an average molecular weight of about 60,000 and a Sn content of 30 ppm was obtained in the same manner as in Example 1 except that the copolymer of L-lactide and glycolide obtained in Production Example 3 was used. .

Example 4 2 kg of the polylactic acid solution obtained in Production Example 4 was dissolved in 3 kg of chloroform, and 100 g of diphenyl ether in which 1% by weight of hydrogen chloride gas was dissolved was added thereto, followed by stirring at room temperature for 1 hour. Next, this polymer solution was dropped into isopropanol stirred at 20 ° C., and the obtained polymer was filtered, washed and dried. The average molecular weight of this polymer was about 110,000, and the Sn content was 60 ppm.

Example 5 A copolymer having an average molecular weight of about 70,000 and an Sn content of 70 ppm was obtained in the same manner as in Example 4 except that the copolymer solution of L-lactic acid and glycolic acid obtained in Production Example 5 was used. Was.

Comparative Example 1 4 kg of the poly L-lactic acid obtained in Production Example 1 was dissolved in 36 kg of methylene chloride and stirred at room temperature for 1 hour. Then 20
This polymer solution was dropped into methanol stirred at ℃, and the obtained polymer was filtered, washed and dried. The average molecular weight of this polymer is about 80,000 and the Sn content is 5
It was 00 ppm. The obtained polymer was treated with a pelletizer to produce pellets having an average molecular weight of about 60,000.

Comparative Example 2 2 kg of the polylactic acid solution obtained in Production Example 4 was dissolved in 3 kg of chloroform and stirred at room temperature for 1 hour. Then 20 ° C
The polymer solution was added dropwise to isopropanol which was being stirred under, and the obtained polymer was filtered, washed and dried.
The average molecular weight of this polymer was about 110,000, and the Sn content was 1800 ppm.

Comparative Example 3 40 g of poly L-lactic acid obtained in Production Example 1 was dissolved in 160 g of methylene chloride, 100 ml of 0.1N hydrochloric acid was added, and the mixture was stirred at room temperature for 1 hour. Subsequently, this solvent phase was dropped into methanol stirred at 20 ° C., and the obtained polymer was filtered, washed and dried. The average molecular weight of this polymer was about 80,000, and the Sn content was 460 ppm.

[0028]

According to the present invention, by treating a high molecular weight lactic acid-based polymer obtained using a catalyst with hydrogen chloride gas according to the method of the present invention, the catalyst can be removed in the form of chloride which can be easily removed. A lactic acid-based polymer that is safe and stable even during heat molding can be obtained.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (3)

(57) [Claims] 1. A polyhydroxycarboxylic acid, comprising treating polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid with hydrogen chloride gas in an organic solvent and mixing with a precipitant to precipitate a polymer. Acid purification method. 2. The method according to claim 1, wherein the lactic acid is L-lactic acid, D-lactic acid or a mixture thereof. 3. The method according to claim 1, wherein the hydroxycarboxylic acid is glycolic acid.