Composite resin molded article and method for producing same

Abstract

A composite resin molded article according to the present invention has a base resin, a plurality of natural fibers dispersed in the base resin, and at least one of a micro-organism and an enzyme supported on each of the plurality of natural fibers, wherein at least one of the plurality of natural fibers has a portion exposed at the surface of the composite resin molded article, and at least a portion of the surface of each of the plurality of natural fibers is covered by a coating resin.

Description

Composite resin molded body and its manufacturing method

[0001] The present disclosure relates to a composite resin molded article having excellent mechanical properties and an adjustable biodegradation rate in a humid environment, and a method for producing the same.

[0002] So-called "general-purpose plastics," such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), are not only very inexpensive, but also easy to mold and are a fraction of the weight of metals or ceramics. For this reason, general-purpose plastics are often used as materials for a variety of everyday items, such as bags, various types of packaging, various containers, and sheets, as well as industrial parts, such as automobile parts and electrical parts, and as materials for daily necessities and miscellaneous goods.

[0003] Under these circumstances, the amount of post-use plastic waste is increasing year by year, and because plastics are difficult to decompose, they accumulate in the natural environment, causing pollution problems such as environmental destruction and contamination.In recent years, biodegradable plastics, which decompose into water and carbon dioxide in the natural environment, have been proposed as one way to solve these problems, and it is expected that their use will expand, replacing general-purpose plastics made from petroleum-based materials.

[0004] However, biodegradable plastics have drawbacks compared to general-purpose plastics, such as insufficient mechanical strength, and therefore do not have the sufficient properties required for materials used in various industrial products, including mechanical products such as automobiles and electrical, electronic, and information products, and the range of their application is currently limited.

[0005] However, the rate at which biodegradable plastics decompose after disposal is greatly affected by the environment. In environments with few microorganisms, such as the ocean, it takes a significantly longer time for them to completely decompose, and their biodegradability is not fully utilized. To solve this problem, various methods have been proposed to accelerate the decomposition of biodegradable plastics after disposal.

[0006] To solve these problems, there have been disclosed products in which biodegradable plastics are combined with microorganisms that have the enzymatic activity to decompose the same materials (see, for example, Patent Document 1), and a method in which microorganisms are microencapsulated in advance and then incorporated into biodegradable plastics (see, for example, Patent Document 2).

[0007] JP 2013-209587 A JP 2020-520794 A

[0008] A composite resin molding according to one aspect of the present disclosure is a composite resin molding having a main resin, a plurality of natural fibers dispersed in the main resin, and at least one of microorganisms and enzymes supported on each of the plurality of natural fibers, wherein at least one of the plurality of natural fibers has a portion exposed on the surface of the composite resin molding, and at least a portion of the surface of each of the plurality of natural fibers is coated with a coating resin.

[0009] A method for manufacturing a composite resin molded body according to one aspect of the present disclosure includes the steps of preparing at least one of microorganisms and enzymes, natural fibers, a water-soluble coating resin, and a base resin; supporting at least one of the microorganisms and the enzymes on the natural fibers; dispersing the natural fibers supported with the at least one of the microorganisms and the enzymes and the coating resin in water, drying and pulverizing them to obtain coated natural fibers in which the coating resin is coated on at least a portion of the surface of the natural fibers; melt-kneading the coated natural fibers together with the base resin to proceed with defibration from the ends in the fiber length direction of the coated natural fibers, thereby obtaining a composite resin member with an increased surface area of ​​the defibrated portions at the ends; and molding the composite resin member to obtain a composite resin molded body.

[0010] Fig. 1 is a schematic diagram showing the cross-sectional structure of a composite resin molded body according to an embodiment. Fig. 2 is a schematic diagram showing the cross-sectional structure of a natural fiber that is a constituent member of the composite resin molded body according to an embodiment. Fig. 3 is a schematic diagram showing the cross-sectional structure of a composite resin molded body containing natural fiber with defibrated portions according to an embodiment. Fig. 4 is a schematic diagram of a manufacturing process for a composite resin molded body according to an embodiment. Fig. 5 is a diagram showing the structure and measurement results of composite resin molded bodies in examples and comparative examples in the embodiment.

