Resin composition

Abstract

A resin composition containing polylactic acid and a copolyester of lactic acid and another hydroxycarboxylic acid. The weight-average molecular weight of the copolymerized polyester is 110,000 or more, and in the copolymerized polyester, the copolymerized randomness calculated from the ratio (b / a) of the theoretical value (b) of the triad ratio of the other hydroxycarboxylic acids to the measured value (a) of the triad ratio of the other hydroxycarboxylic acids is 0.5-3.0. Copolyesters of lactic acid and other hydroxycarboxylic acids can be used as soil biodegradation promoters that promote soil biodegradation of polylactic acid.

Description

Technical Field

[0001] This invention relates to resin compositions or molded articles containing polylactic acid, soil biodegradation promoters that promote the biodegradation of polylactic acid in soil, and their use. Background Technology

[0002] Because plastics are not easily decomposed in the natural environment, the environmental pollution caused by large-scale waste has been raised as a serious problem.

[0003] To address this issue, the practical application of biodegradable plastics, which can be broken down into water and carbon dioxide by microorganisms, is being promoted.

[0004] Polylactic acid (PLA), a representative biodegradable plastic, is a bio-based polymer that can be synthesized from biomass feedstocks. Due to its relatively high rigidity, strength, and transparency, it is being used in a wide range of applications as an alternative to petroleum-based plastics.

[0005] However, since polylactic acid is a very rigid resin, techniques to soften it are being investigated. As such softening techniques, the addition of isobutyl adipate, dioctyl sebacate, tributyl acetyl citrate, and triacetin (…) is known. Methods using low-molecular-weight plasticizers such as )

[0006] In addition, it is known to mix other polymers with polylactic acid. For example, Patent Document 1 describes how polylactic acid can be plasticized by mixing a copolyester of lactic acid and other hydroxycarboxylic acids with polylactic acid without substantially reducing the transparency of polylactic acid.

[0007] On the other hand, polylactic acid (PLA) is known to have a slow biodegradation rate, especially in soil where its biodegradability is insufficient. In standard methods such as home composting and soil burial, PLA cannot be rapidly biodegraded and will remain in the compost and soil for a long time; therefore, it cannot be considered suitable for composting.

[0008] Therefore, technologies to improve the biodegradability of resin materials containing polylactic acid are being researched. For example, Patent Document 2 discloses a method to improve the biodegradability of polylactic acid-containing materials by using regenerated cellulose.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: International Publication No. 2020 / 066679

[0012] Patent Document 2: International Publication No. 2022 / 085725 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] According to the technology described in Patent Document 1, although polylactic acid can be softened, the melt viscosity and melt tension during the melting and processing of the mixture are sometimes insufficient. Therefore, the drawdown can easily become excessive immediately after the melt is extruded from the extruder, which may lead to decreased operability and poor molding.

[0015] Although patent document 2 discloses a technology to improve the biodegradability of polylactic acid-containing materials, its effect is insufficient. In addition, since it is necessary to mix polylactic acid with substances whose chemical structure is very different from that of polylactic acid, there is a risk that the transparency and mechanical properties of polylactic acid may be damaged.

[0016] In view of the above situation, the object of the first aspect of the present invention is to provide a polylactic acid resin composition in which the tensile elongation at break of the polylactic acid is improved and the sag during melting is suppressed.

[0017] The second aspect of the present invention aims to provide a new technology for promoting the biodegradation of polylactic acid in soil.

[0018] Problem Solving Methods

[0019] The inventors have discovered that by incorporating a substance with a specific composition, which is a copolyester of lactic acid and other hydroxycarboxylic acids, into polylactic acid, the tensile elongation at break of polylactic acid is improved, and the sagging during melting is suppressed, thereby completing the first aspect of the present invention.

[0020] In addition, the inventors discovered that the copolyester of lactic acid and other hydroxycarboxylic acids can promote the soil biodegradation of polylactic acid, thus completing the second aspect of the present invention.

[0021] The first aspect of the present invention relates to a resin composition containing polylactic acid and a copolyester of lactic acid and other hydroxycarboxylic acids.

[0022] The weight-average molecular weight of the aforementioned copolyester is above 110,000, and,

[0023] In the above copolyester, the copolymer randomness calculated from the ratio (b / a) of the theoretical value (b) of the triple ratio of the other hydroxycarboxylic acids to the measured value (a) of the triple ratio of the other hydroxycarboxylic acids is 0.5 to 3.0.

[0024] Furthermore, the first aspect of the present invention also relates to a molded body formed by molding the above-described resin composition.

[0025] A second aspect of the present invention relates to a soil biodegradation promoter that promotes the soil biodegradation of polylactic acid, said soil biodegradation promoter containing a copolyester of lactic acid and other hydroxycarboxylic acids.

[0026] In addition, a second aspect of the present invention relates to a resin composition or a molded body formed from the resin composition, said resin composition containing polylactic acid and the aforementioned soil biodegradation promoter.

[0027] Furthermore, a second aspect of the present invention relates to a method for promoting the biodegradation of polylactic acid in soil, the method comprising: contacting polylactic acid with a copolyester of lactic acid and other hydroxycarboxylic acids.

[0028] Furthermore, a second aspect of the present invention also relates to the use of a copolyester of lactic acid and other hydroxycarboxylic acids as a soil biodegradation promoter for promoting the soil biodegradation of polylactic acid.

[0029] The effects of the invention

[0030] According to a first aspect of the present invention, a polylactic acid resin composition is provided in which the tensile elongation at break of the polylactic acid is improved and sagging during melting is suppressed. As a result, the tensile elongation at break of the molded article containing polylactic acid can be improved, and the decrease in workability and poor molding during melt processing of the polylactic acid resin composition can be suppressed.

[0031] A second aspect of the present invention can provide a new technology for promoting the biodegradation of polylactic acid in soil. According to a preferred embodiment, soil biodegradation can be promoted without reducing the biomass ratio of polylactic acid.

[0032] According to a preferred embodiment of the second aspect of the present invention, the soil biodegradation of polylactic acid (PLA) can be promoted without substantially reducing its transparency. Furthermore, the PLA can also be plasticized to increase its elongation. Attached Figure Description

[0033] Figure 1 This is a determination of the copolyester of lactic acid and 3-hydroxybutyric acid. 1 An example of a chart showing the magnified 1.3 ppm area in an H-NMR spectrum.

[0034] Figure 2 Scanning electron microscope images of the freeze-cracked surfaces of the pressed plates formed from polylactic acid and copolyester obtained in Example 8.

[0035] Figure 3 The image is a scanning electron microscope photograph showing the frozen fracture surface of the pressed plate made solely of polylactic acid obtained in Comparative Example 9.

[0036] Figure 4It shows the... Figure 2 A histogram of diameter distribution obtained by measuring 200 circular indentations in a scanning electron microscope image. Detailed Implementation

[0037] The embodiments of the present invention will now be described in detail.

[0038] [First Method]

[0039] The resin composition of the first aspect of the present invention contains polylactic acid and a copolyester of lactic acid and other hydroxycarboxylic acids.

[0040] (Polylactic acid)

[0041] Polylactic acid (PLA) is a polyester with lactic acid as its constituent monomer. PLA can be any conventionally known type and can be optionally crystalline or amorphous. PLA is preferably a homopolymer of lactic acid and may contain trace amounts of other monomers besides lactic acid.

[0042] The lactic acid constituting polylactic acid can be either L-form or D-form, or a mixture of both. In the latter case, the ratio of L-form to D-form is not particularly limited.

