Biodegradable plastic decomposing agent, biodegradable plastic composition, molded article, and method for manufacturing the same.

Abstract

To provide a biodegradable plastic decomposition agent, a biodegradable plastic composition, molded articles, and methods for manufacturing these that can suppress the decrease in biodegradability during the manufacture of plastic products. [Solution] A biodegradable plastic decomposer used to decompose biodegradable plastics, comprising a crude biodegradable plastic decomposer that decomposes biodegradable plastics, and at least one selected from the group consisting of antioxidants and radical scavengers.

Description

[Technical Field]

[0001] This disclosure relates to biodegradable plastic decomposing agents, biodegradable plastic compositions, molded articles, and methods for producing the same. [Background technology]

[0002] Plastics are widely used as packaging materials due to their high moldability, strength, water resistance, and transparency. However, plastics have poor biodegradability and, when discarded into nature after use, can persist for long periods, potentially causing environmental damage. In response to this, biodegradable resins, which are biodegradable or hydrolyzed in soil and water and are useful in preventing environmental pollution, have recently attracted attention, and the practical application of packaging materials using biodegradable resin compositions is progressing. As an example of a resin composition used in packaging materials, Patent Document 1 describes a resin composition containing biodegradable polyesters such as polylactic acid, polysaccharides such as starch, and polyhydric alcohols such as glycerin. However, the presence of microorganisms is necessary for the biodegradation of biodegradable packaging materials like those in Patent Document 1, but it is known that such microorganisms are scarce in the ocean. Therefore, it is known that a long biodegradation period is required to biodegrade such biodegradable packaging materials, and the environmental burden is not reduced. Therefore, Non-Patent Documents 1 and 2 describe enzyme-encapsulated biodegradable plastics that contain a degrading enzyme capable of breaking down biodegradable plastics. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2003-335934 [Non-patent literature]

[0004] [Non-Patent Document 1] Q. Huang et al. Polymer Degradation and Stability, 190, 109647(2021) [Non-Patent Document 2] Q. Huang et al. Biomacromolecules, 24, 5836-5846 (2023) [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, it has been found that enzyme-encapsulated biodegradable plastics, such as those described in Non-Patent Documents 1 and 2, are easily deactivated by the enzymes during the manufacturing of plastic products.

[0006] This disclosure was made to solve the above-mentioned problems and aims to provide a biodegradable plastic decomposition agent, a biodegradable plastic composition, molded articles, and methods for producing the same. [Means for solving the problem]

[0007] This disclosure includes the following aspects: [1] A biodegradable plastic decomposer used to decompose biodegradable plastics, A crude biodegradable plastic decomposer that decomposes biodegradable plastics, At least one selected from the group consisting of antioxidants and radical scavengers, A biodegradable plastic decomposer containing [the specified ingredient]. [2] The biodegradable plastic decomposing agent includes the antioxidant, The biodegradable plastic decomposer according to [1], wherein the antioxidant is at least one selected from the group consisting of glutathione, dibutylhydroxytoluene, L-ascorbic acid, and salts thereof. [3] The biodegradable plastic decomposing agent includes the radical scavenger, The biodegradable plastic decomposer according to [1] or [2], wherein the radical scavenger is a 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl free radical. [4] A biodegradable plastic decomposer described in any one of items [1] to [3], Biodegradable plastics and A biodegradable plastic composition containing [the specified substance]. [5] A method for producing a biodegradable plastic composition, comprising dispersing the biodegradable plastic decomposing agent in the biodegradable plastic by melt-kneading a mixture containing a biodegradable plastic and a biodegradable plastic decomposing agent described in any one of [1] to [3]. [6] A method for producing a biodegradable plastic composition, comprising dispersing the biodegradable plastic decomposition agent or the crude biodegradable plastic decomposition agent described in claim 1 in a biodegradable plastic by melt-kneading a mixture containing a biodegradable plastic and a crude biodegradable plastic decomposition agent for decomposing the biodegradable plastic in a low-oxygen atmosphere. [7] A method for producing a biodegradable plastic composition according to [5] or [6], wherein the melt mixing is carried out at 175°C or below. [8] A method for producing a biodegradable plastic composition according to any one of [5] to [7], wherein the melt mixing is carried out in an atmosphere with an oxygen concentration of 20% by volume or less. [9] A method for producing a biodegradable plastic composition according to any one of [5] to [8], wherein the crude biodegradable plastic decomposing agent is at least one selected from the group consisting of depolymerase, esterase, lipase, cutinase, carboxylesterase, protease, polyesterase, glucanase, cellulase, pullulanase, and amylase.

[10] A method for producing a biodegradable plastic composition according to any one of [5] to [9], wherein the biodegradable plastic is at least one selected from the group consisting of biodegradable polyester, biodegradable polyurethane, biodegradable polycarbonate, biodegradable polyamide, and ester derivatives of polysaccharides.

[11] A molded article formed from a biodegradable plastic composition obtained by the method for producing a biodegradable plastic composition according to any one of [5] to

[10] .

[12] A method for producing a molded article, comprising molding a biodegradable plastic composition obtained by the method for producing a biodegradable plastic composition according to any one of [5] to

[10] .

[13] The method for producing a molded article according to

[12] , wherein the molding is performed under conditions of 175°C or lower.