[0011] In the method described in Patent Document 1, the microorganisms are directly mixed into the biodegradable plastic, so the material is limited to a biodegradable plastic that can be molded at a temperature at which the microorganisms can survive.

[0012] On the other hand, the method described in Patent Document 2 requires physical destruction of the molded body in order to release the microorganisms from the microcapsules, and also has the problem that the rigidity of the molded body decreases as the microcapsule content increases.

[0013] One aspect of the present disclosure is intended to solve the above-described conventional problems, and aims to provide a composite resin molded body that maintains high rigidity during use and that, after disposal, is accelerated to biodegrade in humid environments such as the ocean or soil.

[0014] The composite resin molding of the first aspect is a composite resin molding having a main resin, a plurality of natural fibers dispersed in the main resin, and at least one of microorganisms and enzymes supported on each of the plurality of natural fibers, wherein at least one of the plurality of natural fibers has a portion exposed on the surface of the composite resin molding, and at least a portion of the surface of each of the plurality of natural fibers is coated with a coating resin.

[0015] A composite resin molding according to a second aspect may be the first aspect, wherein the moisture content of the natural fibers is 5% or more as measured by a method specified in JIS L0105:2020.

[0016] The composite resin molding according to the third aspect may be the composite resin molding according to the first or second aspect, wherein the main resin is a biodegradable resin containing any one selected from the group consisting of polyhydroxy acid, polyhydroxyalkanoate, polyalkylene dicarboxylate, and modified starch.

[0017] The composite resin molding according to a fourth aspect is any one of the first to third aspects, wherein the coating resin is any water-soluble resin selected from the group consisting of polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose, and starch-based resins.

[0018] In the composite resin molding of the fifth aspect, in any of the first to fourth aspects described above, when the composite resin molding is taken as 100 volume %, the volume % of the main resin is A, the volume % of the natural fibers 2 carrying at least one of microorganisms and enzymes is B, and the volume % of the coating resin 3 is C, and the following relationships may hold: A + B + C = 100, 0.01B ≦ C ≦ 0.5B, 10 ≦ B + C ≦ 99, and C ≦ A.

[0019] A composite resin molding according to a sixth aspect is any one of the first to fifth aspects, wherein each of the plurality of natural fibers may have at least one of microorganisms and enzymes supported on the fiber surface.

[0020] A composite resin molding according to a seventh aspect is any one of the first to sixth aspects, wherein each of the plurality of natural fibers may be a cellulose.

[0021] The composite resin molding according to an eighth aspect is any one of the first to seventh aspects, wherein each of the plurality of natural fibers may have a defibrated portion at an end in the fiber length direction.

[0022] The method for producing a composite resin molded body according to the ninth aspect includes the steps of preparing at least one of microorganisms and enzymes, natural fibers, a water-soluble coating resin, and a base resin; supporting at least one of the microorganisms and the enzymes on the natural fibers; dispersing the natural fibers supported with the microorganisms and the enzymes and the coating resin in water, drying and pulverizing them to obtain coated natural fibers in which at least a portion of the surface of the natural fibers is coated with the coating resin; melt-kneading the coated natural fibers together with the base resin to proceed with defibration from the ends in the fiber length direction of the coated natural fibers, thereby obtaining a composite resin member with an expanded surface area of ​​the defibrated portions at the ends; and molding the composite resin member to obtain a composite resin molded body.

[0023] Hereinafter, a composite resin molding and a manufacturing method thereof according to an embodiment will be described with reference to the accompanying drawings. In the following description, the same components are denoted by the same reference numerals and the description thereof will be omitted where appropriate.

[0024] 1 is a schematic diagram showing the cross-sectional structure of a composite resin molded body 10 according to an embodiment. FIG. 2 is a schematic diagram showing the cross-sectional structure of a natural fiber that is a constituent member of the composite resin molded body 10 according to the embodiment.

