Resin composition

Abstract

The resin composition contains polylactic acid and a copolyester of lactic acid and another hydroxycarboxylic acid. The copolyester has a weight-average molecular weight of 110,000 or more, and in the copolyester, the copolymerization randomness calculated by the ratio (b / a) of the theoretical value (b) of the triad ratio of the other hydroxycarboxylic acid to the measured value (a) of the triad ratio of the other hydroxycarboxylic acid is 0.5-3.0. The copolyester of lactic acid and another hydroxycarboxylic acid can be used as a soil biodegradation accelerator for promoting the soil biodegradation of polylactic acid.

Description

resin composition

[0001] The present invention relates to a resin composition or molded article containing polylactic acid, a soil biodegradation accelerator that accelerates the soil biodegradation of polylactic acid, and uses thereof.

[0002] Because plastics are difficult to decompose in the natural environment, environmental pollution caused by their mass disposal has become a serious problem. To address this issue, efforts are being made to commercialize biodegradable plastics, which 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, because polylactic acid is an extremely hard resin, techniques to soften it are being investigated, including the addition of low-molecular-weight plasticizers such as isobutyl adipate, dioctyl sebacate, tributyl acetyl citrate, and triacetylene.

[0005] It is also known to blend polylactic acid with other polymers. For example, Patent Document 1 describes that blending polylactic acid with a copolymer polyester of lactic acid and other hydroxycarboxylic acid can plasticize polylactic acid without substantially reducing the transparency of the polylactic acid.

[0006] On the other hand, polylactic acid is known to have a slow biodegradation rate, particularly insufficient biodegradability in soil. In standard methods such as home composting and soil burial, polylactic acid cannot be rapidly biodegraded and remains in the compost or soil for a long period of time, so it is not certified as compostable.

[0007] Therefore, techniques for improving the biodegradation of resin materials containing polylactic acid have been studied. For example, Patent Document 2 discloses that the biodegradation of polylactic acid-containing materials is improved by using regenerated cellulose.

[0008] International Publication No. 2020 / 066679 International Publication No. 2022 / 085725

[0009] Although the technology described in Patent Document 1 can soften polylactic acid, the melt viscosity and melt tension of the blend may be insufficient during melt processing, which can lead to excessive drawdown immediately after the molten material is extruded from the extruder, potentially reducing workability and resulting in molding defects.

[0010] Although Patent Document 2 discloses a technology for improving the biodegradation of polylactic acid-containing materials, the effect is not sufficient, and there are concerns 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.

[0011] In view of the above-mentioned current situation, a first aspect of the present invention aims to provide a polylactic acid-containing resin composition in which the tensile elongation at break of polylactic acid is improved and drawdown during melting is suppressed.

[0012] A second aspect of the present invention aims to provide a novel technology for promoting soil biodegradation of polylactic acid.

[0013] The present inventors discovered that blending a specific copolymer polyester of lactic acid with another hydroxycarboxylic acid improves the tensile elongation at break of polylactic acid and suppresses drawdown during melting, leading to the first aspect of the present invention. The present inventors also discovered that copolymer polyesters of lactic acid with another hydroxycarboxylic acid can promote soil biodegradation of polylactic acid, leading to the second aspect of the present invention.

[0014] That is, a first aspect of the present invention relates to a resin composition containing polylactic acid and a copolymerized polyester of lactic acid and another hydroxycarboxylic acid, wherein the copolymerized polyester has a weight-average molecular weight of 110,000 or more, and wherein the copolymerization randomness of the copolymerized polyester, calculated as the ratio (b / a) of the theoretical triad ratio (b) of the other hydroxycarboxylic acid to the measured triad ratio (a) of the other hydroxycarboxylic acid, is 0.5 to 3.0. The first aspect of the present invention also relates to a molded article obtained by molding the resin composition.

[0015] A second aspect of the present invention relates to a soil biodegradation accelerator for promoting the soil biodegradation of polylactic acid, the soil biodegradation accelerator comprising a copolymerized polyester of lactic acid and another hydroxycarboxylic acid. The second aspect of the present invention also relates to a resin composition comprising polylactic acid and the soil biodegradation accelerator, or a molded article obtained by molding the composition. The second aspect of the present invention also relates to a method for promoting the soil biodegradation of polylactic acid, comprising contacting the copolymerized polyester of lactic acid and another hydroxycarboxylic acid with polylactic acid. The second aspect of the present invention also relates to the use of the copolymerized polyester of lactic acid and another hydroxycarboxylic acid as a soil biodegradation accelerator for promoting the soil biodegradation of polylactic acid.

[0016] According to a first aspect of the present invention, it is possible to provide a polylactic acid-containing resin composition in which the tensile elongation at break of the polylactic acid is improved and drawdown during melting is suppressed. As a result, it is possible to improve the tensile elongation at break of a molded article containing polylactic acid, and to suppress deterioration in workability and molding defects during melt processing of the polylactic acid-containing resin composition.

[0017] The second aspect of the present invention can provide a novel technology for promoting soil biodegradation of polylactic acid. According to a preferred embodiment, soil biodegradation can be promoted without reducing the biomass content of polylactic acid. According to a preferred embodiment of the second aspect of the present invention, soil biodegradation of polylactic acid can be promoted without substantially reducing the transparency of polylactic acid. Furthermore, it is also possible to plasticize polylactic acid and improve its elongation.

[0018] The copolymer polyester of lactic acid and 3-hydroxybutanoic acid was measured. １ An example of a chart enlarging the vicinity of 1.3 ppm of the H-NMR spectrum. A scanning electron micrograph of the freeze-fractured surface of the press plate made of polylactic acid and copolymer polyester obtained in Example 8. A scanning electron micrograph of the freeze-fractured surface of the press plate made of only polylactic acid obtained in Comparative Example 9. A histogram showing the distribution of diameters measured for 200 circular recess structures in the scanning electron micrograph of Figure 2.

[0019] DETAILED DESCRIPTION OF THE INVENTION [First Aspect] A resin composition according to a first aspect of the present invention contains polylactic acid and a copolymer polyester of lactic acid and another hydroxycarboxylic acid.

[0020] (Polylactic acid) Polylactic acid is a polyester containing lactic acid as a constituent monomer. The polylactic acid may be a conventionally known polylactic acid, and may be either crystalline or amorphous. The polylactic acid is preferably a homopolymer of lactic acid, but may also contain a trace amount of other monomers in addition to lactic acid.

[0021] The lactic acid constituting the polylactic acid may be either the L- or D-configuration, or may contain both. In the latter case, the ratio of the L- and D-configuration is not particularly limited. The polylactic acid may be any of poly(L-lactic acid) resin, poly(D-lactic acid) resin, and poly(DL-lactic acid) resin. It may also be a blend of these.

