KR100190230B1 - Method for producing biodegradable polylactic acid - Google Patents

Abstract

The present invention relates to an improved biodegradable polylactic acid produced by direct dehydration condensation reaction of a biodegradable polymer, polylactic acid, from purified lactic acid oligomer, wherein the lactic acid is mixed with antimony trioxide or stannic oxide, etc., Dehydration and polycondensation reaction to obtain a lactic acid oligomer having an average molecular weight of 3,000 or more and then dissolving the lactic acid oligomer in chloroform or methylene chloride and then immersing it in a metal alcohol or directly refining with isopropyl ether to obtain a lactic acid oligomer having an unreacted lactic acid content exceeding 0.5% And the polycondensation reaction is carried out in a second order to produce polylactic acid. The polylactic acid is prepared by adding 0.0005 to 5 wt% of a polycondensation catalyst and 0.0001 to 5 wt% of an antioxidant to 100 parts of lactic acid oligomer or lactic acid, A linear chain having a molecular weight of 30,000 to 250,000 That relates to a process for the preparation of biodegradable polylactic acid having a molecular structure, the present invention is a biodegradable polylactic acid is useful as a medical material or a substitute for general-purpose resins such as a suture for surgery.

Description

Method for producing biodegradable polylactic acid

The present invention relates to a process for producing a modified biodegradable polylactic acid, which comprises a step of subjecting a biodegradable polylactic acid useful as a substitute for a general purpose resin such as a medical material, a foam, a reticulum or the like by direct dehydration condensation reaction of lactic acid without using a cyclic dimer And a method for producing a polylactic acid of a polymer by a simple method.

The non-caking property, which is a characteristic of plastic products, causes serious problems of environmental pollution. Especially, environmental pollution caused by various containers, films, packaging materials and coating materials used after being used as household goods and industrial products in mass- Measures are urgently needed.

Lactic acid is widely distributed in nature and harmless to plants and animals or human body. Its polylactic acid is hydrolyzed relatively easily by water, so it is used as a substitute for general-purpose resin. Recently, And is widely used as a sustained-release polymer.

Polylactic acid, which is a polyhydroxy acid, can generally be produced by ring-opening polymerization of a lactide ring-shaped chain of lactic acid. Conventionally, U.S. Patent No. 2,703,316 discloses oligomerization of DL-lactic acid followed by pyrolysis at 200-250 ° C under reduced pressure to form a lactide, which is a cyclic dimer of lactic acid. The lactic acid is then recrystallized from ethyl acetate to obtain racemic lactide L-lactic acid having an inherent viscosity of 0.45 dl / g or more to produce a strong film and a fiber.

In addition, U.S. Patent No. 2,758,987 discloses a method of obtaining poly L-lactic acid having a solution viscosity of 0.4 dl / g or more by L-lactide having a melting point of 94 ° C or higher obtained by the same method from L-lactic acid, There are many efforts and costs such as distillation and recrystallization.

On the other hand, the direct polycondensation reaction of lactic acid increases the molecular weight in proportion to the esterification reaction time by the base acid and the polyhydric alcohol, and the produced water acts to lower the molecular weight of the polycondensation by hydrolysis, It is necessary to obtain a high molecular weight polylactic acid to remove the polylactic acid.

Japanese Patent Publication No. 59-96123 discloses a method for obtaining a polylactic acid having a molecular weight of 4000 or more by conducting a condensation reaction using a catalyst at a reaction temperature of 220 to 260 ° C and a pressure of 10 mmHg or less.

U.S. Patent No. 4,273,920 proposes a process for producing a copolymer of lactic acid and glycolic acid by removing the catalyst after dehydration condensation using an ion exchange resin with a catalyst.

However, the above-described methods require not only a multi-step reaction process but also a high temperature in order to obtain a polylactic acid having a high molecular weight. The polymer obtained by such a method is easily colored and contains impurities due to thermal decomposition have.

