Impact-resistance improver

Abstract

To provide a new technique for improving impact resistance of a polylactic acid.SOLUTION: An impact-resistance improver for improving impact resistance of a polylactic acid contains a copolyester of a lactic acid and other hydroxycarboxylic acid. The other hydroxycarboxylic acid is preferably a 3-hydroxyalkanoic acid. The copolyester is preferably a random copolymer of a lactic acid and other hydroxycarboxylic acid. A resin composition contains a polylactic acid, and the impact-resistance improver.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an impact modifier for improving the impact resistance of polylactic acid, and to uses thereof. [Background technology]

[0002] Because plastics are difficult to decompose in the natural environment, environmental pollution caused by mass disposal has become a serious problem. To address this issue, efforts are being made to put biodegradable plastics into practical use, which are plastics that can be decomposed into water and carbon dioxide by the action of microorganisms.

[0003] Polylactic acid, a representative biodegradable plastic, is a type of biopolymer that can be synthesized from biomass-derived raw materials. Because it has relatively high rigidity, strength, and transparency, it is being used in a wide range of applications as an alternative to petroleum-derived plastics.

[0004] However, polylactic acid tends to have poorer impact resistance than other molding resins, and therefore the use of additives to improve the impact resistance of polylactic acid has been investigated. For example, Patent Document 1 discloses the use of polybutylene adipate terephthalate resin, amorphous polyhydroxyalkanoate, and the like as an impact resistance improver for polylactic acid.

[0005] On the other hand, Patent Document 2 does not mention improving the impact resistance of polylactic acid, but discloses that by blending polylactic acid with a copolymer polyester of lactic acid and another hydroxycarboxylic acid, polylactic acid can be plasticized without substantially decreasing the transparency of the polylactic acid. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2023-050467 A [Patent Document 2] International Publication No. 2020 / 066679 Summary of the Invention [Problem to be solved by the invention]

[0007] Although Patent Document 1 discloses a technology for improving the impact resistance of polylactic acid, the effect is not sufficient, and there is a concern that the transparency and mechanical properties of polylactic acid may be impaired because a substance with a chemical structure significantly different from that of polylactic acid is mixed into polylactic acid.

[0008] An object of the present invention is to provide a novel technique for improving the impact resistance of polylactic acid. [Means for solving the problem]

[0009] The present inventors have found that a copolymer polyester of lactic acid with another hydroxycarboxylic acid can improve the impact resistance of polylactic acid, and have arrived at the present invention.

[0010] That is, the present invention relates to an impact modifier for improving the impact resistance of polylactic acid, which comprises a copolymer polyester of lactic acid with another hydroxycarboxylic acid. The present invention also relates to a resin composition containing polylactic acid and the impact modifier. The present invention further relates to a molded article obtained by molding the resin composition. Furthermore, the present invention also relates to a method for improving the impact resistance of polylactic acid, which comprises mixing a copolymer polyester of lactic acid and another hydroxycarboxylic acid with polylactic acid. Furthermore, the present invention also relates to the use of a copolymerized polyester of lactic acid and another hydroxycarboxylic acid as an impact modifier for improving the impact resistance of polylactic acid. Effect of the Invention

[0011] The present invention can provide a novel technique for improving the impact resistance of polylactic acid. According to a preferred embodiment, the impact resistance of polylactic acid can be improved without decreasing the biomass content of the polylactic acid. According to a preferred embodiment of the present invention, the impact resistance of polylactic acid can be improved without substantially decreasing the transparency of polylactic acid. Furthermore, it is possible to plasticize polylactic acid and improve its elongation. [Brief description of the drawings]

[0012] [Figure 1] Photograph of the fracture surface observed with a scanning electron microscope when the test piece used in the Charpy impact test evaluation of Example 3 was frozen and fractured. [Diagram 2] A photograph of the fracture surface of the test piece used in the Charpy impact test evaluation of Comparative Example 1, which was frozen and then broken, observed with a scanning electron microscope. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described in detail. The impact resistance modifier according to the present embodiment is an additive for improving the impact resistance of polylactic acid by mixing with the polylactic acid. The impact resistance modifier contains at least a copolymer polyester of lactic acid and another hydroxycarboxylic acid.

