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

Abstract

To provide a biodegradable plastic decomposition agent that exhibits excellent dispersibility in biodegradable plastics and can suppress the reduction in biodegradability and mechanical strength of biodegradable plastics, a biodegradable plastic composition containing the biodegradable plastic decomposition agent, and a molded article thereof. [Solution] A biodegradable plastic decomposer used to decompose biodegradable plastics, 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 covered with the shell layer.

Description

Technical Field

[0001] The present disclosure relates to a biodegradable plastic decomposer, a biodegradable plastic composition, and a molded article thereof.

Background Art

[0002] Plastics are widely used as packaging materials because of their high moldability, strength, water resistance, transparency, etc. However, plastics have poor biodegradability and, when discarded into the natural environment after use, can remain for a long time and cause environmental damage. In contrast, in recent years, biodegradable resins that can be biodegraded or hydrolyzed in soil or water and are useful for preventing environmental pollution have attracted attention, and the practical application of packaging materials using biodegradable resin compositions has been promoted. As a resin composition used for packaging materials, for example, Patent Document 1 describes a resin composition containing a biodegradable polyester such as polylactic acid, a polysaccharide such as starch, and a polyhydric alcohol such as glycerin. However, in order to decompose a biodegradable packaging material such as that of Patent Document 1, the presence of microorganisms is required, but it has been found that such microorganisms are less present in the ocean. Therefore, it has been found that a long biodegradation period is required to decompose such a biodegradable packaging material, and the environmental load is not reduced. Therefore, Non-Patent Documents 1 and 2 describe an enzyme-encapsulated biodegradable plastic containing a degrading enzyme capable of decomposing a biodegradable plastic.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

[0005] However, enzyme-encapsulated biodegradable plastics, such as those described in Non-Patent Documents 1 and 2, are prone to enzyme aggregation within the plastic. It is known that enzyme aggregation in plastics reduces mechanical strength and biodegradability.

[0006] This disclosure is made to solve the above problems and aims to provide a biodegradable plastic decomposition agent that exhibits excellent dispersibility in biodegradable plastics and can suppress the reduction of biodegradability and mechanical strength of biodegradable plastics, a biodegradable plastic composition containing the biodegradable plastic decomposition agent, and a molded article thereof. [Means for solving the problem]

[0007] This disclosure includes the following aspects: [1] A biodegradable plastic decomposer used to decompose biodegradable plastics, A shell layer containing a biodegradable amphiphilic polymer, A core layer containing a crude biodegradable plastic decomposition agent, Includes, A biodegradable plastic decomposer in which at least a portion of the surface of the core layer is covered with the shell layer. [2] Crude biodegradable plastic decomposer: A biodegradable plastic decomposer according to [1], wherein the mass ratio represented by the amphiphilic polymer is 1:10 to 100:1. [3] The biodegradable plastic decomposer according to [1], wherein the core layer and the shell layer are bonded by intermolecular bonds. [4] The biodegradable plastic decomposer according to [1], wherein the amphiphilic polymer is at least one selected from the group consisting of polyethylene glycol, polypropylene glycol, and polyvinyl alcohol. [5] The biodegradable plastic decomposer according to [1], wherein the crude biodegradable plastic decomposer is at least one selected from the group consisting of depolymerase, esterase, lipase, cutinase, carboxylesterase, protease, or polyesterase. [6] The biodegradable plastic decomposer according to [1], wherein the mass-average molecular weight of the amphiphilic polymer is 300 to 30000. [7] The biodegradable plastic decomposer according to [1], wherein the biodegradable plastic is at least one selected from the group consisting of biodegradable polyester, polysaccharide ester derivatives, polycarbonate, polyurethane, and polyamide. [8] The biodegradable plastic decomposing agent according to [1], wherein the biodegradable plastic decomposing agent is used to decompose the biodegradable plastic by immersing a biodegradable plastic composition comprising a biodegradable plastic and the biodegradable plastic decomposing agent, or a molded article formed from the biodegradable plastic composition, in water. [9] A biodegradable plastic composition comprising a biodegradable plastic and a biodegradable plastic decomposer described in any one of items [1] to [8].

[10] A biodegradable plastic composition according to [9] having at least one of the properties of (i) and (ii) below. (i) When the weight loss of an uncoated biodegradable plastic decomposer mixed biodegradable plastic composition, which includes the biodegradable plastic and the same amount of the crude biodegradable plastic decomposer instead of the biodegradable plastic decomposer contained in the biodegradable plastic composition, is set to 100, the weight loss of 105 or more is defined as (i) below. (ii) The uncoated biodegradable plastic composition mixed with the biodegradable plastic decomposition agent has a tensile strength of 0.8 times or more when the tensile strength measured under the conditions of (ii) below is set to 1. Condition (i): A film with a thickness of approximately 50 to 200 μm, prepared by heat-pressing the biodegradable plastic composition, is cut into a 1 cm x 1 cm square. The film is immersed in 2 mL of pH 7.5, 100 mM phosphate buffer in a 5 mL sample bottle, and the mixture is shaken while maintaining the optimal temperature at which the biodegradable plastic decomposition agent decomposes the biodegradable plastic. After 5 days, the film is removed, washed with pure water, wiped dry, and dried at room temperature. The weight loss is then calculated from the measured weight using the following formula [Equation 1]. A film with a thickness of approximately 50-200 μm, prepared by heat-pressing the aforementioned uncoated biodegradable plastic decomposition agent mixed biodegradable plastic composition, is cut into a 1 cm x 1 cm square. The film is immersed in 2 mL of pH 7.5, 100 mM phosphate buffer in a 5 mL sample bottle and maintained at the optimal temperature at which the crude biodegradable plastic decomposition agent contained in the uncoated biodegradable plastic decomposition agent mixed biodegradable plastic composition decomposes the biodegradable plastic. After 5 days, the film is removed, washed with pure water, wiped dry, and dried at room temperature. The weight loss is then calculated from the measured weight using the following formula [Equation 1]. [Formula 1] Weight loss (weight %) = [(Weight of film before immersion) - (Weight of film 5 days after the start of immersion)] ÷ (Weight of film before immersion) × 100 (weight %) Condition (ii): Using a film with a thickness of approximately 50 to 200 μm prepared by heat-pressing the biodegradable plastic composition, the tensile strength of the film obtained from the biodegradable plastic composition is measured in accordance with JIS K-6251-5. Using a film with a thickness of about 50 to 200 μm produced by thermally pressing the uncoated biodegradable plastic decomposer - mixed biodegradable plastic composition, measure the tensile strength of the film obtained from the uncoated biodegradable plastic decomposer - mixed biodegradable plastic composition in accordance with JIS K - 6251 - 5.

