Biodegradable plastic decomposing agent, biodegradable plastic composition, and molded article thereof

Abstract

A biodegradable plastic decomposing agent comprising: a shell layer containing a biodegradable amphiphilic polymer; and a core layer containing a crude biodegradable plastic decomposing agent. At least a portion of the surface of the core layer is covered with the shell layer.

Description

Biodegradable plastic decomposer, biodegradable plastic composition and molded article thereof

[0001] This disclosure relates to a biodegradable plastic decomposer, a biodegradable plastic composition, and a molded article thereof. This application claims priority to Japanese Patent Application No. 2024-155377, filed on September 9, 2024, the contents of which are incorporated herein by reference.

[0002] Plastics are widely used as packaging materials due to their excellent moldability, strength, water resistance, transparency, and other properties. However, plastics are poorly biodegradable, and when discarded in nature after use, they can remain for long periods of time and cause environmental damage. In response to this, biodegradable resins that biodegrade or hydrolyze in soil or water and are useful for preventing environmental pollution have recently attracted attention, and packaging materials using biodegradable resin compositions have been put to practical use. Patent Document 1, for example, describes a resin composition used in packaging materials, containing a biodegradable polyester such as polylactic acid, a polysaccharide such as starch, and a polyhydric alcohol such as glycerin. However, biodegradation of biodegradable packaging materials such as those described in Patent Document 1 requires the presence of microorganisms, but it is known that such microorganisms are scarce in the ocean. Therefore, biodegradation of such biodegradable packaging materials requires a long biodegradation period, and the environmental impact is not reduced. Therefore, Non-Patent Documents 1 and 2 describe enzyme-encapsulated biodegradable plastics that encapsulate degrading enzymes capable of decomposing biodegradable plastics.

[0003] Japanese Patent Application Laid-Open No. 2003-335934

[0004] Q. Huang et al. Polymer Degradation and Stability, 190, 109643(2021)Q. Huang et al. Biomacromolecules, 24, 5836-5846 (2023)

[0005] However, enzymes tend to aggregate inside enzyme-encapsulated biodegradable plastics such as those described in Non-Patent Documents 1 and 2. It is known that enzyme aggregation in plastics reduces mechanical strength and biodegradability.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a decomposer for biodegradable plastics (hereinafter also referred to as "biodegradable plastic decomposer") that has excellent dispersibility in biodegradable plastics and can suppress a decrease in the biodegradability and mechanical strength of biodegradable plastics, a biodegradable plastic composition containing the biodegradable plastic decomposer, and a molded article thereof.

[0007] The present disclosure encompasses the following aspects. [1] A biodegradable plastic decomposer comprising: a shell layer containing a biodegradable amphiphilic polymer; and a core layer containing a crude biodegradable plastic decomposer, wherein at least a portion of the surface of the core layer is coated with the shell layer. [2] The biodegradable plastic decomposer according to [1], wherein the mass ratio of crude biodegradable plastic decomposer to amphiphilic polymer is preferably 1:10 to 100:1, more preferably 1:7 to 70:1, and even more preferably 1:5 to 50:1. [3] The biodegradable plastic decomposer according to [1] or [2], wherein the core layer and the shell layer are preferably bonded by intermolecular bonds, more preferably by hydrogen bonds, hydrophobic interactions, or van der Waals forces. [4] The biodegradable plastic decomposer according to any of [1] to [3], wherein the amphiphilic polymer is preferably at least one selected from the group consisting of polyethylene glycol, polypropylene glycol, and polyvinyl alcohol, more preferably polyethylene glycol. [5] The biodegradable plastic decomposer according to any one of [1] to [4], wherein the crude biodegradable plastic decomposer is preferably at least one selected from the group consisting of depolymerase, esterase, lipase, cutinase, carboxylesterase, protease, and polyesterase, more preferably cutinase, and even more preferably Humicola insolens cutinase (HiC) obtained from the thermophilic fungus Humicola insolens. [6] The biodegradable plastic decomposer according to any one of [1] to [5], wherein the mass average molecular weight of the amphiphilic polymer is preferably 300 to 30,000, more preferably 400 to 20,000, and even more preferably 600 to 15,000.[7] The biodegradable plastic is preferably at least one selected from the group consisting of biodegradable polyesters, ester derivatives of polysaccharides, polycarbonates, polyurethanes, and polyamides, more preferably biodegradable polyesters, even more preferably aliphatic polyesters or aliphatic aromatic polyesters, and particularly preferably PLA (polylactic acid), PHA (polyhydroxyalkanoate), PES (polyethylene succinate), PBS (polybutylene succinate), PBAT (polybutylene adipate terephthalate), PBSA (polybutylene succinate adipate), PGA (polyglycolic acid), PETS (polyethylene terephthalate succinate), PA (polyamide), PC (polycarbonate), PU (polyurethane), or PBSu (polybutylene succinate). [1] The biodegradable plastic decomposition agent according to any one of [6] to [7]. [8] The biodegradable plastic decomposer according to any one of [1] to [7], which is used to decompose biodegradable plastics by immersing in water a biodegradable plastic composition containing biodegradable plastics and the biodegradable plastic decomposer, or a molded article formed from the biodegradable plastic composition. [9] A biodegradable plastic composition containing biodegradable plastics and the biodegradable plastic decomposer according to any one of [1] to [8].

[10] The biodegradable plastic composition according to [9], which has at least one of the following properties (i) and (ii): (i) When the weight loss of an evaluation composition containing the biodegradable plastics and the same amount of crude biodegradable plastic decomposer in place of the biodegradable plastic decomposer contained in the biodegradable plastic composition, measured under the following condition (i), is taken as 100, the weight loss is 105 or more. (ii) When the tensile strength of the composition for evaluation measured under the following condition (ii) is taken as 1, the composition has a tensile strength of 0.8 times or more.Condition (i): A film having a thickness of approximately 50 to 200 μm, prepared by heat-pressing the biodegradable plastic composition, was cut into a 1 cm × 1 cm square, and the film was immersed in 2 mL of 100 mM phosphate buffer solution at pH 7.5 in a 5 mL sample bottle. The film was maintained at the optimum temperature for the biodegradable plastic decomposer to decompose the biodegradable plastic while shaking. After 5 days, the film was removed and washed with pure water. After wiping off the water and drying at room temperature, the weight was measured and the weight loss was calculated using the following formula 1. The evaluation composition was hot-pressed to produce a film approximately 50 to 200 μm thick, which was then cut into a 1 cm x 1 cm square. The film was then immersed in 2 mL of 100 mM phosphate buffer solution at pH 7.5 in a 5 mL sample bottle and shaken while maintained at the optimum temperature at which the crude biodegradable plastic decomposer contained in the evaluation composition decomposes the biodegradable plastic contained in the evaluation composition. After 5 days, the film was removed, washed with pure water, wiped dry, and dried at room temperature. The weight was then measured and the weight loss was calculated using the following formula 1. Formula 1: Weight Loss (wt%) = [(Weight of Film Before Immersion) - (Weight of Film 5 Days After Immersion)] ÷ (Weight of Film Before Immersion) x 100 (wt%) Condition (ii): Using a film approximately 50 to 200 μm thick produced by hot-pressing the biodegradable plastic composition, the tensile strength of the film obtained from the biodegradable plastic composition was measured in accordance with JIS K-6251-5. The composition for evaluation is hot-pressed to produce a film having a thickness of approximately 50 to 200 μm, and the tensile strength of the film obtained from the composition for evaluation is measured in accordance with JIS K-6251-5.

[11] A molded article formed from the biodegradable plastic composition according to [9] or

[10] .

[12] A method for producing the biodegradable plastic decomposer according to any one of [1] to [8].

[13] A method for producing the biodegradable plastic composition according to [9] or

[10] .

[14] A method for producing the biodegradable plastic composition according to [9] or

[10] , which comprises melt-kneading the biodegradable plastic decomposer and the biodegradable plastic.

[15] A method for producing a molded article, comprising molding the biodegradable plastic composition according to [9] or

[10] .

