JP2007045915A - Polylactic acid resin composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve heat resistance and crystallinity of a polylactic acid resin and improve moldability of a stereo complex by partially forming the stereo complex in the polylactic acid resin and industrially readily obtain a highly heat-resistant and high-modulus molded product which has been impossible in a conventional polylactic acid thereby. <P>SOLUTION: The polylactic acid resin composition comprises 2.5-10.0 wt.% poly-D-lactic acid mainly composed of D-lactic acid and 90.0-97.5 wt.% poly-L-lactic acid mainly composed of L-lactic acid, wherein the part forms the stereo complex and the resin composition has at least 4% breaking elongation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polylactic acid resin composition having excellent moldability.

  Poly-L-lactic acid is a kind of biodegradable polymer, and the raw materials are manufactured from recyclable plant resources, food residues from daily life, waste paper, etc., and no petroleum resources are required, and waste is decomposed in nature. It is expected to play a major role in solving resources, energy, and environmental problems from the present to the future. In addition, when used for agricultural materials, etc., it is not necessary to collect after use, and when used for convenience store lunches or food packaging containers, the food is left as it is without being separated after use. It is possible to dispose of the material as a biodegradable resin of plant origin, and it is possible to rationalize the material cycle or logistics, which can greatly contribute to labor saving and energy saving. Even when used in a living body, the decomposition product becomes lactic acid, carbon dioxide and water which are harmless to the human body, and is therefore used for medical materials.

  However, poly-L-lactic acid is excellent in transparency like PS and PET resins, but has problems in terms of thermal properties, mechanical properties, and performance, such as low heat resistance, elongation, and impact properties. It has become a problem when trying to achieve this, and it cannot be said that it is still used sufficiently.

  In order to solve the disadvantages such as heat resistance, low impact resistance and poor moldability of poly L-lactic acid, a method of introducing an amide bond that forms a benzene ring or a hydrogen bond in the poly L-lactic acid skeleton, poly A method of blending L-lactic acid with other resins having excellent heat resistance and mechanical properties has been proposed.

  Lactic acid, which is a raw material for polylactic acid, has an optically active carbon atom in the molecule, and has optical isomers of L-lactic acid and D-lactic acid. Therefore, poly L-lactic acid (hereinafter referred to as PLLA), poly D-lactic acid (hereinafter referred to as PDLA), and copolymers thereof exist. Among these polylactic acids, those having a high ratio of L-lactic acid or D-lactic acid (high optical purity) have high crystallinity and excellent heat resistance and mechanical properties. On the other hand, a copolymer having a relatively high ratio of L-lactic acid in PDLA and a ratio of D-lactic acid in PLLA has low crystallinity or is amorphous, has low heat resistance, and low mechanical properties. When the amount of L-lactic acid in PDLA or D-lactic acid in PLLA usually exceeds 5%, the crystallinity is remarkably lowered, and when it exceeds 10%, it is said to be completely amorphous.

  However, when PDLA and PLLA that are optically active with each other have a certain regular structure, they have a new polylactic acid structure, and heat resistance and mechanical properties are much improved over PLLA and PDLA. This is called a stereo complex. Until now, various methods for forming a stereo complex have been studied. Among them, a method using a solution method (for example, Non-Patent Documents 1 and 2), a melting method for molding at a stereo complex melting point or higher (for example, Patent Documents 1, 2, 3, 4, 5) and the like have been proposed. .

Macromolecules, 20, 906 (1987) Macromolecules, 24, 5651 (1991). JP-A-61-36321 JP 63-24014 A JP 2000-17163 A JP 2002-356543 A JP 2003-238672-A

  However, the conventionally proposed methods and stereocomplex compositions or molded products do not have sufficient performance, or have extremely high hardness, poor melt flowability, poor moldability, and various practical use. A compact has not been obtained.

  The present inventors have intensively studied the above problems and have completed the present invention. That is, the object of the present invention is to improve the heat resistance and crystallinity of the polylactic acid resin and improve the moldability of the stereocomplex by partially forming a stereocomplex in the polylactic acid resin. According to the present invention, a high heat resistance and high elasticity molded body, which has been impossible with conventional polylactic acid, is easily obtained industrially.