[0014] (Polylactic acid) Polylactic acid is a polyester having lactic acid as a constituent monomer. As mentioned above, polylactic acid is known to have insufficient impact resistance. However, by using the impact resistance improver according to the present embodiment, the impact resistance of a molded article made of polylactic acid can be improved.

[0015] The polylactic acid may be any conventionally known polylactic acid, and may be either crystalline or amorphous. The polylactic acid is preferably a homopolymer of lactic acid, but may contain a small amount of other monomers in addition to lactic acid.

[0016] The lactic acid constituting the polylactic acid may be either the L-form or the D-form, or may contain both. In the latter case, the ratio of the L-form to the D-form is not particularly limited. The polylactic acid may be any one of poly(L-lactic acid) resin, poly(D-lactic acid) resin, and poly(DL-lactic acid) resin, or may be a blend of these.

[0017] Examples of the other monomers that may be contained in the polylactic acid include aliphatic hydroxycarboxylic acids other than lactic acid, aliphatic polyhydric alcohols, aliphatic polycarboxylic acids, and polyfunctional polysaccharides. When polylactic acid is a copolymer of lactic acid and other monomers, from the viewpoint of the crystallinity of polylactic acid, the content of the other monomers is preferably about 0 to 3 mol %, more preferably 0 to 2 mol %, based on the total monomers contained in polylactic acid.

[0018] The lactic acid raw material for producing polylactic acid is not particularly limited, and can be L-lactic acid, D-lactic acid, DL-lactic acid, or a mixture thereof, or L-lactide, D-lactide, meso-lactide, or a mixture thereof, etc. Lactic acid obtained by microbial fermentation from renewable raw materials derived from plants such as starch can be suitably used. The method for producing polylactic acid is not particularly limited, and any known method such as dehydration condensation polymerization or ring-opening polymerization can be used.

[0019] The molecular weight of the polylactic acid is not particularly limited and may be appropriately set depending on the application, but the number average molecular weight is preferably 1,000 to 700,000, and more preferably 10,000 to 300,000.

[0020] (copolyester) The impact resistance improver according to the present embodiment contains a copolymer polyester of lactic acid and another hydroxycarboxylic acid as an effective component for improving impact resistance. By mixing the copolymer polyester with polylactic acid, the impact resistance of the polylactic acid itself can be improved.

[0021] In addition, since the copolyester is a polyester containing lactic acid as one of the constituent monomers, it has good compatibility with polylactic acid and can form a homogeneous mixture with polylactic acid. As a result, it is possible to avoid a substantial decrease in the transparency of polylactic acid. In addition, it is possible to plasticize polylactic acid and improve the elongation of polylactic acid.

[0022] In addition, since the copolymer polyester is a polyester containing a hydroxycarboxylic acid other than lactic acid as one of the constituent monomers, it undergoes phase separation from polylactic acid, but as described above, it also has compatibility with polylactic acid. As a result, the copolymer polyester is very finely dispersed in the polylactic acid matrix, and can form a sea-island structure in which the hydroxycarboxylic acid polymer other than lactic acid is the island and the polylactic acid is the sea. When the impact resistance of a polymer is to be improved, polymer blending is a commonly used technique, but controlling the compatibility and miscibility between the blended polymers to form a microphase-separated structure such as the resin composition according to this embodiment is effective in expressing impact resistance.

[0023] The copolyester itself is a polymer material that is biodegradable. Since bacteria that degrade copolymers of lactic acid and 3-hydroxybutyric acid have been isolated from the environment (see Polymer Degradation and Stability, 2014, 110, 44 and Applied Microbiology and Biotechnology, 2015, 99, 9555), it is expected that the copolyester will be highly biodegradable in the environment. In addition, when an enzyme secreted by the isolated copolyester biodegrading bacteria was isolated, it was found that it degrades poly-D-lactic acid, an oligomer of 31 or less.

[0024] The copolyester may be any of a random copolymer, an alternating copolymer, a block copolymer, and a graft copolymer. However, from the viewpoints of impact resistance improvement effect, transparency, mechanical properties, and availability, the copolyester is preferably a random copolymer. A random copolymer refers to a copolymer in which two or more types of monomer units are arranged in a random order. When the copolyester is produced by a microorganism, it is usually a random copolymer.