[14] The method for producing a molded article according to

[12] or

[13] , wherein the molding is performed in an atmosphere with an oxygen concentration of 20% by volume or less. [Effect of the Invention]

[0008] The biodegradable plastic decomposing agent of the present disclosure can improve the biodegradability of the biodegradable plastic when blended with the biodegradable plastic. Therefore, the environmental load can be further reduced. In addition, the biodegradable plastic decomposing agent of the present disclosure can suppress the inactivation of enzymes (crude biodegradable plastic decomposing agents) and the like. Therefore, it is possible to suppress a decrease in biodegradability in the production of biodegradable plastic products containing this. The method for producing a biodegradable plastic decomposing agent of the present disclosure can provide a biodegradable plastic decomposing agent that suppresses the inactivation of enzymes and the like. Therefore, it is possible to suppress a decrease in biodegradability in the production of biodegradable plastic products containing this. The biodegradable plastic composition containing the biodegradable plastic decomposing agent of the present disclosure can improve biodegradability when formed into a molded article. Therefore, the environmental load can be further reduced. In addition, the biodegradable plastic composition of the present disclosure can suppress the inactivation of enzymes and the like. Therefore, when formed into a molded article, it is possible to suppress a decrease in biodegradability. The method for producing a biodegradable plastic composition of the present disclosure can provide a biodegradable plastic composition that suppresses the inactivation of enzymes and the like. Therefore, when formed into a molded article, it is possible to suppress a decrease in biodegradability. The molded product of the present disclosure can suppress the inactivation of biodegradable plastic decomposing agents such as enzymes. Therefore, it is possible to provide a biodegradable plastic product with suppressed reduction in biodegradability. The method for manufacturing the molded product of the present disclosure can provide a molded product with suppressed inactivation of enzymes and the like. Therefore, it is possible to provide a biodegradable plastic product with suppressed reduction in biodegradability.

Brief Description of the Drawings

[0009] [Figure 1] It is a diagram showing molded products (films) manufactured in Examples and Comparative Examples. [Figure 2] It is a graph showing the results of weight change in the decomposition test of molded products (films) when PDLA is used in Examples and Comparative Examples. [Figure 3] It is a diagram showing the appearance of the film surface during decomposition in the decomposition test of molded products (films) when PDLA is used in Examples and Comparative Examples. [Figure 4] It is a graph showing the evaluation results of the mechanical strength of molded products (films) when PDLA is used in Examples and Comparative Examples. [Figure 5] It is a graph showing the enzyme activity (using pNPB as a substrate) after heating a biodegradable plastic containing an enzyme (HiC). [Figure 6] It is a graph showing the enzyme activity (using pNPB as a substrate) after heating a biodegradable plastic containing an enzyme (TfC). [Figure 7] It is a graph showing the effect of oxygen on the weight change in the decomposition test of a molded product (film) containing an enzyme (HiC). [Figure 8] It is a graph showing the enzyme activity after heating an enzyme (HiC) powder containing TEMPOL. [Figure 9] It is a diagram showing the appearance of the enzyme powder after heating. <(

Modes for Carrying Out the Invention

[0010] Hereinafter, the present disclosure will be described in more detail.

[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 crude biodegradable plastic degrading agent that degrades biodegradable plastics, and at least one selected from the group consisting of antioxidants and radical scavengers. 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. When the average particle size is below the above upper limit, it becomes easier to uniformly disperse the biodegradable plastic decomposing agent in the biodegradable plastic, thereby improving biodegradability. When the average particle size is above the above lower limit, it becomes easier to prevent deactivation of crude biodegradable plastic decomposing agents such as enzymes by oxygen and radicals, making it easier to maintain high biodegradability even when molded into a product. The average particle size can be measured by known methods, such as laser diffraction (laser diffraction-scattering method). Biodegradable plastic decomposing agents may be used alone or in combination of two or more types.

[0012] (Crude biodegradable plastic decomposition agent) In this specification, a crude biodegradable plastic decomposing agent is one that can decompose biodegradable plastics. Examples of crude biodegradable plastic decomposing agents include enzymes that can decompose biodegradable plastics, and microorganisms that express enzymes that can decompose biodegradable plastics. Examples of enzymes include, but are not limited to, depolymerase, esterase, lipase, cutinase, carboxylesterase, protease, polyesterase, glucanase, cellulase, pullulanase, or amylase. 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 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] The average particle size of the crude biodegradable plastic decomposer 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. When the average particle size is below the above upper limit, the crude biodegradable plastic decomposer is more easily dispersed uniformly in the biodegradable plastic, thereby improving biodegradability. When the average particle size is above the above lower limit, it is easier to prevent deactivation of the crude biodegradable plastic decomposer by oxygen and radicals, such as enzymes, thereby maintaining high biodegradability even when molded into a product. The average particle size can be measured by known methods, such as laser diffraction (laser diffraction-scattering method).

[0014] The content of the crude biodegradable plastic decomposition agent is preferably 10 to 99% by mass, more preferably 50 to 99% by mass, and even more preferably 90 to 99% by mass, relative to the total mass of the biodegradable plastic decomposition agent. When the content of the crude biodegradable plastic decomposition agent is within the above range, the biodegradability, dispersibility, and mechanical strength of the final molded product are superior.

[0015] (Antioxidant) Antioxidants are compounds that suppress the deactivation of enzymes and other substances by oxygen by inhibiting oxidation reactions. Examples of antioxidants include glutathione, erythorbic acid, dibutylhydroxytoluene, butylhydroxyanisole, α-tocopherol, tocopherol acetate, L-ascorbic acid and its salts, L-ascorbic acid palmitate, L-ascorbic acid stearate, sodium bisulfite, sodium sulfite, triamyl gallate, propyl gallate, or disodium ethylenediaminetetraacetate (EDTA), sodium pyrophosphate, sodium metaphosphate, etc. Among these, dibutylhydroxytoluene, glutathione, ascorbic acid, etc., represented by the following chemical formulas, are preferred.

[0016] [ka]

[0017] These antioxidants may be used individually or in combination of two or more.

[0018] In the biodegradable plastic decomposing agent of this disclosure, it is preferable that the antioxidant forms an intermolecular bond with the crude biodegradable plastic decomposing agent. Examples of intermolecular bonds include hydrophobic bonds and hydrogen bonds.

[0019] The antioxidant content is preferably 1 to 99% by mass, more preferably 1 to 75% by mass, and even more preferably 1 to 40% by mass, relative to the total mass of the biodegradable plastic decomposition agent. When the antioxidant content is below the above upper limit, it adheres more easily to the crude biodegradable plastic decomposition agent, resulting in excellent handling properties. On the other hand, the dispersion of the biodegradable plastic decomposition agent in the plastic improves. When the antioxidant content is above the above lower limit, it is easier to obtain an effect that sufficiently suppresses the deactivation of enzymes and other substances by oxygen.

