JP2007070412A - Polylactic acid composition and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid composition having excellent solvent resistance, and a molded article thereof. <P>SOLUTION: The polylactic acid composition comprises a mixture of a poly-L-lactic acid and a poly-D-lactic acid, and has ≥90% proportion of melting peak derived from a stereo complex crystal, 100,000-300,000 weight average molecular weight, and ≤10% and ≥-10% weight change in a chloroform-resistant test. Preferably, the enthalpy of the melting peak derived from the stereo complex crystal is ≥40 J/g. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polylactic acid composition having high solvent resistance. Moreover, this invention relates to the molded object which consists of said composition.

In recent years, for the purpose of protecting the global environment, biodegradable polymers that are decomposed in a natural environment have attracted attention and are being studied all over the world. As the biodegradable polymer, polyhydroxybutyrate, polycaprolactone, aliphatic polyester, and polylactic acid are known. These can be melt-molded and are expected to be versatile polymers.
Among these, polylactic acid can be produced from lactic acid or lactide, which is a raw material, from natural products, and its use as a general-purpose polymer is being studied.

Polylactic acid is highly transparent and tough, but it is easy to hydrolyze in the presence of water and can be hydrolyzed without any environmental pollution after disposal.
The melting point of polylactic acid is in the range of 150 ° C. to 170 ° C. and is considered insufficient for use as an alternative to engineering plastics such as polyester and polybutylene terephthalate. Moreover, since polylactic acid is easily dissolved in a common organic solvent such as chloroform, it cannot be used for applications that come into contact with an organic solvent such as oil.
On the other hand, stereocomplex polylactic acid is formed by mixing poly-L lactic acid (hereinafter referred to as PLLA) consisting only of L-lactic acid units and poly-D lactic acid consisting only of D-lactic acid units (hereinafter referred to as PDLA) in a solution or in a molten state. Is known (Patent Document 1 and Non-Patent Document 1). This stereocomplex polylactic acid has a higher melting point and higher crystallinity than PLLA and PDLA, and an interesting phenomenon has been discovered, but its solvent resistance has not been studied so far.
JP 63-24014 A Macromolecules, 24,5651 (1991)

  An object of the present invention is to provide a polylactic acid composition having excellent solvent resistance.

  Another object of the present invention is to provide a molded body comprising the polylactic acid composition.

The present inventors have found that a polylactic acid composition formed from poly-L lactic acid and poly-D lactic acid, having a high stereocomplex crystal content, and having a predetermined molecular weight, and its molded product are excellent in solvent resistance. The present invention has been completed.
That is, the present invention comprises a mixture of poly L lactic acid and poly D lactic acid, the ratio of the melting peak derived from the stereocomplex crystal is 90% or more with respect to the total melting peak, and the weight average molecular weight is 100,000 to 300,000. The polylactic acid composition is characterized in that the weight change rate in a chloroform resistance test is ± 10% or less.
The composition preferably has an enthalpy of melting peak derived from a stereocomplex crystal of 40 J / g or more. In the composition, the ratio of poly-L lactic acid to poly-D lactic acid is preferably in the range of the former / the latter = 45/55 to 55/45. The composition has a continuous number of L lactic acid units contained in poly-L lactic acid of 15 or more and a melting point of 150 to 190 ° C., and a continuous number of D lactic acid units contained in poly-D lactic acid is 15 or more and It is preferable that melting | fusing point is 150-190 degreeC. The solvent resistance test is performed by immersing a test piece having a length of 10 mm, a width of 10 mm, and a thickness of 2 mm in chloroform at 25 ° C. for 1 hour.

Moreover, this invention is a composition containing 10-150 weight part filler with respect to 100 weight part said composition. The filler is preferably glass fiber.
The present invention includes a molded article comprising the composition.
Moreover, this invention includes the manufacturing method of the molded object characterized by heat-processing at 100-200 degreeC in a type | mold after shape | molding the said composition.