[0025] The lactic acid monomer unit in the polyester copolymer may be either an L-lactic acid monomer unit or a D-lactic acid monomer unit, or may contain either one of them or both.

[0026] When the copolyester is produced by a microorganism, the lactic acid monomer units in the copolyester are substantially composed of D-lactic acid monomer units. "Substantially composed of D-lactic acid monomer units" means that the proportion of D-lactic acid monomer units in the total amount of lactic acid monomer units is usually 90% or more, preferably 95% or more, more preferably 99% or more.

[0027] The hydroxycarboxylic acid other than lactic acid contained in the polyester copolymer is not particularly limited as long as it is a hydroxyalkanoic acid that can be copolymerized with lactic acid. The number of carbon atoms in the hydroxyalkanoic acid is preferably 3 or more. The upper limit of the number of carbon atoms is preferably 15 or less, more preferably 10 or less, even more preferably 8 or less, even more preferably 6 or less, and particularly preferably 5 or less.

[0028] Examples of hydroxyalkanoic acids include 2-hydroxyalkanoic acids, 3-hydroxyalkanoic acids, and 4-hydroxyalkanoic acids, with 3-hydroxyalkanoic acids being particularly preferred. Specific examples of 3-hydroxyalkanoic acid include 3-hydroxybutanoic acid (hereinafter sometimes abbreviated as 3HB), 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxypentadecanoic acid, and 3-hydroxyhexadecanoic acid. Only one of these may be contained in the copolymer polyester, or two or more may be contained. Among these, it is preferable that at least 3HB is contained. In particular, P(LA-co-3HB) (hereinafter sometimes abbreviated as LAHB), which is a copolymer polyester of lactic acid and 3HB, is the most preferable as the copolymer polyester.

[0029] The ratio of lactic acid units contained in the copolymer polyester is not particularly limited. However, since the effect of improving the impact resistance of polylactic acid is high, the molar fraction of lactic acid units relative to the total monomer units constituting the copolymer polyester is preferably 5 to 70 mol%, more preferably 10 to 60 mol%, and even more preferably 15 to 50 mol%. The value of the molar fraction of lactic acid units can be determined using HPLC. Alternatively, it can be determined using NMR or GC.

[0030] The molecular weight of the copolymer polyester is not particularly limited, but the weight average molecular weight Mw may be, for example, 10,000 to 1,000,000, and is preferably 10,000 to 500,000. The lower limit of the weight average molecular weight is preferably 50,000 or more, more preferably 100,000 or more, and even more preferably 200,000 or more. The value of the weight average molecular weight can be determined based on standard polystyrene using gel permeation chromatography (GPC) (manufactured by Shimadzu Corporation) equipped with a tandem TSKgel Super HZM-H column (manufactured by Tosoh Corporation).

[0031] Copolymer polyesters of lactic acid and other hydroxycarboxylic acids can be produced using organic resources (biomass) derived from living organisms other than fossil fuels, and can be manufactured from 100% biomass-derived raw materials.

[0032] The method for producing the copolymer polyester of lactic acid and other hydroxycarboxylic acid is not particularly limited and may be a conventionally known method. It may be biosynthesized by a microorganism or may be produced by chemical synthesis. In particular, an example of a method for producing P(LA-co-3HB) is a production method using a recombinant microorganism as described in WO 2009 / 131186 and WO 2006 / 126796.

[0033] The impact resistance improver according to the present embodiment may be composed only of a copolymerized polyester of lactic acid and another hydroxycarboxylic acid, or may contain components other than the copolymerized polyester. Examples of such other components include known resin additives, specifically, plasticizers, hydrolysis inhibitors, compatibilizers, antioxidants, UV absorbers, processing aids, antistatic agents, colorants, crystal nucleating agents, inorganic or organic particles, lubricants, release agents, water repellents, inorganic fillers, mildew inhibitors, antibacterial agents, foaming agents, flame retardants, etc.

[0034] The content of the copolymerized polyester in the impact resistance improver is not particularly limited, but may be, for example, 10 to 100% by weight. The lower limit may be 30% by weight or more, 50% by weight or more, 70% by weight or more, 90% by weight or more, or 99% by weight or more.