[11] A molded article formed from the biodegradable plastic composition described in [9].

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

[13] The method for producing a biodegradable plastic composition according to [9].

[14] The method for producing a biodegradable plastic composition according to [9], including melt - kneading the biodegradable plastic decomposer and the biodegradable plastic.

[15] The method for producing a molded article, including molding the biodegradable plastic composition according to [9]. [Effect of the Invention]

[0008] The biodegradable plastic decomposer of the present disclosure can improve the biodegradability of biodegradable plastics when blended with biodegradable plastics. Therefore, the environmental load can be further reduced. In addition, since the biodegradable plastic decomposer of the present disclosure has excellent dispersibility, it can suppress the decrease in the mechanical strength and the decrease in biodegradability of biodegradable plastics. ​​The molded product of the present disclosure contains a biodegradable plastic decomposer, so it has excellent biodegradability. Therefore, the environmental load can be further reduced. In addition, since the biodegradable plastic decomposer in the molded product of the present disclosure is uniformly dispersed, it is possible to suppress a decrease in mechanical strength and a decrease in biodegradability.

Brief Description of the Drawings

[0009] [Figure 1] It is a diagram showing the biodegradable plastic decomposer of the present disclosure. [Figure 2] It is a diagram showing a molded product (film) formed from the biodegradable plastic composition of the present disclosure. [Figure 3] It is a diagram showing the biodegradable plastic decomposers produced in Production Examples 1, 4, and 6. [Figure 4] It is a diagram showing the molded products (films) produced in the Examples and Comparative Examples. [Figure 5] It is a graph showing the results of weight change in the decomposition test of the molded product (film) when PBS was used in the Examples and Comparative Examples. [Figure 6] It is a diagram showing the appearance of the film surface after 24 hours in the decomposition test of the molded product (film) when PBS was used in the Examples and Comparative Examples. [Figure 7] It is a graph showing the results of weight change in the decomposition test of the molded product (film) when PES was used in the Examples and Comparative Examples. [Figure 8] It is a diagram showing the appearance of the film surface in the decomposition test of the molded product (film) when PES was used in the Examples and Comparative Examples. [Figure 9] It is a graph showing the evaluation results of the mechanical strength of the molded product (film) when PBS was used in the Examples and Comparative Examples. [Figure 10] It is a graph showing the evaluation results of the mechanical strength of the molded product (film) when PES was used in the Examples and Comparative Examples. [Figure 11] It is a graph showing the evaluation results of the heat resistance of each biodegradable plastic decomposer. [Figure 12]This graph shows the weight change results in the decomposition test of molded products (films) when PBS was used in the examples and comparative examples, under conditions of extended decomposition time. [Figure 13] This graph shows 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. [Figure 14] This graph shows the weight change results in the decomposition test of molded products (films) when PES was used in the examples and comparative examples, under conditions of extended decomposition time. [Figure 15] This graph shows the relationship between the molecular weight of PEG and the weight change in the degradation test when PES was used in the examples and comparative examples. [Figure 16] This figure shows the surface appearance of molded products (films) after decomposition tests using PBS in the examples and comparative examples, after 3 hours of decomposition. [Figure 17] This figure shows the surface appearance of the molded product (film) after decomposition testing using PES for 3 hours in the examples and comparative examples. [Figure 18] This graph shows the results of evaluating the dispersibility of biodegradable plastic decomposing agents in molded products (films) after 3 hours of decomposition, using PBS and PES in the examples and comparative examples. [Figure 19] This graph shows the results of evaluating the dispersibility of biodegradable plastic decomposing agents in molded products (films) after 24 hours of decomposition, using PBS and PES in the examples and comparative examples. [Figure 20] This graph shows the results of evaluating the mechanical strength (tensile strength) of molded products (films) before immersion in water, when using PBS and PES in the examples and comparative examples. [Figure 21] This graph shows the weight change results in a decomposition test using the weight ratio of biodegradable plastic-degrading enzymes to PEG (5K). [Figure 22] This graph shows the results of evaluating the mechanical strength (tensile strength) based on the weight ratio of biodegradable plastic-degrading enzymes to PEG (5K). [Modes for carrying out the invention]

[0010] The following provides further details about this disclosure.

[0011] Biodegradable plastic decomposition agent The biodegradable plastic degrading agents of this disclosure are used to decompose biodegradable plastics. The biodegradable plastic degrading agent of this disclosure comprises a shell layer containing a biodegradable amphiphilic polymer and a core layer containing a crude biodegradable plastic degrading agent. The biodegradable plastic decomposer of this disclosure has a shell layer covering at least a portion of the surface of the core layer. The average particle size of the biodegradable plastic decomposing agent of this 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 method).

[0012] <Core Layer> (Crude biodegradable plastic decomposition agent) In this specification, "crude biodegradable plastic decomposer" means a substance capable of decomposing biodegradable plastics before they are coated with a shell layer. Crude biodegradable plastic decomposing agents include microorganisms that express and / or secrete enzymes having at least polyester decomposing activity. Examples of enzymes include, but are not limited to, depolymerases, esterases, lipases, cutinases, carboxylesterases, proteases, or polyesterases. Among these, cutinases are preferred from the viewpoint of degradation, and Humicola insolens cutinase (HiC), obtained from the thermophilic fungus Humicola insolens, is more preferred. Microorganisms include those that produce such enzymes naturally or as a result of specific procedures (e.g., recombinant microorganisms). Preferred examples of suitable microorganisms include, but are not limited to, bacteria, fungi, and yeasts. Examples of microorganisms that produce the above enzymes include Humicola insolens, for example. These crude biodegradable plastic decomposing agents may be used individually or in combination of two or more types.

[0013] (Other ingredients) The core layer may contain other components in addition to the crude biodegradable plastic decomposition agent. Other ingredients include surfactants, light stabilizers, and plasticizers. Examples of surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants, among which biodegradable ones are preferred. For example, glycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, soaps, α-sulfo fatty acid methyl ester salts (MES), and α-olefin sulfonates (AOS) are more preferred.

[0014] The content of the crude biodegradable plastic decomposer is preferably 80 to 99% by mass, more preferably 85 to 99% by mass, and even more preferably 90 to 99% by mass, relative to 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 should be biodegradable and preferably have good compatibility (good miscibility) with both crude biodegradable plastic decomposing agents and biodegradable plastics. Examples of amphiphilic polymers include polyethylene glycol (hereinafter also referred to as PEG), ester derivatives of polysaccharides, polyvinyl alcohol, polypropylene glycol, and polyvinylpyrrolidone. PEG is preferred from the viewpoint of ease of handling, cost, and biodegradability. These amphiphilic polymers may be used individually or in combination of two or more types.