[0043] Polylactic acid can be any of poly(L-lactic acid) resin, poly(D-lactic acid) resin, and poly(DL-lactic acid) resin. Alternatively, it can be a mixture thereof.

[0044] Other monomers that may be included in polylactic acid include: aliphatic hydroxycarboxylic acids other than lactic acid, aliphatic polyols, aliphatic polycarboxylic acids, and polyfunctional polysaccharides.

[0045] 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% relative to the total monomers contained in polylactic acid, and more preferably 0 to 2 mol%.

[0046] There are no particular limitations on the lactic acid raw materials used in the manufacture of polylactic acid (PLA). L-lactic acid, D-lactic acid, DL-lactic acid, or mixtures thereof, L-lactide, D-lactide, meso-lactide, or mixtures thereof can be used. Lactic acid obtained from renewable plant-derived raw materials such as starch through microbial fermentation can be appropriately utilized.

[0047] As a method for manufacturing polylactic acid, known methods such as dehydration condensation polymerization and ring-opening polymerization can be used, and there are no particular limitations.

[0048] The molecular weight of polylactic acid is not particularly limited and can be set appropriately according to its application. The number average molecular weight is preferably 1,000 to 700,000, and more preferably 10,000 to 300,000.

[0049] (Copolyester)

[0050] In addition to polylactic acid, the resin composition of the first embodiment of the present invention contains a copolyester of lactic acid and other hydroxycarboxylic acids. By incorporating this copolyester, the elongation at break of polylactic acid can be improved, and sagging during melting can be suppressed.

[0051] Furthermore, since this copolyester 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.

[0052] The aforementioned copolyester is a polymer material that exhibits biodegradability in itself. Bacteria capable of decomposing copolymers of lactic acid and 3-hydroxybutyric acid were isolated from the environment (see Polymer Degradation and Stability, 2014, 110, 44; and Applied Microbiology and Biotechnology, 2015, 99, 9555), thus predicting that the aforementioned copolyester exhibits high biodegradability in environments including soil. Furthermore, upon isolation of enzymes secreted by the isolated copolyester biodegrading bacteria, it was found that they could decompose poly-D-lactic acid oligomers of 31 units or less.

[0053] As for the aforementioned copolyester, considering both improving tensile elongation at break and suppressing sag, a polyester with high copolymer at restorative randomness is used. Specifically, a copolyester with a copolymer at restorative randomness of 0.5 to 3.0, calculated from the ratio (b / a) of the theoretical value (b) of the triplets of other hydroxycarboxylic acids to the measured value (a) of the triplets of other hydroxycarboxylic acids contained in the copolyester, is used. Within this range, the closer the value is to 3, the higher the copolymer at restorative randomness.

[0054] The ratio of copolymer randomness (b / a) is preferably 0.7 or more, more preferably 0.8 or more, and even more preferably 0.9 or more. The upper limit of the ratio (b / a) can be 2.5 or less, 2.0 or less, 1.5 or less, 1.2 or less, or 1.1 or less.

[0055] By using highly randomized copolyesters in this manner, the elongation at break of the molded article can be improved, and sag during melting can be suppressed. If the randomness of the copolymer is less than 0.5, it is not easy to obtain the effect of improving the elongation at break, and excessive sag is prone to occur during melting.

[0056] Here, the ratio of other hydroxycarboxylic acids in triplets refers to the proportion of units HHH linked by three other hydroxycarboxylic acids in the total number of triplets where the other hydroxycarboxylic acid is at the center. The total number of triplets includes HHH and triplets with lactic acid L located adjacent to the other hydroxycarboxylic acids (LHH, LHL, and HHL).

[0057] The theoretical value (b) of the triplet ratio of other hydroxycarboxylic acids refers to the theoretical value of the triplet ratio of other hydroxycarboxylic acids assuming that the arrangement of lactic acid and other hydroxycarboxylic acids in the copolyester is completely random. Since it is the ratio of other hydroxycarboxylic acids with other hydroxycarboxylic acids on both adjacent sides, it is calculated in the form of the square of the mole fraction of other hydroxycarboxylic acids in the copolyester.

[0058] In addition, the determination of the triple ratio of other hydroxycarboxylic acids (a) can be used to analyze the copolyester. 1 H-NMR measurements are performed, and the results are calculated based on the resulting spectra. Specifically, the signal of a specific proton contained in other hydroxycarboxylic acids splits into two types: the signal contained in the triplet of other hydroxycarboxylic acids (HHH), and the signal contained in the triplet of other hydroxycarboxylic acids (LHH, LHL, and HHL). Using these signals, the measured value of the triplet ratio of other hydroxycarboxylic acids can be determined by calculating the integral value of each signal (a).

[0059] Furthermore, when the copolyester is a block copolymer, since the measured value (a) is almost 100%, which is 1, the ratio (b / a) is close to the value of b. On the other hand, when lactic acid and other hydroxycarboxylic acids are arranged in a completely regular pattern, the ratio (b / a) is greater than 1. Here, a completely regular pattern means, for example, when the molar fraction of lactic acid monomer units is 20 mol%, the lactic acid L and other hydroxycarboxylic acids H are arranged in a regular pattern like -LHHHHLHHHHL-. In this case, since there are 2 HHH and a total of 2 LHH and HHL, the measured value (a) is 50%, and the theoretical value (b) is 64% (=80%×80%). Therefore, the ratio (b / a) is 1.28.

[0060] The lactic acid monomer unit in the above-mentioned copolyester can be either L-lactic acid monomer unit or D-lactic acid monomer unit. It may contain either one or both.

[0061] In the case where the aforementioned copolyester is produced by microorganisms, the lactic acid monomer units in the copolyester are substantially composed only of D-lactic acid monomer units. "Substantially composed only of D-lactic acid monomer units" means that, in the total amount of lactic acid monomer units, the proportion of D-lactic acid monomer units is typically 90% or more, preferably 95% or more, and more preferably 99% or more.

[0062] The hydroxycarboxylic acid, excluding lactic acid, included in the aforementioned copolyester can be any hydroxycarboxylic acid capable of copolymerizing with lactic acid; there are no particular limitations. The hydroxycarboxylic acid preferably has 3 or more carbon atoms. The upper limit for the number of carbon atoms is preferably 15 or less, more preferably 10 or less, further preferably 8 or less, even more preferably 6 or less, and particularly preferably 5 or less.

[0063] As a hydroxycarboxylic acid, a hydroxyalkanoic acid is preferred. Specific examples of hydroxyalkanoic acids include 2-hydroxyalkanoic acid, 3-hydroxyalkanoic acid, and 4-hydroxyalkanoic acid, with 3-hydroxyalkanoic acid being particularly preferred.

[0064] Specific examples of 3-hydroxyalkyl acids include: 3-hydroxybutyric acid (hereinafter, sometimes simply referred to as 3HB), 3-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyheptanoate, 3-hydroxyoctanoate, 3-hydroxynonanoate, 3-hydroxydecanoate, 3-hydroxydodecanoate, 3-hydroxytetradecanoate, 3-hydroxypentadecanoate, and 3-hydroxyhexadecanoate. The copolyesters described above may contain only one of these or two or more. Preferably, at least 3HB is included. In particular, P(LA-co-3HB) (hereinafter, sometimes simply referred to as LAHB), a copolyester of lactic acid and 3HB, is most preferably used as the copolyester described above.