The first of the present invention is 2.5 to 10.0% by weight of poly-D-lactic acid mainly composed of D-lactic acid and 90.0 to 97.5% by weight of poly-L-lactic acid mainly composed of L-lactic acid. And a part thereof forms a stereo complex, and is a polylactic acid resin composition having a breaking elongation of at least 4%.
The second of the present invention is 4.0 to 7.5% by weight of poly-D-lactic acid mainly containing D-lactic acid and 92.5 to 96.0% by weight of poly-L-lactic acid mainly containing L-lactic acid. The polylactic acid resin composition according to claim 1.
3rd of this invention is the polylactic acid resin composition of Claim 1 or 2 whose crystallization temperature at the time of temperature rising is 90-105 degreeC, and heat of fusion in 210-230 degreeC is at least 3 J / g. is there.

  According to the present invention, the conventional polylactic acid composition has a low heat resistance and a low crystallization rate, so that it was used only in relatively narrow applications, but the heat resistance is improved by a partially formed stereocomplex. In addition, it is possible to improve the strength and elastic modulus by the filler effect (molecular composite effect) of the stereo complex formed in the molecular order, or increase the molding speed and the stretching temperature and magnification by increasing the crystallization speed. The resulting molded product can be improved in physical properties and moldability, and a molded product that can be used in a wider range of applications and a molding method can be obtained.

Hereinafter, the present invention will be specifically described, but the present invention is not limited thereto. In the present specification, “parts” means “parts by weight” unless otherwise specified.
The poly L-lactic acid and poly D-lactic acid used in the present invention are, for example, L-lactic acid (HOCH (CH ₃ ) obtained from a plant raw material by fermentation as shown in JP-A-9-143253. COOH) or D-lactic acid can be obtained by direct condensation. Further, as disclosed in JP-A-7-208551, a cyclic dimer of lactic acid (D-lactide, L-lactide) obtained by thermally decomposing a low-molecular condensate of lactic acid (lactic acid oligomer) is opened. Similar polylactic acid resins (PDLA, PLLA) can be obtained by ring polymerization. The preferred molecular weight of polylactic acid is naturally determined by the purpose, application, required performance or molding method, but usually GPC (1, 1, 1, 3, 3, 3-hexafluoro-2-isopropanol solvent GPC ( In the gel permeation chromatography) measurement, the number average molecular weight (Mn) is at least 50,000 (in terms of polystyrene), preferably at least 100,000, more preferably 120,000 to 500,000. In addition, in polylactic acid, a weight average molecular weight is 1.1-5xMn normally, Preferably it is 1.1-3xMn. However, in special applications (for example, foaming applications, blown film applications, etc.), it can be used sufficiently outside this range.

  Regarding the polylactic acid composition, 2.5 to 10.0% by weight of poly-D-lactic acid (PDLA) mainly containing D-lactic acid and 90.0 to 97. 9% poly-L-lactic acid (PLLA) mainly containing L-lactic acid. 5% by weight, preferably poly-D-lactic acid (PDLA) mainly composed of D-lactic acid (4.0 to 7.5% by weight) and poly-L-lactic acid mainly composed of L-lactic acid (PLLA) 92.5 Of poly-L-lactic acid mainly composed of D-lactic acid and 5.0-7.0% by weight of poly-D-lactic acid mainly composed of D-lactic acid and 93.0 to 95-poly L-lactic acid mainly composed of L-lactic acid. 0.0% by weight. When the PDLA is less than 2.5% by weight, the physical properties and moldability of the polylactic acid resin are not sufficiently improved. On the other hand, when the PDLA exceeds 10.0% by weight, the stereocomplex portion is increased, and conversely, the moldability is deteriorated and the physical properties are decreased. There is a decline.