  The composition and molded body of the present invention are excellent in chloroform resistance, and the change in weight is small even when immersed in chloroform for a predetermined period.

  The present invention is described in detail below.

(Poly L lactic acid)
Poly-L-lactic acid is a polyester and polyester segment containing L-lactic acid as a main monomer component.
Examples of the poly-L lactic acid include poly-L lactic acid substantially composed only of L-lactic acid units, copolymers with other polyesters, copolymers with other polymers, and the like. It is preferable that it is comprised only by. The polylactic acid has an L-lactic acid unit of preferably 90 to 99 mol%, more preferably 91 to 98 mol%, still more preferably 94 to 98 mol%. The D lactic acid unit and / or the copolymerization component other than lactic acid is preferably 1 to 10 mol%, more preferably 2 to 9 mol%, still more preferably 2 to 6 mol%.

Poly-L lactic acid has crystallinity and preferably has a melting point of 150 to 190 ° C, preferably 160 to 190 ° C. Within this range, poly L-lactic acid itself has high crystallinity, and even when it becomes stereocomplex polylactic acid, a high melting point crystal is formed and the degree of crystallinity is further increased, which is preferable.
The poly-L lactic acid preferably has 15 or more L lactic acid units continuously, more preferably 50 or more. The continuous number of L lactic acid units can be examined by NMR measurement. That is, it is calculated from a chart obtained by ¹³ C-NMR after dissolving poly-L lactic acid in chloroform according to the reference.
The weight average molecular weight of poly L lactic acid is preferably 100,000 to 300,000, and more preferably 100,000 to 250,000. This is because, within this range, good moldability and good mechanical properties can be imparted even after becoming stereocomplex polylactic acid.

  The copolymerization component is not particularly specified. For example, hydroxycarboxylic acids such as D lactic acid, glycolic acid, caprolactone, butyrolactone, propiolactone, ethylene glycol, 1,3-propanediol, 1,2-propane Diol, 1,4-propanediol, 1,5-propanediol, hexanediol, octanediol, decanediol, dodecanediol, aliphatic diols having 2 to 30 carbon atoms, succinic acid, maleic acid, adipic acid, carbon One or more monomers selected from aliphatic dicarboxylic acids of several 2-30, terephthalic acid, isophthalic acid, hydroxybenzoic acid, hydroquinone and other aromatic diols, aromatic dicarboxylic acids and the like can be selected.

(Poly D-lactic acid)
Poly-D lactic acid is a polyester and polyester segment containing D-lactic acid as a main monomer component. Examples of the poly-D lactic acid include poly-D lactic acid substantially composed only of D-lactic acid units, copolymers with other polyesters, copolymers with other polymers, and the like. It is preferable that it is poly-D lactic acid comprised only by. In the poly-D lactic acid, the D lactic acid unit is preferably 90 to 99 mol%, more preferably 91 to 98 mol%, still more preferably 94 to 98 mol%. Moreover, L-lactic acid units and / or copolymerization components other than lactic acid are preferably 1 to 10 mol%, more preferably 2 to 9 mol%, and still more preferably 2 to 6 mol%. The poly-D lactic acid has crystallinity and preferably has a melting point of 150 to 190 ° C. or less, preferably 160 to 190 ° C. or less. Within this range, poly-D lactic acid itself has high crystallinity, and even when it becomes stereocomplex polylactic acid, a high melting point crystal is formed and the degree of crystallinity is further increased, which is preferable.

The poly-D lactic acid preferably has 15 or more D lactic acid units continuously, more preferably 50 or more. The number of consecutive D lactic acid units can be determined by NMR measurement. That is, it is calculated from a chart obtained by ¹³ C-NMR after dissolving poly-D lactic acid in chloroform according to the reference.
The weight average molecular weight of poly-D lactic acid is preferably 100,000 to 300,000, and more preferably 100,000 to 250,000. This is because, within this range, good moldability and good mechanical properties can be imparted even after becoming stereocomplex polylactic acid.