[0008] The biodegradable plastic decomposer of the present disclosure, when blended with biodegradable plastics, can improve the biodegradability of the biodegradable plastics. Therefore, the environmental impact can be further reduced. Furthermore, the biodegradable plastic decomposer of the present disclosure has excellent dispersibility, which can prevent a decrease in the mechanical strength and biodegradability of the biodegradable plastics. A biodegradable plastic composition containing the biodegradable plastic decomposer of the present disclosure can improve the biodegradability of the molded article when formed into a molded article. Therefore, the environmental impact can be further reduced. Furthermore, the biodegradable plastic decomposer of the present disclosure is uniformly dispersed, which can prevent a decrease in the mechanical strength and biodegradability of the molded article when formed into a molded article. The molded article of the present disclosure has excellent biodegradability because it contains the biodegradable plastic decomposer. Therefore, the environmental impact can be further reduced. Furthermore, the molded article of the present disclosure has the biodegradable plastic decomposer uniformly dispersed, which can prevent a decrease in mechanical strength and biodegradability.

[0009] 1 is a diagram showing a biodegradable plastic decomposer according to the present disclosure; FIG. 2 is a diagram showing a molded article (film) formed from the biodegradable plastic composition according to the present disclosure; FIG. 3 is a diagram showing biodegradable plastic decomposers produced in Production Examples 1, 4, and 6; FIG. 4 is a diagram showing molded articles (films) produced in Examples and Comparative Examples; FIG. 5 is a graph showing the results of weight change in a degradation test of a molded article (film) when PBS was used in Examples and Comparative Examples; FIG. 6 is a diagram showing the appearance of a film surface after 24 hours in a degradation test of a molded article (film) when PBS was used in Examples and Comparative Examples; FIG. 7 is a graph showing the results of weight change in a degradation test of a molded article (film) when PES was used in Examples and Comparative Examples; FIG. 8 is a diagram showing the appearance of a film surface in a degradation test of a molded article (film) when PES was used in Examples and Comparative Examples; FIG. 9 is a graph showing the results of evaluation of the mechanical strength of a molded article (film) when PBS was used in Examples and Comparative Examples; FIG. 10 is a graph showing the results of evaluation of the mechanical strength of a molded article (film) when PES was used in Examples and Comparative Examples. 1 is a graph showing the results of weight change in a degradation test of a molded article (film) when the degradation time is extended when PBS is used in the Examples and Comparative Examples. FIG. 2 is a graph showing the relationship between the molecular weight of PEG and the weight change in a degradation test when PBS is used in the Examples and Comparative Examples. FIG. 3 is a graph showing the results of weight change in a degradation test of a molded article (film) when the degradation time is extended when PES is used in the Examples and Comparative Examples. FIG. 4 is a graph showing the relationship between the molecular weight of PEG and the weight change in a degradation test when PES is used in the Examples and Comparative Examples. FIG. 5 is a diagram showing the surface appearance in a degradation test of a molded article (film) after decomposition for 3 hours when PBS is used in the Examples and Comparative Examples. FIG. 6 is a diagram showing the surface appearance in a degradation test of a molded article (film) after decomposition for 3 hours when PES is used in the Examples and Comparative Examples. FIG. 7 is a graph showing the results of evaluating the dispersibility of a biodegradable plastic decomposer in a molded article (film) after decomposition for 3 hours when PBS and PES are used in the Examples and Comparative Examples.1 is a graph showing the results of evaluating the dispersibility of a biodegradable plastic decomposing agent in a molded article (film) after 24 hours of decomposition when PBS and PES were used in Examples and Comparative Examples. 2 is a graph showing the results of evaluating the mechanical strength (tensile strength) of a molded article (film) before immersion in water when PBS and PES were used in Examples and Comparative Examples. 3 is a graph showing the results of weight change in a decomposition test depending on the weight ratio of a biodegradable plastic decomposing enzyme to PEG (5K). 4 is a graph showing the results of evaluating the mechanical strength (tensile strength) depending on the weight ratio of a biodegradable plastic decomposing enzyme to PEG (5K).

[0010] The present disclosure will be described in further detail below.

[0011] <Biodegradable Plastic Decomposer> The biodegradable plastic decomposer of the present disclosure is used to decompose biodegradable plastics. The biodegradable plastic decomposer of the present disclosure includes a shell layer containing a biodegradable amphiphilic polymer and a core layer containing a crude biodegradable plastic decomposer. The core layer and the shell layer are preferably bonded by intermolecular bonds, more preferably by hydrogen bonds, hydrophobic interactions, or van der Waals forces. In the biodegradable plastic decomposer of the present disclosure, at least a portion of the surface of the core layer is coated with the shell layer. The average particle size of the biodegradable plastic decomposer of the present disclosure is preferably 50 nm to 100 μm, more preferably 50 nm to 50 μm, even more preferably 50 nm to 30 μm, even more preferably 50 nm to 10 μm, particularly preferably 50 nm to 5 μm, and most preferably 50 nm to 2 μm. The average particle size can be measured by known methods, such as laser diffraction (laser diffraction / scattering).

[0012] <Core Layer> (Crude Biodegradable Plastic Decomposer) In this specification, the term "crude biodegradable plastic decomposer" refers to a material capable of decomposing biodegradable plastics before it is coated with a shell layer. Crude biodegradable plastic decomposers include microorganisms that express and, optionally, secrete enzymes having at least polyester-degrading activity and / or enzymes having at least polyester-degrading activity. Examples of the enzymes include, but are not limited to, depolymerase, esterase, lipase, cutinase, carboxylesterase, protease, or polyesterase. Among these, cutinase is preferred from the viewpoint of degradability, and Humicola insolens cutinase (HiC) obtained from the thermophilic fungus Humicola insolens is more preferred. Microorganisms include microorganisms that produce such enzymes naturally or as a result of specific manipulation (e.g., recombinant microorganisms). Preferred examples of suitable microorganisms include, but are not limited to, bacteria, fungi, and yeast. Examples of microorganisms that produce the above enzymes include Humicola insolens, etc. These crude biodegradable plastic decomposing agents may be used alone or in combination of two or more.

[0013] (Other Components) The core layer may contain other components in addition to the crude biodegradable plastic decomposer. Examples of such other components include surfactants, light stabilizers, and plasticizers. Examples of surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Of these, biodegradable surfactants are preferred, and more preferred examples include glycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, soaps, α-sulfofatty acid methyl ester salts (MES), and α-olefin sulfonates (AOS).

[0014] The content of the crude biodegradable plastic decomposer is preferably 80 to 99 mass%, more preferably 85 to 99 mass%, and even more preferably 90 to 99 mass%, based on the total mass of the biodegradable plastic decomposer. When the content of the crude biodegradable plastic decomposer is within the above range, the biodegradability, dispersibility, and mechanical strength are superior.

[0015] The content of the crude biodegradable plastic decomposer is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and even more preferably 90 to 100% by mass, relative to the total mass of the core layer. When the content of the crude biodegradable plastic decomposer is within the above range, the biodegradability, dispersibility, and mechanical strength are superior.

[0016] <Shell Layer> (Amphiphilic Polymer) The amphiphilic polymer is preferably biodegradable and compatible (good mixability) with both the crude biodegradable plastic decomposer and the biodegradable plastic. Examples of amphiphilic polymers include polyethylene glycol (hereinafter also referred to as PEG), polysaccharide ester derivatives, polyvinyl alcohol, polypropylene glycol, polyvinylpyrrolidone, etc. PEG is preferred from the viewpoints of handling, cost, and biodegradability. These amphiphilic polymers may be used alone or in combination of two or more.

[0017] The mass average molecular weight of the amphiphilic polymer is preferably 300 to 30000, more preferably 400 to 20000, and even more preferably 600 to 15000. When the mass average molecular weight of the amphiphilic polymer is within the above range, the amphiphilic polymer has better biodegradability, dispersibility, and mechanical strength.

[0018] The content of the amphiphilic polymer is preferably 1 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 1 to 10% by mass, relative to the total mass of the biodegradable plastic decomposer. When the content of the amphiphilic polymer is within the above range, the dispersibility, biodegradability, and mechanical strength are superior.

[0019] The content of the amphiphilic polymer is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and even more preferably 90 to 100% by mass, relative to the total mass of the shell layer. When the content of the amphiphilic polymer is within the above range, the dispersibility, biodegradability, and mechanical strength are superior.