[0017] 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. When the mass-average molecular weight of the amphiphilic polymer is within the above range, it exhibits superior 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 decomposing agent. 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 ingredients) The shell layer may contain other components besides the amphiphilic polymer. Other components include surfactants, etc. Examples of surfactants include those similar to those mentioned above.

[0021] Crude biodegradable plastic decomposing agent: The mass ratio represented by the 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, it is superior in dispersibility, biodegradability, and mechanical strength. The mass ratio of the crude biodegradable plastic decomposer to the 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 this disclosure may be one in which at least a portion of the surface of the crude biodegradable plastic decomposer is coated with an amphiphilic polymer. The area ratio 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%, of the total surface area of ​​the crude biodegradable plastic decomposer. When the area ratio of the portion coated with the amphiphilic polymer is within the above range, it is easier to improve the dispersibility, biodegradability, and mechanical strength obtained by the coating.

[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 individually or in combination of two or more types.

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

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

[0026] Specific examples of derivatives of unsaturated carboxylic acids include maleic anhydride, hymic anhydride, itaconic anhydride, citraconic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, glycidyl acrylate, monoethyl maleate, diethyl maleate, monomethyl itaconicate, diethyl itaconicate, acrylamide, methacrylamide, monoamide maleate, diamide maleate, N-monoethyl maleate, N,N-diethyl maleate, N,N-monobutylamide maleate, N,N-dibutylamide maleate, monoamide fumarate, diamide fumarate, N-monobutylamide fumarate, N,N-dibutylamide fumarate, maleimide, N-butylmaleimide, N-phenylmaleimide, sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate, and the like. These denaturing agents may be used individually or in combination of two or more.

[0027] When modification is performed, the content of constituent units derived from the modifying agent 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. Being unmodified prevents a decrease in biodegradability due to modification, and also avoids the complexities of manufacturing that come with modification.

[0029] In preferred embodiments of this 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. Applying excessively high heat to the biodegradable plastic decomposition agent significantly reduces the effect of promoting the decomposition of the biodegradable plastic. Therefore, having a melting point within the above range makes it easier to produce biodegradable plastics with good decomposition properties. The melting point can be measured by differential scanning calorimeter (DSC).

[0030] In one embodiment of this disclosure, the melt mass flow rate (MFR) of the biodegradable plastic is preferably 1.0 g / 10 min to 30 g / 10 min, more preferably 3.0 g / 10 min to 25 g / 10 min, and even more preferably 5.0 g / 10 min to 20 g / 10 min. Having an MFR within the above range of the biodegradable plastic makes it easier 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 this 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. Having the Mw of the biodegradable plastic within this range makes it easier to improve thermoformability and heat resistance.

[0032] In one embodiment of this 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 above range for Mn in the biodegradable plastic makes it easier to improve thermoformability and heat resistance. Furthermore, the Mw and Mn of biodegradable plastics can be determined by gel permeation chromatography (GPC) measurement and converted to standard polystyrene equivalents.

[0033] When a molded article is manufactured from a biodegradable plastic composition containing the biodegradable plastic decomposition agent of this disclosure, the tensile strength of the molded article is preferably 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, it has sufficient mechanical strength for use as a plastic product, thus achieving both biodegradability and resistance to breakage as a plastic product. Therefore, it is possible to obtain physical properties equivalent to those of a plastic product that does not contain the biodegradable plastic decomposition agent of this disclosure.

[0034] When a molded article is manufactured from a biodegradable plastic composition containing the biodegradable plastic decomposition agent of this disclosure, the elongation at break of the molded article is preferably 300% or more, more preferably 400-1500%, and even more preferably 500-1300%. When the elongation at break of the molded article is within the above range, it possesses sufficient mechanical strength for use as a plastic product, thus achieving both biodegradability and ease of molding as a plastic product. Therefore, physical properties equivalent to those of a plastic product without the biodegradable plastic decomposition agent of this disclosure can be obtained.

[0035] When a molded article is manufactured from a biodegradable plastic composition containing the biodegradable plastic decomposition agent of this disclosure, the Young's modulus of the molded article is preferably 0.3 GPa or higher, more preferably 0.4 to 1.0 GPa, and even more preferably 0.5 to 0.8 GPa. When the Young's modulus of the molded article is within the above range, it possesses sufficient mechanical strength for use as a plastic product, thus achieving both biodegradability and resistance to deformation as a plastic product. Therefore, physical properties equivalent to those of a plastic product without the biodegradable plastic decomposition agent of this disclosure can be obtained.

[0036] In the decomposition test (weight change) described in the examples for an uncoated biodegradable plastic composition containing the biodegradable plastic of the present disclosure and an equal amount of the crude biodegradable plastic decomposer instead of the biodegradable plastic decomposer contained in the biodegradable plastic composition, the weight loss after 5 days is set to 100, and the weight loss is 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 decomposition agent of this disclosure has a tensile strength of 0.8 times or more, preferably 0.9 times or more, and more preferably 1 time or more, compared to the tensile strength of the biodegradable plastic without the biodegradable plastic decomposition agent, when the tensile strength of the biodegradable plastic without the biodegradable plastic decomposition agent is set to 1.

[0038] ≪Method for manufacturing biodegradable plastic decomposition agents≫ The method for producing the biodegradable plastic decomposing agent of this disclosure is not particularly limited, but it can be produced by adding a shell layer forming agent containing an amphiphilic polymer to a core layer forming agent containing a crude biodegradable plastic decomposing agent for forming a core layer. Examples of core layer forming agents include aqueous solutions or aqueous dispersions containing a crude biodegradable plastic decomposition agent. Before preparing the core layer forming agent, a step may be performed in which salts such as ammonium sulfate are added to an aqueous solution of a crude biodegradable plastic decomposition agent to cause salting out and produce a powder. The shell layer forming agent is preferably a liquid containing an amphiphilic polymer, and examples include an amphiphilic polymer, an aqueous solution of an amphiphilic polymer, or an aqueous dispersion of an amphiphilic 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, it becomes easier to increase the solubility or decomposition of the crude biodegradable plastic decomposer in water, 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 decomposition of the crude biodegradable plastic decomposition agent in water is increased, and the yield of the resulting biodegradable plastic decomposition agent can be further improved. The stirring time of the mixture 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 mixture is within the above range, the surface of the crude biodegradable plastic decomposer is sufficiently coated with the amphiphilic polymer, which makes it easier to improve the dispersibility, biodegradability, and mechanical strength of the resulting biodegradable plastic decomposer. A preferred method for producing biodegradable plastic decomposing agents is freeze-drying. For example, a core layer forming agent containing a crude biodegradable plastic decomposing agent is mixed with a shell layer forming agent containing an amphiphilic polymer to create a homogeneous aqueous solution, which is then freeze-dried under vacuum conditions of 10 Pa or less to obtain the biodegradable plastic decomposing agent. The mass ratio of the crude biodegradable plastic decomposer to the 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 greater than 0.2 and less than 10. When the mass ratio is within the above range, the dispersibility, biodegradability, and mechanical strength of the resulting biodegradable plastic decomposer tend to be improved.