[0035] (Usage) By mixing the impact modifier according to this embodiment with polylactic acid, it is possible to obtain an effect of improving the impact resistance of polylactic acid. It is preferable to mix the impact modifier and polylactic acid uniformly, and it is particularly preferable to mix both components uniformly, for example, by melt kneading, mixing in an organic solvent and then removing the solvent.

[0036] (Amount used) The amount of the impact modifier according to the present embodiment may be any amount that can improve the impact resistance of polylactic acid by using the impact modifier. From the viewpoint of the balance between the impact resistance improving effect and the transparency and mechanical properties of polylactic acid, it is preferable to use the impact modifier in an amount such that the amount of copolymerized polyester, which is the active ingredient of the impact modifier, is 0.1 parts by weight or more and 10 parts by weight or less per 100 parts by weight of polylactic acid. The lower limit is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, even more preferably 2 parts by weight or more, and particularly preferably 3 parts by weight or more. The upper limit is preferably 8 parts by weight or less, more preferably 7 parts by weight or less, even more preferably 6 parts by weight or less, even more preferably 5 parts by weight or less, and particularly preferably 4 parts by weight or less.

[0037] (Resin composition) One aspect of the present invention may be a resin composition containing polylactic acid and the impact modifier. Since the impact resistance of the polylactic acid is improved by the incorporation of the impact modifier, the resin composition may exhibit good impact resistance.

[0038] (Other ingredients) The resin composition may contain a thermoplastic resin other than polylactic acid and the copolymer polyester. Such other thermoplastic resin is not particularly limited, and a conventionally known resin may be used. Specifically, biodegradable aliphatic polyesters other than polylactic acid and the copolymer polyester, aromatic polyesters, etc. may be used.

[0039] The amount of the other thermoplastic resin is not particularly limited, but may be, for example, 0 to 200 parts by weight relative to 100 parts by weight of polylactic acid. The upper limit may be 100 parts by weight or less, 50 parts by weight or less, 30 parts by weight or less, or 10 parts by weight or less.

[0040] In addition, resins that are poorly compatible with polylactic acid may deteriorate the transparency of polylactic acid, so it is preferable not to add them or to add them in a small amount when they are added. Although not particularly limited, for example, the amount of polyhydroxyalkanoate resin, which is one of the resins that are poorly compatible with polylactic acid, is preferably about 0 to 100 parts by weight, more preferably about 0 to 50 parts by weight, relative to 100 parts by weight of polylactic acid.

[0041] The resin composition may contain other additives as appropriate within the scope of not impairing the effects of the invention. Such additives are not particularly limited, but examples thereof include plasticizers, hydrolysis inhibitors, compatibilizers, antioxidants, UV absorbers, processing aids, antistatic agents, colorants, crystal nucleating agents, inorganic or organic particles, lubricants, release agents, water repellents, inorganic fillers, antifungal agents, antibacterial agents, foaming agents, and flame retardants. The content of each additive can be appropriately determined depending on the purpose. In addition, only one type of additive may be blended, or two or more types may be blended.

[0042] As the plasticizer, any plasticizer generally used as a plasticizer for polymers can be used. Specific examples of the plasticizer include polyester-based plasticizers, glycerin-based plasticizers, polycarboxylic acid ester-based plasticizers, polyalkylene glycol-based plasticizers, and epoxy-based plasticizers.

[0043] (Application) The resin composition can be prepared by melt-kneading each component, extruding the molten resin into a strand shape, cutting it, and forming it into pellets. The pellets obtained can be dried to remove moisture, and then molded by a known molding method to obtain any molded product. Such a molded product also constitutes one aspect of the present invention. Examples of the molding method include film molding, sheet molding, injection molding, blow molding, fiber spinning, extrusion foaming, and bead foaming.

[0044] The method for producing the film molded body is not particularly limited, but examples thereof include T-die extrusion molding, calendar molding, roll molding, and inflation molding. The obtained film can also be thermoformed by heating, vacuum molded, and press molded.