The molecular weight of the polymer obtained by such a method is also limited. Generally, a high molecular weight polylactic acid having a molecular weight of about 250,000 can be used as a medical material. However, conventional methods have limitations in obtaining such a high molecular weight polylactic acid.

The object of the present invention is to obtain a polylactic acid of a polymer by a simple method by directly obtaining a cyclic dimer from lactic acid and directly carrying out a dehydration polycondensation reaction without performing ring-opening polymerization.

The present invention relates to a process for producing a lactic acid oligomer by condensing lactic acid to obtain a lactic acid oligomer having a molecular weight of 3,000 or more, more preferably 5,000 or more, dissolving the lactic acid oligomer in chloroform or methylene chloride and then immersing it in methanol or directly refining with isopropyl ether, And sufficient removal of moisture to sufficiently remove unreacted lactic acid in an amount not exceeding 0.5% by weight, and the lactic acid oligomer is subjected to condensation reaction again.

If the lactic acid oligomer not sufficiently purified is used, the average molecular weight of the obtained polylactic acid is 30,000 or less. However, when the lactic acid oligomer is dissolved in chloroform or methylene chloride and then immersed in methanol or purified directly with isopropyl ether, the unreacted lactic acid and the lactic acid oligomer sufficiently removed from water are condensed again to obtain polylactic acid having an average molecular weight of 30,000 or more have.

In the method for producing polylactic acid directly from lactic acid, the amount of unreacted lactic acid and water contained in the lactic acid oligomer prepared in the first place greatly affects the molecular weight of the polylactic acid.

In particular, when the content of unreacted lactic acid is large, the polymerization reaction rate is very slow, the depolymerization is promoted and the pyrolysis is promoted.

In the production process of the present invention, the reaction temperature is 90 to 210 占 폚, preferably 140 to 190 占 폚.

The lactic acid used in the present invention exists as an isomer and is a mixture of L-lactic acid, D-lactic acid or L-lactic acid and D-lactic acid. Examples of the catalyst that can be used in the polycondensation reaction include zinc oxide, antimony oxide, antimony chloride, lead oxide, calcium oxide, aluminum oxide, iron oxide, calcium chloride, zinc acetate, paratoluene sulfonic acid, stannous chloride, Tin oxide, tin oxide, stannous octanoate, tetraphenyltin, tin powder, titanium tetrachloride and the like.

The amount of the catalyst to be used is 0.0005 to 5% by weight, more preferably 0.003 to 1% by weight, based on 100% by weight of the lactic acid or lactic acid oligomer used. If it is less than 0.0005% by weight or exceeds 5% by weight, films and moldings made of polylactic acid can not obtain a polylactic acid having a molecular weight of 30,000 to 250,000 which can have a strength suitable for use as an actual product.

The average molecular weight of the polylactic acid obtained by the method of the present invention was about 30,000 to 250,000, depending on the molecular weight of the lactic acid oligomer, the content of the unreacted lactic acid in the lactic acid oligomer, the type and amount of the catalyst, the reaction temperature, and the reaction time. An antioxidant is used to prevent pyrolysis. The amount of the antioxidant to be used is 0.0001 to 5% by weight, more preferably 0.001 to 2% by weight, based on the weight of the lactic acid or the lactic acid oligomer. If it is less than 0.001% by weight or exceeds 5% by weight, polylactic acid having a molecular weight of 30,000 to 250,000, which can have sufficient strength of the film and the molded product, could not be obtained.

Particularly, according to the present invention, polylactic acid having an average molecular weight of 30,000 or more can be easily obtained without using a cyclic dimer such as lactide, which has been conventionally used conventionally.

The high molecular weight polylactic acid thus obtained has a sufficient strength when processed into a film, a molded product and the like, and thus can be suitably used for applications such as packaging materials and containers. When the average molecular weight is less than 30,000 or when the film has an average molecular weight of more than 250,000, it is difficult to use the film as a film due to insufficient tensile strength and elongation. Therefore, when used as a film, the average molecular weight of the polymer in terms of strength and elongation is required to be 30,000 or more, more preferably 50,000 or more. However, according to the production method of the present invention, a high molecular weight poly Lactic acid can be easily obtained. Further, the high molecular weight polylactic acid produced according to the present invention can be subjected to secondary processing such as stretching, blowing, and vacuum molding. Therefore, the high molecular weight polylactic acid obtained by the method according to the present invention can be used as a substitute for a conventional general resin such as a medical material, a foam, a mesh, and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples.