  The copolymer component is not particularly specified. For example, hydroxycarboxylic acids such as L lactic acid, glycolic acid, caprolactone, butyrolactone, propiolactone, ethylene glycol, 1,3-propanediol, 1,2-propane Diol, 1,4-propanediol, 1,5-propanediol, hexanediol, octanediol, decanediol, dodecanediol, aliphatic diols having 2 to 30 carbon atoms, succinic acid, maleic acid, adipic acid, carbon One or more monomers selected from the group consisting of aliphatic dicarboxylic acids of 2 to 30, aromatic diols such as terephthalic acid, isophthalic acid, hydroxybenzoic acid, and hydroquinone, and aromatic dicarboxylic acids can be selected.

  Poly-L lactic acid and poly-D lactic acid can be produced, for example, by a method of directly dehydrating and condensing each lactic acid, or by a method of ring-opening polymerization after each lactic acid is once subjected to dehydration cyclization to lactide. Any catalyst can be used as the catalyst used in these production methods as long as the poly-L lactic acid component and the poly-D lactic acid component can be polymerized so as to have predetermined characteristics. However, tin octylate and tin chloride can be used. And divalent tin compounds such as tin alkoxides, tetravalent tin compounds such as tin oxide, butyltin oxide, and ethyltin oxide, metal tin, zinc compounds, aluminum compounds, calcium compounds, and lanthanide compounds.

(Stereo complex crystal)
The polylactic acid composition of the present invention is a mixture of poly L lactic acid and poly D lactic acid, and the proportion of melting peaks derived from the stereocomplex crystals contained therein preferably accounts for 90% or more of the total melting peak, It is more preferably 95% or more, and further preferably 100%. If it is such a range, the molded object excellent in heat resistance can be obtained favorably. It is known that polylactic acid having a stereocomplex crystal usually exhibits at least two endothermic peaks of a low-temperature crystal melt phase and a high-temperature crystal melt phase depending on the components, composition ratio and production conditions. The melting peak derived from the stereocomplex crystal here refers to a melting peak at 205 ° C. or higher (high temperature), corresponding to the peak of the high-temperature crystal melting phase.

The ratio of poly L lactic acid to poly D lactic acid is preferably in the range of the former / the latter = 45/55 to 55/45.
The continuous number of L lactic acid units contained in poly-L lactic acid is 15 or more and the melting point is 150 to 190 ° C., the continuous number of D lactic acid units contained in poly-D lactic acid is 15 or more and the melting point is 150 to It is preferable that it is 190 degrees C or less.
Furthermore, in the polylactic acid composition and molded product of the present invention, the enthalpy of the melting peak derived from the stereocomplex crystal contained therein is preferably 40 J / g or more, more preferably 42 J / g or more, and even more preferably 50 J / g. That's it. If it is such a range, the molded object excellent in the mechanical physical property can be obtained favorably.
The polylactic acid composition has a weight average molecular weight of 100,000 to 300,000, preferably 100,000 to 250,000.

The polylactic acid composition of the present invention and the molded body thereof have a weight change rate of ± 10% or less, preferably ± 5% or less, more preferably ± 0.5% or less in a chloroform resistance test. It is because it can be used in applications requiring solvent resistance within such a range of change rate.
The chloroform resistance test is performed by immersing a test piece having a length of 10 mm, a width of 10 mm, and a thickness of 2 mm in chloroform at 25 ° C. for 1 hour. Evaluation is performed based on the weight change rate of the test piece.