[0065] The ratio of lactic acid monomer units in the aforementioned copolyester is not particularly limited. However, from the perspective of improving the tensile elongation at break of polylactic acid and effectively suppressing sag during melting, the molar fraction of lactic acid monomer units relative to all monomer units constituting the aforementioned copolyester is preferably 10 to 70 mol%, more preferably 15 to 60 mol%, and even more preferably 15 to 50 mol%. In particular, from the viewpoint of effectively suppressing sag, the upper limit of the above molar fraction is even more preferably 40 mol% or less, particularly preferably 30 mol% or less, and most preferably 25 mol% or less.

[0066] The molar fraction of lactic acid monomer units can be determined using HPLC. Alternatively, it can be determined using NMR or GC.

[0067] Considering both improving tensile elongation at break and suppressing sag, the weight-average molecular weight (Mw) of the aforementioned copolyester was set to be above 110,000. If the weight-average molecular weight of the copolyester is below 110,000, it is not easy to achieve the effect of improving tensile elongation at break, and in addition, excessive sag is likely to occur during melting.

[0068] The weight-average molecular weight is preferably 130,000 or more, preferably 150,000 or more, further preferably 200,000 or more, and particularly preferably 300,000 or more. There is no particular upper limit, but from the viewpoint of productivity and processability during melting, it is preferably 3 million or less, more preferably 2 million or less, further preferably 1.5 million or less, even more preferably 1 million or less, particularly preferably 800,000 or less, and most preferably 600,000 or less.

[0069] The weight-average molecular weight of the copolyester can be determined using gel permeation chromatography (GPC) (manufactured by Shimadzu Corporation) with a tandem TSKgel Super HZM-H column (manufactured by Tosoh Corporation) based on standard polystyrene.

[0070] Copolyesters of lactic acid and other hydroxycarboxylic acids can be produced using organic resources (biomass) other than fossil fuels, and can be manufactured from 100% biomass-derived raw materials.

[0071] There are no particular limitations on the method for manufacturing copolyesters of lactic acid and other hydroxycarboxylic acids; any method known in the past may be used. It can be manufactured through microbial biosynthesis or chemical synthesis. Examples of methods for manufacturing P(LA-co-3HB) include those using recombinant microorganisms, as described in International Publication Nos. 2009 / 131186 and 2006 / 126796.

[0072] In particular, because recombinant microorganisms belonging to the genus *Codonopsis* switch between the cell proliferation stage and the polymer biosynthesis stage during cultivation, thereby continuously producing homogeneous polymers in polymer biosynthesis, they possess the ability to produce highly randomized copolyesters. Therefore, if recombinant microorganisms belonging to the genus *Codonopsis* are used, the copolyester of the first embodiment of the present invention can be easily manufactured.

[0073] In addition, even recombinant microorganisms belonging to genera other than Copper-loving Bacteria (e.g., recombinant microorganisms of Escherichia coli) can produce the copolyester of the first embodiment of the present invention by adjusting the aeration rate and stirring speed during culture.

[0074] The copolyester described above in the first embodiment of the present invention can be used as a soil biodegradation promoter to facilitate the soil biodegradation of polylactic acid. By contacting the copolyester with polylactic acid, the soil biodegradation of polylactic acid can be promoted. Details are described later in the section concerning the second embodiment.

[0075] (Mixing ratio)

[0076] The ratio of polylactic acid to the copolyester in the resin composition of the first aspect of the present invention can be set from the viewpoint of improving tensile elongation at break and suppressing sag, but the amount of copolyester relative to 100 parts by weight of polylactic acid is preferably 10 parts by weight or more and 100 parts by weight or less. 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 can be 15 parts by weight or more, or 20 parts by weight or more.

[0077] (Other ingredients)

[0078] The above-described resin composition may include polylactic acid and thermoplastic resins other than the copolyesters described above. There are no particular limitations on such other thermoplastic resins; conventionally known resins may be used. Specifically, examples include polylactic acid, biodegradable aliphatic polyesters other than the copolyesters described above, aromatic polyesters, etc.

[0079] There are no particular limitations on the amount of other thermoplastic resins used in the formulation, but relative to 100 parts by weight of polylactic acid, it can be, for example, more than 0 parts by weight and less than 200 parts by weight. The upper limit can be less than 100 parts by weight, less than 50 parts by weight, less than 30 parts by weight, less than 10 parts by weight, less than 5 parts by weight, less than 1 part by weight, or less than 0.1 parts by weight.

[0080] Furthermore, since resins with low compatibility with polylactic acid (PLA) can worsen the transparency of PLA, it is preferable not to use them, or to use them in small amounts if used. There are no particular limitations; for example, relative to 100 parts by weight of PLA, the amount of polyhydroxyalkanoate resin, one of the resins with low compatibility with PLA, is preferably about 0 to 100 parts by weight, more preferably about 0 to 50 parts by weight.

[0081] To the extent that it does not impair the effects of the invention, the above-described resin composition may appropriately contain other additives. Such additives are not particularly limited, and examples include: plasticizers, hydrolysis inhibitors, compatibilizers, antioxidants, ultraviolet absorbers, processing aids, antistatic agents, colorants, crystallizing nucleating agents, inorganic or organic particles, lubricants, mold release agents, water repellents, inorganic fillers, mildew inhibitors, antibacterial agents, foaming agents, flame retardants, etc. The content of each additive can be appropriately determined according to its purpose. Furthermore, only one additive may be used, or two or more additives may be used.

[0082] As the aforementioned plasticizer, plasticizers commonly used as plasticizers for polymers can be used, specifically including: polyester plasticizers, glycerol plasticizers, polycarboxylic acid ester plasticizers, polyalkylene glycol plasticizers, epoxy plasticizers, etc.

[0083] (use)

[0084] The resin composition of the first aspect of the present invention can be produced by melt-blending the components, extruding the molten resin into a filament, and then cutting it to form granules. After drying the obtained granules to remove moisture, they are molded using a known molding process to obtain any type of molded body. Such a molded body also constitutes an aspect of the present invention.

[0085] Examples of molding and processing methods include: film molding, sheet molding, injection molding, blow molding, fiber spinning, extrusion foaming, and bead foaming.

[0086] There are no particular limitations on the manufacturing method of the film-formed body; examples include T-die extrusion molding, calendering, roll forming, and blown film forming. Furthermore, the resulting film can be subjected to heat-based thermoforming, vacuum forming, and stamping.

[0087] As a method for manufacturing injection-molded parts, for example, conventional injection molding, gas-assisted molding, and injection compression molding can be used when molding thermoplastic resins. In addition, depending on other purposes, in-mold molding, gas compression molding, two-color molding, sandwich molding, push-pull molding, and scorim molding can also be used, besides the methods mentioned above. However, the injection molding method is not limited to these.

[0088] The above-mentioned resin composition can be processed into granules, films, sheets, or fibers using an extrusion molding machine, or it can be processed into a given shape by injection molding.

[0089] When the above resin composition contains a foaming agent, the above molded body can be a foaming molded body or a molded foamed body obtained by foaming the foaming molded body.

[0090] The above-described resin composition can be processed into molded bodies of various shapes. Examples of such molded bodies include paper, film, sheet, tube, plate, rod, container, bag, component, etc. Furthermore, the above-described molded bodies can be composited with other molded bodies made of materials different from the resin composition of the first aspect of the present invention (e.g., fibers, filaments, ropes, textiles, woven fabrics, nonwoven fabrics, paper, film, sheet, tube, plate, rod, container, bag, component, foam, etc.).