[0020] (Other Components) The shell layer may contain other components in addition to the amphiphilic polymer. Examples of the other components include surfactants. Examples of the surfactants include those similar to those described above.

[0021] The mass ratio of crude biodegradable plastic decomposer to amphiphilic polymer is preferably 1:10 to 100:1, more preferably 1:7 to 70:1, and even more preferably 1:5 to 50:1. When the mass ratio is within the above range, the dispersibility, biodegradability, and mechanical strength are superior. In another aspect, the mass ratio of crude biodegradable plastic decomposer to amphiphilic polymer is preferably 0.1 to 100, more preferably 0.2 to 50, even more preferably 0.2 to 20, and particularly preferably greater than 0.2 and less than 1.0. When the mass ratio is within the above range, the dispersibility, biodegradability, and mechanical strength are superior.

[0022] The biodegradable plastic decomposer of the present disclosure may be such that at least a portion of the surface of the crude biodegradable plastic decomposer is coated with an amphiphilic polymer. The area of ​​the portion coated with the amphiphilic polymer is preferably 50 to 100 area%, more preferably 60 to 100 area%, and even more preferably 70 to 100 area%, relative to the total surface area of ​​the crude biodegradable plastic decomposer. When the area of ​​the portion coated with the amphiphilic polymer is within the above range, the dispersibility, biodegradability, and mechanical strength obtained by the coating are more likely to be improved.

[0023] <Biodegradable Plastics> Examples of biodegradable plastics include biodegradable polyester resins. Examples of biodegradable polyester resins include aliphatic polyesters and aliphatic aromatic polyesters, such as PLA (polylactic acid), PHA (polyhydroxyalkanoate), PES (polyethylene succinate), PBS (polybutylene succinate), PBAT (polybutylene adipate terephthalate), PBSA (polybutylene succinate adipate), PGA (polyglycolic acid), PETS (polyethylene terephthalate succinate), PA (polyamide), PC (polycarbonate), PU (polyurethane), and PBSu (polybutylene succinate). These biodegradable polyester resins may be used alone or in combination of two or more.

[0024] Biodegradable plastics may be produced by conventional methods, or commercially available products may be used. Commercially available biodegradable plastics include polycaprolactone (PCL) sold by Union Carbide under the trade name Tone (trademark) (e.g., Tone P-300, P-700, P-767, and P-787, having weight average molecular weights of about 10,000, 40,000, 43,000, and 80,000, respectively), or polycaprolactone (PCL) sold by Perstorf under the trade names CAPA6800 and CAPAFB100 (having molecular weights of 80,000 and 100,000 Daltons, respectively); polyethylene succinate (PES) and polybutylene succinate (PBS) sold by Showa Highpolymer Co., Ltd. under the trade name Bionolle (trademark) ( Examples include Bionolle™ 1001 (PBS) and Bionolle™ 6000 (PES); polybutylene adipate (PBA) sold under the trade name Skygreen™ SG100 by SK Chemicals (Korea); polybutylene adipate terephthalate (PBAT) aliphatic / aromatic copolyesters such as Ecoflex™ by BASF (Germany) or EnPOL™ G8060 and EnPOL™ 8000 by IreChemical Ltd (Seoul); polybutylene succinate (PBS) and polybutylene succinate adipate (PBSA) sold under the trade name BioPBS™ by Mitsubishi Chemical Corporation.

[0025] The biodegradable plastic may be a modified biodegradable polyester resin or an unmodified biodegradable polyester resin. The modified biodegradable polyester resin is not particularly limited, but may be, for example, a modified biodegradable polyester resin obtained by graft-modifying a biodegradable polyester resin with an unsaturated carboxylic acid and / or its derivative. The unsaturated carboxylic acid used as the modifier is not particularly limited, but examples thereof include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid. Furthermore, the derivative of the unsaturated carboxylic acid is not particularly limited, but examples thereof include acid anhydrides, esters, amides, imides, and metal salts.

[0026] Specific examples of the derivatives of unsaturated carboxylic acids include maleic anhydride, himic anhydride, itaconic anhydride, citraconic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, glycidyl acrylate, maleic acid monoethyl ester, maleic acid diethyl ester, itaconic acid monomethyl ester, itaconic acid diethyl ester, acrylamide, methacrylamide, maleic acid monoamide, maleic acid diamide, maleic acid-N-monoethylamide, maleic acid-N,N-diethylamide, maleic acid-N,N-monobutylamide, maleic acid-N,N-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid-N-monobutylamide, fumaric acid-N,N-dibutylamide, maleimide, N-butylmaleimide, N-phenylmaleimide, sodium acrylate, sodium methacrylate, potassium acrylate, and potassium methacrylate. These modifiers may be used alone or in combination of two or more.

[0027] When modified, the content of the structural unit derived from the modifier is preferably 0.01 to 3.0% by mass, more preferably 0.02 to 1.0% by mass, and even more preferably 0.03 to 0.2% by mass, relative to the mass of the modified biodegradable polyester resin.

[0028] The biodegradable plastic is preferably an unmodified biodegradable polyester resin, which can prevent a decrease in biodegradability due to modification and also avoid the complicated manufacturing process that would be required for modification.

[0029] In a preferred embodiment of the present disclosure, the melting point of the biodegradable plastic is preferably 70 to 200°C, more preferably 80 to 150°C, even more preferably 90 to 140°C, even more preferably 100 to 130°C, and particularly preferably 105 to 120°C. If excessive heat is applied to the biodegradable plastic decomposition agent, the effect of promoting the decomposition of the biodegradable plastic will be significantly reduced, so if the melting point of the biodegradable plastic is within the above range, it will be easier to produce a biodegradable plastic with good decomposition properties. The melting point can be measured using a differential scanning calorimeter (DSC).

[0030] In one embodiment of the present disclosure, the melt mass flow rate (MFR) of the biodegradable plastic is preferably 1.0 g / 10 min or more and 30 g / 10 min or less, more preferably 3.0 g / 10 min or more and 25 g / 10 min or less, and even more preferably 5.0 g / 10 min or more and 20 g / 10 min or less. Having an MFR of the biodegradable plastic within the above range makes it easy to improve heat resistance and thermoformability. The MFR can be measured in accordance with ISO 1133 under conditions of 200°C and 2.16 kg.

[0031] In one embodiment of the present disclosure, the mass average molecular weight (Mw) of the biodegradable plastic is preferably 10,000 to 500,000, more preferably 30,000 to 500,000, and even more preferably 50,000 to 200,000. When the Mw of the biodegradable plastic is within the above range, it is easy to improve the thermoformability and heat resistance.

[0032] In one embodiment of the present disclosure, the number average molecular weight (Mn) of the biodegradable plastic is preferably 5,000 to 200,000, more preferably 10,000 to 100,000, and even more preferably 20,000 to 50,000. Having the Mn of the biodegradable plastic within the above range facilitates improving thermoformability and heat resistance. The Mw and Mn of the biodegradable plastic can be determined by gel permeation chromatography (GPC) measurement and standard polystyrene conversion.

[0033] When a molded article is produced from a biodegradable plastic composition containing the biodegradable plastic decomposer of the present disclosure, the molded article preferably has a tensile strength of 25 MPa or more, more preferably 30 to 100 MPa, and even more preferably 50 to 80 MPa. When the tensile strength of the molded article is within the above range, the molded article has sufficient mechanical strength for use as a plastic product, thereby achieving both biodegradability and resistance to fracture as a plastic product. Therefore, it is possible to obtain physical properties equivalent to those of plastic products that do not contain the biodegradable plastic decomposer of the present disclosure.

[0034] When a molded article is produced from a biodegradable plastic composition containing the biodegradable plastic decomposer of the present disclosure, the breaking elongation of the molded article is preferably 300% or more, more preferably 400 to 1500%, and even more preferably 500 to 1300%. When the breaking elongation of the molded article is within the above range, the molded article has sufficient mechanical strength for use as a plastic product, thereby achieving both biodegradability and ease of molding into a plastic product. Therefore, it is possible to obtain physical properties equivalent to those of plastic products that do not contain the biodegradable plastic decomposer of the present disclosure.