The molded body made of the composition of the present invention may contain various additives, fillers, dyes, pigments and the like. Examples of such additives include antioxidants, heat stabilizers, chain extenders, lubricants, nucleating agents, and release agents. Examples of the filler include glass fiber, carbon fiber, aramid fiber, talc, hydrotalcite, layered silicate, potassium titanate whisker, and the like, and particularly, long fiber or short fiber glass fiber can be used. It is preferable in terms of economical and physical properties.
It is preferable to contain 10 to 150 parts by weight, more preferably 15 to 70 parts by weight of filler with respect to 100 parts by weight of the polylactic acid composition. Within this range, good mechanical properties and the like can be imparted while maintaining appropriate moldability.

  The polylactic acid composition and molded body of the present invention can be produced by mixing poly L lactic acid and poly D lactic acid so that stereocomplex crystals can be sufficiently formed. For example, (i) a method in which poly L lactic acid and poly D lactic acid are melted and mixed at a sufficiently high temperature, and (ii) poly L lactic acid and poly D lactic acid are blended in a solid state and then melted to a sufficiently high temperature. And (iii) a method of dissolving and mixing poly-L lactic acid and poly-D lactic acid.

  In the case of taking a method of melting and mixing, a method using a single or twin screw extruder, a method using a kneader, a method using a reaction vessel equipped with a stirring device, and the like can be exemplified. The mixing temperature is preferably 230 to 290 ° C, more preferably 240 to 280 ° C, and even more preferably 260 to 280 ° C. In addition, when mixing as a solution, it is possible to take a method in which each component is dissolved in a solution composed of one or more solvents selected from chloroform, dichloromethane, phenol, tetrachloroethane, hexafluoroisopropanol and the like and then mixed. I can do it.

  For the molding, any method used for molding a resin, such as injection molding, sheet extrusion, or blow molding, may be used. In particular, when performing injection molding, the temperature of the mold is preferably 40 to 140 ° C, more preferably 80 to 120 ° C, and even more preferably 90 to 110 ° C. Moreover, it is preferable to heat-process the obtained molded object at 100-200 degreeC, and to improve crystallinity more, and it is more preferable to heat-process at 130-160 degreeC. This is because heat resistance can be improved by performing such heat treatment.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. Moreover, each value in an Example was calculated | required with the following method.

(1) Reduced viscosity:
0.12 g of the polymer was dissolved in 10 mL of tetrachloroethane / phenol (volume ratio 1/1), and the reduced viscosity (mL / g) at 35 ° C. was measured.

(2) Weight average molecular weight (Mw):
The polymer weight average molecular weight used GPC-11 made by Shodex, 50 mg of polylactic acid 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.

(3) Crystallization point, melting point, proportion of melting peak derived from stereocomplex crystal and melting enthalpy:
Using a differential scanning calorimeter (DSC), measurement was carried out under a nitrogen atmosphere at a heating rate of 20 ° C./min, and the crystallization point (Tc), melting point (Tm) and melting enthalpy (ΔHm) were determined.
The ratio (R) of the melting peak derived from the stereocomplex crystal was calculated from the melting peak area of 205 ° C. or higher (high temperature) and the melting peak area of 140 to 180 ° C. (low temperature) by the following formula.
R (%) = A _{205 or more} / (A _{205 or more} + A _{140 to 180} ) × 100
R: Ratio of melting peak derived from stereocomplex crystal (%)
A _{205 or higher} : melting peak area of 205 ° C. or higher
A _140-180 : melting peak area of 140-180 ° C.

(4) Chloroform resistance test:
A test piece was prepared by cutting out a resin piece having a length of 10 mm, a width of 10 mm, and a thickness of 2 mm, and the surface of the test piece was wiped off with a cloth moistened with methyl alcohol. Weighed. The test piece was completely immersed in a container containing 50 mL of the test solution chloroform, the container was sealed, and allowed to stand at 25 ° C. for 1 hour. However, the test solution was gently stirred several times within 30 minutes after immersion. One hour later, the test piece was taken out from the test solution, and the liquid adhering to the surface of the test piece was gently wiped off with a dry filter paper, and immediately put into a balance and weighed. The appearance of each test piece after completion of the test was observed and examined for the presence of gloss loss, discoloration, cloudiness, cracks, cracks, swelling, warpage, decomposition, dissolution, adhesion, and the like. In addition, the appearance of the test solution after the test was observed, and changes or turbidity in transparency and color tone, and the presence or absence of precipitates were examined.
The weight change rate M (%) of the test piece before and after the test is expressed by the following formula.
M (%) = (M ₂ −M ₁ ) / M ₁ × 100
M: Weight change rate (%)
M ₁ : Weight of test specimen before test (mg)
M ₂ : Weight of test piece after test (mg)