[0091] The uses of the above-mentioned molded articles are not particularly limited and can be appropriately used in agriculture, fisheries, forestry, horticulture, medicine, hygiene products, clothing, non-clothing materials, packaging, automobiles, and building materials. They can also be appropriately used in other fields.

[0092] [Second Method]

[0093] The second aspect of the soil biodegradation promoter of the present invention is an agent that promotes the soil biodegradation of polylactic acid by using it. This soil biodegradation promoter contains at least a copolyester of lactic acid and other hydroxycarboxylic acids.

[0094] (Polylactic acid)

[0095] As mentioned above, polylactic acid (PLA) is known to have low biodegradability in soil. However, by using the soil biodegradation promoter of the second aspect of the present invention, the biodegradation of PLA in soil can be promoted.

[0096] Biodegradation refers to the decomposition of the target resin into water and carbon dioxide under the action of microorganisms, while soil biodegradation refers to the biodegradation of the target resin in the soil.

[0097] If the soil biodegradation promoter of the second aspect of the present invention is used, not only can the standard method of industrial composting be used to compost plastic materials with polylactic acid as the main component, but also home composting or soil burial methods can be used for composting.

[0098] Except for the points described below, the polylactic acid in the second method is the same as that in the first method, therefore detailed descriptions are omitted.

[0099] (Copolyester)

[0100] The second embodiment of the soil biodegradation promoter of the present invention contains a copolyester of lactic acid and other hydroxycarboxylic acids as an effective component for promoting soil biodegradation. This copolyester, through contact with polylactic acid, can promote the soil biodegradation of polylactic acid itself.

[0101] Furthermore, since this copolyester is a polyester containing lactic acid as one of its constituent monomers, it has good compatibility with polylactic acid (PLA) and can form a homogeneous mixture with PLA. As a result, a substantial decrease in the transparency of PLA can be avoided. Additionally, PLA can be plasticized, which can improve its elongation.

[0102] The copolyester described in the second method may be the same as the copolyester described in the first method, or it may be a copolyester of lactic acid and other hydroxycarboxylic acids that is not a copolyester described in the first method.

[0103] In the second embodiment, the copolyester can be any of the following: random copolymer, alternating copolymer, block copolymer, or graft copolymer. However, from the viewpoints of promoting soil biodegradation, transparency, and mechanical properties, and further from the viewpoint of availability, the copolyester is preferably a random copolymer. A random copolymer is a copolymer in which two or more monomer units are arranged in an irregular order. In the case where the copolyester is produced by microorganisms, it is usually a random copolymer.

[0104] However, the copolyester used in the second method may or may not meet the ratio of copolymer randomness described in the first method.

[0105] In the second approach, the lactic acid monomer unit in the copolyester can be either an L-lactic acid monomer unit or a D-lactic acid monomer unit. It can contain either one or both.

[0106] In the second embodiment, where the copolyester is produced by microorganisms, the lactic acid monomer units in the copolyester are substantially composed only of D-lactic acid monomer units. "Substantially composed 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 typically 90% or more, preferably 95% or more, and more preferably 99% or more.

[0107] The definition, specific examples, and preferred examples of the hydroxycarboxylic acids other than lactic acid contained in the copolyester of the second embodiment are the same as those described for the first embodiment, and therefore are omitted.

[0108] The ratio of lactic acid monomer units in the copolyester described in the second embodiment is not particularly limited. However, from the perspective of promoting the soil biodegradation of polylactic acid, the molar fraction of lactic acid monomer units relative to the total monomer units constituting the copolyester is preferably 10 to 70 mol%, more preferably 15 to 60 mol%, and even more preferably 15 to 50 mol%.

[0109] The molecular weight of the copolyester in the second embodiment is not particularly limited, and the weight-average molecular weight Mw can be, for example, 10,000 to 1,000,000, preferably 10,000 to 500,000. Furthermore, the weight-average molecular weight of the copolyester in the second embodiment is within the same range as that of the copolyester described in the first embodiment. This weight-average molecular weight value can be determined as described above.

[0110] The method for manufacturing the aforementioned copolyester in the second approach is not particularly limited and can be any method known in the past. Specifically, the method described above can be cited as an example.

[0111] The soil biodegradation promoter of the second aspect of the present invention may be formed solely from a copolyester of lactic acid and other hydroxycarboxylic acids, or may contain components other than the copolyester. Such other components include known resin additives, specifically: plasticizers, hydrolysis inhibitors, compatibilizers, antioxidants, ultraviolet 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.

[0112] There is no particular limitation on the content of copolyester in soil biodegradation promoters; for example, it can be 10-100% by weight. The lower limit can be 30% or more by weight, 50% or more by weight, 70% or more by weight, 90% or more by weight, or 99% or more by weight.

[0113] (How to use)

[0114] By using the soil biodegradation promoter of the second aspect of the present invention in contact with polylactic acid, the effect of promoting the soil biodegradation of polylactic acid can be obtained. Specifically, it is preferable to mix the two components in a manner that brings the soil biodegradation promoter and polylactic acid into contact with each other. For example, it is particularly preferable to uniformly mix the two components by melt mixing, mixing in an organic solvent, and subsequent solvent removal.

[0115] (Usage)

[0116] The amount of soil biodegradation promoter used in the second aspect of the present invention is sufficient to promote the 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 promoter in an amount of 1 part by weight or more and 200 parts by weight or less relative to 100 parts by weight of polylactic acid. More preferably, it is 5 parts by weight or more and 100 parts by weight or less, and even more preferably, it is 10 parts by weight or more and 80 parts by weight or less. The lower limit of the above-mentioned amount of copolyester can be 20 parts by weight or more, and it can also be 30 parts by weight or more. The upper limit can be 60 parts by weight or less, and it can also be 50 parts by weight or less.

[0117] The amount of soil biodegradation promoter used can be in the same range as the amount of copolyester relative to 100 parts by weight of polylactic acid as described in the first embodiment.

[0118] (Resin Composition)

[0119] A second aspect of the present invention can be a resin composition containing polylactic acid and the aforementioned soil biodegradation promoter. By incorporating the aforementioned soil biodegradation promoter, the soil biodegradation of polylactic acid is promoted, thus the aforementioned resin composition exhibits good soil biodegradability.

[0120] (Other ingredients)

[0121] The resin composition in the second embodiment may include polylactic acid and a thermoplastic resin other than the copolyester described above. There are no particular limitations on the other thermoplastic resin used; conventionally known resins may be used. Specific examples and proportions are the same as those described for the first embodiment.

[0122] The resin composition in the second embodiment may, to the extent that it does not impair the effects of the invention, appropriately contain other additives, just as in the first embodiment.

[0123] (use)

[0124] Similar to the first embodiment, the resin composition described above in the second embodiment can be formed into granules, which can be molded using a known molding process to obtain any molded article. Such a molded article also constitutes an embodiment of the present invention. The detailed and specific uses of the molded article are the same as in the first embodiment, and therefore are omitted here.

[0125] Because the molded body described above in the second method exhibits good soil biodegradability, it is particularly suitable for applications that can be composted through home composting or disposed of through soil burial. Specific examples include: packaging materials, food packaging materials, tableware, garbage bags, agricultural materials, coated paper, etc., but are not limited to these.

[0126] Preferred embodiments of this disclosure are set forth in the following items, but the invention is not limited to the following items.