  The poly-D-lactic acid (PDLA) mainly composed of D-lactic acid refers to polylactic acid having a D-lactic acid content of at least 96% by weight, preferably 98% by weight or more, and more preferably 99% by weight or more. Further, poly-L-lactic acid (PLLA) mainly composed of L-lactic acid means polylactic acid containing L-lactic acid of at least 96% by weight, preferably 98% by weight or more, and more preferably 99% by weight or more. If it is less than 96% by weight, the crystallinity of PDLA or PLLA is not sufficient, respectively, and the heat resistance and mechanical properties of the molded product deteriorate. Components other than D-lactic acid or L-lactic acid may be L-lactic acid or D-lactic acid, and other components that can be polymerized into lactic acid (for example, a divalent or higher valent alcohol compound or a divalent or higher carboxylic acid compound, Alternatively, it is a compound capable of ring-opening polymerization (for example, cyclic lactone, cyclic ether, cyclic lactam, etc.).

  The polylactic acid resin composition of the present invention has a breaking elongation of at least 4%, preferably at least 10%, more preferably 15-30%. The conventional polylactic acid resin or stereocomplex resin has a breaking elongation of at most 3%, and as a result, is poor in moldability and impact strength. The reason for the improvement in the elongation at break according to the present invention is not completely understood, but is presumed as follows. For example, because PLLA alone has a very simple molecular structure, there is almost no interaction between molecular chains (for example, hydrogen bond, π-π electron interaction, ionic bond, etc.), and the external force applied to PLLA is PLLA It concentrates on the weakest part of the molecule and the molecule breaks. When this happens, the external force causes the next molecule to break, and further induces the next molecule to break. Thus, a mere single molecule break leads to the entire material breaking. However, in the present invention, the elongation at break is surprisingly extremely large due to the presence of the PLLA / PDLA stereocomplex in PLLA, although only a few percent. The reason for this is not clear, but the PLLA / PDLA stereocomplex is formed in a very small order, preferably a width or diameter of at most about 10 μm, more preferably a width or diameter of at most about 1 μm, particularly preferably at most 0.1 μm. It is formed with a region having a certain width or diameter. Ultimately, a molecular complex composed of PLLA1 molecule and PDLA1 molecule (molecular stereocomposite) is formed, so that the stereocomplex region reinforces other PLLA regions. It is considered that the degree of freedom of deformation has increased in order to prevent stress concentration in the course of breaking, resulting in a higher elongation at break. In order to efficiently form a stereo complex and form it in as small an area as possible for reinforcement, there is a flow of resin in a certain direction like a biaxial extruder, and both resins can be mixed in a very small order. The technique is preferred. Alternatively, it is also preferable that PLLA and PDLA are melted in separate melt extruders, flowed at a predetermined flow rate, and merged by mixing them in a polymer tube. At this time, the stereo complex formation efficiency is further improved by using a static kneading element. The effect of the static kneading element is not only to efficiently form a stereo complex, but also the size and amount of the formed stereo complex can be arbitrarily controlled, and the formed stereo complex can be elongated and in a certain direction. It is a point to be oriented. For this purpose, for example, the preferred one can be taken depending on the use of stretching or deformation in a certain method such as film or fiber.

  The determination of the presence or absence of the stereo complex is, for example, when the composition is measured by DSC during the temperature rising process, crystallization exotherm is observed at a lower temperature (Tc1) than the crystallization temperature (Tc) of normal PLLA or PDLA, Further, it can be easily judged from the fact that a new melting point (Tm1) is shown at a temperature higher than the melting point (Tm) of PLLA or PDLA. The heat of fusion (ΔHm1) at the melting point (Tm1) is proportional to the amount of PDLA in PLLA or the amount of PLLA in PDLA. This makes it possible to quantify the amount of stereo complex in PLLA or the amount of stereo complex in PDLA.

  The polylactic acid resin composition of the present invention is characterized in that it forms a stereocomplex even in a solution state, as a matter of course in a solid state. For example, the GPC curve (dashed line) shown in FIG. 2 shows the PLLA resin composition in which a small amount of PDLA is blended in PLLA to form a stereo complex in part, 1, 1, 1, 3, 3, 3- This was dissolved in a hexafluoro-2-isopropanol solution and measured by GPC. What can be seen here is a component with a short retention time and a component with a long retention time in addition to the original (solid line) molecular weight distribution. This indicates that PLLA and PDLA form a stereocomplex with part of the molecular structure. That is, the component with a short retention time has a substantially long molecular weight, and it seems that the molecular weight is increased because PLLA and PDLA form a stereo complex with a part of the molecule. On the other hand, components with a long retention time indicate that the molecular weight is short in general GPC interpretation, but in this case, the molecular weight is not shortened, and the stereocomplex of PLLA and PDLA is generated over almost the entire molecule. Further, the solubility of the produced stereocomplex in the solvent is lowered (that is, the molecular spread is reduced), and as a result, a peak appears where the retention time is long.