[0045] As a method for producing an injection molded article, for example, injection molding methods generally used when molding a thermoplastic resin, such as injection molding, gas-assisted molding, and injection compression molding, can be used. In addition, in addition to the above-mentioned methods, in-mold molding, gas press molding, two-color molding, sandwich molding, PUSH-PULL, SCORIM, and the like can also be used according to other purposes. However, the injection molding method is not limited to these.

[0046] The resin composition may be processed into pellets, or into a molded article in the form of a film, sheet, fiber, or the like, using an extrusion molding machine, or it can also be processed into a molded article of a predetermined shape by injection molding.

[0047] When the resin composition contains a foaming agent, the molded article may be a foamable molded article, or may be a molded foam obtained by foaming the foamable molded article.

[0048] The resin composition can be processed into molded articles of various shapes. Examples of the molded articles include paper, film, sheet, tube, plate, rod, container, bag, parts, etc. The molded article can also be compounded with other molded articles (e.g., fiber, thread, rope, woven fabric, knitted fabric, nonwoven fabric, paper, film, sheet, tube, plate, rod, container, bag, part, foam, etc.) made of a material different from the resin composition according to the present embodiment.

[0049] The applications of the molded articles are not particularly limited, and they can be suitably used in the fields of agriculture, fisheries, forestry, horticulture, medicine, sanitary products, clothing, non-clothing, packaging, automobiles, building materials, and others.

[0050] The following items enumerate preferred aspects of the present disclosure, but the present invention is not limited to the following items. [Item 1] An impact resistance modifier for improving the impact resistance of polylactic acid, which comprises a copolymer polyester of lactic acid and another hydroxycarboxylic acid. [Item 2] 2. The impact modifier according to claim 1, wherein the other hydroxycarboxylic acid is a 3-hydroxyalkanoic acid. [Item 3] 3. The impact modifier according to item 1 or 2, wherein the other hydroxycarboxylic acid is at least one selected from the group consisting of 3-hydroxybutanoic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxypentadecanoic acid, and 3-hydroxyhexadecanoic acid. [Item 4] 4. The impact modifier according to any one of items 1 to 3, wherein the other hydroxycarboxylic acid is 3-hydroxybutanoic acid. [Item 5] 5. The impact modifier according to any one of items 1 to 4, wherein the copolyester is a random copolymer of lactic acid and another hydroxycarboxylic acid. [Item 6] 6. The impact modifier according to any one of items 1 to 5, wherein the lactic acid monomer of the copolyester is a D-lactic acid monomer. [Item 7] 7. The impact modifier according to any one of items 1 to 6, wherein the molar fraction of lactic acid units in the copolymer polyester is 5 to 70 mol %. [Item 8] 8. The impact resistance improver according to any one of items 1 to 7, wherein the copolymer polyester has a weight average molecular weight of 10,000 to 1,000,000. [Item 9] A resin composition comprising polylactic acid and the impact modifier according to any one of items 1 to 8. [Item 10] Item 10. The resin composition according to item 9, wherein the amount of the copolyester is 0.1 to 8 parts by weight based on 100 parts by weight of the polylactic acid. [Item 11] 11. A molded article obtained by molding the resin composition according to item 9 or 10. [Item 12] A method for improving the impact resistance of polylactic acid, which comprises contacting the polylactic acid with a copolymer polyester of lactic acid and another hydroxycarboxylic acid. [Item 13] Use of a copolymer polyester of lactic acid with another hydroxycarboxylic acid as an impact modifier for improving the impact resistance of polylactic acid. EXAMPLES

[0051] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. The overall genetic manipulation can be carried out, for example, as described in Molecular Cloning (Cold Spring Harbor Laboratory Press (1989)). Enzymes, cloning hosts, and the like used in the genetic manipulation can be purchased from commercial suppliers and used according to their instructions. The enzymes are not particularly limited as long as they can be used in genetic manipulation.

[0052] [Breeding of hydrogen-producing bacteria producing copolymer polyester (LAHB)] Cupriavidus necator H16 strain was genetically modified to express the PHA polymerase gene phaC 1Re was replaced with another PHA polymerase gene, and the PHA decomposition enzyme gene phaZ 1,2,6 In order to enhance glucose utilization, the 793rd base of the N-acetylglucosamine uptake gene nagE was replaced with a G to C, and the nagR gene encoding a transcription factor was also disrupted. 1,2,6 / nagE G793C.dR strain (see International Publication No. 2017 / 104722) was prepared.