[0025] The composite resin molding 10 according to the embodiment is made of a melt-kneaded mixture of a base resin 1 and natural fibers 2 carrying microorganisms and / or enzymes 4 (at least one of microorganisms and enzymes) and coated with a coating resin 3. As shown in the schematic diagram showing the cross-sectional structure of Figure 1, the composite resin molding 10 has natural fibers 2 carrying microorganisms and / or enzymes 4 coated with a coating resin 3 dispersed in the base resin 1.

[0026] 3, which is a schematic diagram showing the cross-sectional structure of a composite resin molding 10 containing natural fibers 2 with defibrated portions according to an embodiment, having defibrated portions at the ends of the natural fibers 2 increases the specific surface area of ​​the defibrated portions and increases the number of contact points between the natural fibers 2. This makes it possible for water to be absorbed into the composite resin molding 10 through the contact points between the natural fibers 2 in a humid environment.

[0027] This composite resin molding 10 has at least one natural fiber 2 exposed on the surface of the composite resin molding and the natural fibers 2 are in contact with each other, which not only gives it a high elastic modulus but also high water absorption. In a humid environment, when the coating resin 3 is dissolved by the absorption of water by the natural fibers 2, the microorganisms and / or enzymes 4 carried by the natural fibers 2 are released, accelerating the decomposition of the base resin 1. Therefore, it is possible to realize a composite resin molding 10 that maintains high rigidity during use and has excellent biodegradability in humid environments such as the ocean or soil after disposal.

[0028] Each of the components constituting this composite resin molded body will be described below.

[0029] <Main Resin> In this embodiment, the main resin 1 is preferably a biodegradable plastic containing any one selected from the group consisting of polyhydroxy acid, polyhydroxyalkanoate, polyalkylene dicarboxylate, and modified starch. Furthermore, to ensure good moldability, a thermoplastic resin is preferred, and the above resins may be used alone or in combination of two or more. Note that the main resin 1 is not limited to the above materials as long as it is biodegradable.

[0030] In the present embodiment, "biodegradable plastic" refers to "a resin that has the same functions as conventional petroleum-derived resins during use, and that is ultimately decomposed into water and carbon dioxide by microorganisms in the soil or ocean in nature after use." Specific examples include polyester resins such as polyhydroxyalkanoates, such as polyhydroxybutyrate and polyhydroxyvalerate; polyhydroxy acids, such as polylactic acid, polyglycolic acid, and polycaprolactone; polyalkylene dicarboxylates, such as polybutylene adipate terephthalate, polyethylene succinate, and polybutylene succinate; polyamides; and modified starch. Biodegradable plastics include homopolymers of the above-mentioned resin monomers, as well as copolymers of monomers, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and copolymers of monomers with other copolymerizable monomers.

[0031] <Natural Fiber> Next, the natural fiber 2 will be described. The first main purpose of adding the natural fiber 2 (hereinafter, sometimes simply referred to as "fiber") to the composite resin molded body 10 according to this embodiment is to allow the coating resin 3 to come into contact with water and dissolve by absorbing water in soil or the ocean without placing a burden on the environment when the composite resin molded body 10 is discarded after use. For this purpose, the natural fiber 2 preferably has high water absorption, and the moisture content of the natural fiber 2 is preferably 5% or more as measured by the method specified in JIS L0105:2020. Specifically, pulp, cellulose, cellulose nanofiber, lignocellulose, lignocellulose nanofiber, cotton, silk, hemp, or the like is preferred.

[0032] The second purpose of adding natural fibers 2 is to improve mechanical properties and dimensional stability by reducing the linear expansion coefficient. For this purpose, it is preferable that the natural fibers 2 have a higher elastic modulus than the base resin 1. Specific examples include pulp, cellulose, cellulose nanofibers, lignocellulose, lignocellulose nanofibers, cotton, silk, wool, and hemp. Among these, celluloses are particularly preferable from the viewpoints of availability, high elastic modulus, and low linear expansion coefficient. However, the natural fibers 2 are not limited to the above materials as long as they can improve mechanical properties and have water absorbency.