The following examples do not limit the scope of the present invention.

The average molecular weight of the polylactic acid of the present invention was obtained by comparison with a polystyrene standard sample when measured by gel permeation chromatography (column temperature: 40 DEG C, solvent: chloroform, model 150C, manufactured by WATERS).

The content of unreacted lactic acid and impurities contained in the lactic acid oligomer was measured using a DL 25 automatic titration apparatus of METTLER Co. using a non-titrant electrode and a DRX-300 nuclear magnetic resonance spectrometer of BRUKER Co. Respectively.

The tensile strength and elongation of the prepared film samples were measured using MODEL 4201 manufactured by INSTRON Co.,

[Example 1]

Lactic acid was added to 33.0 g of L-lactic acid as a catalyst together with 0.06 g of antimony trioxide, followed by dehydration and polycondensation reaction under reduced pressure of 30 to 50 mmHg at 150 DEG C for 3 hours while stirring. The reaction was then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 12,500 and the content of the unreacted lactic acid contained was determined to be 0.05% by weight. 0.03 g of antimony trioxide as a catalyst in 15 g of lactic acid oligomer and 0.0045 g of Irganox 1010 (IRGANOX 1010) as an antioxidant were charged in a reactor and heated to 180 DEG C under a reduced pressure of 2 mmHg for 7 hours Polymerization reaction was carried out. After completion of the polymerization reaction, the polylactic acid was taken out from the reactor, pulverized, and then placed in a vacuum oven at 50 ° C. and dried at a reduced pressure of 0.3 mmHg for 24 hours or more. The molecular weight of the prepared polylactic acid was 250,000. The polylactic acid was dissolved in a chloroform solution, and the solution was cast to a film having a thickness of 38 to 40 탆 to measure its mechanical properties. The tensile strength was 550 kg / cm 2 and the elongation was 6%.

[Example 2]

Lactic acid was added to 33.0 g of L-lactic acid as a catalyst together with 0.06 g of antimony trioxide, followed by dehydration and polycondensation reaction under reduced pressure of 30 to 50 mmHg at 150 DEG C for 2 hours while stirring. The reaction is then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 3,500, and the content of the unreacted lactic acid contained was determined to be 0.4% by weight. Then, polylactic acid was produced in the same manner as in Example 1 to produce a film. The molecular weight of polylactic acid was 40,000, and the tensile strength and elongation of the film were excellent as 370 kg / cm 2 and 8%, respectively.

[Example 3]

Lactic acid was added to 33.0 g of L-lactic acid as a catalyst together with 0.06 g of antimony trioxide, and dehydration and polycondensation reaction were carried out at 150 ° C. and 30 to 50 mmHg for 3 hours while stirring. The reactants are then pulverized to produce the lactic acid oligomer in powder form and then washed three more times with isopropylene ether. The powder was sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 3,300 and the content of unreacted lactic acid was 0.5% by weight. Then, polylactic acid was produced in the same manner as in Example 1 to produce a film. The polylactic acid had a molecular weight of 30,000, and the tensile strength and elongation of the film were excellent at 350 kg / cm 2 and 10%, respectively.

[Example 4]

Lactic acid was added to 33.0 g of L-lactic acid as a catalyst together with 0.06 g of antimony trioxide, followed by dehydration and polycondensation reaction at 90 ° C. and 10 to 20 mmHg for 3 hours while stirring. The reaction was then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 3,800 and the content of unreacted lactic acid was 0.3% by weight. The polylactic acid was produced in the same manner as in Example 1 except that the polylactic acid was produced by a polycondensation reaction at 90 DEG C for 30 hours. The molecular weight of the polylactic acid was 50,000, and the tensile strength and elongation Were respectively excellent at 410 kg / cm 2 and 10%.