[0053] Furthermore, the KNK005ΔphaZ 1,2,6 The PHA polymerase gene phaC on the genome of the / nagE G793C.dR strain 1Re The STQK mutant (Pseudomonas sp. 61-3 derived polymerase PhaC1 Ps H16 phaC (PHA synthase) in which the 325th serine was converted to threonine and the 481st glutamine was converted to lysine 1Re ::STQK ΔphaZ 1,2,6 / nagE G793C.dR was prepared and used as the host (1).

[0054] (Preparation of plasmid for gene disruption) PCR was performed using the genomic DNA of C. necator H16 strain as a template and the oligo DNAs shown in SEQ ID NO: 1 and SEQ ID NO: 2 as primers. Prime STAR GXL DNA polymerase (Takara Bio) was used as the DNA polymerase. Similarly, PCR was performed using the DNAs shown in SEQ ID NO: 3 and SEQ ID NO: 4 as primers. Overlap PCR was performed using the two DNA fragments obtained by the above PCR as templates and the DNAs shown in SEQ ID NO: 3 and SEQ ID NO: 4 as primers. The obtained DNA fragment is a fragment in which about 500 base pairs upstream and about 500 base pairs downstream of the ORF of acetyl-CoA acetyltransferase (Locus tag: H16_A1438) are linked. This DNA fragment was treated with the restriction enzyme SmiI and ligated with the vector pNS2X-sacB (described in JP 2007-259708 A) that had also been treated with SmiI using DNA ligase. The obtained gene disruption plasmid containing the base sequence shown in SEQ ID NO: 5 was named pNS2X-sacB-ΔphaA. This gene disruption plasmid is a plasmid used to disrupt the gene phaA:A1438 that codes for acetyl-CoA acetyltransferase.

[0055] (Preparation of plasmid for gene introduction) A plasmid was constructed to introduce the genes required for LAHB production into the genome of C. necator. The genes were inserted into the genome of host (1) under the REP promoter, replacing the ORF of phaJ4b (Locus tag: H16_B0397) on the genome of host (1). Lm pNS2X-sacB-phaJ4b::REP-LDH, which can be used to introduce a gene sequence that expresses Lm This plasmid was prepared by inserting the DNA fragment represented by SEQ ID NO:6 into the pNS-sacB vector by ligation. By using this plasmid, it is possible to impart the ability to produce D-lactic acid from glucose to C. necator. This plasmid is designated as gene introduction plasmid (1).

[0056] Similarly, the propionyl-CoA transferase PCR product from Epulopiscium sp. was expressed under the lacN17 promoter, replacing the ORF of phaJ4a (Locus tag: H16_A1070) on the genome of the host (1). Es pNS2X-sacB-phaJ4a::lacN17-PCT, which can be used to introduce a gene sequence that expresses Es was prepared. This plasmid was prepared by inserting the DNA fragment represented by SEQ ID NO: 7 into the pNS-sacB vector by ligation. By using this plasmid, it becomes possible to add CoA to lactic acid produced from glucose to supply a substrate for polyester copolymerization enzyme. This plasmid is designated as gene introduction plasmid (2).

[0057] (Genetic modification of C. necator by homologous recombination) The gene disruption plasmid or the gene introduction plasmid was introduced into Escherichia coli S17-1 strain (ATCC47055) by electroporation, and the resulting strain was co-cultured with the target C. necator recombinant strain on Nutrient Agar medium (Difco) to perform conjugative transfer.

[0058] From the bacterial group after the mixed culture, strains with the plasmid inserted in the genome were selected and isolated on Simmons agar medium (sodium citrate 2g / L, sodium chloride 5g / L, magnesium sulfate heptahydrate 0.2g / L, diammonium hydrogen phosphate 1g / L, agar 15g / L, pH 6.8) containing 250mg / L kanamycin sulfate. The strains isolated on Nutrient Agar medium containing 250mg / L kanamycin sulfate were further purified and then inoculated into Nutrient Agar medium containing 15% sucrose to obtain strains from which the plasmid had been removed. Two types of strains were generated at the stage of plasmid removal by homologous recombination: one that returned to the original genome sequence and one that had undergone the desired genetic modification, and the latter was isolated by colony PCR. The obtained genetically modified strain was purified again on Nutrient Agar medium containing sucrose to obtain a homologous recombinant strain.