[0033] After the microorganisms and / or enzymes 4 are supported on the natural fibers 2 and at least a portion of the natural fibers are coated with the coating resin 3, the content of the natural fibers 2 supported with the microorganisms and / or enzymes 4 and the coating resin 3 in the composite resin molded body 10 is preferably 10% by volume or more and 99% by volume or less, when the composite resin molded body 10 is taken as 100% by volume. If the content of the natural fibers 2 supported with the microorganisms and / or enzymes 4 and the coating resin 3 is less than 10% by volume, the natural fibers 2 are unlikely to come into contact with each other within the composite resin molded body 10, resulting in insufficient water absorption. On the other hand, if the content of the natural fibers 2 supported with the microorganisms and / or enzymes 4 and the coating resin 3 is more than 99% by volume, the proportion of the main resin 1 becomes small, which results in the loss of the effect of adhering the natural fibers 2 to each other and poor moldability.

[0034] The form of the natural fibers 2 in the composite resin molded body 10 will be described. A larger bonding interface between the natural fibers 2 and the coating resin 3 promotes dissolution of the coating resin 3 when the natural fibers 2 absorb water, so a high specific surface area of ​​the natural fibers 2 is preferred. On the other hand, to improve the water absorption of the composite resin molded body 10, it is preferred that the natural fibers 2 are exposed on the surface of the composite resin molded body 10. By exposing the natural fibers 2 on the surface of the composite resin molded body 10, water is absorbed from the exposed portions of the natural fibers 2, and the water is absorbed into the interior of the composite resin molded body 10 due to capillary action of the fibers that make up the natural fibers. The smaller the specific surface area of ​​the exposed portions of the natural fibers 2 on the surface of the composite resin molded body 10, the higher the water absorption. This is because when the specific surface area of ​​the exposed portions of the natural fibers 2 on the surface is large, the water repellency is enhanced due to the effect of fine unevenness. Furthermore, as shown in Figure 3, by having defibrated areas at the ends of the natural fibers 2, the specific surface area of ​​the defibrated areas increases, and the number of contact points between the natural fibers 2 increases, making it possible to increase the water absorption rate through the contact points of the natural fibers 2 in a humid environment.

[0035] The central portion of the undefibrated natural fibers 2, which has a small specific surface area, is less entangled with the main resin 1 and is more likely to be exposed on the surface of the composite resin molded product depending on the molding conditions. Conversely, the tip portions of the defibrated natural fibers 2 are more entangled with the main resin 1 and penetrate into the interior together with the main resin 1. This allows for the production of a composite resin molded product 10 in which the central portions of the natural fibers 2, excluding both end portions, are exposed on the surface.

[0036] The combined length of the tip defibrated portions at both ends of the natural fibers 2 is preferably 5% or more and 50% or less of the fiber length L of the entire natural fibers 2. If the defibrated portions are less than 5% of the entire fiber length L, the specific surface area is small and no improvement in the elastic modulus is observed, and if they are longer than 50%, the defibrated portions with a large aspect ratio are exposed on the surface of the composite resin molding, resulting in a deterioration in water absorbency.

[0037] Next, the characteristics of the natural fibers 2 will be described. The types of base resin 1 and natural fibers 2 are as described above. However, if the natural fibers 2 are too soft relative to the base resin 1, i.e., if the natural fibers 2 have a low modulus of elasticity, the composite resin molding 10 will have a low overall modulus of elasticity, resulting in reduced strength. On the other hand, if the natural fibers 2 are too hard relative to the base resin 1, i.e., if the natural fibers 2 have a high modulus of elasticity, shock waves generated upon impact will not propagate but will be absorbed at the interface between the base resin 1 and the natural fibers 2, making cracks and crazes more likely to occur near the interface, resulting in reduced impact resistance. Therefore, the relationship between the modulus of elasticity of the base resin 1 and the natural fibers 2 is such that the modulus of elasticity of the natural fibers 2 is higher than that of the base resin 1, and the difference between them should preferably be as small as possible. The optimal relationship is calculated from simulation results, and the difference in modulus of elasticity between the base resin 1 and the natural fibers 2 is preferably within 20 GPa.