[0020] (Radical scavenger) Radical scavengers are substances used to capture active radicals (free radicals) generated by heating during the processing process and suppress their reactivity. Radicals (alkyl radicals (R·), peroxy radicals (RO·), alkoxy radicals (RO·)) present in crude biodegradable plastic decomposition agents during heating cause oxidation; therefore, adding a radical scavenger can suppress this oxidation. Examples of radical scavengers include hindered amine radical scavengers (HALS), piperidine radical scavengers, and hindered phenol radical scavengers. Among these, compounds represented by the following chemical formulas are preferred.

[0021] [ka]

[0022] [ka]

[0023] In formulas (A) to (C), R is any substituent. The bond between R and the carbon atom may be a double bond. Examples of substituents include oxygen atoms, hydroxyl groups, amino groups, carboxyl groups, halogen atoms, N-acetylamino groups, C1-C6 alkyl groups, C1-C6 alkoxy groups, succinimide groups, triethylammonium C2-C10 alkanoylamino groups, and the like. In formulas (St1)~(St3), R 3 ~R 7Each of these is an arbitrary substituent, independently of the others. 3 ~R 7 The bond between the atom and the carbon atom may be a double bond. Examples of substituents are the same as those mentioned above.

[0024] Among these, the compound represented by the following chemical formula is more preferred.

[0025] [ka]

[0026] [ka]

[0027] These radical scavengers may be used individually or in combination of two or more.

[0028] In the biodegradable plastic decomposition agent of this disclosure, it is preferable that the radical scavenger forms an intermolecular bond with the crude biodegradable plastic decomposition agent. Examples of intermolecular bonds include hydrophobic bonds and hydrogen bonds.

[0029] The radical scavenger content is preferably 1 to 99% by mass, more preferably 1 to 75% by mass, and even more preferably 1 to 40% by mass, relative to the total mass of the biodegradable plastic decomposition agent. When the radical scavenger content is below the above upper limit, it adheres more easily to the crude biodegradable plastic decomposition agent, resulting in excellent handling properties. On the other hand, the dispersion of the biodegradable plastic decomposition agent in the plastic improves. When the radical scavenger content is above the above lower limit, it is easier to obtain an effect that sufficiently suppresses the deactivation of enzymes and other substances by oxygen.

[0030] (Other ingredients) The biodegradable plastic degrading agents of this disclosure may contain additives other than crude biodegradable plastic degrading agents, antioxidants, and radical scavengers, to the extent that they do not impair the purpose or effect of this disclosure. Examples of additives include water, organic solvents, spin probes, spin traps, fillers, surfactants, processing stabilizers, weather stabilizers, colorants, UV absorbers, heat stabilizers, light stabilizers, antistatic agents, flame retardants, plasticizers, lubricants, fragrances, foaming agents, deodorizers, bulking agents, release agents, mold release agents, reinforcing agents, antifungal agents, preservatives, and crystallization rate retarders. These additives can be used individually or in combination of two or more.

[0031] Spin probes are reagents used in spin probe methods to observe electron spin resonance, and are compounds that can bind to other radical species. Examples of spin probes include PROXYL derivatives and TEMPO derivatives represented by the following chemical formulas.

[0032] [ka]

[0033] In the formula (PROXYL derivative), R 1 is an arbitrary substituent. Examples of arbitrary substituents include C1-C6 alkyl groups, C1-C6 alkoxy groups, carboxyl groups, phosphate groups, C2-C7 alkoxycarbonyl groups, primary amino groups, secondary amino groups, tertiary amino groups, trialkylammonio groups, amide groups, alkylcarbonylamino groups, and the like. In formula (TEMPO derivative), R 2 is any substituent. Examples of arbitrary substituents are the same as those mentioned above.

[0034] Among these, the compound represented by the following chemical formula is preferred.

[0035] [ka]

[0036] These spin probe agents may be used individually or in combination of two or more.

[0037] Examples of surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Among these, biodegradable surfactants are preferred, and 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.

[0038] <Biodegradable plastics> Biodegradable plastics can be those that are broken down into monomer units by a crude biodegradable plastic decomposition agent, or broken down into polymers that can be decomposed in the environment by removing chemically modifying groups such as acetyl groups by a crude biodegradable plastic decomposition agent. Examples of biodegradable plastics include biodegradable polyesters, polyurethanes, polycarbonates, polyamide resins, and ester derivatives of polysaccharides. Examples of biodegradable polyester resins include polylactic acids such as PDLA (poly-D lactic acid) and PLLA (poly-L lactic 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), such as aliphatic polyesters and aliphatic aromatic polyesters. Examples of polysaccharide ester derivatives include cellulose acetate and pullulan acetate. These biodegradable polyester resins may be used individually or in combination of two or more types.

[0039] 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 copolyester, 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®. Examples include cellulose acetate resin sold by Daicel Corporation under the product names Acethi (trademark) and CAFBLO (trademark).

[0040] Biodegradable plastics may be modified or unmodified biodegradable plastics. Modified biodegradable plastics are not particularly limited, but may include, for example, modified biodegradable polyester resins obtained by graft-modifying a biodegradable polyester resin with an unsaturated carboxylic acid and / or its derivatives. Unsaturated carboxylic acids as modifying agents are not particularly limited, but examples include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, etc. Derivatives of unsaturated carboxylic acids are not particularly limited, but examples include acid anhydrides, esters, amides, imides, metal salts, etc.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] In preferred embodiments of this disclosure, the melting point of the biodegradable plastic is preferably 70 to 175°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. Having a melting point within this range makes it easier to suppress the deactivation of enzymes and other components, and to maintain biodegradability during the manufacturing of molded articles. The melting point can be measured using a differential scanning calorimeter (DSC).

[0045] The melt mass flow rate (MFR) of biodegradable plastics 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 this range makes it easier to improve the heat resistance and thermoformability of biodegradable plastics. The MFR can be measured in accordance with ISO 1133 under conditions of 200°C and 2.16 kg.

[0046] 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 its thermoformability and heat resistance.

[0047] The number-average molecular weight (Mn) of biodegradable plastics is preferably 5,000 to 200,000, more preferably 10,000 to 100,000, and even more preferably 20,000 to 50,000. Having Mn within this range of biodegradable plastics 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.