[0035] When a molded article is produced from a biodegradable plastic composition containing the biodegradable plastic decomposer of the present disclosure, the Young's modulus of the molded article is preferably 0.3 GPa or more, more preferably 0.4 to 1.0 GPa, and even more preferably 0.5 to 0.8 GPa. If the Young's modulus of the molded article produced is within the above range, the molded article has sufficient mechanical strength for use as a plastic product, thereby achieving both biodegradability and resistance to deformation as a plastic product. Therefore, it is possible to obtain physical properties equivalent to those of plastic products that do not contain the biodegradable plastic decomposer of the present disclosure.

[0036] In a decomposition test (weight change) described in the examples for an evaluation composition containing the biodegradable plastic of the present disclosure and the same amount of crude biodegradable plastic decomposer in place of the biodegradable plastic decomposer contained in the biodegradable plastic composition, when the weight loss after 5 days is taken as 100, the weight loss is preferably 105 or more, more preferably 110 or more, more preferably 125 or more, more preferably 140 or more, more preferably 160 or more, more preferably 180 or more, and even more preferably 200 or more.

[0037] The biodegradable plastic composition containing the biodegradable plastic decomposer of the present disclosure has a mechanical strength (tensile strength) described in the examples that is preferably 0.8 times or more, more preferably 0.9 times or more, and even more preferably 1 time or more, when the tensile strength of the biodegradable plastic not containing the biodegradable plastic decomposer is taken as 1.

[0038] <<Method for Producing Biodegradable Plastic Decomposer>> The method for producing the biodegradable plastic decomposer of the present disclosure is not particularly limited, but can be produced by adding a shell layer forming agent containing an amphipathic polymer for forming a shell layer to a core layer forming agent containing a crude biodegradable plastic decomposer for forming a core layer. Examples of the core layer forming agent include an aqueous solution or aqueous dispersion containing the crude biodegradable plastic decomposer. Prior to preparing the core layer forming agent, a salting-out step of adding a salt such as ammonium sulfate to the aqueous solution of the crude biodegradable plastic decomposer to form a powder may be performed. The shell layer forming agent is preferably a liquid containing an amphipathic polymer, such as an amphipathic polymer or an aqueous solution or aqueous dispersion of an amphipathic polymer. The content of the crude biodegradable plastic decomposer in the core layer forming agent is preferably 80 to 95% by mass, more preferably 85 to 93% by mass, and even more preferably 90 to 91% by mass, based on the total mass of the aqueous solution or aqueous dispersion. When the content of the crude biodegradable plastic decomposer is within the above range, the solubility or decomposability of the crude biodegradable plastic decomposer in water is easily increased, and the yield of the resulting biodegradable plastic decomposer can be further improved. The temperature of the core layer forming agent is preferably 10 to 60°C, more preferably 15 to 40°C, and even more preferably 20 to 30°C. When the temperature of the core layer forming agent is within the above range, the solubility or decomposability of the crude biodegradable plastic decomposer in water is easily increased, and the yield of the resulting biodegradable plastic decomposer can be further improved. The stirring time of the mixed solution after adding the shell layer forming agent is preferably 1 to 15 minutes, more preferably 3 to 10 minutes, and even more preferably 5 to 7 minutes. When the stirring time of the mixed solution is within the above range, the surface of the crude biodegradable plastic decomposer is sufficiently coated with the amphiphilic polymer, and the dispersibility, biodegradability, and mechanical strength of the resulting biodegradable plastic decomposer can be further improved. The biodegradable plastic decomposer is preferably produced by freeze-drying. For example, a shell layer forming agent containing an amphiphilic polymer is added to a core layer forming agent containing a crude biodegradable plastic decomposer to form a homogeneous aqueous solution, which is then freeze-dried under vacuum conditions of 10 Pa or less to obtain the biodegradable plastic decomposer.The mass ratio of crude biodegradable plastic decomposer to amphiphilic polymer used is preferably 0.1 to 100, more preferably 0.2 to 50, even more preferably 0.2 to 20, and particularly preferably more than 0.2 and less than 10. When the mass ratio is within the above range, the dispersibility, biodegradability, and mechanical strength of the obtained biodegradable plastic decomposer are more likely to be improved.

[0039] <Biodegradable Plastic Composition> The biodegradable plastic composition of the present disclosure includes a biodegradable plastic and the biodegradable plastic decomposer of the present disclosure. In the biodegradable plastic composition of the present disclosure, the biodegradable plastic decomposer of the present disclosure is dispersed in the biodegradable plastic. In one embodiment of the present disclosure, the content of the biodegradable plastic decomposer is preferably 0.0001 to 10 mass%, more preferably 0.001 to 5 mass%, and even more preferably 0.01 to 3 mass%, relative to the total mass of the biodegradable plastic composition. When the content of the biodegradable plastic decomposer is within the above range, a molded article with excellent dispersibility, biodegradability, and mechanical strength can be provided.

[0040] In one embodiment of the present disclosure, the content of the biodegradable plastic is preferably 90 to 99.99 mass%, more preferably 95 to 99.985 mass%, and even more preferably 99 to 99.98 mass%, relative to the total mass of the biodegradable plastic composition. When the content of the biodegradable plastic is within the above range, a molded article having excellent dispersibility, biodegradability, and mechanical strength can be provided.

[0041] The biodegradable plastic composition of the present disclosure may contain additives other than biodegradable plastics and biodegradable plastic decomposers, provided that the purpose and effects of the present disclosure are not impaired. Examples of additives include water, organic solvents, fillers, processing stabilizers, weathering stabilizers, colorants, UV absorbers, heat stabilizers, light stabilizers, antistatic agents, flame retardants, plasticizers, lubricants, fragrances, foaming agents, deodorizers, extenders, release agents, mold release agents, reinforcing materials, mildew inhibitors, preservatives, crystallization rate retarders, and resins other than biodegradable polyester-based resins. These additives can be used alone or in combination.

[0042] Fillers may be added from the viewpoints of easily increasing hardness and rigidity, easily preventing blocking, etc. Examples of fillers include inorganic fillers such as mica, kaolin, kaolinite, clay, talc, acid clay, silica, alumina, diatomaceous earth, bentonite, montmorillonite, kibushi clay, gairome clay, rosewood, alumite, china clay, feldspar, asbestos, perlite, calcium carbonate, magnesium hydroxide, carbon black, vermiculite, titanium oxide, mica, zirconium oxide, boron nitride, aluminum nitride, shirasu, glass, and glass fiber, and organic fillers such as urea-formalin-based resins and melamine-formalin-based resins. These fillers can be used alone or in combination of two or more.

[0043] Examples of other resins include non-biodegradable resins, such as polyphenylene ether resins, polycarbonate resins, polyamide resins such as nylon 66 and nylon 11, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, styrene resins such as polystyrene, and (meth)acrylate resins such as polymethyl methacrylate resins. These other resins can be used alone or in combination. From the standpoint of environmental impact, it is preferable that the composition does not contain non-biodegradable resins.

[0044] The content of the additive is not particularly limited as long as it is added within a range that does not impair the purpose and effects of the present disclosure, but may be, for example, 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and preferably 0% by mass or more, for example 0.1% by mass or more or 1% by mass or more, relative to the mass of the biodegradable plastic composition.

[0045] <<Method for Producing Biodegradable Plastic Composition>> The method for producing the biodegradable plastic composition of the present disclosure is not particularly limited, and may include, for example, a method of mixing a biodegradable plastic, a biodegradable plastic decomposer of the present disclosure, and, if necessary, additives. A conventional mixer, preferably a melt kneader, can be used for mixing. The temperature during mixing or kneading may be any temperature that does not cause alteration (e.g., polymerization, decomposition, etc.) of the amphiphilic polymer or denaturation of the enzyme, and is preferably 40 to 200°C, more preferably 80 to 140°C, and even more preferably 100 to 120°C. The rotation speed of the kneader is preferably 20 to 1000 ppm, more preferably 40 to 500 rpm. Alternatively, these components may be premixed using a mixer or the like and then introduced into the melt kneader.

[0046] In one embodiment of the present disclosure, a biodegradable plastic composition can be obtained by melt-kneading using an extruder. A twin-screw extruder can be preferably used as the extruder. The twin-screw extruder may be either co-rotating or counter-rotating. The screw rotation speed can be selected from the same range as the rotation speed of the kneader described above. The cylinder temperature can be selected from the temperature range for mixing or kneading described above. Each component can be directly introduced into the extruder.