[0127] [Project 1]

[0128] A resin composition comprising polylactic acid and a copolyester of lactic acid and other hydroxycarboxylic acids, wherein,

[0129] The copolyester has a weight-average molecular weight of 110,000 or higher, and

[0130] In the copolyester, the copolymer randomness calculated from the ratio (b / a) of the theoretical value (b) of the triple ratio of the other hydroxycarboxylic acids to the measured value (a) of the triple ratio of the other hydroxycarboxylic acids is 0.5 to 3.0.

[0131] [Project 2]

[0132] According to the resin composition described in Project 1, wherein...

[0133] The other hydroxycarboxylic acids are 3-hydroxyalkyl acids.

[0134] [Project 3]

[0135] The resin composition according to item 1 or 2, wherein,

[0136] The other hydroxycarboxylic acids are selected from at least one of 3-hydroxybutyric acid, 3-hydroxyvalerate, 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.

[0137] [Project 4]

[0138] The resin composition according to any one of items 1 to 3, wherein,

[0139] The other hydroxycarboxylic acid is 3-hydroxybutyric acid.

[0140] [Project 5]

[0141] The resin composition according to any one of items 1 to 4, wherein,

[0142] The lactic acid monomer unit in the copolyester is a D-lactic acid monomer unit.

[0143] [Project 6]

[0144] The resin composition according to any one of items 1 to 5, wherein,

[0145] The molar fraction of the lactic acid monomer unit in the copolyester is 10 to 70 moles.

[0146] [Project 7]

[0147] The resin composition according to any one of items 1 to 6, wherein,

[0148] The weight-average molecular weight of the copolyester is above 200,000 and below 800,000.

[0149] [Project 8]

[0150] The resin composition according to any one of claims 1 to 7, wherein,

[0151] The copolymer randomness is 0.8~3.0.

[0152] [Project 9]

[0153] The resin composition according to any one of items 1 to 8, wherein,

[0154] The amount of the copolyester is 10 to 100 parts by weight relative to 100 parts by weight of the polylactic acid.

[0155] [Project 10]

[0156] The resin composition according to any one of items 1 to 9, wherein,

[0157] The copolyester is a soil biodegradation promoter that facilitates the biodegradation of polylactic acid in soil.

[0158] [Project 11]

[0159] A molded body formed from any one of the resin compositions described in items 1 to 10.

[0160] [Project 12] A soil biodegradation promoter that promotes the soil biodegradation of polylactic acid.

[0161] The soil biodegradation promoter contains a copolyester of lactic acid and other hydroxycarboxylic acids.

[0162] The copolyester has a weight-average molecular weight of 110,000 or higher, and

[0163] In the copolyester, the copolymer randomness calculated from the ratio (b / a) of the theoretical value (b) of the triple ratio of the other hydroxycarboxylic acids to the measured value (a) of the triple ratio of the other hydroxycarboxylic acids is 0.5 to 3.0.

[0164] [Project 13]

[0165] A method for promoting the biodegradation of polylactic acid in soil, wherein the method involves contacting polylactic acid with a copolyester of lactic acid and other hydroxycarboxylic acids.

[0166] The copolyester has a weight-average molecular weight of 110,000 or higher, and

[0167] In the copolyester, the copolymer randomness calculated from the ratio (b / a) of the theoretical value (b) of the triple ratio of the other hydroxycarboxylic acids to the measured value (a) of the triple ratio of the other hydroxycarboxylic acids is 0.5 to 3.0.

[0168] [Project 14] The use of copolyesters of lactic acid and other hydroxycarboxylic acids as soil biodegradation promoters for polylactic acid.

[0169] The copolyester has a weight-average molecular weight of 110,000 or higher, and

[0170] In the copolyester, the copolymer randomness calculated from the ratio (b / a) of the theoretical value (b) of the triple ratio of the other hydroxycarboxylic acids to the measured value (a) of the triple ratio of the other hydroxycarboxylic acids is 0.5 to 3.0.

[0171] [Item 15] A soil biodegradation promoter that promotes the soil biodegradation of polylactic acid, said soil biodegradation promoter containing a copolyester of lactic acid and other hydroxycarboxylic acids.

[0172] [Project 16]

[0173] A resin composition comprising polylactic acid and the soil biodegradation promoter described in item 15.

[0174] [Project 17]

[0175] A method for promoting the biodegradation of polylactic acid in soil, the method comprising: contacting polylactic acid with a copolyester of lactic acid and other hydroxycarboxylic acids.

[0176] [Project 18]

[0177] The use of copolyesters of lactic acid and other hydroxycarboxylic acids as soil biodegradation promoters to promote the biodegradation of polylactic acid.

[0178] Example

[0179] The present invention will be further described in detail below through examples. However, the present invention is not limited to these examples. Furthermore, the overall gene manipulation can be performed, for example, as described in Molecular Cloning (Cold Spring Harbor Laboratory Press (1989)). In addition, the enzymes, cloning hosts, etc. used in gene manipulation can be purchased from commercial suppliers and used according to their instructions. It should be noted that, as an enzyme, any enzyme that can be used in gene manipulation is acceptable, and there is no particular limitation.

[0180] Breeding of hydrogen-producing bacteria from copolyester (LAHB)

[0181] Gene recombination was performed on Cupriavidus necator H16 strain, and the PHA polymerase gene phaC was added to the genome. 1Re Replace with another PHA polymerase gene, and destroy the PHA degradase gene phaZ. 1,2,6 To enhance glucose utilization, the G at position 793 of the N-acetylglucosamine-introducing gene nagE was replaced with C, thereby preparing the KNK005ΔphaZ gene, which further disrupts the gene nagR encoding a transcriptional regulator. 1,2,6 / nagE G793C.dR strain (refer to International Publication No. 2017 / 104722).

[0182] In addition, preparations were made to use the aforementioned KNK005ΔphaZ 1,2,6 The PHA polymerase gene phaC on the genome of / nagE G793C.dR strain 1Re Replace with the STQK mutant (replacing the polymerase PhaC1 from Pseudomonas sp. 61-3). Ps The H16 phaC of PHA polymerase (where serine at position 325 is replaced with threonine and glutamine at position 481 is replaced with lysine) 1Re ::STQK ΔphaZ 1,2,6 / nagE G793C.dR. This strain was used as the host (1).

[0183] (Preparation of plasmids for gene destruction)

[0184] Using genomic DNA from *C. necator* strain H16 as a template, PCR was performed using oligomeric DNA as primers (Sequence Nos. 1 and 2). Prime STAR GXL DNA polymerase (manufactured by Takara-bio) was used as the DNA polymerase. Similarly, PCR was performed using DNA as primers (Sequence Nos. 3 and 4). Using the two DNA fragments obtained from the above PCR as templates, overlap PCR was performed using DNA as primers (Sequence Nos. 3 and 4). The resulting DNA fragment was a fragment approximately 500 base pairs upstream and downstream of the ORF of acetyl-CoA acetyltransferase (Locus tag: H16_A1438). This DNA fragment was treated with the restriction endonuclease *SmiI*, and then ligated using DNA ligase to the similarly *SmiI*-treated vector pNS2X-sacB (documented in Japanese Patent Application Laid-Open No. 2007-259708). The resulting gene-destroying plasmid containing the base sequence shown in Sequence No. 5 was named pNS2X-sacB-ΔphaA. The plasmid used for gene disruption is a plasmid that is used to disrupt the gene phaA:A1438, which encodes acetyl-CoA acetyltransferase.