  Due to the formation of the above two stereocomplexes, the material has excellent molding due to the presence of the partial stereocomplex that improves the elongation of the material with excellent affinity between PLLA and the complete stereocomplex part as a filler that enhances the properties of the material. The strength and physical properties were confirmed, and the strength comparable to that of a normal poly L-lactic acid molded product could be maintained. In particular, the peak area on the high molecular weight side is preferably 45 to 60%, more preferably at least 48 to 53% with respect to the total area. If it is less than 45%, the moldability may be somewhat lowered, and if it is more than 60%, the mechanical properties may be lowered. The low molecular weight side is preferably 40 to 55%, more preferably 47 to 52%. If it is less than 40%, the reinforcing effect may not be sufficient, and if it is greater than 55%, the reinforcing effect may be sufficient even if the reinforcing effect is sufficient.

  In the present invention, the crystallization temperature at the time of temperature rise is preferably 90 to 105 ° C, more preferably 95 to 100 ° C, and the heat of fusion at 210 to 230 ° C is preferably at least 3 J / g, more preferably Is 5-18 J / g. When the crystallization temperature is lower than 90 ° C, the molding cycle becomes short, but it may be difficult to control the crystallinity during molding. For example, the physical properties may change from batch to batch, or the crystal may vary depending on the part or part of the molded product. Or the transparency, gloss, or distortion due to the difference in crystallinity. On the other hand, when the temperature is higher than 105 ° C., the mold temperature may be increased or the time may be lengthened for complete crystallization, resulting in lower productivity. On the other hand, if the heat of fusion is less than 3 J / g, the crystallinity is low, so cooling takes time and the molding cycle tends to be long.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Unless otherwise specified, “%” or “part” in the examples represents “% by weight” or “part by weight”.

(Experimental example 1)
As PLLA, PLLA having a weight average molecular weight of 200,000 and an optical purity of 99% was used. As PDLA, PDLA manufactured by PURAC having a weight average molecular weight of 400,000 and an optical purity of 99% was used. This PLLA / PDLA was dry blended at 100/0, 95/5, 90/10, 75/25 (weight ratio), and melt blended at 200 ° C. for 5 minutes in a twin-screw kneader. The strand at the outlet of the melt kneader has a diameter of about 3 mm. Transparent strands were obtained with 100% PLLA, but there was some haze for those with PDLA of 5, 10 and 25%, and it can be seen that a stereo complex has already been formed at this point. The obtained strand is cut into a length of 3 to 5 mm with a pelletizer to obtain pellets. The pellet was immediately hot-pressed at 200 ° C. under a pressure of 30 MPa for 3 minutes, and then rapidly cooled to prepare a 1 mm thick sheet.