[0022] Examples of the other monomers that may be contained in polylactic acid include aliphatic hydroxycarboxylic acids other than lactic acid, aliphatic polyhydric alcohols, aliphatic polycarboxylic acids, polyfunctional polysaccharides, etc. 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.

[0023] The lactic acid raw material for producing polylactic acid is not particularly limited, and examples thereof include L-lactic acid, D-lactic acid, DL-lactic acid, or a mixture thereof, and L-lactide, D-lactide, meso-lactide, or a mixture thereof. Lactic acid obtained by microbial fermentation from renewable plant-derived raw materials such as starch is preferably used. The method for producing polylactic acid is not particularly limited, and known methods such as dehydration condensation polymerization and ring-opening polymerization can be used.

[0024] The molecular weight of the polylactic acid is not particularly limited and may be set appropriately 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.

[0025] (Copolyester) The resin composition according to the first aspect of the present invention contains, in addition to polylactic acid, a copolymer polyester of lactic acid and another hydroxycarboxylic acid. By blending the copolymer polyester, it is possible to improve the tensile elongation at break of the polylactic acid and suppress drawdown during melting.

[0026] Furthermore, since the copolyester contains lactic acid as one of its constituent monomers, it has good compatibility with polylactic acid and can form a homogeneous mixture with polylactic acid, thereby preventing a substantial decrease in the transparency of polylactic acid.

[0027] The copolyester itself is a biodegradable polymer material. 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). Therefore, the copolyester is expected to exhibit high biodegradability in the environment, including soil. Furthermore, isolation of enzymes secreted by isolated copolyester-biodegrading bacteria revealed that they degrade poly-D-lactic acid oligomers with a mer content of 31 or less.

[0028] The copolymer polyester used has a high copolymerization randomness from the viewpoint of achieving both improved tensile elongation at break and suppressed drawdown. Specifically, a copolymer polyester is used whose copolymerization randomness, calculated by the ratio (b / a) of the measured triad ratio (a) of the other hydroxycarboxylic acid contained in the copolymer polyester to the theoretical triad ratio (b) of the other hydroxycarboxylic acid, is 0.5 to 3.0. As long as this value does not exceed 3, the closer it is to 3, the higher the copolymerization randomness. The copolymerization randomness ratio (b / a) is preferably 0.7 or greater, more preferably 0.8 or greater, and even more preferably 0.9 or greater. The upper limit of the ratio (b / a) may be 2.5 or less, 2.0 or less, 1.5 or less, 1.2 or less, or 1.1 or less.

[0029] By using a copolymer polyester having such a high degree of copolymerization randomness, it is possible to improve the tensile elongation at break of a molded product and suppress drawdown during melting. If the copolymerization randomness is less than 0.5, it is difficult to obtain an improvement in the tensile elongation at break, and excessive drawdown is likely to occur during melting.

[0030] Here, the triad ratio of other hydroxycarboxylic acid refers to the ratio of units H-H-H in which three other hydroxycarboxylic acid H units are linked to the total number of triads in which other hydroxycarboxylic acid is located at the center. The total number of triads includes H-H-H and triads in which lactic acid L is located next to other hydroxycarboxylic acid (L-H-H, L-H-L, and H-H-L).

[0031] The theoretical value (b) of the triad ratio of the other hydroxycarboxylic acid refers to the theoretical value of the triad ratio of the other hydroxycarboxylic acid when it is assumed that the arrangement order of lactic acid and the other hydroxycarboxylic acid in the copolymer polyester is completely random. This is the ratio at which both sides of the other hydroxycarboxylic acid are other hydroxycarboxylic acids, and is therefore calculated as the square of the molar fraction of the other hydroxycarboxylic acid in the copolymer polyester.

[0032] The measured triad ratios (a) of other hydroxycarboxylic acids were also １ The triad ratio (a) can be calculated based on the spectrum obtained by H-NMR measurement. Specifically, the signal of a specific proton contained in the other hydroxycarboxylic acid is split into a signal contained in the triad (H-H-H) of the other hydroxycarboxylic acid and a signal contained in the other triads (L-H-H, L-H-L, and H-H-L) by calculating the integral value of each signal, thereby determining the measured value of the triad ratio (a) of the other hydroxycarboxylic acid.

[0033] In addition, when the copolymerized polyester is a block copolymer, the measured value (a) is nearly 100%, i.e., 1, and the ratio (b / a) is close to b. On the other hand, when lactic acid and other hydroxycarboxylic acids are arranged in a completely regular manner, the ratio (b / a) is greater than 1. Here, completely regular arrangement means, for example, when the molar fraction of lactic acid monomer units is 20 mol%, lactic acid L and other hydroxycarboxylic acids H are arranged in a regular manner such as -L-H-H-H-H-L-H-H-H-H-L-. In this case, there are two H-H-Hs, and a total of two L-H-Hs and H-H-Ls, so the measured value (a) is 50%, and the theoretical value (b) is 64% (= 80% × 80%). Therefore, the ratio (b / a) is 1.28.

[0034] The lactic acid monomer unit in the copolymer polyester may be either an L-lactic acid monomer unit or a D-lactic acid monomer unit, and may contain either one or both.

[0035] When the copolymer polyester is produced by a microorganism, the lactic acid monomer units in the copolymer polyester are composed substantially only of D-lactic acid monomer units. "Composed substantially only 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, and more preferably 99% or more.

[0036] The hydroxycarboxylic acid other than lactic acid contained in the copolymer polyester is not particularly limited as long as it is a hydroxycarboxylic acid copolymerizable with lactic acid. The number of carbon atoms in the hydroxycarboxylic 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.

[0037] The hydroxycarboxylic acid is preferably a hydroxyalkanoic acid. Specific examples of the hydroxyalkanoic acid include 2-hydroxyalkanoic acid, 3-hydroxyalkanoic acid, and 4-hydroxyalkanoic acid, with 3-hydroxyalkanoic acid being particularly preferred.

[0038] Specific examples of 3-hydroxyalkanoic acids 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), a copolymer polyester of lactic acid and 3HB, is the most preferable copolymer polyester.

[0039] The ratio of lactic acid monomer units contained in the copolymer polyester is not particularly limited. However, because of the high effect of improving the tensile elongation at break of polylactic acid and suppressing drawdown during melting, the molar fraction of lactic acid monomer units relative to all monomer units constituting the copolymer polyester is preferably 10 to 70 mol%, more preferably 15 to 60 mol%, and even more preferably 15 to 50 mol%. In particular, because of the high effect of suppressing drawdown, the upper limit of the molar fraction is even more preferably 40 mol% or less, particularly preferably 30 mol% or less, and most preferably 25 mol% or less. The molar fraction of lactic acid monomer units can be determined using HPLC. Alternatively, it can also be determined using NMR or GC.