(Production Example 1: Production of polymer A ¹ )
After adding 100 parts by weight of L-lactide (Musashino Chemical Laboratory Co., Ltd.) to the polymerization vessel and replacing the system with nitrogen, 0.2 part by weight of stearyl alcohol and 0.05 part by weight of tin octylate as a catalyst were added. Polymerization was carried out at 2 ° C. for 2 hours to produce a polymer. The polymer was washed with acetone solution of 7% 5N hydrochloric acid to remove the catalyst and to obtain a polymer A ^1. Obtained had a reduced viscosity of the polymer ^{A 1} is 2.92 (mL / g), a weight average molecular weight 190,000. The melting point (Tm) was 168 ° C. The crystallization point (Tc) was 122 ° C.

(Production Example 2: Production of Polymer ^{A 2)}
After adding 100 parts by weight of D-lactide (Musashino Chemical Laboratory Co., Ltd.) to the polymerization vessel and replacing the system with nitrogen, 0.2 parts by weight of stearyl alcohol and 0.05 parts by weight of tin octylate as a catalyst were added. Polymerization was carried out at 2 ° C. for 2 hours to produce a polymer. The polymer was washed with acetone solution of 7% 5N hydrochloric acid to remove the catalyst and to obtain a polymer A ^2. The reduced viscosity of the obtained polymer ^{A 2} is 2.65 (mL / g), a weight average molecular weight of 200,000. The melting point (Tm) was 176 ° C. The crystallization point (Tc) was 139 ° C.

Example 1
Polymer A ¹ and Polymer A ² are mixed at 5: 5, put into an injection molding machine, melt-kneaded at a melting temperature of 260 ° C., molded, and then clamped at a mold temperature of 100 ° C. for 90 seconds to obtain a molded body. It was. A test piece was prepared from the obtained molded body. The ratio of the melting peak derived from the stereocomplex crystal of the test piece was 95% with respect to the total melting peak, and the enthalpy of the melting peak derived from the stereocomplex crystal was 45 J / g.
As a result of the chloroform resistance test, the weight change rate was 1%. Changes in the test piece and test solution were not observed visually. The results are shown in Table 1.

(Example 2)
Polymer A ¹ , Polymer A ² , and glass fiber (manufactured by Asahi Glass Fiber, fiber diameter 10 μm, fiber length 3 mm) are mixed at 3.5: 3.5: 3, charged into an injection molding machine, and melt temperature 260 ° C. After being melt-kneaded and molded, the mold was clamped for 90 seconds at a mold temperature of 100 ° C. to obtain a molded body. A test piece was prepared from the obtained molded body. The ratio of the melting peak derived from the stereocomplex crystal of the test piece was 96% with respect to the total melting peak, and the enthalpy of the melting peak derived from the stereocomplex crystal was 42 J / g.
As a result of the chloroform resistance test, the weight change rate was 3%. Changes in the test piece and test solution were not observed visually.

(Example 3)
Polymer A ¹ and Polymer A ² are mixed at 5: 5, put into an injection molding machine, melt-kneaded at a melting temperature of 260 ° C., molded, and then clamped at a mold temperature of 100 ° C. for 90 seconds to obtain a molded body. It was. A test piece was prepared from the obtained molded body, and the test piece was heat-treated at 140 ° C. for 1 hour. The ratio of the melting peak derived from the stereocomplex crystal of the test piece was 96% with respect to the total melting peak, and the enthalpy of the melting peak derived from the stereocomplex crystal was 50 J / g.
The result of the chloroform resistance test was a weight change rate of -6%. Changes in the test piece and test solution were not observed visually.