[0059] Using the gene transfer plasmid (1) and the gene transfer plasmid (2), the host (1) was genetically modified by the above-mentioned method to produce H16 phaC 1Re ::STQK ΔphaZ 1,2,6 / nagE G793C.dR phaJ4a::lacN17-PCT Es phaJ4b::REP-LDH Lm Furthermore, this strain was genetically modified using a gene disruption plasmid by the above-mentioned method to produce H16 phaC 1Re ::STQK ΔphaZ 1,2,6 / nagE G793C.dR phaJ4a::lacN17-PCT Es phaJ4b::REP-LDH Lm ΔphaA was constructed and used as the host (2).

[0060] A DNA fragment encoding STQK was amplified by PCR, and the DNA fragment was treated with MunI and SpeI in pCUP2 vector (see International Publication No. 2007 / 049716) and ligated with DNA ligase to obtain a vector that expresses STQK under the strong lacUV5 promoter (SEQ ID NO: 8). This expression vector was introduced into host (2) by electroporation to obtain host (3). Kanamycin was added appropriately to maintain the plasmid.

[0061] Using this host (3), a polyester copolymer (LAHB) was produced in a jar fermenter with glucose as the carbon source.

[0062] First, as a preculture, the bacteria were cultured overnight at 30°C using meat medium (composition: 1% (w / v) meat extract, 1% (w / v) bactotryptone, 0.2% (w / v) yeast extract, 0.9% (w / v) disodium hydrogen phosphate dodecahydrate, 0.15% (w / v) potassium dihydrogen phosphate, and 50 μg / L kanamycin).

[0063] This preculture solution was added to a 500 ml Sakaguchi flask containing 100 ml of meat medium, and cultured with shaking at 30° C. for 6 hours.

[0064] Next, the above culture solution was inoculated into a 5 L jar fermenter (Bioneer Neo type, manufactured by Marubishi Bioengineering) containing 1.8 L of PHA production medium. The operating conditions were a culture temperature of 30°C, an agitation speed of 500 rpm, and an aeration rate of 1.8 L / min. The culture was continued for 48 hours while controlling the pH between 6.7 and 6.8. A 7% aqueous solution of ammonium hydroxide was used for pH control.

[0065] The composition of the PHA production medium was 0.578% (w / v) disodium hydrogen phosphate dodecahydrate, 0.101% (w / v) potassium dihydrogen phosphate, 0.437% (w / v) ammonium sulfate, 0.15% (w / v) magnesium sulfate heptahydrate, and 0.75% (v / v) trace metal salt solution (1.6% (w / v) iron(II) chloride hexahydrate, 1% (w / v) calcium chloride dihydrate, 0.02% (w / v) cobalt chloride hexahydrate, 0.016% (w / v) copper sulfate pentahydrate, and 0.012% (w / v) nickel chloride hexahydrate dissolved in 0.1N hydrochloric acid). The carbon source was glucose, with an initial concentration of 20 g / L, and after glucose was consumed to 10 g / L, it was maintained at 10 g / L.

[0066] The cells were collected from the culture medium by centrifugation, purified with pure water and ethanol, and then dried in a vacuum. The polymer was extracted from the dried cells with chloroform, and the chloroform was completely removed using an evaporator and a vacuum dryer to obtain a copolymer polyester of lactic acid and 3-hydroxybutanoic acid (LAHB).

[0067] The resulting copolymer polyester was 1 The mole fraction of lactic acid measured by 1 H NMR was 20 mol %, and the weight average molecular weight was 370,000.

[0068] Example 1 [Making compound pellets] 10 g of a mixture consisting of 99.5% by weight of polylactic acid (Ingeo 2003D, NatureWorks) and 0.5% by weight of the copolymer polyester was dried at 50°C for 12 hours, and then melt-kneaded and extruded in a twin-screw extruder (ULTNano05, Technobel, screw diameter 1.5 cm, L / D = 13.33) with the barrel and die temperatures set to 190°C. The molten strand emerging from the die with a diameter of 2.5 mm was taken off and air-cooled in a cooling process, and then cut to a length of approximately 4 mm in a pelletizer to obtain compound pellets.