[0185] (Preparation of plasmids for gene transfer)

[0186] To introduce the gene clusters required for LAHB generation into the C. necator genome, a plasmid for gene introduction was prepared. The plasmid pNS2X-sacB-phaJ4b::REP-LDH was created. Lm It can be introduced via the REP promoter into the lactate dehydrogenase LDH from Leuconostocmesenteroides in the form of an ORF that replaces phaJ4b (Locus tag:H16_B0397) on the host genome (1). Lm The gene arrangement expressed. This plasmid is a plasmid into the pNS2X-sacB vector by ligation of the DNA fragment shown in sequence number 6. By using this plasmid, C. necator can be endowed with the ability to produce D-lactic acid from glucose. This plasmid was used as a gene introduction plasmid (1).

[0187] Similarly, pNS2X-sacB-phaJ4a::lacN17-PCT was fabricated. Es It can be introduced via the lacN17 promoter into the propionyl-CoA transferase PCT from Epulopiscium sp. in the form of an ORF that replaces phaJ4a (Locus tag:H16_A1070) on the host genome (1). EsThe expressed gene sequence. This plasmid is a plasmid into the pNS2X-sacB vector by ligating the DNA fragment shown in sequence number 7. By using this plasmid, CoA can be added to lactate generated from glucose, thereby supplying the matrix for copolyester polymerase. This plasmid is used as a gene introduction plasmid (2).

[0188] (Genetic alterations in C. necator based on homologous recombination)

[0189] The aforementioned gene-destruction plasmid or gene-introduction plasmid was introduced into Escherichia coli S17-1 strain (ATCC47055) via electroporation and then mixed with the target C. necator gene recombinant strain on Nutrient Agar medium (Difco) for conjugation transfer.

[0190] Strains with plasmids inserted into their genomes were screened and isolated from a mixed culture on Simon's agar medium containing 250 mg / L 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). After further purification of the isolates on Nutrient Agar medium containing 250 mg / L kanamycin sulfate, the strains were transferred to Nutrient Agar medium containing 15% sucrose to obtain plasmid-free strains. Through homologous recombination, two strains were generated during the plasmid-free stage: a strain reverting to the original genome arrangement and a strain with the target gene altered. The latter was isolated by colony PCR. The genetically altered strain was purified again on Nutrient Agar medium containing sucrose to obtain the homologous recombinant strain.

[0191] Using gene transfer plasmid (1) and gene transfer plasmid (2), the host (1) was genetically altered using the above method to create H16 phaC. 1Re ::STQK ΔphaZ 1,2,6 / nagE G793C.dR phaJ4a::lacN17-PCT Es phaJ4b::REP-LDH Lm Using it as a host (2). Furthermore, using a gene-destructive plasmid, gene alterations were performed on this strain using the methods described above, resulting in the creation of H16 phaC. 1Re ::STQK ΔphaZ 1,2,6 / nagE G793C.dR phaJ4a::lacN17-PCT Es phaJ4b::REP-LDH LmΔphaA. Use it as the host (3).

[0192] The DNA fragment encoding STQK was amplified by PCR, and then ligated with a DNA fragment obtained by treating the pCUP2 vector with MunI and SpeI (refer to International Publication No. 2007 / 049716) using DNA ligase to obtain a vector expressing the strong lacUV5 promoter (Sequence No. 8). This expression vector was introduced into hosts (2) and (3) via electroporation to obtain strains that served as hosts (2') and (3'). Kanamycin was added appropriately to maintain the plasmid.

[0193] Using the host (2') and (3'), copolyester (LAHB) was manufactured using glucose as a carbon source in a fermenter.

[0194] First, as a pre-culture, overnight culture was performed at 30°C using meat medium (composition: 1% (w / v) meat extract, 1% (w / v) Bacto tryptone, 0.2% (w / v) yeast extract, 0.9% (w / v) disodium hydrogen phosphate 1 / 2 hydrate, 0.15% (w / v) potassium dihydrogen phosphate, 50 μg / L kanamycin).

[0195] Add the pre-culture solution to a 500ml Sakaguchi flask containing 100ml meat culture medium and incubate with shaking at 30°C for 6 hours.

[0196] Next, the culture medium was inoculated into a 5L fermenter (Maru-Dashi Bioengineering Bioneer Neo type) containing 1.8L of PHA production medium. Operating conditions were set at a culture temperature of 30°C, a stirring speed of 500 rpm, and an aeration rate of 1.8L / min. The pH was maintained between 6.7 and 6.8 for 48 hours. A 7% ammonium hydroxide aqueous solution was used for pH adjustment.

[0197] The PHA production medium consisted of: 0.578% (w / v) disodium hydrogen phosphate di-1,2-hydrate, 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 (containing 1.6% (w / v) ferric(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, initially at a concentration of 20 g / L. If glucose was consumed to 10 g / L, it was maintained at 10 g / L thereafter.

[0198] The bacterial cells were recovered from the culture medium by centrifugation, purified with pure water and ethanol, and then dried under vacuum. The polymer was extracted from the dried bacterial cells with chloroform, and the chloroform was completely removed using a rotary evaporator and a vacuum dryer to obtain a copolyester of lactic acid and 3-hydroxybutyric acid (LAHB).

[0199] The copolyester obtained from the host (2') through 1 The molar fraction of lactic acid determined by ¹H NMR was 15 mol%, and the weight-average molecular weight was 540,000. This was designated as HPL-1.

[0200] The copolyester obtained from the host (3') through 1 The molar fraction of lactic acid determined by ¹H NMR was 20 mol%, and the weight-average molecular weight was 370,000. This was designated as HPL-2.

[0201] (Synthesis Example 1) [Synthesis of ENL-1]

[0202] Reference: Following the description in PNAS 105(45)17323-17327(2008), a copolyester of lactic acid and 3-hydroxybutyric acid was biosynthesized using recombinant Escherichia coli. The copolyester was extracted from the bacterial cells using chloroform after culturing at an aeration rate of 1 vvm and stirring at 500 rpm.

[0203] The obtained copolyester had a lactic acid molar fraction of 45 mol and a weight-average molecular weight (Mw) of 119,000.

[0204] (Synthesis Example 2) [Synthesis of ENL-2]

[0205] Using the same method as described above, the copolyester was cultured at an aeration rate of 2 vvm and a stirring rate of 500 rpm, resulting in a lactic acid mole fraction of 22 mol% and a weight-average molecular weight (Mw) of 76,000.

[0206] (Synthesis Example 3) [Synthesis of ENL-3]

[0207] Using the same method as described above, the copolyester was cultured at an aeration rate of 0.5 vvm and a stirring speed of 500 rpm, resulting in a lactic acid molar fraction of 41 mol% and a weight-average molecular weight (Mw) of 54,000.

[0208] (Synthesis Example 4) [Synthesis of ENL-4]

[0209] Using the same method as described above, the copolyester was cultured at an aeration rate of 0.5 vvm and a stirring rate of 300 rpm, resulting in a lactic acid mole fraction of 54 mol% and a weight-average molecular weight (Mw) of 73,000.

[0210] (Synthetic Example 5) [Synthesis of PHBH-1]

[0211] According to International Patent Publication No. 2015 / 115619, a copolyester of 3-hydroxyhexanoic acid and 3-hydroxybutyric acid was biosynthesized by recombinant hydrogen bacteria. The biosynthesized copolyester was extracted from the bacterial cells using chloroform.

[0212] The obtained copolyester had a 3-hydroxyhexanoic acid molar fraction of 11 mol% and a weight-average molecular weight (Mw) of 63,000.

