JP2008038054A - Method for producing polylactic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a polylactic acid which suppresses reduction in modulus of elasticity in the vicinity of a crystallization temperature and has improved heat resistance. <P>SOLUTION: The method for producing a polylactic acid comprises making at least one of a poly-L-lactic acid (PLLA) and a poly-D-lactic acid (PDLA) into a fibrous state and melting and kneading PLLA and PDLA at 170-190°C when PLLA and PDLA are melted and kneaded. The polylactic acid is processed into various moldings, films, sheets, fibers and composite material with other materials by injection molding, extrusion molding, etc., and useful for various uses demanding heat resistance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing polylactic acid using poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA).

  Conventionally, there are various methods for producing polylactic acid, such as a method of synthesizing lactide, which is a cyclic dimer of lactic acid from lactic acid, to obtain a polymer by this ring-opening polymerization, and a method by direct polymerization from lactic acid. Are known.

  Polylactic acid includes a stereocomplex polymer of polylactic acid. This stereocomplex polymer is a mixture of poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA). By using polylactic acid as a stereocomplex polymer, for example, (1) PLLA chain and Each PDLA chain has higher cohesion than a single one, exhibits high crystallinity, (2) has a high melting point and improves thermal stability, (3) has a draw ratio in the production of fibers, films, etc. It is said that it has improved properties and has high physical properties, and can be molded at the same temperature as PLLA, but it exhibits the characteristics such as a higher melting point of the stretched and oriented material.

  A stereocomplex polymer of polylactic acid can generally be obtained by drawing a fiber obtained by spinning a blend of poly-L-lactide and poly-D-lactide in a solution state. PLLA generally has low heat resistance, but heat resistance can be improved by mixing PDLA to form a stereo complex.

In relation to the method for producing a stereocomplex polymer, at least one crystallized pellet made of poly-L-lactic acid (A) based on L-lactic acid and poly-D-based on D-lactic acid. Disclosed is a crystalline polylactic acid stereocomplex polymer composition obtained by melting and blending lactic acid (B) pellets at a mixing weight ratio in the range of (A) :( B) = 10: 90 to 90:10. (For example, refer to Patent Document 1). Here, using pellets made of poly-L-lactic acid and pellets made of poly-D-lactic acid, both pellets are mixed (dry blended), heated and melted and mixed in the same molding machine, or separately melted. It is described that mixing is performed after melting in an apparatus.
JP 2000-0117164 A

  However, in the method of mixing PLLA and PDLA in the form of pellets and heating and melting them to make a stereo complex as described above, since the degree of crystallinity is not sufficient, it is around the crystallization temperature (for example, around 80 ° C.). Decrease in elastic modulus is large and is insufficient as heat resistance.

  The present invention has been made in view of the above, and provides a method for producing polylactic acid capable of suppressing the decrease in elastic modulus near the crystallization temperature (for example, around 80 ° C.) and obtaining polylactic acid having high heat resistance. It aims at providing and makes it a subject to achieve this objective.

  The present invention has obtained the knowledge that fibrous polylactic acid has a high crystalline state and can be oriented and crystallized when introduced as a nucleus during melt-kneading, and can form a crystal-rich state. Based on that.

  In order to achieve the above object, the method for producing polylactic acid of the present invention comprises poly-L-lactic acid (hereinafter sometimes abbreviated as “PLLA”) and poly-D-lactic acid (hereinafter referred to as “PDLA”). May be abbreviated)), and at least one of PLLA and PDLA is added in a fiber state and melt kneaded.

  In the method for producing polylactic acid of the present invention, when melt-kneading poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA), PLLA or PDLA, or PLLA and PDLA are added in a fiber state. , Because fiber-like PLLA and PDLA have a high crystal state, they become oriented as a nucleus and are easy to grow crystals, and can be solidified in a state where there are many crystals (stereo complex crystals). Compared with the case where it is added in the form of pellets or powder, it is possible to suppress a decrease in elastic modulus near the crystallization temperature (around 80 ° C.), and to effectively improve the heat resistance of polylactic acid.

In the present invention, the “fiber state” has a length such that the ratio (aspect ratio) of the length and the maximum diameter of the cross section having the normal direction in the length direction (diameter in the case of a circular cross section) is 10: 1 or more. In addition to the (long and narrow) string shape, the shape is not limited, and includes a short rod shape and a needle shape satisfying the aspect, for example, a length of less than 30 nm.
For example, the fiber state having the aspect ratio can be obtained by applying centrifugal force to cause oriented crystals.

  The term “polylactic acid” includes polylactide (polylactic acid obtained by ring-opening polymerization of lactide).