[Example 5]

Lactic acid was added to 33.0 g of L-lactic acid as a catalyst together with 0.06 g of antimony trioxide, and dehydration and polycondensation reaction were carried out at 150 ° C. and 30 to 50 mmHg for 3 hours while stirring. The reaction was then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 12,000 and the content of unreacted lactic acid was 0.2% by weight. Next, a polylactic acid was produced in the same manner as in Example 1 except that the polycondensation reaction was carried out at 210 캜 for 5 hours, and a film was produced. The molecular weight of the polylactic acid was 89,000, and the strength and elongation were 430kg / ㎠, and 8%, respectively.

[Example 6]

L-lactic acid, 0.03 g of antimony trioxide and 0.03 g of 1-tin oxide were fed together as a catalyst, and dehydration and polycondensation reaction were carried out for 3 hours at 150 ° C with stirring. 100 ml of methylene chloride And poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 12,500 and the content of unreacted lactic acid was 0.1% by weight. Next, a polylactic acid was produced in the same manner as in Example 1, except that the polycondensation reaction was carried out at 190 캜 for 8 hours, and a film was produced. The molecular weight of polylactic acid was 170,000, and the tensile strength The elongation was excellent as 510 kg / ㎠ and 10%, respectively.

[Example 7]

Lactic acid was added to 33.0 g of L-lactic acid as a catalyst together with 0.06 g of antimony trioxide in a reactor, followed by dehydration and polycondensation reaction at 150 ° C for 3 hours while stirring. The reaction was then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 11,000 and the content of lactic acid was 0.1% by weight. Then, the same procedure as in Example 1 was carried out except that tin oxide was used as the catalyst. When polylactic acid was prepared by this method, the molecular weight of polylactic acid was 190,000, and the tensile strength and elongation of the film were excellent as 525 kg / cm 2 and 5%, respectively.

[Example 8]

33.0 g of 90% L-lactic acid and 3.0 g of 90% D, L-lactic acid were placed in a reactor and dehydration and polycondensation reaction were carried out under the same conditions as in Example 1 to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 7,000 and the content of unreacted lactic acid was 0.4% by weight. Then, polylactic acid was produced in the same manner as in Example 1 to produce a film. The molecular weight of polylactic acid was 90,000, and the tensile strength and elongation of the film were excellent as 420 kg / cm 2 and 11%, respectively.

[Comparative Example 1]

Polylactic acid was produced in the same manner as in Example 1 except that 0.5% by weight of lactic acid was added to the lactic acid oligomer obtained in Example 1 to prepare a film. The molecular weight of the polylactic acid was 15,000, and the tensile strength And shindo were 120kg / ㎠ and 11%, respectively.

[Comparative Example 2]

Lactic acid was added to 33.0 g of L-lactic acid as a catalyst together with 0.06 g of antimony trioxide, followed by dehydration and polycondensation reaction at 150 DEG C under a reduced pressure of 30 to 50 mmHg for 1 hour and 30 minutes. The reaction was then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 2,900 and the unreacted lactic acid content was 0.4% by weight. Then, polylactic acid was produced in the same manner as in Example 1 to prepare a film. The molecular weight of the polylactic acid was 25,000, and the tensile strength and elongation of the film were 150 kg / cm 2 and 6%, respectively.

[Comparative Example 3]

Lactic acid was added to 33.0 g of L-lactic acid as a catalyst together with 0.0001 g of antimony trioxide as a catalyst, followed by dehydration and polycondensation reaction at 150 占 폚 for 3 hours while stirring. The reaction was then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 2,500 and the content of unreacted lactic acid was 0.1% by weight. Then, polylactic acid was produced in the same manner as in Example 1 except that the amount of catalyst used was changed to 0.0001 g, and the molecular weight of the polylactic acid was 5,000. The tensile strength and elongation of the film were 50 kg / 6%.