[0040] The weight-average molecular weight Mw of the copolymer polyester is set to 110,000 or more from the viewpoint of both improving the tensile elongation at break and suppressing drawdown. If the weight-average molecular weight Mw of the copolymer polyester is less than 110,000, it is difficult to obtain the effect of improving the tensile elongation at break, and excessive drawdown is likely to occur when melted.

[0041] The weight-average molecular weight is preferably 130,000 or more, more preferably 150,000 or more, more preferably 200,000 or more, and particularly preferably 300,000 or more. The upper limit is not particularly limited, but from the viewpoints of productivity and processability in melting, it is preferably 3,000,000 or less, more preferably 2,000,000 or less, even more preferably 1,500,000 or less, even more preferably 1,000,000 or less, particularly preferably 800,000 or less, and most preferably 600,000 or less.

[0042] The weight-average molecular weight of the copolymerized polyester 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).

[0043] Copolymerized 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 produced from raw materials derived entirely from biomass.

[0044] The method for producing the copolymer polyester of lactic acid and another hydroxycarboxylic acid is not particularly limited and may be a conventionally known method. It may be biosynthesized using a microorganism or 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.

[0045] In particular, recombinant microorganisms belonging to the genus Capriavidus alternate between a bacterial cell growth phase and a polymer biosynthesis phase during culture, and thus continue to produce homogeneous polymers during polymer biosynthesis, giving them the ability to produce highly random copolymerized polyesters. Therefore, the use of recombinant microorganisms belonging to the genus Capriavidus facilitates the production of copolymerized polyesters according to the first aspect of the present invention. Furthermore, even with recombinant microorganisms belonging to genera other than Capriavidus (e.g., recombinant Escherichia coli microorganisms), it is possible to produce the copolymerized polyester according to the first aspect of the present invention by adjusting the aeration volume and agitation speed during culture.

[0046] The copolyester according to the first aspect of the present invention can be used as a soil biodegradation accelerator for promoting soil biodegradation of polylactic acid. By contacting the copolyester with polylactic acid, soil biodegradation of polylactic acid can be promoted. Details will be described later in relation to the second aspect.

[0047] (Bundling ratio) The blending ratio of polylactic acid and the copolymer polyester in the resin composition according to the first aspect of the present invention can be set from the viewpoint of improving tensile elongation at break and suppressing drawdown, and the blending amount of the copolymer polyester is preferably 10 parts by weight or more and 100 parts by weight or less per 100 parts by weight of polylactic acid. From the viewpoint of improving tensile elongation at break, the upper limit is preferably 80 parts by weight or less, more preferably 60 parts by weight or less, and particularly preferably 50 parts by weight or less. The lower limit may be 15 parts by weight or more, or may be 20 parts by weight or more.

[0048] (Other Components) 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 conventionally known resins can be used. Specific examples include biodegradable aliphatic polyesters other than polylactic acid and the copolymer polyester, and aromatic polyesters.

[0049] 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, 10 parts by weight or less, 5 parts by weight or less, 1 part by weight or less, or 0.1 parts by weight or less.

[0050] Furthermore, resins that are poorly compatible with polylactic acid may deteriorate the transparency of polylactic acid, so it is preferable that they are not blended in, or that they be blended in in small amounts if blended in. Although not particularly limited, for example, the blending 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, and more preferably about 0 to 50 parts by weight, per 100 parts by weight of polylactic acid.

[0051] The resin composition may contain other additives as appropriate, provided that the effects of the present invention are not impaired. Examples of such additives include, but are not limited to, plasticizers, hydrolysis inhibitors, compatibilizers, antioxidants, UV absorbers, processing aids, antistatic agents, colorants, nucleating agents, inorganic or organic particles, lubricants, release agents, water repellents, inorganic fillers, mildew inhibitors, antibacterial agents, foaming agents, and flame retardants. The content of each additive can be determined appropriately depending on the purpose. Only one type of additive may be blended, or two or more types may be blended.

[0052] As the plasticizer, any plasticizer generally used as a plasticizer for polymers can be used, and specific examples thereof include polyester-based plasticizers, glycerin-based plasticizers, polycarboxylic acid ester-based plasticizers, polyalkylene glycol-based plasticizers, and epoxy-based plasticizers.

[0053] (Uses) The resin composition according to the first aspect of the present invention can be prepared by melt-kneading the components, extruding the molten resin into strands, and then cutting them into pellets. The resulting pellets can be dried to remove moisture, and then molded by a known molding method to obtain any molded article. Such molded articles also constitute one aspect of the present invention. Examples of molding methods include film molding, sheet molding, injection molding, blow molding, fiber spinning, extrusion foaming, and bead foaming.

[0054] The method for producing the film molded article 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 formed, and press molded.

[0055] As a method for producing an injection-molded article, for example, injection molding methods generally used when molding thermoplastic resins, such as injection molding, gas-assisted molding, and injection compression molding, can be used. Furthermore, 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 depending on other purposes. However, the injection molding method is not limited to these.

[0056] The resin composition may be processed into pellets or a molded article such as a film, sheet, or fiber using an extrusion molding machine, or it can also be processed into a molded article of a predetermined shape by injection molding.

[0057] 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.

[0058] The resin composition can be processed into molded articles of various shapes. Examples of such molded articles include paper, film, sheet, tube, plate, rod, container, bag, part, etc. The molded article can also be combined 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 first aspect of the present invention.

[0059] The uses of the molded articles are not particularly limited, and they can be suitably used in the fields of agriculture, fisheries, forestry, horticulture, medicine, hygiene products, clothing, non-clothing, packaging, automobiles, building materials, and other fields.

[0060] [Second Aspect] A soil biodegradation accelerator according to a second aspect of the present invention is an agent for accelerating soil biodegradation of polylactic acid by being used on polylactic acid. This soil biodegradation accelerator contains at least a copolymer polyester of lactic acid and another hydroxycarboxylic acid.

[0061] (Polylactic acid) As mentioned above, polylactic acid is known to have low biodegradability in soil. However, by using the soil biodegradation accelerator according to the second aspect of the present invention, the biodegradation of polylactic acid in soil can be promoted. Here, biodegradation means that the target resin is decomposed into water and carbon dioxide by the action of microorganisms, and soil biodegradation means that the target resin is biodegraded in soil.

[0062] By using the soil biodegradation accelerator according to the second aspect of the present invention, plastic materials containing polylactic acid as a main component can be composted not only by the standard industrial composting method, but also by the home composting method or the soil burial method.

[0063] The polylactic acid in the second embodiment is the same as the polylactic acid described in the first embodiment except for the points described below, so detailed description will be omitted.

[0064] (Copolymer Polyester) The soil biodegradation accelerator according to the second aspect of the present invention contains a copolymer polyester of lactic acid and another hydroxycarboxylic acid as an active ingredient for promoting soil biodegradation. When the copolymer polyester comes into contact with polylactic acid, the soil biodegradation of the polylactic acid itself can be promoted.