[0048] 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 20 MPa or more, more preferably 25 to 100 MPa, and even more preferably 30 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.

[0049] 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 1.0% or more, more preferably 2.0 to 15%, and even more preferably 3.0 to 13%. When the elongation at break 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 ease of molding 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.

[0050] 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 2.5 GPa, and even more preferably 0.5 to 2.0 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.

[0051] When a molded article A, manufactured from a biodegradable plastic composition containing the biodegradable plastic decomposition agent of this disclosure, and a molded article B, manufactured from a biodegradable plastic composition not containing either the biodegradable plastic decomposition agent or the crude biodegradable plastic decomposition agent of this disclosure, are compared in the decomposition test (weight change) described in the examples, the weight loss of molded article A after 5 days 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, compared with the weight loss of molded article B after 5 days, where the weight loss of molded article B after 5 days is set to 100.

[0052] 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.

[0053] ≪Method for manufacturing biodegradable plastic decomposition agents≫ The method for producing the biodegradable plastic degrading agent of this disclosure is not particularly limited, but it can be produced by adding a first degrading agent forming agent containing a crude biodegradable plastic degrading agent to a second degrading agent forming agent containing at least one selected from the group consisting of antioxidants and radical scavengers. Examples of the first decomposition agent forming agent include aqueous solutions or aqueous dispersions containing a crude biodegradable plastic decomposition agent. Before preparing the first decomposition agent forming agent, a step may be performed in which salts such as ammonium sulfate are added to an aqueous solution of the crude biodegradable plastic decomposition agent to cause salting out and form a powder. The second decomposition agent forming agent is preferably a liquid containing at least one selected from the group consisting of antioxidants and radical scavengers. Examples include aqueous solutions or aqueous dispersions of at least one selected from the group consisting of antioxidants and radical scavengers. The content of the crude biodegradable plastic decomposer in the first decomposer-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 content of at least one selected from the group consisting of antioxidants and radical scavengers in the second decomposition agent forming agent is preferably close to a saturated aqueous solution of antioxidants and radical scavengers, and more preferably is the saturated aqueous solution of antioxidants and radical scavengers itself. When the content of at least one selected from the group consisting of antioxidants and radical scavengers is within the above range, a sufficient amount to suppress the deactivation of the resulting biodegradable plastic decomposition agent is easily incorporated into the particles of the crude biodegradable plastic decomposition agent. The temperature of the second decomposition agent 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 second decomposition agent 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 first decomposition agent 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, at least one selected from the group consisting of antioxidants and radical scavengers is more easily incorporated into the particles of the crude biodegradable plastic decomposition agent, which makes it easier to improve the dispersibility, biodegradability, and mechanical strength of the resulting biodegradable plastic decomposition agent. A preferred method for producing biodegradable plastic decomposing agents is freeze-drying. For example, a first decomposing agent forming agent containing a crude biodegradable plastic decomposing agent is added to a second decomposing agent forming agent containing at least one selected from the group consisting of antioxidants and radical scavengers. The mixture is then converted into an aqueous solution and freeze-dried under vacuum conditions of 10 Pa or less to obtain a biodegradable plastic decomposing agent. The mass ratio expressed as [mass of crude biodegradable plastic decomposing agent] / [mass of at least one selected from the group consisting of antioxidants and radical scavengers] / is preferably 0.01 to 200, more preferably 0.01 to 100, even more preferably 0.1 to 50, and particularly preferably 1 to 20. When the mass ratio is within the above range, the dispersibility, biodegradability, and mechanical strength of the resulting biodegradable plastic decomposing agent tend to be improved.

[0054] The biodegradable plastic decomposer of this disclosure may be manufactured by mixing a powder of a crude biodegradable plastic decomposer with at least one powder selected from the group consisting of antioxidants and radical scavengers.

[0055] ≪Biodegradable Plastic Composition 1≫ A biodegradable plastic composition according to a first aspect of the present disclosure comprises a biodegradable plastic and a biodegradable plastic degrading agent of the present disclosure. In the biodegradable plastic composition of the present disclosure, the biodegradable plastic degrading agent of the present disclosure is dispersed in the biodegradable plastic. In a first aspect 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, molded articles with superior dispersibility, biodegradability, and mechanical strength can be provided.

[0056] In a first 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 with superior dispersibility, biodegradability, and mechanical strength.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] ≪Biodegradable Plastic Composition 2≫ A biodegradable plastic composition according to a second aspect of the present disclosure is a composition obtained by melt-kneading a mixture containing a biodegradable plastic and a crude biodegradable plastic decomposer that decomposes the biodegradable plastic under a low-oxygen atmosphere. In the biodegradable plastic composition of the present disclosure, the crude biodegradable plastic decomposer is dispersed in the biodegradable plastic. Examples of melt-mixing conditions include those described later in Methods 1 and 2 for Manufacturing Biodegradable Plastic Compositions.

[0062] In a second aspect of this disclosure, the content of the crude 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 crude biodegradable plastic decomposer is within the above range, molded articles with superior dispersibility, biodegradability, and mechanical strength can be provided.

[0063] In a second 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 with superior dispersibility, biodegradability, and mechanical strength.

[0064] In the second aspect of this disclosure, when a molded article is manufactured from a biodegradable plastic composition, the tensile strength of the molded article is preferably 20 MPa or more, more preferably 25 to 100 MPa, and even more preferably 30 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 a crude biodegradable plastic decomposition agent.

[0065] When a molded article is manufactured from the biodegradable plastic composition according to the second aspect of this disclosure, the elongation at break of the molded article is preferably 1.0% or more, more preferably 2.0 to 15%, and even more preferably 3.0 to 13%. When the elongation at break 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 ease of molding as a plastic product. Therefore, it is possible to obtain physical properties equivalent to those of a plastic product that does not contain a crude biodegradable plastic decomposition agent.