Example 4
Polymer A ¹ , Polymer A ² , and glass fiber (manufactured by Asahi Glass Fiber, fiber diameter 10 μm, fiber length 3 mm) are mixed at 3.5: 3.5: 3, charged into an injection molding machine, and melt temperature 260 ° C. After being melt-kneaded and molded, the mold was clamped for 90 seconds at a mold temperature of 100 ° C. to obtain a molded body. A test piece was prepared from the obtained molded body, and the test piece was heat-treated at 140 ° C. for 1 hour. The ratio of the melting peak derived from the stereocomplex crystal of the test piece was 98% with respect to the total melting peak, and the enthalpy of the melting peak derived from the stereocomplex crystal was 51 J / g.
The result of the chloroform resistance test was a weight change rate of −1%. Changes in the test piece and test solution were not observed visually.

(Comparative Example 1)
Polymer A ¹ was charged into the injection molding machine, it was molded by melt kneading at a melt temperature of 220 ° C., to obtain a mold temperature 30 ° C. At 40 seconds mold clamping molded body. A test piece was prepared from the obtained molded body, and the test piece was heat-treated at 100 ° C. for 1 hour.
The result of the chloroform resistance test was a weight change rate of −31%. The test piece dissolved vigorously and stagnation was observed in the test solution.

(Comparative Example 2)
Polymer A ¹ and glass fibers (Asahi Glass-fiber, fiber diameter 10 [mu] m, fiber length 3mm) and 7 were mixed with 3, was charged into the injection molding machine, it was melt-kneaded and molded at a melt temperature of 220 ° C., mold temperature The mold was clamped at 30 ° C. for 40 seconds to obtain a molded body. A test piece was prepared from the obtained molded body, and the test piece was heat-treated at 100 ° C. for 1 hour.
The result of the chloroform resistance test was a weight change rate of -25%. The specimen was severely deformed, the test solution was stagnation, and a precipitate was observed.
The results of Examples 1-4 and Comparative Examples 1-2 are summarized in Table 1.

The polylactic acid composition and molded article of the present invention can be used in fields where resistance to solvents such as chloroform, which has conventionally been difficult to use polylactic acid, is required.

Claims (9)

  Made of a mixture of poly-L lactic acid and poly-D lactic acid, the proportion of melting peak derived from stereocomplex crystals is 90% or more with respect to the total melting peak, the weight average molecular weight is 100,000-300,000, and chloroform resistant A polylactic acid composition having a weight change rate in a test of ± 10% or less.   The composition according to claim 1, wherein the enthalpy of melting peak derived from the stereocomplex crystal is 40 J / g or more.   2. The composition according to claim 1, wherein the ratio of poly L lactic acid to poly D lactic acid is in the range of the former / the latter = 45/55 to 55/45.   The continuous number of L lactic acid units contained in poly-L lactic acid is 15 or more and its melting point is 150 to 190 ° C., and the continuous number of D lactic acid units contained in poly-D lactic acid is 15 or more and its melting point is 150 to 190. The composition of claim 1 which is at ° C.   The composition according to claim 1, wherein the chloroform resistance test is performed by immersing a test piece having a length of 10 mm, a width of 10 mm, and a thickness of 2 mm in chloroform at 25 ° C. for 1 hour.   The composition containing 10-150 weight part filler with respect to the composition of Claim 1 of 100 weight part.   The composition according to claim 6, wherein the filler is glass fiber.   The molded object which consists of a composition as described in any one of Claims 1-7. A method for producing a molded body, wherein the composition according to any one of claims 1 to 7 is molded, and then heat-treated at 100 to 200 ° C in a mold.