For physical property evaluation, a test piece using a punched dumbbell shape (JIS No. 2 piece) was used. The tensile strength is JIS K 7161, AUTOGRAPH made by Shimadzu Corporation
Measured at 5000. The thermal properties were measured with a RIGAKU DSC8230 manufactured by Rigaku Corporation. The ratio of the stereo complex was calculated from the ratio of the heat of fusion of poly L-lactic acid and poly D-lactic acid homopolymer to the heat of fusion of stereo complex. GPC measurement is JASCO
ENGINEERING RI-930 detector, pump 880-PU, Tosoh TOSOH-TSKGEL GMHHr-M, 1, 1, 1, 3, 3, 3-hexafluoro-2 -Isopropanol was used as the fluid phase. FIG. 1 shows the SS curve of the tensile test. Table 1 shows the results. A very characteristic result was shown between the ratio of the stereo complex and the tensile properties. That is, when the percentage of PDLA is 0% or 20% or more, the elongation at break in the tensile test is about 5% or less, but when the amount of PDLA is 2.5 to 10%, the elongation at break is 10%. Characteristically larger. The elongation at break depends on how uniformly the polymer molecular chain can disperse the external force with respect to the external force. It can be seen that when the amount of PDLA is less than 2.5%, the structure is almost similar to PLLA, and therefore, the external force is less likely to disperse and deal with such external forces, and is very easily broken. The stereocomplex is a stereocomplex composed of PLLA / PDLA double strands, has high molecular rigidity, and is easily crystallized. For this reason, it is considered that it functions as a reinforcing material on the molecular order or as a crystal nucleating agent in PLLA. On the other hand, when the amount of PDLA is 20% or more, the amount of stereocomplex is too large to be easily deformed, and stress concentration is likely to occur in a place weak against external force, so that it may be easily broken. Accordingly, in order to combine good physical properties and moldability, the amount of PDLA in PLLA is suitably 2.5 to 10%.

In the table, T is transparent, H is opaque, and TH is intermediate.

(Experimental example 2)
A stretching test was conducted using the sheet sample of Experimental Example 1. The stretching sample used was a JIS No. 2 dumbbell punched out with a hot cutter. The dumbbell test piece was hand-drawn and stretched in a stretching bath at a temperature shown in Table 2 by a stretching machine. When the amount of PDLA is less than 2.5 to 10%, when the stretching temperature is 110 ° C. or higher, the sample is softened and hardly stretched. On the other hand, if it exceeds 10%, it becomes hard and hardly stretched. When the amount of PDLA is 2.5% or more, a sufficient temperature is applied at the time of stretching, and uniform stretching is possible even at a wide range of stretching ratios, resulting in high strength, high elasticity, and high productivity.

  As an application of the present invention, the heat resistance and molding cycle can be improved particularly in the ordinary polylactic acid field, and the industrial value is great. Conventionally known PLLA / PDLA stereocomplexes can hardly be molded, and the physical properties of the molded body are very brittle, which is a serious problem in practical use. This proposal makes it possible to remarkably expand the uses of polylactic acid resin by achieving both formability and heat resistance, and thus the industrial value becomes extremely high. The proposed molded product can be applied to various fields such as normal injection molding, extrusion molding, inflation molding, fiber manufacturing, fine particle manufacturing, coating materials and adhesives fields, greatly changing molding conditions and equipment specifications. It is possible to implement without.

FIG. 1 shows a sheet (2) obtained from the resin composition of the present invention, a sheet (1) obtained from PLLA as a control, and a sheet (3) obtained from PLLA / PDLA (50/50) stereocomplex. It is a stress-strain curve in a tensile test. The horizontal axis indicates the elongation (%) of the sheet, and the vertical axis indicates the stress applied to the sheet. In the curves (2) and (3), the origin is shifted in the positive direction of the horizontal axis. FIG. 2 shows the GPC curves of the resin composition (broken line) and PLLA (solid line) of the present invention. The horizontal axis represents the molecular weight expressed from the retention time, and the vertical axis represents the ratio of the molecular weight. The resin composition of the present invention comprises a high molecular weight side component (I in the figure) and a low molecular weight side component (II in the figure), and the amount of each component is the ratio of the area to the total area. Is required.

Claims (3)

  It consists of 2.5 to 10.0% by weight of poly-D-lactic acid mainly composed of D-lactic acid and 90.0 to 97.5% by weight of poly-L-lactic acid mainly composed of L-lactic acid, part of which is stereo. A polylactic acid resin composition forming a complex and having a breaking elongation of at least 4%.   The poly according to claim 1, comprising 4.0 to 7.5% by weight of poly-D-lactic acid mainly composed of D-lactic acid and 92.5 to 96.0% by weight of poly-L-lactic acid mainly composed of L-lactic acid. Lactic acid resin composition. The polylactic acid resin composition according to claim 1 or 2, wherein the crystallization temperature at the time of temperature rise is 90 to 105 ° C and the heat of fusion at 210 to 230 ° C is at least 3 J / g.