  The temperature at the time of melt kneading is desirably in the range of 170 to 190 ° C., more preferably in the range of 180 ± 5 ° C., since fibrous polylactic acid has a higher melting point.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the polylactic acid which can suppress the fall of the elasticity modulus near crystallization temperature (for example, 80 degreeC vicinity) and can obtain polylactic acid with high heat resistance can be provided.

Hereafter, the manufacturing method of the polylactic acid of this invention is demonstrated in detail.
The method for producing polylactic acid according to the present invention comprises a step of adding poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA) with at least one of PLLA and PDLA in a fiber state and melt-kneading them. It has been done. If necessary, it may further include other steps.

  Polylactic acid can be obtained, for example, as a stereocomplex polymer of polylactic acid by mixing PLLA and PDLA at an arbitrary ratio and then heat-melting or mixing at an arbitrary ratio after heat-melting. Here, in the present invention, PLLA and / or PDLA are present in a fiber state during melt kneading. At this time, PLLA and / or PDLA in the fiber state can be present by mixing and mixing at least one of the PLLA and / or PDLA before melt kneading, and after the start of melt kneading. Fiber-like PLLA and / or PDLA can be mixed and present.

  In the present invention, either or both of PLLA and PDLA are present in the fiber state at the time of melt-kneading, so that the fiber component in the crystalline state becomes crystal nuclei and the orientation progresses, and the crystal is solidified in an increased state. Since the stereocomplex polymer is formed, polylactic acid having a high crystallinity and a high melting point can be obtained, and high heat resistance can be ensured.

  Poly-L-lactic acid (PLLA) is polylactic acid having L-lactic acid as a main constituent unit, and includes polylactic acid having 100 to 20 mol% of L-lactic acid units.

  Poly-D-lactic acid (PDLA) is polylactic acid containing D-lactic acid as a main constituent unit, and includes polylactic acid having 100 to 20 mol% of D-lactic acid units.

For the PLLA and PDLA in the fiber state, for example, a PLLA pellet (or PDLA pellet) or the like is heated and then crystallized while being centrifuged and crystallized by orientation, or a PLLA or PDLA having a commercially available fiber shape (for example, , PURASORB PD manufactured by PURAC, etc.) can be appropriately selected according to the purpose.
In the case of crystallizing the crystal by orientation, the temperature at which the crystallization is performed is preferably a glass transition temperature of PLLA or PDLA and a melting point or less. Usually, it is a temperature range of about 58-180 degreeC.

  The fiber state is the maximum length of the cross section with the length and the length direction as the normal direction (for example, the diameter in the case of a perfect circle, the maximum diameter in the case of a cross ellipse, It refers to a long shape (e.g., rod shape, needle shape) having a length (diagonal length) ratio (aspect ratio) of 10: 1 or more, and an aspect ratio of 100: 1 or more is more preferable. The upper limit of the aspect ratio is preferably 1000: 1. Among these, 100: 1 is particularly preferable. Within this aspect ratio range, the long side length (cut length) of the fiber shape is preferably selected within a range of 50 ± 30 nm.

Further, the fiber state can be represented by a unit T (decitex) of the thickness of the yarn, and a fiber state of 10T or less is preferable, and more preferably in a range of 3T to 0.3T.
Decitex (T) represents the number of grams per 10,000 m.

  Lactic acid monomer or other monomer component copolymerizable with lactide may be included, for example, dicarboxylic acid, polyhydric alcohol, hydroxycarboxylic acid, lactone etc. having two or more ester bond-forming functional groups, and these monomers Examples include various polyesters composed of components, various polyethers, and various polycarbonates.

  Examples of the dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the polyhydric alcohol include aromatic polyvalents such as those obtained by addition reaction of bisphenol with ethylene oxide. Alcohol, ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, glycerin, sorbitan, trimethylolpropane, neopentyl glycol and other aliphatic polyhydric alcohols, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol and other ethers Glycol and the like. Examples of the hydroxycarboxylic acid include glycolic acid, hydroxybutylcarboxylic acid, and others described in JP-A-6-184417. Examples of the lactone include glycolide, ε-caprolactone glycolide, ε-caprolactone, Examples include β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, and δ-valerolactone.

For production of poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA), basically any known polymerization method can be employed. There is no restriction | limiting in this polymerization method, Well-known methods, such as a condensation polymerization method and a ring-opening polymerization method, are mentioned.
For example, in the case of the condensation polymerization method, PLLA and PDLA can be formed into an arbitrary composition by directly dehydrating condensation polymerization of L-lactic acid or D-lactic acid (along with other monomer components and the like as necessary). In addition, in the case of the ring-opening polymerization method, lactide, which is a cyclic dimer of lactic acid, is mixed with a polymerization regulator or the like as necessary, and polymerized using a catalyst to form PLLA having an arbitrary composition. , PDLA. Examples of the lactide include L-lactide which is a dimer of L-lactic acid, D-lactide which is a dimer of D-lactic acid, L-lactic acid, and DL-lactide composed of D-lactic acid.