[0065] Furthermore, since the copolymer polyester is a polyester containing lactic acid as one of its constituent monomers, it has good compatibility with polylactic acid and can form a homogeneous mixture with polylactic acid. As a result, a substantial decrease in the transparency of polylactic acid can be avoided. Furthermore, it can plasticize polylactic acid and improve the elongation of polylactic acid.

[0066] The copolyester in the second embodiment may be the same as the copolyester described in the first embodiment, or may be a copolyester of lactic acid and another hydroxycarboxylic acid that does not fall under the copolyester described in the first embodiment.

[0067] The copolyester in the second embodiment may be any of a random copolymer, an alternating copolymer, a block copolymer, and a graft copolymer. However, from the viewpoints of the soil biodegradation promoting 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 an irregular order. When the copolyester is produced by a microorganism, it is usually a random copolymer. However, the copolyester used in the second embodiment may or may not satisfy the ratio of copolymerization randomness described for the first embodiment.

[0068] The lactic acid monomer unit in the copolyester in the second embodiment may be either an L-lactic acid monomer unit or a D-lactic acid monomer unit, or may contain either one or both.

[0069] In the second aspect, when the copolyester is produced by a microorganism, the lactic acid monomer units in the copolyester are composed substantially only of D-lactic acid monomer units. "Composed substantially only 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, and more preferably 99% or more.

[0070] The definition, specific examples, and preferred examples of the hydroxycarboxylic acid other than lactic acid contained in the copolymer polyester in the second embodiment are the same as those explained in the first embodiment, and therefore will not be described again.

[0071] The ratio of lactic acid monomer units contained in the copolymer polyester in the second aspect is not particularly limited, but because of the high effect of promoting soil biodegradation of polylactic acid, the molar fraction of lactic acid monomer units relative to all monomer units constituting the copolymer polyester is preferably 10 to 70 mol%, more preferably 15 to 60 mol%, and even more preferably 15 to 50 mol%.

[0072] The molecular weight of the copolymer polyester in the second embodiment is not particularly limited, but the weight average molecular weight Mw may be, for example, 10,000 to 1,000,000, and preferably 10,000 to 500,000. The weight average molecular weight of the copolymer polyester in the second embodiment may be in the same range as the weight average molecular weight of the copolymer polyester described in the first embodiment. The value of the weight average molecular weight can be determined as described above.

[0073] The method for producing the copolymer polyester in the second embodiment is not particularly limited and may be a conventionally known method, specifically the methods described above.

[0074] The soil biodegradation accelerator according to the second aspect of the present invention may be composed solely of a copolymerized polyester of lactic acid and another hydroxycarboxylic acid, or may contain components other than the copolymerized polyester. Such other components include known resin additives, such as plasticizers, hydrolysis inhibitors, compatibilizers, antioxidants, UV absorbers, processing aids, antistatic agents, colorants, nucleating agents, inorganic or organic particles, lubricants, release agents, water repellents, inorganic fillers, antifungal agents, antibacterial agents, foaming agents, and flame retardants.

[0075] The content of the copolymerized polyester in the soil biodegradation accelerator is not particularly limited, but may be, for example, 10 to 100% by weight, with the lower limit being 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.

[0076] (Mode of Use) By using the soil biodegradation accelerator according to the second mode of the present invention so as to contact it with polylactic acid, it is possible to obtain the effect of promoting the soil biodegradation of polylactic acid. Specifically, it is preferable to mix the soil biodegradation accelerator and polylactic acid so as to bring them into contact with each other, and it is particularly preferable to mix the two components uniformly, for example, by melt-kneading, mixing in an organic solvent and then removing the solvent, or the like.

[0077] (Amount Used) The amount of the soil biodegradation accelerator according to the second aspect of the present invention may be any amount sufficient to promote soil biodegradation of polylactic acid. From the viewpoint of balancing the soil biodegradation promoting effect with the transparency and mechanical properties of polylactic acid, it is preferable to use the soil biodegradation accelerator in an amount such that the amount of copolymerized polyester, the active ingredient of the soil biodegradation accelerator, is 1 to 200 parts by weight per 100 parts by weight of polylactic acid. More preferably, it is 5 to 100 parts by weight, and even more preferably, it is 10 to 80 parts by weight. The lower limit of the amount of copolymerized polyester may be 20 parts by weight or more, or may be 30 parts by weight or more. The upper limit may be 60 parts by weight or less, or may be 50 parts by weight or less. The amount of the soil biodegradation accelerator may be in the same range as the amount of copolymerized polyester per 100 parts by weight of polylactic acid described for the first aspect.

[0078] (Resin Composition) A second aspect of the present invention may be a resin composition containing polylactic acid and the soil biodegradation accelerator. Since the incorporation of the soil biodegradation accelerator promotes the soil biodegradation of polylactic acid, the resin composition can exhibit good soil biodegradation.

[0079] (Other Components) The resin composition in the second embodiment may contain a thermoplastic resin other than polylactic acid and the copolymer polyester. Such other thermoplastic resins are not particularly limited, and conventionally known resins can be used. Specific examples and amounts of the other thermoplastic resins may be the same as those described for the first embodiment.

[0080] The resin composition in the second embodiment may contain other additives as appropriate, as in the first embodiment, within the range that does not impair the effects of the invention.

[0081] (Uses) The resin composition in the second embodiment can be formed into pellets, as in the first embodiment, and can be molded by a known molding method to obtain any molded body. Such molded bodies also constitute one aspect of the present invention. The details and specific uses of the molded body are the same as those of the first embodiment, so a description thereof will be omitted. The molded body in the second embodiment exhibits good soil biodegradability and is therefore particularly suitable for use in applications where the molded body may be composted in a home compost or disposed of by burying in soil. Specific examples include, but are not limited to, packaging materials, food packaging materials, cutlery, rubber bags, agricultural materials, and coated paper.