[0047] The molten biodegradable plastic composition that has been forced through the extruder while being melt-kneaded is extruded through a die. The die temperature may be preferably 100 to 200° C., more preferably 100 to 140° C. The extrusion rate is preferably 1 to 10 kg / h, more preferably 2 to 5 kg / h.

[0048] The extruded biodegradable plastic composition (melt) can be extruded into a sheet, film or strand shape, during which the biodegradable plastic composition (melt) is cooled and dried.

[0049] When the mixture is extruded into strands, it can be extruded through a strand nozzle with multiple holes and cut with a rotary cutter to form pellets. To prevent the pellets from sticking together, vibration can be applied periodically or constantly, and moisture in the pellets can be removed using hot air, dehumidified air, or an infrared heater.

[0050] When the mixture is extruded into a sheet or film, the mixture can be extruded through a film-forming die and then cooled and dried while being taken up by a take-up roller. Cooling between the die and the roller is preferred to prevent the mixture from adhering to the roller. The biodegradable plastic composition of the present disclosure may also be formed into a sheet or film by a conventional film-forming method (e.g., cast film formation).

[0051] The biodegradable plastic composition (for example, a pellet-like biodegradable plastic composition) may be formed into a sheet or film by a conventional method such as extrusion molding, compression molding, or press molding.

[0052] <<Molded Article>> The molded article of the present disclosure can be obtained by molding the biodegradable plastic composition of the present disclosure. The form of the molded article is not particularly limited, and it may be a pellet, sheet, or film. That is, it may be a pellet, sheet, or film containing or consisting of the biodegradable plastic composition. The thickness of the sheet or film can be selected appropriately depending on the application, and is preferably 5 to 1000 μm, more preferably 10 to 500 μm. The thickness of the film or sheet can be measured using a thickness gauge.

[0053] <<Method for Producing Molded Articles>> A biodegradable plastic composition (e.g., a pelletized biodegradable plastic composition) may be formed into a sheet or film by a conventional method such as extrusion molding, compression molding, or press molding. The molding temperature during molding is preferably 40 to 200°C, more preferably 80 to 150°C, and even more preferably 100 to 140°C. When the molding temperature is below the upper limit, thermoformability is easily enhanced, making it easier to mold the resulting laminate into a desired shape. This also prevents the deactivation of crude biodegradable plastic decomposers such as enzymes and prevents the coated amphiphilic polymer from melting. The molding time during molding is preferably 30 seconds to 30 minutes, more preferably 1 to 10 minutes, and even more preferably 1 to 5 minutes. When the molding time is below the upper limit, the resulting laminate is easily molded into a desired shape. This also prevents the deactivation of crude biodegradable plastic decomposers such as enzymes and prevents the coated amphiphilic polymer from melting. The molding pressure during molding is preferably 1 to 50 MPa, more preferably 1 to 10 MPa, and even more preferably 3 to 8 MPa. When the molding time is equal to or less than the above upper limit, the resulting laminate can be easily molded into a predetermined shape. In addition, the deactivation of the crude biodegradable plastic decomposer, such as an enzyme, can be suppressed, and the coated amphiphilic polymer can be prevented from melting.

[0054] <Laminate> The laminate of the present disclosure has two or more layers, including at least one biodegradable plastic layer formed from the biodegradable plastic composition of the present disclosure. When the laminate of the present disclosure has two or more biodegradable plastic layers of the present disclosure, the biodegradable plastic layers may have the same or different compositions. The form of the biodegradable plastic layer is not particularly limited and may be, for example, a film or sheet. The laminate may also include layers other than the biodegradable plastic layer. Examples of such layers include a biodegradable resin layer containing a biodegradable plastic but not a biodegradable plastic decomposer, and paper. The type of biodegradable plastic contained in the biodegradable resin layer may be the same as or different from that contained in the biodegradable plastic layer. By including layers other than the biodegradable plastic layer, when the laminate is used as a packaging container, etc., the coated amphiphilic polymer dissolves in water when the biodegradable plastic layer comes into contact with water, which activates a crude biodegradable plastic decomposer such as an enzyme, preventing the biodegradation of the biodegradable plastic.

[0055] The thickness of the biodegradable plastic layer can be appropriately selected depending on the application, and is preferably 5 to 1000 μm, more preferably 10 to 500 μm. The thickness of the layer in the laminate of the present disclosure can be measured with a thickness meter.

[0056] The biodegradable plastic contained in the biodegradable resin layer is not particularly limited, and examples thereof include the same biodegradable plastics as those described above. From the viewpoints of adhesiveness and biodegradability, it is preferable that the biodegradable plastic contained in the biodegradable resin layer and the biodegradable plastic contained in the biodegradable plastic layer formed from the biodegradable plastic composition of the present disclosure are the same type.

[0057] The thickness of the biodegradable resin layer can be appropriately selected depending on the application, and is preferably 5 to 1000 μm, more preferably 10 to 500 μm.

[0058] The paper is not particularly limited, and examples thereof include kraft paper, double-bleached kraft paper, fine paper, construction paper, glassine paper, parchment paper, synthetic paper, white cardboard, Manila cardboard, milk carton base paper, cup base paper, ivory paper, and silver paper.

[0059] The thickness of the paper can be appropriately selected depending on the application, and is preferably 5 to 1000 μm, more preferably 10 to 500 μm.

[0060] The thickness of the laminate of the present disclosure can be appropriately selected depending on the application, and is preferably 10 to 2000 μm, more preferably 20 to 1000 μm.

[0061] The laminate of the present disclosure may have an adhesive layer for adhering each layer. The adhesive layer is preferably formed from an adhesive containing a biodegradable plastic. From the viewpoints of adhesion and biodegradability, it is preferable that the biodegradable plastic contained in the adhesive layer and the biodegradable plastic contained in the biodegradable plastic layer formed from the biodegradable plastic composition of the present disclosure are of the same type.

[0062] Examples of laminates of the present disclosure include laminates including a biodegradable resin layer / biodegradable plastic layer in this order; laminates including a biodegradable resin layer / biodegradable plastic layer / biodegradable resin layer in this order; and laminates including a biodegradable resin layer / adhesive layer / biodegradable plastic layer / adhesive layer / biodegradable resin layer in this order. These laminates may include layers other than the biodegradable resin layer and the biodegradable resin layer between or on the outside of each layer, but it is preferable that no such layers are included between each layer, i.e., that each layer is adjacent. Having each layer adjacent to each other makes it easier to improve the biodegradability of the laminate.

[0063] <<Method for Producing Laminate>> The laminate of the present disclosure can be produced by laminating two or more layers, at least one of which is a biodegradable plastic layer formed from the biodegradable plastic composition of the present disclosure.

[0064] The laminate of the present disclosure can be produced by laminating a biodegradable plastic layer and another layer by a conventional method such as a coextrusion molding method (coextrusion lamination method, coextrusion sheet molding method, coextrusion inflation molding method, coextrusion blow molding method, etc.), a coinjection molding method, an extrusion lamination method, or a dry lamination method. For example, the laminate may be a method of coextruding or laminating a biodegradable plastic layer and another layer, or a method of forming another layer on a biodegradable plastic layer. When laminating, a biodegradable resin layer-forming agent for forming the biodegradable resin layer may be applied to the surface of the biodegradable plastic layer, or extrusion coated onto the surface of the biodegradable plastic layer.

[0065] When laminating a biodegradable plastic layer and the biodegradable resin layer, a biodegradable resin layer-forming agent for forming the biodegradable resin layer can be applied to the biodegradable plastic layer and dried to form a biodegradable resin layer, or a biodegradable plastic composition containing a biodegradable plastic decomposing agent can be applied to the biodegradable resin layer and dried to produce a laminate. Alternatively, an adhesive layer can be provided between the biodegradable plastic layer and the biodegradable resin layer, and then the two layers can be laminated.

[0066] The biodegradable resin layer forming agent may include one that contains a biodegradable plastic but does not contain a biodegradable plastic decomposing agent, and may contain, for example, the above-mentioned other components in addition to a biodegradable plastic.