[0213] [Calculation of Copolymer Randomness]

[0214] Nuclear magnetic resonance (NMR) was used on various copolyesters (LAHB) under the conditions of deuterated chloroform as solvent, room temperature, and a cumulative total of 8 times. 1 The H-NMR spectrum was measured.

[0215] Based on the obtained spectrum, the signal areas (X) in the 1.25–1.29 ppm region and (Y) in the 1.25–1.39 ppm region when tetramethylsilane was 0 ppm were measured. The triploid ratio of 3-hydroxybutyric acid (3HB) was calculated using the formula: (X / Y) × 100 (a). Here, the signal in the 1.25–1.39 ppm region represents the signal from all the methyl groups in 3-hydroxybutyric acid, and the signal in the 1.25–1.29 ppm region represents the signal from the methyl group contained in the 3-hydroxybutyric acid triploid (3HB-3HB-3HB). As an example of these signals, the range of... 1 The illustration of the H-NMR spectrum near 1.3 ppm is shown in the figure. Figure 1 .

[0216] Furthermore, when the monomer arrangement is completely random, the mole fraction of 3HB is set as Z, and through Z... 2 The ratio of 3HB triplet to all 3HB triplet is obtained, i.e., the theoretical value of the 3HB triplet ratio (b).

[0217] Copolymer randomness, representing the degree of proximity between the monomer arrangement and random arrangement of the copolyester, is determined in the form of b / a. The results are shown in Table 1.

[0218] (Example 1)

[0219] [Determination of tensile elongation at break]

[0220] 10 g of a mixture consisting of 70 wt% polylactic acid (Ingeo 10361D, NatureWorks) and 30 wt% copolyester (HPL-1) was dissolved in chloroform. The solvent was removed / dried to obtain a polymer mixture sample. The obtained sample was formed into a 0.2 mm thick film using a vacuum hot press at 180 °C. The sample was then punched into the shape of a JIS 5B tensile test piece to produce a test piece.

[0221] For this test piece, the tensile elongation at break was determined using a Shimadzu AG-IS universal testing machine equipped with a constant temperature bath. The testing temperature was 22±1℃, and the testing speed was 1 mm / min.

[0222] [Drape Evaluation]

[0223] A twin-screw extruder (Technovel ULTNano05, screw diameter 1.5cm, L / D=13.33) with the barrel and die temperature set to 140°C was used to melt-blend and extrude 10g of a mixture consisting of 70% by weight polylactic acid (Ingeo 10361D, NatureWorks) and 30% by weight copolyester (HPL-1). The molten thread extruded from the 2.5mm diameter die was collected and fed to the cooling process. The operability at this stage was evaluated as an indicator of sag, as described below.

[0224] The extruded molten wire has sufficient melt viscosity / tension to ensure that wire of a certain thickness is stably collected for the cooling process.

[0225] ○: The extruded molten wire has a moderate melt viscosity / tension, and the speed at which the wire is fed to the cooling process can be controlled by the sag of the molten resin at the die exit, and then collected in the cooling process.

[0226] The extruded molten wire has low melt viscosity / tension. Although the wire thickness fluctuates, it can still be continuously collected to the cooling process.

[0227] ×: The melt viscosity / tension of the extruded molten wire is too low. When collecting, the wire is excessively stretched and breaks during the collection process, making it difficult to transport to the cooling process.

[0228] (Examples 2-4)

[0229] Using HPL-2 as the copolyester, the mixing ratio of polylactic acid and copolyester was changed to the ratio shown in Table 1. Otherwise, the polymer mixed film was obtained in the same manner as in Example 1. The tensile elongation at break was measured, and the drape was evaluated by melt extrusion.

[0230] (Example 5)

[0231] Using ENL-1 as the copolyester, the mixing ratio of polylactic acid and copolyester was changed to the ratio shown in Table 1. Otherwise, the polymer mixed film was obtained in the same manner as in Example 1. The tensile elongation at break was measured, and the drape was evaluated by melt extrusion.

[0232] (Comparative Example 1)

[0233] Polylactic acid (Ingeo 10361D, NatureWorks) was used alone, and the elongation at break was measured in the same manner as in Example 1. The drape was evaluated by melt extrusion.

[0234] (Comparative Example 2)

[0235] Using PHBH-1 as the copolyester, the mixing ratio of polylactic acid and copolyester was changed to the ratio shown in Table 1. Otherwise, the polymer mixed film was obtained in the same manner as in Example 1. The tensile elongation at break was measured, and the drape was evaluated by melt extrusion.

[0236] (Comparative Example 3)

[0237] Using ENL-2 as the copolyester, the mixing ratio of polylactic acid and copolyester was changed to the ratio shown in Table 1. Otherwise, the polymer mixed film was obtained in the same manner as in Example 1. The tensile elongation at break was measured, and the drape was evaluated by melt extrusion.

[0238] (Comparative Example 4)

[0239] Using ENL-3 as the copolyester, the mixing ratio of polylactic acid and copolyester was changed to the ratio shown in Table 1. Otherwise, the polymer mixed film was obtained in the same manner as in Example 1. The tensile elongation at break was measured, and the drape was evaluated by melt extrusion.

[0240] (Comparative Examples 5-8)

[0241] Using ENL-4 as the copolyester, the mixing ratio of polylactic acid and copolyester was changed to the ratio shown in Table 1. Otherwise, the polymer mixed film was obtained in the same manner as in Example 1. The tensile elongation at break was measured, and the drape was evaluated by melt extrusion.

[0242]

[0243] As shown in Table 1, in Examples 1 to 5, which are polylactic acid copolymers with a Mw of 110,000 or more and a copolymer randomness of 0.5 to 3.0, the tensile elongation at break is significantly improved and the drape is also improved compared with Comparative Example 1, which uses polylactic acid monomers.

[0244] On the other hand, in Comparative Example 2, which incorporated PHBH-1, a copolyester without lactic acid, the elongation at break was slightly improved but not sufficiently, and the drape was not improved. Furthermore, in Comparative Examples 3-8, which did not meet either or both of the conditions for Mw and the conditions for copolymer randomness, the elongation at break and drape were not sufficiently improved.

[0245] [Preparation of test samples]

[0246] Polylactic acid (Ingeo 2003D, NatureWorks, 4 mol% D body) was melt-blended with copolyester (HPL-2) at a weight ratio of 60:40 or 70:30, then freeze-crushed to adjust the average particle size to approximately 500 μm. The resulting powder was used as the test sample for Examples 6 and 7. Cellulose (Cellulose microcrystalline, Merck KGaA) was used as a control (Ref. Example 1).

[0247] [Home Composting Experiment]

[0248] A home composting experiment was conducted in accordance with JIS K6953-2.

[0249] For evaluating biodegradability (soil decomposition), compost was prepared by mixing plant-based soil (100g, matured at 28°C for 14 days), sea sand (85g), and water (15g). The resulting compost was placed in a glass container, and then mixed with 7g of cellulose (used as a test sample or control) and 7g of water. The mixture was kept at 28°C. The biodegradability was determined by subtracting the carbon dioxide production without the mixed test sample or cellulose from the carbon dioxide production, and then dividing by the theoretical carbon dioxide production. Water was added to the compost weekly to maintain its initial weight. The results are shown in Table 2.

[0250]

[0251] The test results confirmed that the biodegradation of cellulose in Reference Example 1 proceeded smoothly.