[0066] When a molded article is manufactured from the biodegradable plastic composition according to the second aspect of this disclosure, the Young's modulus of the molded article is preferably 0.3 GPa or higher, more preferably 0.4 to 2.5 GPa, and even more preferably 0.5 to 2.0 GPa. When the Young's modulus 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 deformation as a plastic product. Therefore, it is possible to obtain physical properties equivalent to those of a plastic product that does not contain a crude biodegradable plastic decomposition agent.

[0067] When a molded article C produced from a biodegradable plastic composition according to a second aspect of this disclosure and a molded article B produced from a biodegradable plastic composition that does not contain either the biodegradable plastic decomposer or the crude biodegradable plastic decomposer of this disclosure are compared in the decomposition test (weight change) described in the examples, the weight loss of molded article C after 5 days 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, compared with the weight loss of molded article B after 5 days, where the weight loss of molded article B after 5 days is set to 100.

[0068] The biodegradable plastic composition in the second aspect 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, when the tensile strength of the biodegradable plastic without the crude biodegradable plastic decomposer is set to 1, in the mechanical strength (tensile strength) described in the examples.

[0069] Other conditions may be the same as those described in Biodegradable Plastic Composition 1 in the First Aspect of the Disclosure above.

[0070] Method 1 for producing a biodegradable plastic composition A method for producing a biodegradable plastic composition according to a first aspect of the present disclosure includes dispersing the biodegradable plastic decomposer in the biodegradable plastic by melt-kneading a mixture comprising a biodegradable plastic and a biodegradable plastic decomposer of the present disclosure. By melt-mixing, the biodegradable plastic decomposition agent is more easily dispersed within the biodegradable plastic, thereby promoting the uniform biodegradation of the biodegradable plastic.

[0071] The above mixture may be mixed with the additives mentioned above as needed. A conventional mixer, preferably a melt kneader, is suitable for mixing. The temperature during mixing or kneading should be such that no denaturation of enzymes occurs, preferably 40 to 200°C, more preferably 80 to 140°C, and even more preferably 100 to 120°C. Setting the melt kneading temperature below the above upper limit makes it easier to suppress the denaturation of crude biodegradable plastic decomposing agents such as enzymes. It also prevents discoloration of enzymes and improves the appearance of the product. Setting the melt kneading temperature above the above lower limit makes it easier to sufficiently disperse enzymes and other substances in the biodegradable plastic, and makes it easier to suppress the decrease in mechanical strength due to the aggregation of enzymes and other substances. 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.

[0072] In a first aspect 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.

[0073] Melt mixing is preferably carried out under a low-oxygen atmosphere. The oxygen concentration in the low-oxygen atmosphere is preferably 20% by volume or less, more preferably 10% by volume or less, even more preferably 5% by volume or less, and particularly preferably 1% by volume or less. The low-oxygen atmosphere is preferably carried out under an inert gas atmosphere such as nitrogen or argon gas, and more preferably under a nitrogen atmosphere. Heating under a low-oxygen atmosphere makes it easier to suppress enzyme inactivation by oxygen.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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).

[0078] 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.

[0079] Method 2 for producing biodegradable plastic compositions A method for producing a biodegradable plastic composition according to a second aspect of the present disclosure includes dispersing the crude biodegradable plastic decomposer in the biodegradable plastic by melt-kneading a mixture containing a biodegradable plastic and a crude biodegradable plastic decomposer that decomposes the biodegradable plastic under a low-oxygen atmosphere. In a second embodiment, melt mixing is preferably carried out under a low-oxygen atmosphere. The oxygen concentration in the low-oxygen atmosphere is preferably 20% by volume or less, more preferably 10% by volume or less, even more preferably 5% by volume or less, and particularly preferably 1% by volume or less. The low-oxygen atmosphere is preferably carried out under an inert gas atmosphere such as nitrogen or argon gas, and more preferably under a nitrogen atmosphere. Heating under a low-oxygen atmosphere makes it easier to suppress enzyme inactivation by oxygen.

[0080] By melt-mixing, the crude biodegradable plastic decomposition agent is more easily dispersed within the biodegradable plastic, thereby promoting the uniform biodegradation of the biodegradable plastic.

[0081] The above mixture may be mixed with the additives mentioned above as needed. A conventional mixer, preferably a melt kneader, is suitable for mixing. The temperature during mixing or kneading should be such that no denaturation of enzymes occurs, preferably 40 to 200°C, more preferably 80 to 140°C, and even more preferably 100 to 120°C. Setting the melt kneading temperature below the above upper limit makes it easier to suppress the denaturation of crude biodegradable plastic decomposing agents such as enzymes. It also prevents discoloration of enzymes and improves the appearance of the product. Setting the melt kneading temperature above the above lower limit makes it easier to sufficiently disperse enzymes and other substances in the biodegradable plastic, and makes it easier to suppress the decrease in mechanical strength due to the aggregation of enzymes and other substances. 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.

[0082] Other conditions may be the same as those described in Method 1 for Producing a Biodegradable Plastic Composition in the First Aspect of the Present Disclosure.

[0083] ≪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.

[0084] ≪Method for manufacturing molded products≫ The molded articles of this disclosure may be manufactured by forming the biodegradable plastic composition of this disclosure (for example, a pelletized biodegradable plastic composition, etc.) into a sheet or film by conventional methods such as extrusion molding, compression molding, or press molding.

[0085] The molding temperature is preferably 40 to 175°C, more preferably 80 to 150°C, and even more preferably 100 to 140°C. When the molding temperature is below the upper limit, it becomes easier to suppress the deactivation of crude biodegradable plastic decomposing agents such as enzymes, and it becomes easier to prevent discoloration of enzymes and improve the appearance of the product. When the molding temperature is above the lower limit, it becomes easier to improve thermoformability, and the biodegradable plastic composition of this disclosure can be easily molded into a predetermined shape.

[0086] 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 upper limit, it becomes easier to suppress the deactivation of crude biodegradable plastic decomposing agents such as enzymes, and it becomes easier to prevent discoloration of enzymes and improve the appearance of the product. In addition, it becomes easier to improve productivity by reducing energy consumption. When the molding time is above the lower limit, it becomes easier to improve thermoformability, and the biodegradable plastic composition of this disclosure can be easily molded into a predetermined shape.