[0067] When laminating a molded article and paper, a laminate can be produced by applying a biodegradable plastic composition containing a biodegradable plastic decomposer to the paper and drying it. Alternatively, a laminate can be produced by laminating paper on a molded article. The above-mentioned pressure-sensitive adhesive layer can be provided between the molded article and the paper.

[0068] <<Uses of Molded Articles and Laminates>> The uses of the molded articles and laminates disclosed herein are not particularly limited, but they can be suitably used as packaging materials, particularly food packaging materials. Food packaging materials are not particularly limited, but can be used, for example, not limited to solid foods, but also for liquid foods. When the food contains water, it is preferable to prevent contact between the food and the layer containing the biodegradable plastic decomposer. For example, it is preferable to form a laminate by providing a biodegradable resin layer on the layer containing the biodegradable plastic decomposer, thereby preventing the biodegradable plastic decomposer from being activated by the moisture contained in the food. This results in superior storage stability and safety of the food. In the case of molded articles that do not have a biodegradable resin layer, they are preferably used as packaging materials for items that do not contain moisture.

[0069] <<Method for Degrading Biodegradable Plastic Compositions, Molded Articles, and Laminates>> The method for degrading biodegradable plastic compositions, molded articles, and laminates disclosed herein includes immersing the biodegradable plastic compositions, molded articles, and laminates disclosed herein in water to decompose the biodegradable plastics. Immersion in water causes the amphiphilic polymer coating the crude biodegradable plastic decomposer to dissolve in water, and the crude biodegradable plastic decomposer is activated upon contact with water, thereby promoting a biodegradable plastic degradation reaction. Examples of the degradation reaction include hydrolysis. The water immersion time is preferably at least one hour, more preferably at least one hour but not more than one year, and even more preferably at least three hours but not more than six months. Water immersion times within the above ranges further reduce environmental impact. The water immersion temperature is preferably 10 to 60°C, more preferably 15 to 50°C, and even more preferably 20 to 40°C. Water immersion temperatures within the above ranges eliminate the need for heating the water, allowing for low-cost biodegradation. The pH of the water at 25°C is preferably 6 to 12, more preferably 7 to 11, and even more preferably 8 to 10. When the pH of the water at 25°C is within the above range, there is no need to adjust the pH, and the water can be biodegraded at low cost by, for example, immersing it in seawater.

[0070] <Actions and Effects> The biodegradable plastic decomposer of the present disclosure has a core layer containing a crude biodegradable plastic decomposer coated on its surface with a shell layer containing an amphipathic polymer. This improves dispersibility in biodegradable plastics, thereby suppressing aggregation of the crude biodegradable plastic decomposer. By improving the dispersibility of the biodegradable plastic decomposer, the biodegradability of the biodegradable plastic decomposer is also improved, and a decrease in mechanical strength can be suppressed. Because the biodegradable plastic decomposer is coated with an amphipathic polymer, it is presumed that the amphipathic polymer, such as PEG, dissolves in water after immersion in water, and biodegradation reactions such as hydrolysis reactions proceed when the crude biodegradable plastic decomposer, such as enzymes, comes into contact with water. The biodegradable plastic decomposer of the present disclosure disperses uniformly when blended with biodegradable plastics to form molded articles, resulting in a faster biodegradation rate and superior mechanical strength of the biodegradable plastics. The biodegradable plastic decomposing agent of the present disclosure does not decompose when used as a plastic product, but after use of the plastic product, the encapsulated enzyme comes into contact with water due to surface wear or destruction, which activates the enzyme and initiates biodegradation, thereby combining high biodegradability with practicality as a plastic product.

[0071] The present disclosure will be specifically explained below using examples, but the present disclosure is not limited to these examples.

[0072] <Evaluation Methods> (1) Weight-Average Molecular Weight The weight-average molecular weight of PEG was determined by gel permeation chromatography (GPC). (2) Degradation Test (Weight Change) The weight change due to the degradation of biodegradable plastics was evaluated. Films approximately 50 to 200 μm thick, prepared by hot pressing, were cut into 1 cm x 1 cm squares to serve as test samples. The films were immersed in 2 mL of 100 mM phosphate buffer, pH 7.5, in a 5 mL sample bottle and maintained at 45°C, the optimal temperature for the enzyme, while being shaken. The films were removed at regular intervals, washed with pure water, wiped dry, dried at room temperature, and weighed. Three samples were used in all experiments. After weight measurement, the samples were returned to their original sample bottles, and the degradation experiment was continued. The weight loss (unit: wt%) was calculated using the following formula: Weight loss (wt%) = [(film weight before immersion) - (film weight after a certain time from the start of immersion)] ÷ (film weight before immersion) × 100 (wt%). (3) Decomposition Test (Surface Appearance) Changes in surface appearance due to biodegradable plastic degradation were observed. The surface morphology of the film before and during decomposition (24 hours later) was observed using a benchtop scanning electron microscope (JCM-7000, JEOL, Japan). The accelerating voltage was set to 5.0 kV. The sample was gold-coated using a magnetron sputtering device (MSP-1S, Vacuum Device, Japan). (4) Mechanical Strength (Tensile Strength) The tensile strength of the film obtained in each example was measured in accordance with JIS K-6251-5. Figure 2 shows an example of a film obtained in each example. Tensile tests of the film were performed using a small benchtop testing machine (EZ-LX, Shimadzu Corporation, Japan). The film was cut using a dumbbell cutter (SDL-100, Dumbbell, Japan) equipped with a 1 / 3 scaled-down type super dumbbell cutter (SDK-500, Dumbbell, Japan) to prepare dumbbell test pieces conforming to JIS K-6251-5. The thickness of the test piece was taken as the average value of the three central points. Measurements were performed at room temperature with an initial length of 8.4 mm and a tensile speed of 50 mm / min. The number of samples was 5 to 8, and the average value was used as the measurement result. (5) Mechanical strength (elongation at break) The elongation at break was measured using the same tensile test as in (4). (6) Mechanical strength (Young's modulus) Young's modulus was measured using the same tensile test as in (4).

[0073] <Biodegradable Plastics> The following biodegradable plastics were used: PBS (Mitsubishi Chemical Corporation's "BioPBS" ＴＭ ", Mw = 130,000, melting point = 114°C) - PES (provided by Team Leader Hideki Abe of the Institute of Physical and Chemical Research, Mw = 100,000, melting point = 104°C) <Biodegradable plastic decomposers> The following crude biodegradable plastic decomposers were used: - Enzyme (cutinase, "Novozyme 51032 (Humicola insolens cutinase, HiC)" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) The following amphiphilic polymers were used. PEG (Sigma-Aldrich "Poly(ethylene glycol)", Mw = 400, melting point = 4-8°C) PEG (Sigma-Aldrich "Poly(ethylene glycol) methyl ether", Mw = 2000, melting point = 52-56°C) PEG (Sigma-Aldrich "Poly(ethylene glycol)", Mw = 3350, melting point = 53-58°C) PEG (Sigma-Aldrich "Poly(ethylene glycol) methyl ether", Mw = 5000, melting point = 60-64°C) PEG (Sigma-Aldrich "Poly ethylene glycol 10000", Mw = 10000, melting point = 53-58°C) PEG (Fujifilm Wako Pure Chemical Industries, Ltd. "Poly ethylene glycol 20000", Mw = 20000, melting point 60°C) <Phosphate buffer> The following reagents were used: Sodium dihydrogen phosphate Dipotassium hydrogen phosphate

[0074] <Preparation Example 1> Preparation of Biodegradable Plastic Degrader 1-1: Preparation of Enzyme (HiC) Powder 250 mL of Novozyme 51032 enzyme stock solution was diluted with 750 mL of purified water, and the solution was cooled in an ice bath. While cooling, 472 g of ammonium sulfate was slowly added while gently stirring the enzyme solution. After all the solution was added, the mixture was stirred for an additional 30 minutes. The mixture was left to stand overnight at 4°C to precipitate the enzyme, and then centrifuged at 4°C and 17,000 x g for 20 minutes to remove the supernatant. The precipitate was dissolved in as little purified water as possible and desalted using a PD-10 column (Citiva, Sweden). For desalting, 2.5 mL of enzyme solution was added, and an additional 3.5 mL of purified water was added to recover the enzyme. The column was washed with purified water and reused. The recovered enzyme solution was lyophilized at -84°C and 10 Pa or less to obtain enzyme (HiC) powder. The powder was stored at 4°C until use.