[0039] Biodegradable Plastic Compositions The biodegradable plastic composition of this disclosure comprises a biodegradable plastic and a biodegradable plastic degrading agent of this disclosure. In the biodegradable plastic composition of this disclosure, the biodegradable plastic degrading agent of this disclosure is dispersed in the biodegradable plastic. In one embodiment of this disclosure, the content of the biodegradable plastic decomposer is preferably 0.0001 to 10% by mass, more preferably 0.001 to 5% by mass, and even more preferably 0.01 to 3% by mass, based on the total mass of the biodegradable plastic composition. When the content of the biodegradable plastic decomposer is within the above range, it is possible to provide molded articles that are superior in dispersibility, biodegradability, and mechanical strength.

[0040] In one embodiment of this disclosure, the biodegradable plastic content is preferably 90 to 99.99% by mass, more preferably 95 to 99.985% by mass, and even more preferably 99 to 99.98% by mass, based on the total mass of the biodegradable plastic composition. When the biodegradable plastic content is within the above range, it is possible to provide molded articles that are superior in dispersibility, biodegradability, and mechanical strength.

[0041] The biodegradable plastic compositions of this disclosure may contain additives other than biodegradable plastics and biodegradable plastic decomposing agents, to the extent that they do not impair the purpose or effects of this disclosure. Examples of additives include water, organic solvents, fillers, processing stabilizers, weather stabilizers, colorants, UV absorbers, heat stabilizers, light stabilizers, antistatic agents, flame retardants, plasticizers, lubricants, fragrances, foaming agents, deodorants, bulking agents, release agents, mold release agents, reinforcing agents, antifungal agents, preservatives, crystallization rate retarders, and other resins other than biodegradable polyester resins. These additives can be used individually or in combination of two or more.

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

[0043] 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. Other resins can be used individually or in combination of two or more. From the viewpoint of environmental impact, it is preferable not to include non-biodegradable resins.

[0044] The amount of additives is not particularly limited as long as it is added in a manner that does not impair the purpose or effect of this disclosure, but is, 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 1% by mass or more, relative to the mass of the biodegradable plastic composition.

[0045] Method for producing biodegradable plastic compositions The method for producing the biodegradable plastic composition of this disclosure is not particularly limited, but may include, for example, a method of mixing a biodegradable plastic, the biodegradable plastic decomposition agent of this disclosure, and additives as needed. A conventional mixer, preferably a melt kneader, can be suitably used for mixing. The temperature during mixing or kneading should be such that no alteration of the amphiphilic polymer (e.g., polymerization, decomposition, etc.) or denaturation of enzymes occurs, 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 pre-mixed using a mixer or the like before being introduced into the melt kneader.

[0046] In one embodiment of this disclosure, a biodegradable plastic composition can be obtained by melt-kneading using an extruder. Preferably, a twin-screw extruder can be used as the extruder. The twin-screw extruder may rotate in both directions. The rotational speed of the screws can be selected from the same range as the rotational speed of the kneader described above. The cylinder temperature can be selected from the temperature range used for mixing or kneading described above. Each component can be introduced directly into the extruder.

[0047] The molten biodegradable plastic composition, which has been pushed through the extruder while being melted and kneaded, is extruded from the die. The die temperature is preferably 100 to 200°C, more preferably 100 to 140°C. The discharge rate is preferably 1 to 10 kg / h, more preferably 2 to 5 kg / h.

[0048] The extruded biodegradable plastic composition (molten material) can be extruded into sheet, film, or strand form. During this process, the biodegradable plastic composition (molten material) is cooled and dried.

[0049] When extruding a mixture into strands, the strands can be formed into pellets by extruding them through a multi-hole strand nozzle and cutting them with a rotary cutter. To prevent the pellets from sticking together, vibration can be applied periodically or continuously, and moisture can be removed from the pellets 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 from a film-forming die and then cooled and dried while being wound up on a take-up roller. It is preferable to cool the mixture between the die and the roller to prevent it from adhering to the roller. The biodegradable plastic composition of this disclosure may also be formed into a sheet or film by conventional film-forming methods (e.g., casting).

[0051] Biodegradable plastic compositions (for example, pelletized biodegradable plastic compositions) may be formed into sheets or films by conventional methods such as extrusion molding, compression molding, or press molding.

[0052] ≪Molded products≫ The molded articles of this disclosure are obtained by molding the biodegradable plastic composition of this disclosure. The form of the molded articles is not particularly limited and may be pellets, sheets, or films. That is, they may be pellets, sheets, or films containing or comprising the biodegradable plastic composition. The thickness of the sheet or film can be appropriately selected depending on the application, preferably 5 to 1000 μm, more preferably 10 to 500 μm. The thickness of the film or sheet can be measured by a thickness gauge.

[0053] ≪Method for manufacturing molded products≫ Biodegradable plastic compositions (for example, pelletized biodegradable plastic compositions) may be formed into sheets or films by conventional methods such as extrusion molding, compression molding, or press molding. The molding temperature 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 above upper limit, the thermoformability is easily improved, making it easy to mold the resulting laminate into a predetermined shape. Furthermore, it is possible to suppress the deactivation of crude biodegradable plastic decomposition agents such as enzymes, and to prevent the coated amphiphilic polymer from melting. The molding time 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 above upper limit, the resulting laminate can be easily molded into a predetermined shape. Furthermore, it is possible to suppress the deactivation of crude biodegradable plastic decomposition agents such as enzymes, and to prevent 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. If the molding time is below the above upper limit, the resulting laminate can be easily molded into a predetermined shape. Furthermore, it is possible to suppress the deactivation of crude biodegradable plastic decomposition agents such as enzymes, and to prevent the coated amphiphilic polymer from melting.