[0087] 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 pressure is below the above upper limit, it becomes easier to suppress the deactivation of crude biodegradable plastic decomposing agents such as enzymes, and it becomes easier to prevent discoloration of enzymes and improve the appearance of the product. In addition, it becomes easier to improve productivity by reducing energy consumption. When the molding pressure is above the above lower limit, it becomes easier to improve thermoformability, and the biodegradable plastic composition of this disclosure can be easily molded into a predetermined shape.

[0088] ≪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 or crude 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., it is possible to prevent the biodegradation of the biodegradable plastic from progressing due to the activation of crude biodegradable plastic decomposition agents such as enzymes when the biodegradable plastic layer comes into contact with water.

[0089] 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. If the thickness of the biodegradable plastic layer is below the above upper limit, it exhibits excellent flexibility and ease of handling as a plastic product. If the thickness of the biodegradable plastic layer is above the above lower limit, it is easier to improve the mechanical strength of the laminate. The thickness of the layers in the laminate of this disclosure can be measured using a thickness gauge.

[0090] 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.

[0091] 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. When the thickness of the biodegradable resin layer is below the above upper limit, it exhibits excellent flexibility and ease of handling as a plastic product. Furthermore, it becomes easier to biodegrade due to enzymes in the biodegradable plastic layer, thus reducing the environmental burden. When the thickness of the biodegradable resin layer is above the above lower limit, it becomes easier to improve the mechanical strength of the laminate. Furthermore, it becomes easier to more reliably prevent the enzymes in the biodegradable plastic layer from becoming activated and decomposing during use of the plastic product.

[0092] 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.

[0093] The paper thickness can be appropriately selected depending on the application, preferably 5 to 1000 μm, and more preferably 10 to 500 μm. When the paper thickness is below the above upper limit, it exhibits excellent flexibility and ease of handling as a plastic product. Furthermore, it becomes easier to biodegrade by enzymes and microorganisms in the environment, thus further reducing the environmental impact. When the paper thickness is above the above lower limit, it becomes easier to improve the mechanical strength of the laminate. Furthermore, it becomes easier to more reliably prevent the activation of enzymes etc. in the biodegradable plastic layer and the subsequent decomposition during use of the plastic product.

[0094] The thickness of the laminate according to this disclosure can be appropriately selected depending on the application, preferably 10 to 2000 μm, and more preferably 20 to 1000 μm. When the thickness of the laminate is below the above upper limit, it exhibits excellent flexibility and ease of handling as a plastic product. When the thickness of the laminate is above the above lower limit, it is easier to improve the mechanical strength of the laminate.

[0095] 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.

[0096] 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.

[0097] ≪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.

[0098] 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.

[0099] The temperature of the biodegradable plastic composition during lamination is preferably 40 to 175°C, more preferably 80 to 150°C, and even more preferably 100 to 140°C. If the lamination temperature is below the above upper limit, it becomes easier to suppress the deactivation of crude biodegradable plastic decomposing agents such as enzymes, and it becomes easier to prevent discoloration of enzymes and improve the appearance of the product. If the lamination temperature is above the above lower limit, it is easier to improve thermoformability, so the resulting laminate can be easily molded into a predetermined shape.

[0100] 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 the biodegradable plastic composition of this disclosure 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.

[0101] Examples of the biodegradable resin layer-forming agent include those that contain biodegradable plastics but do not contain either a biodegradable plastic decomposition agent or a crude biodegradable plastic decomposition agent. For example, in addition to biodegradable plastics, it may also contain the other components mentioned above.

[0102] When laminating a molded product with paper, the biodegradable plastic composition of this disclosure 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.

[0103] 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 biodegradable plastic layer. For example, it is preferable to form a laminate by providing a biodegradable resin layer on top of a biodegradable plastic layer and protecting the surface of the biodegradable resin layer, thereby suppressing the activation of crude biodegradable plastic decomposing agents such as enzymes by the moisture contained in the food while it is used as food packaging material. 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.

[0104] 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 plastic in water, the crude biodegradable plastic decomposition agent comes into contact with the water and becomes activated, causing the decomposition reaction of the biodegradable plastic to proceed. Examples of decomposition reactions include hydrolysis.

[0105] 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. If the immersion time in water is below the above upper limit, the biodegradable plastic composition will not be taken up by aquatic organisms, resulting in less harm. If the immersion time in water is above the above lower limit, the environmental burden can be further reduced.

[0106] 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. If the temperature at which the material is immersed in water is below the above upper limit, the energy consumption required to heat the water can be reduced, thus enabling biodegradation at a lower cost. If the temperature at which the material is immersed in water is above the above lower limit, the biodegradation reaction can proceed more easily, thus further reducing the burden on the environment.

[0107] 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 below the above upper limit, the use of reagents to adjust the pH can be reduced, allowing for low-cost biodegradation, for example, by immersion in seawater. If the pH of water at 25°C is above the above lower limit, the hydrolysis reaction proceeds more easily, and the biodegradation reaction by enzymes, etc., proceeds more easily, thus further reducing the burden on the environment. It can also be decomposed by burying it in soil that is well-hydrated. The biodegradable plastic compositions, molded articles, and laminates of this disclosure can be biodegraded without the formation of microplastics.

[0108] <Effects and Actions> The biodegradable plastic degrading agent of this disclosure suppresses the deactivation of crude biodegradable plastic degrading agents such as enzymes. By suppressing the deactivation of enzymes, the biodegradability of biodegradable plastics can be improved. The biodegradable plastic composition, molded articles, and laminates of this disclosure do not decompose when used as plastic products, but after use as plastic products, biodegradation begins when enzymes exposed on the surface come into contact with water, or when encapsulated enzymes come into contact with water due to surface abrasion or fracture, thereby activating the enzymes. This makes it possible to achieve both high biodegradability and practicality as a plastic product. [Examples]

[0109] The present disclosure will be specifically illustrated by the following examples, but this disclosure is not limited to these examples.