[0075] 1-2: Preparation of biodegradable plastic decomposer (PEG-coated HiC powder) PEG-coated HiC powder was prepared so that the HiC powder and PEG were mixed at a weight ratio of 10:1. A 10 mg / mL HiC aqueous solution and a 1 mg / mL PEG aqueous solution were prepared with pure water, and the two solutions were mixed and diluted with pure water to a final HiC concentration of 1 mg / mL and a final PEG concentration of 0.1 mg / mL, stirred, and then lyophilized. PEG-coated HiC powder was thus obtained. This powder was stored at 4°C until use.

[0076] <Production Examples 2 to 6> Biodegradable plastic decomposing agents were prepared in the same manner as in Production Example 1, except that the mass average molecular weight of PEG was changed as shown in Table 1. Table 1 shows the compositions of the biodegradable plastic decomposing agents prepared in Production Examples 1 to 6.

[0077]

[0078] Fig. 3 shows the biodegradable plastic decomposing agents produced in Production Examples 1, 4 and 6. Powders were obtained in all cases.

[0079] Example 1: Preparation of a film containing a biodegradable plastic decomposer. The biodegradable plastic decomposer obtained in Production Example 1 was added to biodegradable plastic in the proportions shown in Table 2 and hot-kneaded in a twin-screw extruder (HAAKE Minilab, Thermo Fisher Scientific, USA). The two screws rotated counterclockwise at 120 rpm, the kneading temperature was 130°C, and the kneading time was 2 minutes. A rectangular extrusion die measuring 1 mm x 2 mm was used. After extrusion, the sample was water-cooled and removed from the kneader. The kneaded samples were stored at room temperature in a desiccator containing silica gel as a desiccant. Approximately 500 to 1000 mg of the kneaded material was hot-pressed for 1 minute 30 seconds at the same temperature as during kneading, and then immediately quenched in an ice-water bath for 5 seconds to produce a film. The pressure was 5 MPa. The films were thoroughly wiped dry and stored at room temperature in the same desiccator.

[0080] Examples 2 to 12 Films were produced in the same manner as in Example 1, except that the type and amount of the biodegradable plastic decomposer in Production Example 1 were changed as shown in Tables 2 and 3, and the type and amount of the biodegradable plastic were changed as shown in Tables 2 and 3.

[0081] Comparative Example 1 Biodegradable plastic containing no enzyme powder was also formed into a film by hot pressing in the same manner as in Example 1 and stored.

[0082] Comparative Example 2 A film was formed by hot pressing and stored in the same manner as in Example 1, except that HiC powder before being coated with PEG was used.

[0083] Comparative Example 3 Films were formed by hot pressing and stored in the same manner as in Comparative Example 1, except that the biodegradable plastic was changed as shown in Table 4.

[0084] Comparative Example 4 Films were formed by hot pressing and stored in the same manner as in Comparative Example 2, except that the biodegradable plastic was changed as shown in Table 4.

[0085] Tables 2 to 4 show the films produced in Examples 1 to 12 and Comparative Examples 1 to 4.

[0086]

[0087]

[0088]

[0089] In Table 5, various biodegradable plastics containing Hic coated with various PEGs were molded into films, and the left column shows the film immediately after molding. The left column shows the film immediately after molding, and the right column shows the film immediately after molding. The left column shows the film immediately after molding. The ... ２ Indicates the number of holes per unit area.

[0090]

[0091] Table 6 shows various physical properties of the tensile test.

[0092]

[0093] Figure 4 shows the molded articles (films) produced in the Examples and Comparative Examples. The films without biodegradable plastic decomposers (no additives), films with uncoated crude biodegradable plastic decomposers (enzyme only), and films with PEG-coated biodegradable plastic decomposers (PEG-coated) were all milky white and had the same appearance. Figure 5 is a graph showing the weight change results of the degradation tests of molded articles (films) using PBS in the Examples and Comparative Examples. The additive-free film showed almost no weight change even after five days. The uncoated film with only enzyme added showed a weight change of about 30% by weight even after five days. The film with PEG-coated biodegradable plastic decomposers was almost completely decomposed after four days. In particular, the biodegradable plastic decomposers with a PEG molecular weight of 5,000 (5K) decomposed faster than biodegradable plastic decomposers with PEG molecular weights of 400 and 20,000 (20K), and were almost completely decomposed after two days. Figure 6 shows the appearance of the film surface after 24 hours in a degradation test of a molded article (film) when PBS was used in the Examples and Comparative Examples. After 24 hours, the surface of the film containing the biodegradable plastic decomposer of the present disclosure had uniformly distributed pores of large size, indicating excellent dispersibility of the biodegradable plastic decomposer and rapid degradation of biodegradable plastics by the biodegradable plastic decomposer. On the other hand, after 24 hours, the surface of the film containing uncoated enzyme had uneven pore distribution, but large pores were also observed. This indicates that coating at least a portion of the surface of the crude biodegradable plastic decomposer with an amphiphilic polymer improves both dispersibility and degradation rate. Figure 7 is a graph showing the weight change results of a degradation test of a molded article (film) using PES in the Examples and Comparative Examples. As with PBS, the additive-free film showed almost no weight change even after 5 days. The weight change of the film containing only uncoated enzyme after 5 days was approximately 10% by weight, less than that of PBS. The films to which the PEG-coated biodegradable plastic decomposing agent was added showed a greater change in weight than these comparative examples.In particular, films containing biodegradable plastic decomposers coated with PEG with a molecular weight of 5,000 (5K) were almost completely degraded within three days. Films containing biodegradable plastic decomposers with molecular weights of 400 and 20,000 (20K) degraded more slowly than films containing PEG with a molecular weight of 5,000 (5K). Figure 8 shows the appearance of the film surface after 24 hours in a degradation test of molded products (films) using PES in the Examples and Comparative Examples. The surface of the film containing the biodegradable plastic decomposer after 24 hours had uniformly distributed pores, which were large in size, demonstrating excellent dispersibility of the biodegradable plastic decomposer and rapid degradation of biodegradable plastics by the biodegradable plastic decomposer. On the other hand, the surface of the film containing the uncoated enzyme after 24 hours had uneven pore distribution and small pore sizes. This indicates that coating at least a portion of the surface of the crude biodegradable plastic decomposer with an amphiphilic polymer improves dispersibility and degradation rate. Figure 9 is a graph showing the evaluation results of the mechanical strength of molded articles (films) when PBS was used in the Examples and Comparative Examples. Films containing biodegradable plastic decomposers achieved tensile strength equivalent to that of untreated films. Films containing uncoated enzymes and films containing PEG with a molecular weight of 400 exhibited slightly lower tensile strength than untreated films, but were still within a practical range for films. Figure 10 is a graph showing the evaluation results of the mechanical strength of molded articles (films) when PES was used in the Examples and Comparative Examples. Unexpectedly, films containing biodegradable plastic decomposers achieved tensile strength far superior to that of untreated films or films containing uncoated enzymes. Figure 11 is a graph showing the evaluation results of the heat resistance of each biodegradable plastic decomposer. Films containing biodegradable plastic decomposers did not exhibit a significant decrease in enzyme activity compared to uncoated and unheated films. This indicates that the film containing the biodegradable plastic decomposer has excellent formability. The biodegradable plastic decomposer is also superior in usability at temperatures below 160°C.FIG. 12 is a graph showing the weight change results of a degradation test of a molded article (film) when PBS was used in the Examples and Comparative Examples and the degradation time was extended. It was found that films containing a biodegradable plastic decomposer had an excellent degradation rate, even when the molecular weight of PEG was changed. It was also found that the degradation rate can be controlled by changing the molecular weight of PEG. FIG. 13 is a graph showing the relationship between the molecular weight of PEG and the weight change in the degradation test when PBS was used in the Examples and Comparative Examples. Focusing on the degradation rate over one day, it was found that a PEG with a molecular weight of 5,000 had the best degradation rate. FIG. 14 is a graph showing the weight change results of a degradation test of a molded article (film) when PES was used in the Examples and Comparative Examples and the degradation time was extended. As with the case of using PBS, it was found that films containing a biodegradable plastic decomposer also had an excellent degradation rate when PES was used, even when the molecular weight of PEG was changed. It was also found that the degradation rate can be controlled by changing the molecular weight of PEG. FIG. 15 is a graph showing the relationship between the molecular weight of PEG and the weight change during the degradation test when PES was used in the Examples and Comparative Examples. Unlike when PBS was used, the daily degradation rate was found to be the best for films using PEG with a molecular weight of 2,000 (2K). FIG. 16 is a diagram showing the surface appearance of a molded article (film) after a 3-hour degradation test when PBS was used in the Examples and Comparative Examples. Even when the molecular weight of PEG was changed, the films to which a biodegradable plastic decomposer was added had uniformly distributed pores, and large pores were also observed, demonstrating excellent dispersibility and degradation rate. FIG. 17 is a diagram showing the surface appearance of a molded article (film) after a 3-hour degradation test when PES was used in the Examples and Comparative Examples. As with the case of PBS, even when PES was used, the films to which a biodegradable plastic decomposer was added had uniformly distributed pores, and large pores were also observed, demonstrating excellent dispersibility and degradation rate.Figure 18 is a graph showing the results of evaluating the dispersibility of biodegradable plastic decomposers in molded articles (films) after 3 hours of decomposition when PBS and PES were used in the examples and comparative examples. Figure 19 is a graph showing the results of evaluating the weight change (dispersibility) of biodegradable plastic decomposers in molded articles (films) after 24 hours of decomposition when PBS and PES were used in the examples and comparative examples. The number of holes after 3 hours of decomposition was considered to be the dispersibility of the enzyme, and was compared with the hole area percentage and weight loss after 24 hours of decomposition. For PEGs with different molecular weights, the shapes of the graphs for the number of holes, area percentage, and decomposition were generally consistent, indicating that dispersibility has a significant impact on decomposition. Figure 20 is a graph showing the results of evaluating the mechanical strength (tensile strength) of molded articles (films) before immersion in water when PBS and PES were used in the examples and comparative examples. The tensile strength results in Figure 20 were compared with the number of holes and hole area percentage results in Figure 18 and the weight change results in Figure 19. Since the shapes of these graphs were roughly consistent, it is believed that dispersibility also has a significant effect on tensile strength. Figure 21 is a graph showing the results of weight change in a decomposition test depending on the weight ratio of biodegradable plastic-degrading enzyme to PEG (5K). Figure 22 is a graph showing the results of evaluating mechanical strength (tensile strength) depending on the weight ratio of biodegradable plastic-degrading enzyme to PEG (5K). A weight ratio of enzyme:PEG5K = 10:1 was optimal for both decomposition and mechanical properties.