  The mass average molecular weight of PLLA and PDLA is preferably in the range of 1,000 to 500,000, more preferably in the range of 50,000 to 500,000, from the viewpoint of the fluidity of the resin.

The mixing ratio (mass ratio) of PLLA and PDLA is not particularly limited, but is in the range of PLLA: PDLA = 85: 15 to 15:85 from the viewpoint of increasing the elastic modulus E ′ near the crystallization temperature of PLLA and PDLA. From the viewpoint of increasing the elastic modulus E ′ in the vicinity of the crystallization temperature of PLLA and PDLA, particularly in the vicinity of 80 ° C. to exceed 3.0 × 10 ⁸ , PLLA: PDLA = 70: 30 to 30:70 More preferably, it is the range.
What is necessary is just to select this mixing ratio suitably according to the intended purpose.

In addition to PLLA and PDLA, conventionally known plasticizers, antioxidants, heat stabilizers, light stabilizers, UV absorbers, colorants such as dyes / pigments, various fillers, charging, etc. Various additives such as an inhibitor, a release agent, a fragrance, a lubricant, a flame retardant, a foaming agent, a filler, an antibacterial / antifungal agent, and a nucleating agent may be added. In order to finely disperse PLLA and PDLA, inorganic fillers such as talc, mica, calcium carbonate, and glass fiber may be used.
These various additives can be added, for example, when producing a stereocomplex polymer.

  The melt-kneading of PLLA and PDLA is performed by a melt-kneading method. Specifically, after PLLA and PDLA are uniformly blended using a mixer or the like, a melt extruder such as a twin screw extruder or a mill such as a lab plast mill is used. Etc. can be performed by heating and melting within a temperature range of 170 to 190 ° C. (for example, a temperature range of 160 to 200 ° C. for a twin screw extruder).

  When blending, either PLLA or PDLA can be used in the form of pellets or powder, for example, without using the fiber state. Here, the pellets are those whose aspect ratio is outside the above range and whose sheet is crushed or cut, and those which are spherical or fluorite.

  Heating is preferably performed by fluidizing PLLA and PDLA. By fluidizing, fusion between pellets when PLLA / PDLA or fibers or pellets are used can be prevented. If it is fused, it may be pulverized mechanically.

  When using a melt extruder, PLLA and PDLA and other components as necessary are loaded into the melt extruder and melted and kneaded while being heated and / or pressurized with a rotary screw provided in the machine. It may be.

  After the melt-kneading, for example, a resin composition is obtained in the form of pellets, and the obtained resin composition is introduced into, for example, an injection molding machine to obtain desired molding conditions (for example, a cylinder set temperature of 155 to 200 ° C., gold Mold temperature 30 to 80 ° C., injection and holding pressure time 10 to 30 seconds, cooling time 10 to 60 seconds) or injection-molding, or melt-kneaded resin composition on a desired substrate, for example Extruded from an extrusion die of a melt extruder and extruded and coated by nip and pressing the extruded resin composition, or after extrusion, the resin composition is subjected to predetermined conditions (for example, temperature 150 to 230 ° C., processing time) 1-10 minutes) under press molding (if necessary, press molding under predetermined conditions (for example, temperature 10-40 ° C., processing time 1-10 minutes) using a heating / cooling compression molding machine) Desired including film or film It is possible to obtain a resin molded body of the shape.

  The polylactic acid (stereocomplex polymer) obtained by the method for producing polylactic acid of the present invention is an injection molded product, an extrusion molded product, a vacuum / pressure molded product, a blow molded product, a film, a sheet, a nonwoven fabric, a fiber / cloth, and the like. Can be used for composites with materials, agricultural materials, horticultural materials, fishery materials, civil engineering / architectural materials, stationery, medical supplies, or other molded products, especially those requiring heat resistance It is suitable for the use of goods. In addition, shaping | molding can be performed by a conventional method.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. The following “parts” are based on mass.

(Example 1)
70 parts U'z-B0 [mass average molecular weight: 200,000, pellets; poly-L-lactic acid (PLLA)] manufactured by Toyota Motor Corporation, and PURASORB PD [mass average molecular weight: 102, manufactured by PURAC 000, fiber shape {2.2T (decitex), cut length: 51 mm}; poly-D-lactic acid (PDLA)] 30 parts, and 175 using Labo Plast Mill (Toyo Seiko Co., Ltd.). A PLA composition was obtained by uniformly melt-kneading at 0 ° C. (stereo complex formation).