[0069] [Charpy impact strength measurement] The compound pellets were dried for 4 hours under vacuum at 80°C using a vacuum heating dryer (DP300 manufactured by Yamato Scientific), and then a press plate with a thickness of 4 mm was produced using a hydraulic vacuum heating press (IMC-11FD type manufactured by Imoto Seisakusho) under vacuum at 170°C and a molding pressure of 1.4 MPa. The press plate was cut to a length of 80 mm and a width of 10 mm to obtain five test pieces of 80 mm x 10 mm x 4 mm. The test pieces were subjected to a Charpy impact test in accordance with JIS K7110, and the average value of the results of five measurements was recorded as the impact strength (kJ / m 2 The results are shown in Table 1.

[0070] (Examples 2 to 4) Compound pellets were prepared in the same manner as in Example 1, except that the mixing ratio of polylactic acid and copolymer polyester was changed to the ratio shown in Table 1, and the Charpy impact strength was measured. The results are shown in Table 1.

[0071] Comparative Example 1 Polylactic acid (Ingeo 2003D, NatureWorks) was used alone to prepare compound pellets in the same manner as in Example 1, and the Charpy impact strength was measured.

[0072] [Table 1]

[0073] From Table 1, it can be seen that in Examples 1 to 4, in which a copolyester was blended with polylactic acid, the impact strength was improved compared to Comparative Example 1, which contained only polylactic acid. This clearly shows that the impact resistance of polylactic acid can be improved by blending a copolyester.

[0074] The test pieces used in the Charpy impact test evaluation of Example 3 and Comparative Example 1 were frozen in liquid nitrogen and fractured, and the fracture surfaces were observed with a scanning electron microscope (SEM), and photographs of these are shown in Figures 1 and 2. In the test piece of Example 3 shown in Figure 1, numerous circular depression structures were observed, which were formed by the extremely fine dispersion of the copolymer polyester of 3-hydroxybutanoic acid and lactic acid in the polylactic acid. On the other hand, no such structures were observed in the test piece of Comparative Example 1 shown in Figure 2.

Claims

1. An impact resistance modifier for improving the impact resistance of polylactic acid, which comprises a copolymer polyester of lactic acid and another hydroxycarboxylic acid.

2. 2. The impact modifier of claim 1, wherein the other hydroxycarboxylic acid is a 3-hydroxyalkanoic acid.

3. The impact resistance modifier according to claim 1, wherein the other hydroxycarboxylic acid is at least one selected from the group consisting of 3-hydroxybutanoic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxypentadecanoic acid, and 3-hydroxyhexadecanoic acid.

4. 2. The impact modifier of claim 1, wherein said other hydroxycarboxylic acid is 3-hydroxybutanoic acid.

5. 5. The impact modifier according to claim 1, wherein the copolyester is a random copolymer of lactic acid and another hydroxycarboxylic acid.

6. The impact modifier according to any one of claims 1 to 4, wherein the lactic acid monomer of the copolyester is a D-lactic acid monomer.

7. 5. The impact modifier according to claim 1, wherein the molar fraction of lactic acid units in the copolymer polyester is 5 to 70 mol %.

8. The impact resistance improver according to any one of claims 1 to 4, wherein the weight average molecular weight of the copolymer polyester is from 10,000 to 1,000,000.

9. A resin composition comprising polylactic acid and the impact modifier according to any one of claims 1 to 4.

10. The resin composition according to claim 9, wherein the amount of the copolyester is 0.1 to 8 parts by weight based on 100 parts by weight of the polylactic acid.

11. A molded article obtained by molding the resin composition according to claim 9.

12. A method for improving the impact resistance of polylactic acid, which comprises mixing a copolymer polyester of lactic acid and another hydroxycarboxylic acid with the polylactic acid.

13. Use of a copolymer polyester of lactic acid with another hydroxycarboxylic acid as an impact modifier for improving the impact resistance of polylactic acid.

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