[0082] The following items list preferred aspects of the present disclosure, but the present invention is not limited to each of the following items. [Item 1] A resin composition containing polylactic acid and a copolymerized polyester of lactic acid and another hydroxycarboxylic acid, wherein the copolymerized polyester has a weight-average molecular weight of 110,000 or more, and wherein the copolymerization randomness of the copolymerized polyester, calculated as the ratio (b / a) of the theoretical value (b) of the triad ratio of the other hydroxycarboxylic acid to the measured value (a) of the triad ratio of the other hydroxycarboxylic acid, is 0.5 to 3.0. [Item 2] The resin composition according to Item 1, wherein the other hydroxycarboxylic acid is a 3-hydroxyalkanoic acid. [Item 3] The resin composition 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] The resin composition according to any one of Items 1 to 3, wherein the other hydroxycarboxylic acid is 3-hydroxybutanoic acid. [Item 5] The resin composition according to any one of Items 1 to 4, wherein the lactic acid monomer unit in the copolymerized polyester is a D-lactic acid monomer unit. [Item 6] The resin composition according to any one of Items 1 to 5, wherein the molar fraction of lactic acid monomer units in the copolymerized polyester is 10 to 70 mol%. [Item 7] The resin composition according to any one of Items 1 to 6, wherein the weight-average molecular weight of the copolymerized polyester is 200,000 or more and 800,000 or less. [Item 8] The resin composition according to any one of items 1 to 7, wherein the copolymerization randomness is 0.8 to 3.0. [Item 9] The resin composition according to any one of items 1 to 8, wherein the amount of the copolyester is 10 to 100 parts by weight per 100 parts by weight of the polylactic acid. [Item 10] The resin composition according to any one of items 1 to 9, wherein the copolyester is a soil biodegradation accelerator that promotes soil biodegradation of polylactic acid.[Item 11] A molded article obtained by molding the resin composition according to any one of Items 1 to 10. [Item 12] A soil biodegradation accelerator that accelerates the soil biodegradation of polylactic acid, comprising a copolymerized polyester of lactic acid and another hydroxycarboxylic acid, wherein the copolymerized polyester has a weight-average molecular weight of 110,000 or more, and wherein the copolymerization randomness of the copolymerized polyester, calculated as the ratio (b / a) of the theoretical value (b) of the triad ratio of the other hydroxycarboxylic acid to the measured value (a) of the triad ratio of the other hydroxycarboxylic acid, is 0.5 to 3.0. [Item 13] A method for promoting soil biodegradation of polylactic acid, characterized by contacting a copolymer polyester of lactic acid and another hydroxycarboxylic acid with polylactic acid, wherein the copolymer polyester has a weight-average molecular weight of 110,000 or more, and wherein the copolymerization randomness calculated by the ratio (b / a) of the theoretical value (b) of the triad ratio of the other hydroxycarboxylic acid to the measured value (a) of the triad ratio of the other hydroxycarboxylic acid is 0.5 to 3.0. [Item 14] Use of a copolymer polyester of lactic acid and another hydroxycarboxylic acid as a soil biodegradation accelerator for promoting soil biodegradation of polylactic acid, wherein the copolymer polyester has a weight-average molecular weight of 110,000 or more, and wherein the copolymerization randomness calculated by the ratio (b / a) of the theoretical value (b) of the triad ratio of the other hydroxycarboxylic acid to the measured value (a) of the triad ratio of the other hydroxycarboxylic acid is 0.5 to 3.0. [Item 15] A soil biodegradation accelerator for accelerating the soil biodegradation of polylactic acid, the soil biodegradation accelerator comprising a copolymer polyester of lactic acid and another hydroxycarboxylic acid. [Item 16] A resin composition comprising polylactic acid and the soil biodegradation accelerator according to Item 15. [Item 17] A method for accelerating the soil biodegradation of polylactic acid, comprising contacting a copolymer polyester of lactic acid and another hydroxycarboxylic acid with polylactic acid. [Item 18] Use of a copolymer polyester of lactic acid and another hydroxycarboxylic acid as a soil biodegradation accelerator for accelerating the soil biodegradation of polylactic acid.

[0083] 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 as described in, for example, Molecular Cloning (Cold Spring Harbor Laboratory Press (1989)). Enzymes, cloning hosts, and the like used in genetic manipulation can be purchased from commercial suppliers and used according to their instructions. The enzymes used are not particularly limited as long as they can be used in genetic manipulation.

[0084] [Breeding of hydrogen bacteria producing copolymer polyester (LAHB)] The Cupriavidus necator H16 strain was genetically modified to clone the PHA synthase gene phaC on the genome. １Ｒｅ is replaced with another PHA polymerase gene, and the PHA decomposition enzyme gene phaZ １，２，６ In order to enhance glucose utilization ability, the 793rd base of the N-acetylglucosamine uptake gene nagE, G, was replaced with C, and further, the gene encoding the transcriptional regulator nagR was disrupted. １，２，６ / nagE G793C.dR strain (see International Publication No. 2017 / 104722) was prepared.

[0085] Furthermore, the KNK005ΔphaZ １，２，６ / nagE G793C. PHA synthase gene phaC on the genome of the dR strain １Ｒｅ The STQK mutant (Pseudomonas sp. 61-3 derived polymerase PhaC1 Ｐｓ H16 phaC (a 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 This strain was used as the host (1).

[0086] (Preparation of a Plasmid for Gene Disruption) PCR was performed using the genomic DNA of the 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 PCR as templates and the DNAs shown in SEQ ID NO: 3 and SEQ ID NO: 4 as primers. The resulting DNA fragment is a fragment formed by linking approximately 500 base pairs upstream and approximately 500 base pairs downstream of the ORF of acetyl-CoA acetyltransferase (Locus tag: H16_A1438). This DNA fragment was treated with the restriction enzyme SmiI and ligated using DNA ligase to the vector pNS2X-sacB (described in JP 2007-259708 A), which had also been treated with SmiI. The resulting gene disruption plasmid containing the nucleotide sequence shown in SEQ ID NO:5 was named pNS2X-sacB-ΔphaA. This gene disruption plasmid is used to disrupt the gene phaA:A1438, which encodes acetyl-CoA acetyltransferase.

[0087] (Preparation of a plasmid for gene introduction) A plasmid for gene introduction was prepared to introduce the genes necessary for LAHB production into the genome of C. necator. The gene was inserted into the genome of host (1) under the control of the REP promoter, replacing the ORF of phaJ4b (Locus tag: H16_B0397) on the genome of host (1). Ｌｍ pNS2X-sacB-phaJ4b::REP-LDH into which a gene sequence expressing Ｌｍ This plasmid was prepared by inserting the DNA fragment represented by SEQ ID NO: 6 into the pNS2X-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).

[0088] Similarly, a propionyl-CoA transferase PCR product derived from Epulopiscium sp. was inserted under the lacN17 promoter in place of the ORF of phaJ4a (Locus tag: H16_A1070) on the genome of the host (1). Ｅｓ pNS2X-sacB-phaJ4a::lacN17-PCT into which a gene sequence expressing Ｅｓ was prepared. This plasmid was prepared by inserting the DNA fragment represented by SEQ ID NO: 7 into the pNS2X-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).

[0089] (Gene 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 mixture was mixed and cultured with the target C. necator genetically modified strain on Nutrient Agar medium (manufactured by Difco) to perform conjugative transfer.