[Comparative Example 4]

Lactic acid was added to 33.0 g of 90% L-lactic acid together with 1.55 g of antimony trioxide as a catalyst, followed by dehydration and polycondensation reaction at 150 ° C for 3 hours while stirring. The reaction was then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 6,000 and the content of unreacted lactic acid was 0.2% by weight. The polylactic acid was produced in the same manner as in Example 1 except that the amount of catalyst used was changed to 1.55 g. The molecular weight of the polylactic acid was 13,000, and the tensile strength and elongation of the film were 110 kg / ㎠, 9%.

[Comparative Example 5]

To 33.0 g of 90% L-lactic acid was added 0.0001 g of 1 tin oxidizing agent as a catalyst, followed by dehydration and polycondensation reaction at 150 占 폚 for 3 hours while stirring. Then, the reaction mixture was sufficiently dissolved in 100 ml of methylene chloride, and 100 ml of methanol was poured to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 2,800 and the content of unreacted lactic acid was 0.1% by weight. The polylactic acid was produced in the same manner as in Example 1 except that the amount of tin oxide used was changed to 0.0001 g as a catalyst. The polylactic acid had a molecular weight of 18,000, and the tensile strength and elongation Were 130 kg / cm 2 and 5%, respectively.

[Comparative Example 6]

To 33.0 g of 90% L-lactic acid, 1.55 g of 1 tin oxidizing agent was added to the reactor, followed by dehydration and polycondensation reaction at 150 ° C. for 3 hours while stirring. The reaction was then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 8,000 and the content of unreacted lactic acid was 0.2% by weight. The polylactic acid was produced in the same manner as in Example 1 except that the amount of catalyst used was changed to 1.55 g. The molecular weight of polylactic acid was 28,000, and the tensile strength and elongation of the film were 210 kg / ㎠, and 7%, respectively.

[Comparative Example 7]

Lactic acid was added to 33.0 g of L-lactic acid as a catalyst together with 0.06 g of antimony trioxide in a reactor, followed by dehydration and polycondensation reaction at 150 ° C for 3 hours while stirring. The reaction was then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 12,500 and the content of unreacted lactic acid was 0.1% by weight. 0.045 g of antimony trioxide as a catalyst in 15 g of lactic acid oligomer and 0.0001 g of Irganox 1010 as an antioxidant were placed in a reactor and then the same procedure as in Example 1 was carried out to prepare polylactic acid The molecular weight of the polylactic acid was 22,000, and the tensile strength and elongation of the film were 175 kg / cm 2 and 6%, which was not good.

[Comparative Example 8]

Lactic acid was added to 33.0 g of L-lactic acid as a catalyst together with 0.06 g of antimony trioxide in a reactor, followed by dehydration and polycondensation reaction at 150 ° C for 3 hours while stirring. The reaction was then sufficiently dissolved in 100 ml of methylene chloride and poured into 100 ml of methanol to obtain crystals. The crystals were filtered, washed with methanol three times or more, and sufficiently dried to obtain a white lactic acid oligomer. The molecular weight of the lactic acid oligomer was 12,500 and the content of unreacted lactic acid was 0.1% by weight. 0.045 g of antimony trioxide as a catalyst in 15 g of lactic acid oligomer and 0.8 g of Irganox 1010 as a catalyst were placed in a reactor and then polylactic acid was produced in the same manner as in Example 1 to prepare a film, The molecular weight was 26,000, and the tensile strength and elongation of the film were 205 kg / cm 2, 6%, which was not good.

Claims (1)

Lactic acid is firstly subjected to dehydration and polycondensation reaction to obtain a lactic acid oligomer having an average molecular weight of 3,000 or more and then the unreacted lactic acid is sufficiently removed so that the content of unreacted lactic acid does not exceed 0.5 wt% Wherein the catalyst is prepared by adding 0.0005 to 5 wt% of a catalyst and 0.0001 to 5 wt% of an antioxidant to 100 parts by weight of lactic acid or lactic acid oligomer in the polycondensation reaction.