[0110] <Evaluation Method> (1) Mass average molecular weight The mass-average molecular weight of biodegradable plastics 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 1 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). (7) Evaluation of enzyme activity (using pNPB as a substrate) The enzyme solution contained the enzyme at a concentration of 1 μg / ml (or higher if heat-treated) in 100 mM phosphate buffer, and the substrate solution consisted of acetonitrile, ethanol, and 100 mM phosphate buffer at a specific pH. Next, a 2 mL reaction mixture was assembled, consisting of substrate solution (1780 μL), p-nitrophenylbutyric acid (pNPB) (20 μL), and enzyme solution (200 μL) or buffer as a control. This mixture was incubated at 37°C, and the change in absorbance at 405 nm was monitored over time using a UV spectrophotometer. Enzyme activity was calculated in units per milligram (U / mg) using the following formula.

[0111]

number

[0112] Here, ΔAbs / min is the change in absorbance per minute, and ε is the molar extinction coefficient of 4-nitrophenol (18,000 M). -1 ·cm -1 ), l represents the path length of the cuvette (1 cm), V represents the reaction volume (2 mL), and Wenzyme represents the number of milligrams of enzyme used in the reaction.

[0113] <Biodegradable plastic> The following biodegradable plastics were used. The following biodegradable plastics were used. · PBS ("BioPBS" manufactured by Mitsubishi Chemical Corporation, Mw = 130,000, melting point = 114°C) TM ", Mw = 130000, melting point = 114°C) · PES (provided by Team Leader Hideyoshi Abe of the Institute of Physical and Chemical Research, Mw = 100,000, melting point = 104°C) · PBAT ("ECOFLEX" manufactured by BASF, Mw = 160,000, melting point = 125°C) · PDLA ("Luminy D120" from TotalEnergies Corbion, Mw = 154,000, melting point = 170°C) <Biodegradable plastic decomposing agent> The following enzymes were used as crude biodegradable plastic decomposing agents. · Enzyme (cutinase, "Novozyme 51032 (Humicola insolens cutinase, HiC)" manufactured by Fujifilm Wako Pure Chemical Corporation) · Enzyme (cutinase, genetically engineered, (thermobifida fusca, TfC) The following antioxidants were used. · BHT (dibutylhydroxytoluene, Sigma - Aldrich) · Vc (vitamin C (ascorbic acid), Sigma - Aldrich) · Irganox1076 (octadecyl 3-(3,5 - di - tert - butyl - 4 - hydroxyphenyl) propanoate, Sigma - Aldrich) · Glutathione (Sigma - Aldrich) The following radical scavengers were used. · TEMPOL (4 - hydroxy - 2,2,6,6 - tetramethylpiperidine 1 - oxyl free radical, Sigma - Aldrich) <Phosphate buffer> The following reagents were used. Sodium dihydrogen phosphate Dipotassium hydrogen phosphate

[0114] <Manufacturing Example A> Preparation of a crude biodegradable plastic decomposition agent 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.

[0115] <Manufacturing Example 1> Preparation of a biodegradable plastic decomposition agent Preparation of TEMPOL-containing enzyme (HiC) powder TEMPOL-containing enzyme (HiC) powder was prepared by mixing HiC powder and TEMPOL in a weight ratio of 10:8.2. A 10 mg / mL aqueous solution of HiC and a 10 mg / mL aqueous solution of TEMPOL were prepared with pure water. The two solutions were mixed to combine HiC powder and TEMPOL in a weight ratio of 10:8.2, diluted with pure water, stirred, and then freeze-dried. This yielded TEMPOL-containing enzyme (HiC) powder. This powder was stored at 4°C until use.

[0116] <Manufacturing Example 2> Preparation of Biodegradable Plastic Degrading Agent Preparation of BHT-containing enzyme (HiC) powder BHT-containing enzyme (HiC) powder was prepared by mixing HiC powder and BHT in a weight ratio of 1:2. A 10 mg / mL aqueous solution of HiC and a 10 mg / mL aqueous solution of TEMPOL were prepared with pure water. The two solutions were mixed to combine HiC powder and TEMPOL in a weight ratio of 1:2, diluted with pure water, stirred, and then freeze-dried. This yielded BHT-containing enzyme (HiC) powder. This powder was stored at 4°C until use.

[0117] <Manufacturing Examples 3-5> A biodegradable plastic decomposer was prepared in the same manner as in Production Example 1, except that the antioxidant and its amount were changed as shown in Table 1. Table 1 shows the composition of the biodegradable plastic decomposing agents prepared in Production Examples 1 to 5.

[0118] [Table 1]

[0119] <Example 1> Preparation of a film containing a crude biodegradable plastic decomposition agent The crude biodegradable plastic decomposer obtained in Production Example 1-1 was added to the biodegradable plastic in the proportions shown in Table 2, and the mixture was hot-mixed under a nitrogen atmosphere using a twin-screw extruder (HAAKE Minilab, Thermo Fisher, USA). The two screws rotated in opposite directions at 120 rpm, the mixing temperature was 175°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.

[0120] <Examples 2-5> A film was prepared in the same manner as in Example 1, except that the type and amount of the biodegradable plastic decomposition agent were changed as shown in Table 2, the melt mixing was performed in an air atmosphere, and the type and amount of the biodegradable plastic were changed as shown in Table 2.

[0121] <Comparative Example 1> The film was prepared in the same manner as in Example 1, except that the biodegradable plastic was changed to one that does not contain enzyme powder.

[0122] <Comparative Example 2> The film was prepared in the same manner as in Example 1, except that the melt mixing was performed under an air atmosphere.

[0123] Table 2 shows the compositions of the films prepared in Examples 1-5 and Comparative Examples 1-2.

[0124] [Table 2]

[0125] Table 3 shows the various physical properties obtained from the tensile test.

[0126] [Table 3]

[0127] Figure 1 shows molded articles (films) produced in the examples and comparative examples. Films without any biodegradable plastic decomposition agent or crude biodegradable plastic decomposition agent (no additives), films with a crude biodegradable plastic decomposition agent added but melt-kneaded under an oxygen atmosphere (enzymes only, air), films with a crude biodegradable plastic decomposition agent added and melt-kneaded under a nitrogen atmosphere (enzymes only, nitrogen), and films with the biodegradable plastic decomposition agent of this disclosure added (with decomposition agent) were all transparent films and had roughly the same appearance.