[0094] The biodegradable plastic decomposer of the present disclosure, when blended with biodegradable plastics, can improve the biodegradability of the biodegradable plastics. Therefore, the environmental impact can be further reduced. Furthermore, the biodegradable plastic decomposer of the present disclosure has excellent dispersibility, which can prevent a decrease in the mechanical strength and biodegradability of the biodegradable plastics. A biodegradable plastic composition containing the biodegradable plastic decomposer of the present disclosure can improve the biodegradability of the molded article when formed into a molded article. Therefore, the environmental impact can be further reduced. Furthermore, the biodegradable plastic decomposer of the present disclosure is uniformly dispersed, which can prevent a decrease in the mechanical strength and biodegradability of the molded article when formed into a molded article. The molded article of the present disclosure has excellent biodegradability because it contains the biodegradable plastic decomposer. Therefore, the environmental impact can be further reduced. Furthermore, the molded article of the present disclosure has the biodegradable plastic decomposer uniformly dispersed, which can prevent a decrease in mechanical strength and biodegradability.

Claims

1. A biodegradable plastic decomposing agent comprising: a shell layer containing a biodegradable amphiphilic polymer; and a core layer containing a crude biodegradable plastic decomposing agent, wherein at least a portion of the surface of the core layer is coated with the shell layer.

2. A biodegradable plastic decomposing agent according to claim 1, in which the mass ratio of crude biodegradable plastic decomposing agent to amphiphilic polymer is 1:10 to 100:

1.

3. The biodegradable plastic decomposing agent according to claim 1, wherein the core layer and the shell layer are bonded by an intermolecular bond.

4. The biodegradable plastic decomposing agent according to claim 1, wherein the amphiphilic polymer is at least one selected from the group consisting of polyethylene glycol, ester derivatives of polysaccharides, polyvinyl alcohol, polypropylene glycol, and polyvinylpyrrolidone.

5. The biodegradable plastic decomposing agent according to claim 1, wherein the crude biodegradable plastic decomposing agent is at least one selected from the group consisting of depolymerase, esterase, lipase, cutinase, carboxylesterase, protease, and polyesterase.

6. The biodegradable plastic decomposing agent according to claim 1, wherein the mass average molecular weight of the amphiphilic polymer is 300 to 30,000.

7. The biodegradable plastic decomposing agent according to claim 1, wherein the biodegradable plastic is at least one selected from the group consisting of biodegradable polyesters and ester derivatives of polysaccharides.

8. The biodegradable plastic decomposer according to claim 1, which is used to decompose biodegradable plastics by immersing a biodegradable plastic composition containing biodegradable plastics and the biodegradable plastic decomposer, or a molded article formed from the biodegradable plastic composition, in water.

9. A biodegradable plastic composition comprising a biodegradable plastic and the biodegradable plastic decomposing agent according to any one of claims 1 to 8.

10. The biodegradable plastic composition according to claim 9, having at least one of the following properties (i) and (ii): (i) When the weight loss of an evaluation composition containing the biodegradable plastic and the same amount of crude biodegradable plastic decomposer in place of the biodegradable plastic decomposer contained in the biodegradable plastic composition, measured under the following condition (i), is taken as 100, the composition has a weight loss of 105 or more. (ii) When the tensile strength of the evaluation composition, measured under the following condition (ii), is taken as 1, the composition has a tensile strength of 0.8 or more times. Condition (i): A film having a thickness of approximately 50 to 200 μm, prepared by heat-pressing the biodegradable plastic composition, was cut into a 1 cm × 1 cm square, and the film was immersed in 2 mL of 100 mM phosphate buffer solution at pH 7.5 in a 5 mL sample bottle. The film was maintained at the optimum temperature for the biodegradable plastic decomposer to decompose the biodegradable plastic while shaking. After 5 days, the film was removed and washed with pure water. After wiping off the water and drying at room temperature, the weight was measured and the weight loss was calculated using the following formula 1. The evaluation composition was hot-pressed to produce a film approximately 50 to 200 μm thick, which was then cut into a 1 cm x 1 cm square. The film was then immersed in 2 mL of 100 mM phosphate buffer solution at pH 7.5 in a 5 mL sample bottle and shaken while maintained at the optimum temperature at which the crude biodegradable plastic decomposer contained in the evaluation composition decomposes the biodegradable plastic contained in the evaluation composition. After 5 days, the film was removed, washed with pure water, wiped dry, and dried at room temperature. The weight was then measured and the weight loss was calculated using the following formula 1. Formula 1: Weight Loss (wt%) = [(Weight of Film Before Immersion) - (Weight of Film 5 Days After Immersion)] ÷ (Weight of Film Before Immersion) x 100 (wt%) Condition (ii): Using a film approximately 50 to 200 μm thick produced by hot-pressing the biodegradable plastic composition, the tensile strength of the film obtained from the biodegradable plastic composition was measured in accordance with JIS K-6251-5.The composition for evaluation is heat-pressed to produce a film having a thickness of about 50 to 200 μm, and the tensile strength of the film obtained from the composition for evaluation is measured in accordance with JIS K-6251-5.

11. A molded article formed from the biodegradable plastic composition according to claim 9.

12. A method for producing a biodegradable plastic decomposing agent according to any one of claims 1 to 8.

13. A method for producing the biodegradable plastic composition according to claim 9.

14. A method for producing a biodegradable plastic composition according to claim 9, which comprises melt-kneading the biodegradable plastic decomposing agent and the biodegradable plastic.

15. A method for producing a molded article, comprising molding the biodegradable plastic composition according to claim 9.

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