[0054] ≪Laminated structure≫ The laminate of this disclosure has two or more layers, each containing at least one biodegradable plastic layer formed from the biodegradable plastic composition of this disclosure. When the laminate of this disclosure has two or more biodegradable plastic layers, the compositions of the biodegradable plastic layers may be the same or different. The form of the biodegradable plastic layer is not particularly limited and may be, for example, a film or a sheet. The laminate may contain other layers besides the biodegradable plastic layer. Examples of other layers include a biodegradable resin layer containing a biodegradable plastic but not a biodegradable plastic decomposition agent, and paper, etc. The type of biodegradable plastic contained in the biodegradable resin layer may be the same or different from that contained in the biodegradable plastic layer. By having other layers besides the biodegradable plastic layer, when the laminate is used as a packaging container, etc., the biodegradable plastic layer comes into contact with water, preventing the coating amphiphilic polymer from dissolving in water and activating crude biodegradable plastic decomposition agents such as enzymes, thereby preventing the biodegradation of the biodegradable plastic from progressing.

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

[0056] The biodegradable plastic contained in the biodegradable resin layer is not particularly limited, and examples include those similar to those described above for biodegradable plastics. From the viewpoint of adhesion 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 this disclosure are of the same type.

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

[0058] The type of paper used is not particularly limited and includes, for example, kraft paper, double-bleached kraft paper, fine paper, imitation 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 paper thickness can be appropriately selected depending on the application, preferably 5 to 1000 μm, and more preferably 10 to 500 μm.

[0060] The thickness of the laminate of this 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 this disclosure may have an adhesive layer for bonding each layer. The adhesive layer is preferably formed from an adhesive containing a biodegradable plastic. From the viewpoint 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 this disclosure are of the same type.

[0062] Examples of laminates of this disclosure include laminates containing a biodegradable resin layer / biodegradable plastic layer in that order; laminates containing a biodegradable resin layer / biodegradable plastic layer / biodegradable resin layer in that order; and laminates containing a biodegradable resin layer / adhesive layer / biodegradable plastic layer / adhesive layer / biodegradable resin layer in that order. These laminates may contain other layers besides biodegradable resin layers between or outside each layer, but it is preferable that there are no other layers between each layer, i.e., that each layer is adjacent to the others. The adjacent arrangement of each layer makes it easier to improve the biodegradability of the laminate.

[0063] ≪Method for manufacturing laminates≫ The laminate of the present disclosure can be manufactured by laminating two or more layers, each containing at least one biodegradable plastic layer formed from the biodegradable plastic composition of the present disclosure.

[0064] The laminates of this disclosure can be manufactured by laminating a biodegradable plastic layer with other layers using conventional methods such as co-extrusion molding (co-extrusion lamination, co-extrusion sheet molding, co-extrusion inflation molding, co-extrusion blow molding, etc.), co-injection molding, extrusion lamination, and dry lamination. For example, the method may involve co-extruding or laminating the biodegradable plastic layer with other layers; or forming other layers on the 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 extruded onto the surface of the biodegradable plastic layer.

[0065] When laminating a biodegradable plastic layer and a 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 the biodegradable resin layer, thereby producing a laminate; or a biodegradable plastic composition containing a biodegradable plastic decomposition 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 before laminating them.

[0066] Examples of the biodegradable resin layer-forming agent include those that contain biodegradable plastics but do not contain biodegradable plastic decomposing agents, and for example, they may contain biodegradable plastics as well as the other components mentioned above.

[0067] When laminating a molded product with paper, a biodegradable plastic composition containing a biodegradable plastic decomposition agent can be applied to the paper and dried to produce a laminate. Alternatively, the paper can be laminated onto the molded product to produce a laminate. The adhesive layer described above may be provided between the molded product and the paper.

[0068] <<Applications of molded products and laminates>> The uses of the molded articles and laminates of this disclosure are not particularly limited, but they are suitably used as packaging materials, especially food packaging materials. As food packaging materials, they are not particularly limited, but can be used not only for solid foods but also for foods containing liquids. When food contains water, it is preferable to prevent contact between the food and the layer containing the biodegradable plastic decomposition agent. For example, it is preferable to form a laminate by providing a biodegradable resin layer on top of the layer containing the biodegradable plastic decomposition agent, thereby suppressing the activation of the biodegradable plastic decomposition agent by the moisture contained in the food. This results in superior storage stability and safety of the food. In the case of molded articles without a biodegradable resin layer, it is preferable to use them as packaging materials for articles that do not contain moisture.

[0069] Methods for decomposing biodegradable plastic compositions, molded articles, and laminates. The method for decomposing the biodegradable plastic composition, molded article, and laminate of this disclosure includes decomposing the biodegradable plastic by immersing the biodegradable plastic composition, molded article, and laminate of this disclosure in water. By immersing the crude biodegradable plastic decomposition agent in water, the amphiphilic polymer coating the agent dissolves in the water, and the crude biodegradable plastic decomposition agent comes into contact with the water, becoming activated and the decomposition reaction of the biodegradable plastic proceeds. One example of the decomposition reaction is hydrolysis. The immersion time in water is preferably 1 hour or more, more preferably 1 hour to 1 year, and even more preferably 3 hours to 6 months. Keeping the immersion time within the above range further reduces the environmental burden. The temperature at which the material is immersed in water is preferably 10 to 60°C, more preferably 15 to 50°C, and even more preferably 20 to 40°C. When the temperature at which the material is immersed in water is within the above range, there is no need to heat the water, and therefore biodegradation can be carried out at a low cost. The pH of water at 25°C is preferably 6 to 12, more preferably 7 to 11, and even more preferably 8 to 10. If the pH of water at 25°C is within the above range, there is no need to adjust the pH, and it can be biodegraded at low cost, for example by immersing it in seawater.

[0070] <Effects and Actions> The biodegradable plastic decomposition agent of this disclosure has a core layer containing a crude biodegradable plastic decomposition agent coated with a shell layer containing an amphiphilic polymer. Therefore, its dispersibility in biodegradable plastics is improved, thereby suppressing aggregation of the crude biodegradable plastic decomposition agent. By improving the dispersibility of the biodegradable plastic decomposition agent, the biodegradability of the biodegradable plastic is also improved, and the decrease in mechanical strength can be suppressed. Because it is coated with an amphiphilic polymer, it is presumed that after immersion in water, the amphiphilic polymer such as PEG dissolves in the water, and when the crude biodegradable plastic decomposition agent such as enzymes comes into contact with the water, biodegradation reactions such as hydrolysis proceed. The biodegradable plastic decomposition agent of this disclosure disperses uniformly even when compounded with biodegradable plastics to form molded products, resulting in a faster biodegradation rate and excellent mechanical strength of the biodegradable plastic. The biodegradable plastic decomposition agent of this disclosure does not decompose when used as a plastic product, but after use of the plastic product, biodegradation begins when the encapsulated enzymes come into contact with water due to surface abrasion or fracture and are activated, thus combining high biodegradability with practicality as a plastic product. [Examples]

[0071] The present disclosure will be specifically illustrated by the following examples, but this disclosure is not limited to these examples.