[0128] Figure 2 is a graph showing the weight change results in the decomposition test of molded products (films) when PDLA was used in Examples 2-6 and Comparative Example 2. The film without additives showed almost no weight change even after 5 days. The film with added enzymes, which was melt-kneaded in an air atmosphere, showed a weight change of approximately 22.7% by weight even after 5 days. The film to which the biodegradable plastic decomposition agent of this disclosure was added showed decomposition of more than 30% by weight after 21 days. The activity loss during the processing of the crude biodegradable plastic decomposition agent was reduced, and rapid biodegradation of the molded product (film) was achieved.

[0129] Figure 3 shows the appearance of the film surface after 21 days in a decomposition test of molded products (films) when PDLA was used in the examples and comparative examples. After 21 days, the surface of the film, which was melt-kneaded with the enzyme of this disclosure and under a nitrogen atmosphere, and the film, which was also treated with a biodegradable plastic decomposition agent, showed the formation and distribution of pores due to decomposition. On the other hand, it was also confirmed that the thickness of the film, which was melt-kneaded with the enzyme of this disclosure and under a nitrogen atmosphere, decreased significantly after 21 days. From this, it was found that the activity loss of the crude biodegradable plastic decomposition agent during the processing was reduced, and the decomposition rate of the molded product (film) was improved.

[0130] Figure 4 is a graph showing the evaluation results of the mechanical strength of molded products (films) when PDLA was used in the examples and comparative examples. The film prepared by adding enzymes and melt-kneading under a nitrogen atmosphere, and the film prepared by adding the biodegradable plastic decomposition agent of this disclosure, showed slight changes in mechanical properties compared to the film without additives, but were found to be within a range that was still practical for use as a film.

[0131] Figure 5 is a graph showing the enzyme activity (using pNPB as a substrate) after heating the enzyme (HiC). The results of heating under air or nitrogen atmospheres showed that enzyme activity was higher under nitrogen atmosphere, indicating that enzyme inactivation could be suppressed by using a low-oxygen atmosphere.

[0132] Figure 6 is a graph showing the enzyme activity (using pNPB as a substrate) after heating the enzyme (TfC). Heating under air or nitrogen atmospheres resulted in higher enzyme activity under nitrogen atmosphere, indicating that enzyme inactivation could be suppressed by using a low-oxygen atmosphere.

[0133] Figure 7 is a graph showing the effect of oxygen on weight change in a decomposition test of an enzyme (HiC)-containing molded product (film). Heating under a nitrogen atmosphere resulted in a high weight loss, indicating that enzyme deactivation could be suppressed by using a low-oxygen atmosphere.

[0134] Figure 8 is a graph showing the enzyme activity after heating TEMPOL-containing enzyme (HiC) powder. Heating in an air or nitrogen atmosphere in the presence of TEMPOL resulted in high enzyme activity, indicating that TEMPOL was able to suppress enzyme inactivation.

[0135] Figure 9 shows the appearance of the enzyme powder after heating. Below 175°C, the enzyme maintained its water solubility and showed little discoloration. Above 175°C, the enzyme lost its water solubility and discoloration was observed.

Claims

1. A biodegradable plastic decomposer used to decompose biodegradable plastics, A crude biodegradable plastic decomposer that decomposes biodegradable plastics, At least one selected from the group consisting of antioxidants and radical scavengers, A biodegradable plastic decomposer containing [the specified ingredient].

2. The biodegradable plastic decomposing agent includes the antioxidant, The biodegradable plastic decomposer according to claim 1, wherein the antioxidant is at least one selected from the group consisting of glutathione, dibutylhydroxytoluene, L-ascorbic acid, and salts thereof.

3. The biodegradable plastic decomposing agent includes the radical scavenger, The biodegradable plastic decomposer according to claim 1, wherein the radical scavenger is a 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl free radical.

4. A biodegradable plastic decomposer according to any one of claims 1 to 3, Biodegradable plastics and A biodegradable plastic composition containing [the specified substance].

5. A method for producing a biodegradable plastic composition, comprising dispersing the biodegradable plastic decomposition agent in the biodegradable plastic by melt-kneading a mixture containing a biodegradable plastic and the biodegradable plastic decomposition agent described in claim 1.

6. A method for producing a biodegradable plastic composition, comprising dispersing the biodegradable plastic decomposition agent or the crude biodegradable plastic decomposition agent described in claim 1 in a biodegradable plastic by melt-kneading a mixture containing a biodegradable plastic and a crude biodegradable plastic decomposition agent for decomposing the biodegradable plastic in a low-oxygen atmosphere.

7. A method for producing a biodegradable plastic composition according to claim 5 or 6, wherein the melt mixing is performed at 175°C or below.

8. A method for producing a biodegradable plastic composition according to claim 5 or 6, wherein the melt kneading is carried out in an atmosphere with an oxygen concentration of 20% by volume or less.

9. A method for producing a biodegradable plastic composition according to claim 5 or 6, wherein the crude biodegradable plastic decomposing agent is at least one selected from the group consisting of depolymerase, esterase, lipase, cutinase, carboxylesterase, protease, polyesterase, glucanase, cellulase, pullulanase, and amylase.

10. A method for producing a biodegradable plastic composition according to claim 5 or 6, wherein the biodegradable plastic is at least one selected from the group consisting of biodegradable polyester, biodegradable polyurethane, biodegradable polycarbonate, biodegradable polyamide, and ester derivatives of polysaccharides.

11. A molded article formed from a biodegradable plastic composition obtained by the method for producing a biodegradable plastic composition according to claim 5 or 6.

12. A method for producing a molded article, comprising molding a biodegradable plastic composition obtained by the method for producing a biodegradable plastic composition described in claim 5 or 6.

13. The method for manufacturing a molded article according to claim 12, wherein the molding is performed under conditions of 175°C or lower.

14. The method for manufacturing a molded article according to claim 12, wherein the molding is carried out in an atmosphere with an oxygen concentration of 20% by volume or less.

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