[0090] From the bacterial population after mixed culture, strains with the plasmid inserted into the genome were selected and isolated on Simmons agar medium containing 250 mg / L of kanamycin sulfate (sodium citrate 2 g / L, sodium chloride 5 g / L, magnesium sulfate heptahydrate 0.2 g / L, diammonium hydrogen phosphate 1 g / L, agar 15 g / L, pH 6.8). The strains isolated in Nutrient Agar medium containing 250 mg / L of 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: strains that return to the original genome sequence and strains with the desired genetic modification, and the latter was isolated and obtained by colony PCR. The obtained genetically modified strain was again purified in Nutrient Agar medium containing sucrose to obtain a homologous recombinant strain.

[0091] Using the gene transfer plasmid (1) and the gene transfer plasmid (2), the host (1) was genetically modified by the above-mentioned method to obtain H16 phaC. １Ｒｅ ::STQK ΔphaZ １，２，６ / nagE G793C. dR phaJ4a::lacN17-PCT Ｅｓ phaJ4b::REP-LDH Ｌｍ This was used as host (2). Furthermore, this strain was genetically modified using the gene disruption plasmid by the above-mentioned method to generate 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 (3).

[0092] A DNA fragment encoding STQK was amplified by PCR, and the pCUP2 vector (see International Publication No. 2007 / 049716) was treated with MunI and SpeI. This DNA fragment was then ligated using DNA ligase to obtain a vector that expresses STQK under the strong lacUV5 promoter (SEQ ID NO: 8). This expression vector was introduced into hosts (2) and (3) by electroporation, resulting in strains designated as hosts (2') and (3'). Kanamycin was added as appropriate to maintain the plasmid.

[0093] Using these hosts (2') and (3'), a polyester copolymer (LAHB) was produced using glucose as a carbon source in a jar fermenter.

[0094] 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, 50 μg / L kanamycin).

[0095] 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.

[0096] Next, the culture solution was inoculated into a 5 L jar fermenter (Bioneer Neo model, manufactured by Marubishi Bioengine) 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 carried out for 48 hours while controlling the pH between 6.7 and 6.8. A 7% aqueous ammonium hydroxide solution was used for pH control.

[0097] The PHA production medium consisted of 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 in 0.1 N hydrochloric acid). The carbon source was glucose, initially at a concentration of 20 g / L, which was then maintained at 10 g / L after glucose was consumed to 10 g / L.

[0098] The cells were collected from the culture medium by centrifugation, purified with pure water and ethanol, and then vacuum dried to dryness. 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).

[0099] The copolymerized polyester obtained from the host (2') is １ The molar fraction of lactic acid measured by H NMR was 15 mol %, and the weight average molecular weight was 540,000. This was designated HPL-1. The copolymerized polyester obtained from the host (3') was １ The mole fraction of lactic acid measured by H NMR was 20 mol %, and the weight average molecular weight was 370,000. This is designated as HPL-2.

[0100] (Synthesis Example 1) [Synthesis of ENL-1] A copolymer polyester of lactic acid and 3-hydroxybutanoic acid was biosynthesized using recombinant Escherichia coli according to the description in the literature: PNAS 105(45)17323-17327(2008). The culture was carried out at an aeration rate of 1 vvm and stirring at 500 rpm, and the biosynthesized copolymer polyester was extracted from the cells with chloroform. The obtained copolymer polyester had a lactic acid molar fraction of 45 mol% and a weight-average molecular weight Mw of 119,000.

[0101] (Synthesis Example 2) [Synthesis of ENL-2] Culture was carried out in the same manner as above with an aeration volume of 2 vvm and stirring at 500 rpm, and the obtained copolymerized polyester had a lactic acid molar fraction of 22 mol% and a weight average molecular weight Mw of 76,000.

[0102] (Synthesis Example 3) [Synthesis of ENL-3] Culture was carried out in the same manner as above, with an aeration volume of 0.5 vvm and stirring at 500 rpm. The obtained copolymerized polyester had a lactic acid molar fraction of 41 mol% and a weight average molecular weight Mw of 54,000.

[0103] (Synthesis Example 4) [Synthesis of ENL-4] Culture was carried out in the same manner as above, with an aeration volume of 0.5 vvm and stirring at 300 rpm. The obtained copolymerized polyester had a lactic acid molar fraction of 54 mol% and a weight average molecular weight Mw of 73,000.

[0104] (Synthesis Example 5) [Synthesis of PHBH-1] A copolymer polyester of 3-hydroxyhexanoic acid and 3-hydroxybutanoic acid was biosynthesized using recombinant hydrogen bacteria according to the description in WO 2015 / 115619. The biosynthesized copolymer polyester was extracted from the bacterial cells with chloroform. The obtained copolymer polyester had a molar fraction of 3-hydroxyhexanoic acid of 11 mol% and a weight-average molecular weight Mw of 63,000.

[0105] [Calculation of copolymerization randomness] １The H-NMR spectrum was measured using a nuclear magnetic resonance spectrometer (Bruker Avance III 600 MHz) with deuterated chloroform as the solvent at room temperature and with eight accumulations. From the obtained spectrum, the area (X) of the signal in the region of 1.25 to 1.29 ppm, when tetramethylsilane was set to 0 ppm, and the area (Y) of the signal in the region of 1.25 to 1.39 ppm were measured, and the triad ratio measurement value (a) of 3-hydroxybutanoic acid (3HB) was calculated using the formula: (X / Y) × 100. Here, the signals in the region of 1.25 to 1.39 ppm are signals derived from all methyl groups in 3-hydroxybutanoic acid, and of these, the signals in the region of 1.25 to 1.29 ppm are signals derived from the methyl groups contained in the 3-hydroxybutanoic acid triad (3HB-3HB-3HB). Examples of these signals include: １ An enlarged view of the H-NMR spectrum around 1.3 ppm is shown in Figure 1. When the arrangement of the monomers is completely random, the theoretical 3HB triad ratio (b), which is the ratio of 3HB triads to the total 3HB, is Z, where Z is the mole fraction of 3HB. ２ The copolymerization randomness, which indicates the proximity of the monomer sequence of the copolymerized polyester to a random sequence, was calculated as b / a. The results are shown in Table 1.

[0106] Example 1 [Measurement of Tensile Elongation at Break] 10 g of a mixture consisting of 70 wt % polylactic acid (Ingeo 10361D, manufactured by NatureWorks) and 30 wt % copolymer polyester (HPL-1) was dissolved in chloroform, and the solvent was removed and the mixture was dried to obtain a polymer blend sample. The obtained sample was molded into a 0.2 mm thick film at 180°C using a vacuum heating press, and a sample was punched into the shape of a JIS 5B type tensile test specimen to obtain a test specimen. The tensile elongation at break of this test specimen was measured using a Shimadzu Corporation universal testing machine AG-IS equipped with a thermostatic chamber. The measurement temperature was 22±1°C, and the test speed was 1 mm / min.