  The obtained PLA composition is loaded into a precision pressure press machine (manufactured by Kotaki Seiki Co., Ltd.), and press molding is performed with this precision pressure press machine at a temperature of 180 ° C., a load of 20 tons and a press time of 180 seconds. It was. Subsequently, using a heating / cooling compression tester (manufactured by Toho International Co., Ltd.), press molding was performed under the processing conditions of a temperature of 30 ° C., a load of 60 kN, and a press time of 120 seconds to obtain a 0.7 mm thick PLA sheet. .

<Evaluation>
About the obtained PLA sheet | seat, the elastic modulus E '[Pa] was measured by measuring a viscoelastic property using the dynamic viscoelasticity testing machine (DVE-V4, Rheology Co., Ltd. product). The measurement results are shown in FIG. Here, the elastic modulus E ′ at 80 ° C. was 7.00 × 10 ⁸ Pa.
In addition, elastic modulus E 'shows that it is excellent in heat resistance, so that a value is large.

(Examples 2 to 4)
In Example 1, the amounts of PLLA and PDLA were as follows: PLLA / PDLA = 80 parts / 20 parts (Example 2), PLLA / PDLA = 60 parts / 40 parts (Example 3), PLLA / PDLA = 30 parts / 70 A PLA sheet was produced in the same manner as in Example 1 except that the part was changed to the part (Example 4), and the elastic modulus was measured.

As a result of measuring the elastic modulus in the same manner as in Example 1, the drop in elastic modulus in the vicinity of 70 to 100 ° C. was suppressed in the same manner as in FIG. 1, and a high heat-resistant PLA sheet could be obtained. Here, the elastic modulus E ′ at 80 ° C. of the PLA sheet obtained in each example is 3.00 × 10 ⁸ Pa (Example 2), 9.00 × 10 ⁸ Pa (Example 3), 7 It was 0.000 × 10 ⁸ Pa (Example 4), and all exhibited good heat resistance.

(Example 5)
In Example 1, U'z-B0 (pellet-shaped PLLA) and PURASORB PD (fiber-shaped PDLA) were each made into fiber-shaped PLLA (mass average molecular weight: 200000, (2.2T, cut length: 51 mm), A PLA sheet was produced in the same manner as in Example 1 except that it was replaced with U'z-B0 (manufactured by Toyota Motor Corporation) and pellet-like PDLA (mass average molecular weight: 120,000, PURASORB PD manufactured by PURAC). Then, the elastic modulus was measured.
As a result of measuring the elastic modulus, the same result as in Example 1 was obtained.

(Example 6)
In Example 1, U'z-B0 (pellet-like PLLA) was replaced with fiber-shaped PLLA (mass average molecular weight: 200000, (2.2T, cut length: 51 mm), U'z manufactured by Toyota Motor Corporation. A PLA sheet was produced in the same manner as in Example 1 except that it was changed to -B0), and the elastic modulus was measured.
As a result of measuring the elastic modulus, the same result as in Example 1 was obtained.

(Comparative Example 1)
In Example 1, a PLA sheet was produced in the same manner as in Example 1 except that PURASORB PD (fiber-shaped PDLA) was not mixed and only 100 parts of U'z-B0 (PLLA) was used. The rate was measured.
The measurement results are shown in FIG. Further, the elastic modulus E ′ at 80 ° C. was 1.00 × 10 ⁷ Pa.

(Comparative Example 2)
In Example 1, the fiber-shaped PDLA [PURASORB PD (mass average molecular weight: 102,000) manufactured by PURAC] was replaced with pellet-shaped PDLA (mass average molecular weight: 120,000, PURASORB PD manufactured by PURAC). A PLA sheet was produced in the same manner as in Example 1 except that the elastic modulus was measured.
The measurement results are shown in FIG. Further, the elastic modulus E ′ at 80 ° C. was 3.00 × 10 ⁸ Pa.

  As shown in FIG. 1, compared to the case where only PLLA is used (Comparative Example 1) or the case where pellet-like PDLA is mixed and melt-kneaded (Comparative Example 2), the case where fiber-shaped PDLA is melt-kneaded in PLLA In the present invention, the drop in the elastic modulus in the vicinity of 70 to 100 ° C. (particularly in the vicinity of 80 ° C.) is remarkably suppressed, and the heat resistance can be effectively improved. In particular, high heat resistance was obtained when PLLA: PDLA = 70: 30 to 30:70 (Examples 1, 3, and 4).

It is a figure which shows the relationship between the heating temperature of polylactic acid, and elastic modulus E '.

Claims (2)

  A method for producing polylactic acid, comprising adding poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA) in a fiber state to at least one of said PLLA and PDLA and melt-kneading them.   The method for producing polylactic acid according to claim 1, wherein the melt-kneading is performed within a range of 170 to 190 ° C.

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