[0072] <Evaluation Method> (1) Mass average molecular weight The mass-average molecular weight of PEG was determined by gel permeation chromatography (GPC). (2) Disassembly test (weight change) We evaluated the weight change due to the decomposition of biodegradable plastics. Films with a thickness of approximately 50-200 μm, 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 at pH 7.5 in a 5 mL sample bottle and maintained at 45°C, the optimal temperature for the enzyme, while shaking. The films were removed at regular intervals, washed with pure water, wiped dry, dried at room temperature, and weighed. The number of samples was always 3. After weighing, the samples were returned to their original sample bottles, and the decomposition experiment was continued. The weight loss (in weight %) was calculated using the following formula. Weight loss (weight %) = [(weight of film before immersion) - (weight of film after a certain time from the start of immersion)] ÷ (weight of film before immersion) × 100 (weight %) (3) Decomposition test (surface appearance) We observed the changes in surface appearance due to the decomposition of biodegradable plastics. Using a benchtop scanning electron microscope (JCM-7000, JEOL, Japan), we observed the surface morphology of the film before and during decomposition (after 24 hours). The acceleration voltage was set to 5.0 kV. The samples were coated with gold using a magnetron sputtering apparatus (MSP-1S, Vacuum Devices, Japan). (4) Mechanical strength (tensile strength) The tensile strength of the films obtained in each example was measured in accordance with JIS K-6251-5. Figure 2 shows an example of the films obtained in each example. Tensile tests were performed on the film using a small benchtop testing machine (EZ-LX, Shimadzu Corporation, Japan). The film was cut using a dumbbell cutter (SDL-100, dumbbell, Japan) fitted with a 1 / 3 reduction type super dumbbell cutter (SDK-500, dumbbell, Japan), and dumbbell test specimens conforming to JIS K-6251-5 were prepared. The thickness of the test specimen was the average of the three central points. Measurements were performed at an initial length of 8.4 mm, a tensile speed of 50 mm / min, and at room temperature. The number of samples was 5 to 8 for each test, and the average value of these samples 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) The Young's modulus was measured using the same tensile test as in (4).

[0073] <Biodegradable plastics> The following biodegradable plastics were used. The following biodegradable plastics were used. ·PBS (BioPBS manufactured by Mitsubishi Chemical Corporation) TM (Mw=130000, melting point=114℃) • PES (provided by Hideki Abe, team leader at RIKEN; Mw=100000, melting point=104℃) <Biodegradable plastic decomposition agent> The following crude biodegradable plastic decomposing agents were used. • Enzyme (cutinase, manufactured by Fujifilm & Wako Pure Chemical Industries, Ltd., "Novozyme 51032 (Humicola insolens cutinase, HiC)") The following amphiphilic polymers were used. • PEG (Sigma-Aldrich "Poly(ethylene glycol)", Mw=400, melting point=4-8℃) • PEG (Poly(ethylene glycol)methyl ether, manufactured by Sigma-Aldrich, Mw=2000, melting point=52-56℃) • PEG (Sigma-Aldrich "Poly(ethylene glycol)", Mw=3350, melting point=53-58℃) • PEG (Poly(ethylene glycol)methyl ether, manufactured by Sigma-Aldrich, Mw=5000, melting point=60-64℃) • PEG (Sigma-Aldrich "Polyethylene Glycol 10000", Mw=10000, melting point=53-58℃) • PEG (Polyethylene glycol 20000, manufactured by Fujifilm & Wako Pure Chemical Industries, Mw=20000, melting point 60℃) <Phosphate buffer> Use the following reagents. Sodium dihydrogen phosphate Dipotassium hydrogen phosphate

[0074] <Manufacturing Example 1> Preparation of a biodegradable plastic decomposition agent 1-1: Preparation of enzyme (HiC) powder 250 mL of Novozyme 51032 enzyme stock solution was diluted with 750 mL of distilled water, and the solution was cooled in an ice bath. While cooling, 472 g of ammonium sulfate was slowly added to the enzyme solution while gently stirring it, and after all of it had been added, stirring was continued for another 30 minutes. The mixture was allowed to stand overnight at 4°C to precipitate the enzyme, and then centrifuged at 17,000 × g at 4°C for 20 minutes to remove the supernatant. The precipitate was dissolved with as little distilled water as possible, and desalted using a PD-10 column (Citiva, Sweden). For desalting, 2.5 mL of enzyme solution was added, followed by 3.5 mL of distilled water to recover the enzyme. The column was washed with distilled water and reused. The recovered enzyme solution was freeze-dried at -84°C and below 10 Pa to obtain enzyme (HiC) powder. This powder was stored at 4°C until use.

[0075] 1-2: Preparation of biodegradable plastic decomposition agent (PEG-coated HiC powder) PEG-coated HiC powder was prepared by mixing HiC powder and PEG in a weight ratio of 10:1. A 10 mg / mL aqueous HiC solution and a 1 mg / mL aqueous PEG solution were prepared with pure water. 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. After stirring, the mixture was freeze-dried. This yielded PEG-coated HiC powder. This powder was stored at 4°C until use.

[0076] <Manufacturing Examples 2-6> A biodegradable plastic decomposing agent was 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] [Table 1]

[0078] Figure 3 shows the biodegradable plastic decomposing agents produced in production examples 1, 4, and 6. In all cases, powder form was obtained.

[0079] <Example 1> Preparation of a film containing a biodegradable plastic decomposition agent The biodegradable plastic degrading agent obtained in Production Example 1 was added to the biodegradable plastic in the proportions shown in Table 2, and the mixture was hot-mixed using a twin-screw extruder (HAAKE Minilab, Thermo Fisher, USA). The two screws rotated in opposite directions at 120 rpm, the mixing temperature was 130°C, and the mixing time was 2 minutes. A 1 mm x 2 mm rectangular extruder die was used. After extrusion, the mixture was water-cooled and the remaining sample in the mixer was removed. The mixed samples were stored at room temperature in a desiccator with silica gel as a desiccant. Approximately 500-1000 mg of the mixture was hot-pressed for 1 minute 30 seconds at the same temperature as the mixing, and immediately quenched in an ice bath for 5 seconds to produce a film. The pressure was 5 MPa. After thoroughly wiping off the water from the films, they were stored at room temperature in a similar desiccator.