[0107] [Evaluation of Drawdown Property] 10 g of a mixture consisting of 70 wt% polylactic acid (Ingeo 10361D, manufactured by NatureWorks) and 30 wt% copolymer polyester (HPL-1) was melt-kneaded and extruded using a twin-screw extruder (ULTNano05 manufactured by Technovel, screw diameter 1.5 cm, L / D = 13.33) with the barrel and die temperatures set to 140°C. The molten strand emerging from the die with a diameter of 2.5 mm was taken up and transported to a cooling step. The workability at this time was evaluated as follows, and used as an index of drawdown property. ⊚: The extruded molten strand had sufficient melt viscosity and tension, and a strand of a constant thickness could be stably taken up to the cooling step. ◯: The extruded molten strand had appropriate melt viscosity and tension, and the speed at which the strand was transported to the cooling step was controlled in accordance with the sagging of the molten resin at the die outlet, allowing it to be taken up to the cooling step. △: The melt viscosity and tension of the extruded molten strand were low, but the strand thickness varied, but it was somehow able to be continuously taken up to the cooling process. ×: The melt viscosity and tension of the extruded molten strand were too low, and when an attempt was made to take up the strand, the strand stretched too much, causing it to break during take-up, making it difficult to transport to the cooling process.

[0108] Examples 2 to 4 Polymer blend films were obtained in the same manner as in Example 1, except that HPL-2 was used as the copolymer polyester and the mixing ratio of polylactic acid to the copolymer polyester was changed to the ratio shown in Table 1, and the tensile elongation at break was measured and the drawdown property was evaluated by melt extrusion.

[0109] Example 5 A polymer blend film was obtained in the same manner as in Example 1, except that ENL-1 was used as the copolymer polyester and the mixing ratio of polylactic acid to the copolymer polyester was changed to the ratio shown in Table 1, and the tensile elongation at break was measured and the drawdown property was evaluated by melt extrusion.

[0110] Comparative Example 1 Polylactic acid (Ingeo 10361D, manufactured by NatureWorks) was used alone, and the tensile elongation at break was measured in the same manner as in Example 1, and the drawdown property was evaluated by melt extrusion.

[0111] Comparative Example 2 A polymer blend film was obtained in the same manner as in Example 1, except that PHBH-1 was used as the copolymer polyester and the mixing ratio of polylactic acid to the copolymer polyester was changed to the ratio shown in Table 1, and the tensile elongation at break was measured and the drawdown property was evaluated by melt extrusion.

[0112] Comparative Example 3 A polymer blend film was obtained in the same manner as in Example 1, except that ENL-2 was used as the copolymer polyester and the mixing ratio of polylactic acid to the copolymer polyester was changed to the ratio shown in Table 1, and the tensile elongation at break was measured and the drawdown property was evaluated by melt extrusion.

[0113] Comparative Example 4 A polymer blend film was obtained in the same manner as in Example 1, except that ENL-3 was used as the copolymer polyester and the mixing ratio of polylactic acid to the copolymer polyester was changed to the ratio shown in Table 1, and the tensile elongation at break was measured and the drawdown property was evaluated by melt extrusion.

[0114] Comparative Examples 5 to 8 Polymer blend films were obtained in the same manner as in Example 1, except that ENL-4 was used as the copolymer polyester and the mixing ratio of polylactic acid to the copolymer polyester was changed to the ratio shown in Table 1, and the tensile elongation at break was measured and the drawdown property was evaluated by melt extrusion.

[0115]

[0116] Table 1 shows that in Examples 1 to 5, in which polylactic acid was blended with a copolymer polyester having an Mw of 110,000 or more and a copolymerization randomness of 0.5 to 3.0, the tensile elongation at break was significantly improved and the drawdown properties were also improved compared to Comparative Example 1, which used polylactic acid alone. On the other hand, in Comparative Example 2, in which PHBH-1, a copolymer polyester not containing lactic acid, was blended, the tensile elongation at break was slightly improved but not sufficiently, and the drawdown properties were not improved. Furthermore, in Comparative Examples 3 to 8, which did not satisfy either or both the Mw requirement and the copolymerization randomness requirement, the tensile elongation at break and the drawdown properties were not sufficiently improved.

[0117] [Preparation of Test Samples] Polylactic acid (Ingeo 2003D, manufactured by NatureWorks, D-isomer 4 mol %) and a copolymer polyester (HPL-2) were melt-kneaded in a weight ratio of 60:40 or 70:30, and then freeze-crushed to prepare powders with an average particle size of about 500 μm, which were used as test samples in Examples 6 and 7. Cellulose (Cellulose microcrystalline, manufactured by Merck KGaA) (Reference Example 1) was used as a reference.

[0118] [Home Composting Test] A home composting test was conducted in accordance with JIS K6953-2. To evaluate biodegradability (soil decomposition), a plant source (100 g of soil, aged for 14 days at 28°C), sea sand (85 g), and water (15 g) were mixed to prepare compost. The resulting compost was placed in a glass container, and then 7 g of test sample or reference cellulose and 7 g of water were mixed. The compost was kept at 28°C, and the amount of carbon dioxide generated was subtracted from the amount of carbon dioxide generated when the test sample or cellulose was not mixed, and the result was divided by the theoretical amount of carbon dioxide generated to determine the biodegradability. Water was replenished to the compost every week to maintain the initial weight of the compost. The results are shown in Table 2.

[0119]

[0120] The measurement results confirmed that biodegradation proceeded smoothly for the cellulose of Reference Example 1. In the test sample of Example 6, the biodegradation rate was 42% assuming that only the copolymerized polyester was completely biodegraded and converted to carbon dioxide, and 32% for Example 7. A biodegradation rate higher than this indicates that biodegradation of components other than the copolymerized polyester, i.e., polylactic acid, also proceeded in addition to the copolymerized polyester. The measurement results showed that the biodegradation rate exceeded the rate assumed when only the copolymerized polyester was completely biodegraded on the 124th day in Example 6 and on the 150th day in Example 7, confirming that biodegradation of polylactic acid proceeded in addition to the copolymerized polyester. These results demonstrate that the presence of the copolymerized polyester promoted the biodegradation of polylactic acid in the compost.

[0121] The degree of biodegradation after 180 days was 48% in Example 6 and 34% in Example 7.

[0122] <Discussion> The blend of the copolyester and polylactic acid exhibits high transparency, which suggests that the two components are either mutually compatible or form a morphology in which islands of the copolyester are finely dispersed in the polylactic acid at a scale smaller than the wavelength of light.

[0123] In the former case, the plasticizing effect of the copolymer polyester may have made the molecular chains of polylactic acid more mobile, making it easier for decomposing enzymes to bind and for water molecules to penetrate, which may have resulted in a phenomenon in which biodegradation of polylactic acid proceeds more quickly.