[0252] In the test sample of Example 6, it was assumed that only the copolyester underwent complete biodegradation and was converted into carbon dioxide, at which point the degree of biodegradation was 42%, compared to 32% in Example 7. The presence of biodegradation degrees above these levels implies that, in addition to the copolyester, other components, namely polylactic acid, also underwent biodegradation.

[0253] The measurement results show that at day 124 in Example 6 and day 150 in Example 7, the biodegradation rate exceeded the rate assumed when only the copolyester underwent complete biodegradation, confirming that polylactic acid (PLA) biodegradation also occurred in addition to the copolyester. Based on these results, it can be concluded that the presence of the copolyester promotes the biodegradation of PLA in compost.

[0254] The biodegradability at day 180 reached 48% in Example 6 and 34% in Example 7.

[0255] <Inspection>

[0256] The aforementioned mixture of copolyester and polylactic acid exhibits high transparency. This suggests that the two components are compatible with each other; or that, on a scale smaller than the wavelength of light, islands of the copolyester are formed in a micro-dispersed morphology within the polylactic acid.

[0257] In the former case, due to the plasticizing effect of the copolyester, the molecular chains of polylactic acid are easy to move, degrading enzymes are easy to bind, or water molecules are easy to penetrate. As a result, the biodegradation of polylactic acid may be easy.

[0258] In the latter case, the islands of copolyester exposed on the surface of the mixture are decomposed by copolyester-degrading enzymes, creating voids and forming very fine irregularities on the polylactic acid (PLA) surface, potentially significantly increasing the surface area. As a result, chemical hydrolysis of PLA proceeds, generating enzymatically degradable oligomers, possibly promoting the biodegradation of PLA. At this point, the low-molecular-weight copolyester retained in the PLA voids acts as an acid, potentially further promoting surface hydrolysis.

[0259] In addition, if the surface of the mixture contains copolyester, microorganisms that can secrete enzymes that hydrolyze the copolyester and utilize the decomposition products will preferentially proliferate. The hydrolytic enzymes produced by these microorganisms are present in high concentrations, which may promote the hydrolysis of polylactic acid.

[0260] It is speculated that the soil biodegradation promoting effect of polylactic acid is achieved based on any one or a combination of two or more of the mechanisms described above.

[0261] (Example 8)

[0262] [Preparation of Complex Particles]

[0263] 10g of a mixture consisting of 97% by weight polylactic acid (Ingeo 2003D, NatureWorks) and 3% by weight copolyester (HPL-2) was dried at 50°C for 12 hours. The mixture was then melt-blended and extruded using a twin-screw extruder (Technovel ULTNano05, screw diameter 1.5cm, L / D=13.33) with the barrel and die set to 190°C. The molten wire extruded from the die with a diameter of 2.5mm was collected, air-cooled in the cooling process, and then cut into granules of approximately 4mm in length using a granulator to obtain composite particles.

[0264] (Comparative Example 9)

[0265] Only 10g of polylactic acid (Ingeo 2003D, manufactured by NatureWorks) was used, otherwise, polylactic acid particles were obtained in the same manner as in Example 8.

[0266] Using a vacuum heating dryer (YAMATO Scientific DP300), the composite particles or particles obtained in Example 8 or Comparative Example 9 were dried at 80°C under vacuum for 4 hours. Then, using a hydraulic vacuum hot press (IMC-11FD type manufactured by Imoto Manufacturing Co., Ltd.), a pressed plate with a thickness of 4 mm was produced at 170°C under vacuum and a molding pressure of 1.4 MPa.

[0267] The pressed plate was frozen and fractured using liquid nitrogen. Images of the fracture surface observed using a scanning electron microscope (SEM, JSM-IT300HR, manufactured by Nippon Electron Ltd.) are shown below. Figure 2 and Figure 3 .

[0268] exist Figure 2 In the test piece of Example 8 shown, numerous circular depressions were observed on the surface. These depressions were formed by a very fine dispersion of a copolyester of 3-hydroxybutyric acid and lactic acid in polylactic acid.

[0269] On the other hand, Figure 3 Such a structure was not identified in the test piece of Comparative Example 9 shown.

[0270] for Figure 2 Based on SEM observations, the diameters of 200 circular indentations were measured using the image analysis software ImageJ. A histogram representing the distribution of the obtained diameters is presented below. Figure 4 The diameters are roughly distributed in the range of 100~350nm, with an average diameter of 185±5nm.

Claims

1. A resin composition comprising polylactic acid and a copolyester of lactic acid and other hydroxycarboxylic acids, wherein, The copolyester has a weight-average molecular weight of 110,000 or higher, and In the copolyester, the copolymer randomness calculated from the ratio (b / a) of the theoretical value (b) of the triple ratio of the other hydroxycarboxylic acids to the measured value (a) of the triple ratio of the other hydroxycarboxylic acids is 0.5 to 3.

0.

2. The resin composition according to claim 1, wherein, The other hydroxycarboxylic acids are 3-hydroxyalkyl acids.

3. The resin composition according to claim 1, wherein, The other hydroxycarboxylic acids are selected from at least one of 3-hydroxybutyric acid, 3-hydroxyvalerate, 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-hydroxybutyric 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. The resin composition according to any one of claims 1 to 4, wherein, The molar fraction of the lactic acid monomer unit in the copolyester is 10 to 70 moles.

7. The resin composition according to any one of claims 1 to 4, wherein, The weight-average molecular weight of the copolyester is above 200,000 and below 800,000.

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

0.

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

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

11. A molded article formed from the resin composition according to any one of claims 1 to 4.

12. A soil biodegradation promoter that promotes the soil biodegradation of polylactic acid. The soil biodegradation promoter contains a copolyester of lactic acid and other hydroxycarboxylic acids. The copolyester has a weight-average molecular weight of 110,000 or higher, and In the copolyester, the copolymer randomness calculated from the ratio (b / a) of the theoretical value (b) of the triple ratio of the other hydroxycarboxylic acids to the measured value (a) of the triple ratio of the other hydroxycarboxylic acids is 0.5 to 3.

0.

13. A method for promoting the biodegradation of polylactic acid in soil, wherein the method involves contacting a copolyester of lactic acid and other hydroxycarboxylic acids with polylactic acid. The copolyester has a weight-average molecular weight of 110,000 or higher, and In the copolyester, the copolymer randomness calculated from the ratio (b / a) of the theoretical value (b) of the triple ratio of the other hydroxycarboxylic acids to the measured value (a) of the triple ratio of the other hydroxycarboxylic acids is 0.5 to 3.

0.

14. The use of copolyesters of lactic acid and other hydroxycarboxylic acids as soil biodegradation promoters for polylactic acid. The copolyester has a weight-average molecular weight of 110,000 or higher, and In the copolyester, the copolymer randomness calculated from the ratio (b / a) of the theoretical value (b) of the triple ratio of the other hydroxycarboxylic acids to the measured value (a) of the triple ratio of the other hydroxycarboxylic acids is 0.5 to 3.

0.

15. A soil biodegradation promoter that promotes the soil biodegradation of polylactic acid, said soil biodegradation promoter comprising a copolyester of lactic acid and other hydroxycarboxylic acids.

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

17. A method for promoting the biodegradation of polylactic acid in soil, the method comprising: This involves contacting polylactic acid with a copolyester containing lactic acid and other hydroxycarboxylic acids.

18. The use of copolyesters of lactic acid and other hydroxycarboxylic acids as soil biodegradation promoters to promote the soil biodegradation of polylactic acid.

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