[0080] <Examples 2-12> A film was prepared in the same manner as in Example 1, except that the type and amount of biodegradable plastic decomposing agent were changed as shown in Tables 2 and 3, and the type and amount of biodegradable plastic were changed as shown in Tables 2 and 3.

[0081] <Comparative Example 1> Biodegradable plastics that did not contain enzyme powder were also filmed by hot pressing and stored in the same manner as in Example 1.

[0082] <Comparative Example 2> Except for using HiC powder before coating with PEG, the film was formed by hot pressing and stored in the same manner as in Example 1.

[0083] <Comparative Example 3> Except for changing the biodegradable plastic as shown in Table 4, the film was formed by hot pressing and stored in the same manner as in Comparative Example 1.

[0084] <Comparative Example 4> Except for changing the biodegradable plastic as shown in Table 4, the film was formed by hot pressing and stored in the same manner as in Comparative Example 2.

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

[0086] [Table 2]

[0087] [Table 3]

[0088] [Table 4]

[0089] Table 5 shows the surface appearance of various biodegradable plastics containing Hic coated with various PEGs, which were formed into films. The left column shows the surface immediately after molding, and the left column shows the surface appearance 24 hours after immersion in 100 mM phosphate buffer (pH 7.5). The 1 mm thickness was calculated using the image analysis software ImageJ. 2 This indicates the number of holes per unit area.

[0090] [Table 5]

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

[0092] [Table 6]

[0093] Figure 4 shows the molded products (films) produced in the examples and comparative examples. The film without added biodegradable plastic decomposition agent (no additive), the film with uncoated crude biodegradable plastic decomposition agent (enzyme only), and the film with PEG-coated biodegradable plastic decomposition agent (PEG coated) were all milky white films and had the same appearance. Figure 5 is a graph showing the weight change results in the decomposition test of molded products (films) using PBS in the examples and comparative examples. The film without additives showed almost no weight change even after 5 days. The film with only uncoated enzyme added showed a weight change of about 30% by weight even after 5 days. The film with PEG-coated biodegradable plastic decomposer added was almost completely decomposed after 4 days. In particular, the biodegradable plastic decomposer with a PEG molecular weight of 5000 (5K) decomposed faster than the biodegradable plastic decomposers with PEG molecular weights of 400 and 20000 (20K), and was almost completely decomposed after 2 days. Figure 6 shows the appearance of the film surface after 24 hours in a decomposition test of molded products (films) using PBS in the examples and comparative examples. After 24 hours, the surface of the film to which the biodegradable plastic decomposition agent of this disclosure was added showed a uniform distribution of pores, and the pores were large in size, indicating excellent dispersibility of the biodegradable plastic decomposition agent and rapid decomposition of biodegradable plastics by the biodegradable plastic decomposition agent. On the other hand, after 24 hours, the surface of the film to which the uncoated enzyme was added showed an uneven distribution of pores, but large pores were also observed. From this, it was found that coating at least a portion of the surface of the crude biodegradable plastic decomposition agent with an amphiphilic polymer improves both dispersibility and decomposition rate. Figure 7 is a graph showing the weight change results in the decomposition test of molded products (films) when PES was used in the examples and comparative examples. Similar to the PBS example, the untreated film showed almost no weight change even after 5 days. The film with only the uncoated enzyme added showed less weight change after 5 days than the PBS example, at about 10% by weight. The films with PEG-coated biodegradable plastic decomposers added showed a larger weight change than these comparative examples. In particular, the film with a biodegradable plastic decomposer coated with PEG with a molecular weight of 5000 (5K) was almost completely decomposed after 3 days. Films with biodegradable plastic decomposers with molecular weights of 400 or 20000 (20K) decomposed more slowly than those using PEG with a molecular weight of 5000 (5K). Figure 8 shows the appearance of the film surface after 24 hours in a decomposition test of molded products (films) using PES in the examples and comparative examples. After 24 hours, the surface of the film to which the biodegradable plastic decomposition agent was added showed a uniform distribution of pores, and the pore size was large, indicating excellent dispersibility of the biodegradable plastic decomposition agent and rapid decomposition of biodegradable plastics by the biodegradable plastic decomposition agent. On the other hand, after 24 hours, the surface of the film to which the uncoated enzyme was added showed an uneven distribution of pores, and the pore size was small. From this, it was found that coating at least a portion of the surface of the crude biodegradable plastic decomposition agent with an amphiphilic polymer improves both dispersibility and decomposition rate. Figure 9 is a graph showing the evaluation results of the mechanical strength of molded products (films) when PBS was used in the examples and comparative examples. Films containing a biodegradable plastic decomposition agent achieved tensile strength equivalent to that of films without the additive. Films containing an uncoated enzyme, and films using PEG with a molecular weight of 400, showed slightly lower tensile strength than the films without the additive, but were found to be within a range suitable for practical use. Figure 10 is a graph showing the evaluation results of the mechanical strength of molded products (films) when PES was used in the examples and comparative examples. Unexpectedly, the film with the added biodegradable plastic decomposition agent achieved significantly higher tensile strength than the film without the additive or the film with the uncoated enzyme. Figure 11 is a graph showing the evaluation results of the heat resistance of each biodegradable plastic decomposition agent. Films treated with a biodegradable plastic decomposition agent did not show a significant decrease in enzyme activity compared to untreated and unheated films. This indicates that films treated with a biodegradable plastic decomposition agent exhibit superior moldability. Furthermore, the biodegradable plastic decomposition agent was found to be more effective at temperatures below 160°C. Figure 12 is a graph showing the weight change results in the decomposition test of molded products (films) when PBS was used in the examples and comparative examples, with extended decomposition times. Films containing a biodegradable plastic decomposition agent were found to exhibit superior decomposition rates, even when the molecular weight of PEG was altered. It was also found that the decomposition rate could be controlled by changing the molecular weight of PEG. Figure 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 PEG with a molecular weight of 5000 showed the best degradation rate. Figure 14 is a graph showing the weight change results in the decomposition test of molded products (films) when PES was used in the examples and comparative examples, with extended decomposition times. Similar to the case using PBS, it was found that films containing a biodegradable plastic decomposition agent, even when the molecular weight of PEG was changed, exhibited superior decomposition rates when using PES. It was also found that the decomposition rate could be controlled by changing the molecular weight of PEG. Figure 15 is a graph showing the relationship between the molecular weight of PEG and the weight change in the degradation test when PES was used in the examples and comparative examples. Unlike when PBS was used, it was found that the film using PEG with a molecular weight of 2000 (2K) showed the best degradation rate per day. Figure 16 shows the surface appearance of molded products (films) after decomposition tests using PBS in the examples and comparative examples, after 3 hours of decomposition. The film to which the biodegradable plastic decomposition agent was added showed excellent dispersibility and decomposition rate, as the pores were uniformly distributed and large pores were observed, even when the molecular weight of PEG was changed. Figure 17 shows the surface appearance of the molded product (film) after decomposition testing using PES for 3 hours in the examples and comparative examples. Similar to the case using PBS, when PES was used, the films to which the biodegradable plastic decomposition agent was added showed a uniform distribution of pores, even when the molecular weight of PEG was changed, and large pores were also observed, indicating excellent dispersibility and decomposition rate. Figure 18 is a graph showing the results of evaluating the dispersibility of biodegradable plastic degrading agents in molded products (films) after 3 hours of decomposition when using PBS and PES in the examples and comparative examples. Figure 19 is a graph showing the results of evaluating the weight change (dispersibility) of biodegradable plastic degrading agents in molded products (films) after 24 hours of decomposition when using PBS and PES in the examples and comparative examples. The number of pores after 3 hours of degradation was considered to represent the enzyme's dispersibility, and this was compared with the pore area ratio and the weight loss after 24 hours of degradation. For PEGs with different molecular weights, the shape of the graphs for the number of pores, area ratio, and degradation were generally consistent, indicating that dispersibility significantly influences degradation. Figure 20 is a graph showing the results of evaluating the mechanical strength (tensile strength) of molded products (films) before immersion in water, when using PBS and PES in the examples and comparative examples. The tensile strength results in Figure 20 were compared with the results for the number of holes and the area ratio of holes in Figure 18, and the results for the weight change in Figure 19. Since the shapes of these graphs were generally consistent, it is considered that dispersibility greatly affects tensile strength. Figure 21 is a graph showing the weight change results in a degradation test based on the weight ratio of biodegradable plastic-degrading enzyme to PEG(5K). Figure 22 is a graph showing the results of evaluating the mechanical strength (tensile strength) based on the weight ratio of biodegradable plastic-degrading enzyme to PEG(5K). For both degradation and mechanical properties, the optimal weight ratio was enzyme:PEG5K = 10:1.