[0124] In the latter case, the action of the copolyester-degrading enzyme decomposes the copolyester islands exposed on the surface of the blend, creating voids, forming very fine irregularities on the polylactic acid surface and dramatically increasing the surface area. As a result, chemical hydrolysis of the polylactic acid may progress, producing enzymatically degradable oligomeric polylactic acid, which may accelerate the biodegradation of the polylactic acid. In this case, the low-molecular-weight copolyesters retained in the voids of the polylactic acid may act as acids, accelerating the hydrolysis of the polylactic acid surface.

[0125] Furthermore, when the copolymer polyester is present on the surface of the blend, microorganisms that secrete enzymes that hydrolyze the copolymer polyester and can assimilate the degradation products preferentially grow, and the high concentration of hydrolytic enzymes produced by these microorganisms may have promoted the hydrolysis of polylactic acid.

[0126] It is presumed that the effect of promoting soil biodegradation of polylactic acid is exerted by one of the above-mentioned mechanisms, or a combination of two or more of them.

[0127] Example 8 Preparation of Compound Pellets 10 g of a mixture consisting of 97% by weight of polylactic acid (Ingeo 2003D, manufactured by NatureWorks) and 3% by weight of copolymer polyester (HPL-2) was dried at 50°C for 12 hours, and then melt-kneaded and extruded in a twin-screw extruder (ULTNano05 manufactured by Technovel Co., Ltd., 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 up, air-cooled in a cooling step, and then cut into lengths of approximately 4 mm using a pelletizer to obtain compound pellets.

[0128] Comparative Example 9 Polylactic acid pellets were obtained in the same manner as in Example 8, except that 10 g of polylactic acid (Ingeo 2003D, manufactured by NatureWorks) was used.

[0129] The compound pellets or pellets obtained in Example 8 or Comparative Example 9 were dried for 4 hours under vacuum at 80°C using a vacuum heating dryer (DP300 manufactured by Yamato Scientific Co., Ltd.), and then pressed into a 4 mm thick press plate at 170°C under vacuum at a molding pressure of 1.4 MPa using a hydraulic vacuum heating press (IMC-11FD manufactured by Imoto Manufacturing Co., Ltd.).

[0130] The obtained press plate was frozen with liquid nitrogen and fractured, and the fracture surface was observed with a scanning electron microscope (SEM, JEOL Ltd., JSM-IT300HR scanning electron microscope), and photographs of the fracture surface are shown in Figures 2 and 3. In the test piece of Example 8 shown in Figure 2, numerous circular depression structures were observed on the surface. These depression structures were formed because the copolymer polyester of 3-hydroxybutanoic acid and lactic acid was dispersed very finely in the polylactic acid. On the other hand, no such structures were observed in the test piece of Comparative Example 9 shown in Figure 3.

[0131] The diameters of 200 circular depression structures were measured using the image analysis software ImageJ for the SEM observation results shown in Figure 2. A histogram showing the obtained diameter distribution is shown in Figure 4. The diameters were distributed in the range of approximately 100 to 350 nm, with an average diameter of 185±5 nm.

Claims

1. A resin composition containing polylactic acid and a copolymerized polyester of lactic acid and another hydroxycarboxylic acid, wherein the copolymerized polyester has a weight average molecular weight of 110,000 or more, and wherein the copolymerization randomness of the copolymerized polyester, calculated as the ratio (b / a) of the theoretical value (b) of the triad ratio of the other hydroxycarboxylic acid to the measured value (a) of the triad ratio of the other hydroxycarboxylic acid, is 0.5 to 3.

0.

2. The resin composition according to claim 1, wherein the other hydroxycarboxylic acid is a 3-hydroxyalkanoic acid.

3. The resin composition 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. The resin composition according to claim 1, wherein the other hydroxycarboxylic acid is 3-hydroxybutanoic acid.

5. The resin composition according to any one of claims 1 to 4, wherein the lactic acid monomer unit in the copolyester is a D-lactic acid monomer unit.

6. A resin composition according to any one of claims 1 to 4, wherein the molar fraction of lactic acid monomer units in said copolyester is 10 to 70 mol %.

7. The resin composition according to any one of claims 1 to 4, wherein the weight average molecular weight of the copolymer polyester is 200,000 or more and 800,000 or less.

8. The resin composition according to any one of claims 1 to 4, wherein the copolymerization randomness is 0.8 to 3.

0.

9. The resin composition according to any one of claims 1 to 4, wherein the amount of said copolyester per 100 parts by weight of said polylactic acid is 10 to 100 parts by weight.

10. A resin composition according to any one of claims 1 to 4, wherein the copolyester is a soil biodegradation promoter that promotes soil biodegradation of polylactic acid.

11. A molded article obtained by molding the resin composition according to any one of claims 1 to 4.

12. A soil biodegradation promoter for promoting the soil biodegradation of polylactic acid, comprising a copolymer polyester of lactic acid and another hydroxycarboxylic acid, the copolymer polyester having a weight-average molecular weight of 110,000 or more, and the copolymerization randomness of the copolymer polyester, calculated as the ratio (b / a) of the theoretical value (b) of the triad ratio of the other hydroxycarboxylic acid to the measured value (a) of the triad ratio of the other hydroxycarboxylic acid, is 0.5 to 3.

0.

13. A method for promoting soil biodegradation of polylactic acid, comprising contacting a copolymer polyester of lactic acid and another hydroxycarboxylic acid with polylactic acid, wherein the copolymer polyester has a weight average molecular weight of 110,000 or more, and wherein the copolymerization randomness of the copolymer polyester, calculated as the ratio (b / a) of the theoretical value (b) of the triad ratio of the other hydroxycarboxylic acid to the measured value (a) of the triad ratio of the other hydroxycarboxylic acid, is 0.5 to 3.

0.

14. Use of a copolymer polyester of lactic acid and another hydroxycarboxylic acid as a soil biodegradation promoter for promoting the soil biodegradation of polylactic acid, wherein the copolymer polyester has a weight average molecular weight of 110,000 or more, and the copolymerization randomness of the copolymer polyester calculated by the ratio (b / a) of the theoretical value (b) of the triad ratio of the other hydroxycarboxylic acid to the measured value (a) of the triad ratio of the other hydroxycarboxylic acid is 0.5 to 3.

0.

15. A soil biodegradation promoter that promotes the soil biodegradation of polylactic acid, the soil biodegradation promoter comprising a copolymer polyester of lactic acid and another hydroxycarboxylic acid.

16. A resin composition comprising polylactic acid and the soil biodegradation promoter according to claim 15.

17. A method for promoting soil biodegradation of polylactic acid, comprising contacting polylactic acid with a copolymer polyester of lactic acid and another hydroxycarboxylic acid.

18. Use of a copolymer polyester of lactic acid with another hydroxycarboxylic acid as a soil biodegradation promoter for promoting the soil biodegradation of polylactic acid.

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