Claims

1. A biodegradable plastic decomposer used to decompose biodegradable plastics, A shell layer containing a biodegradable amphiphilic polymer, A core layer containing a crude biodegradable plastic decomposition agent, Includes, A biodegradable plastic decomposer in which at least a portion of the surface of the core layer is covered with the shell layer.

2. Crude biodegradable plastic decomposing agent: The biodegradable plastic decomposing agent according to claim 1, wherein the mass ratio represented by the 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 together by intermolecular bonds.

4. The biodegradable plastic decomposer according to claim 1, wherein the amphiphilic polymer is at least one selected from the group consisting of polyethylene glycol (hereinafter also referred to as PEG), polysaccharide ester derivatives, polyvinyl alcohol, polypropylene glycol, and polyvinylpyrrolidone.

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

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

7. The biodegradable plastic decomposer 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 decomposing agent according to claim 1, wherein the biodegradable plastic decomposing agent is used to decompose the biodegradable plastic by immersing a biodegradable plastic composition comprising a biodegradable plastic and the biodegradable plastic decomposing agent, or a molded article formed from the biodegradable plastic composition, in water.

9. A biodegradable plastic composition comprising a biodegradable plastic and a 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 properties of (i) and (ii) below. (i) When the weight loss of an uncoated biodegradable plastic decomposer mixed biodegradable plastic composition, which includes the biodegradable plastic and the same amount of the crude biodegradable plastic decomposer instead of the biodegradable plastic decomposer contained in the biodegradable plastic composition, is set to 100, the weight loss of 105 or more is defined as (i) below. (ii) The uncoated biodegradable plastic mixed biodegradable plastic composition has a tensile strength of 0.8 times or more when the tensile strength measured under the conditions (ii) below is set to 1. Condition (i): A film with a thickness of approximately 50 to 200 μm, prepared by heat-pressing the biodegradable plastic composition, is cut into a 1 cm x 1 cm square. The film is immersed in 2 mL of pH 7.5, 100 mM phosphate buffer in a 5 mL sample bottle, and the mixture is shaken while maintaining the optimal temperature at which the biodegradable plastic decomposition agent decomposes the biodegradable plastic. After 5 days, the film is removed, washed with pure water, wiped dry, and dried at room temperature. The weight loss is then calculated from the measured weight using the following formula [Equation 1]. A film with a thickness of approximately 50 to 200 μm, prepared by heat-pressing the aforementioned uncoated biodegradable plastic decomposition agent mixed biodegradable plastic composition, is cut into a 1 cm x 1 cm square. The film is immersed in 2 mL of pH 7.5, 100 mM phosphate buffer in a 5 mL sample bottle and maintained at the optimal temperature at which the crude biodegradable plastic decomposition agent contained in the uncoated biodegradable plastic decomposition agent mixed biodegradable plastic composition decomposes the biodegradable plastic. After 5 days, the film is removed, washed with pure water, wiped dry, and dried at room temperature. The weight loss is then calculated from the measured weight using the following formula [Formula 1]. [Formula 1] Weight loss (weight %) = [(Weight of film before immersion) - (Weight of film 5 days after the start of immersion)] ÷ (Weight of film before immersion) × 100 (weight %) Condition (ii): Using a film with a thickness of approximately 50 to 200 μm prepared by heat-pressing the biodegradable plastic composition, the tensile strength of the film obtained from the biodegradable plastic composition is measured in accordance with JIS K-6251-5. Using a film with a thickness of approximately 50 to 200 μm prepared by hot-pressing the aforementioned uncoated biodegradable plastic decomposition agent mixed biodegradable plastic composition, the tensile strength of the film obtained from the uncoated biodegradable plastic decomposition agent mixed biodegradable plastic composition is measured in accordance with JIS K-6251-5.

11. A molded article formed from the biodegradable plastic composition described in claim 9.

12. A method for producing a biodegradable plastic decomposition 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, comprising 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 described in claim 9.

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