[0038] Furthermore, these natural fibers 2 may be surface-treated for the purpose of improving adhesion to the base resin 1 or the coating resin 3 or dispersibility in the composite resin molding 10, but if the surface treatment impairs the water absorption properties of the natural fibers 2, it is preferable not to perform the surface treatment in advance.

[0039] <Additives> Additives may be used as needed for the purpose of improving the affinity between the base resin 1 and the natural fibers 2. Any additives that are commonly used can be used.

[0040] <Coating Resin> Next, the coating resin 3 will be described. In this embodiment, the coating resin 3 protects the microorganisms and / or enzymes 4 supported on the natural fibers 2 during the production of the composite resin molded body 10 and suppresses thermal damage to the microorganisms and / or enzymes 4 from the molten base resin 1. Furthermore, during the use of the composite resin molded body 10, the coating resin 3 is used to protect the microorganisms and / or enzymes 4 supported on the natural fibers 2 and prevent them from coming into contact with the base resin 1. After disposal of the composite resin molded body 10, the coating resin 3 must dissolve and release the microorganisms and / or enzymes 4 supported on the natural fibers 2 to promote biodegradation in a humid environment. For this reason, the coating resin 3 is preferably a water-soluble resin that is soluble in water at a temperature of 20°C. Specific examples include polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose, and modified starches. The above resins may be used alone or in combination. The coating resin 3 is not limited to the above materials as long as they are water-soluble.

[0041] Furthermore, in order for the coating resin 3 to maintain a state in which it coats at least a portion of the surface of the natural fibers 2 in the composite resin molded body 10, when the composite resin molded body 10 is taken as 100 volume %, the volume % of the base resin 1 is A, the volume % of the natural fibers 2 carrying the microorganisms and / or enzymes 4 is B, and the volume % of the coating resin 3 is C, it is preferable that A + B + C = 100, 0.01B ≦ C ≦ 0.5B, and C ≦ A are satisfied. If 0.5B < C, the volume % of the coating resin 3 is too large relative to the natural fibers 2, making it difficult to maintain contact between the natural fibers 2. If C < 0.01B, the volume % of the coating resin 3 is too small relative to the natural fibers 2, making it difficult to protect the microorganisms and / or enzymes 4 carried by the natural fibers 2. If A < C, the volume % of the coating resin 3 is too large, making it difficult to maintain durability because the water-soluble coating resin 3 exposed on the surface of the composite resin molded body 10 is easily deteriorated.

[0042] The state of the coating resin 3 in the composite resin molding 10 will be described below. By controlling the volume percentage of the coating resin 3 relative to the natural fibers 2, it is possible to delay the release of the microorganisms and / or enzymes 4 carried by the natural fibers 2 and control the decomposition rate.

[0043] <Microorganisms and / or Enzymes> Next, the microorganisms and / or enzymes 4 will be described. The microorganisms and / or enzymes 4 in this embodiment are used for the purpose of accelerating the decomposition of the composite resin molded body 10 in a humid environment. The microorganisms and / or enzymes 4 in this embodiment vary depending on the base resin 1. Specific examples of the microorganisms and / or enzymes 4 include Amulatopsis microorganisms as decomposers of polylactic acid and polybutylene succinate. Examples of poly-3-hydroxybutyrate decomposers include Streptomyces microorganisms and Pseudomonas microorganisms, such as Pseudomonas lemony, Alcaligenes microorganisms, and Alcaligenes paradoxus. Examples of polyether decomposers, such as polyethylene glycol, include Pseudomonas microorganisms, such as Pseudomonas sutzerii, Pseudomonas aeruginosa, Pseudomonas vesicularis, Alcaligenes microorganisms, Acinetobacter microorganisms, and Xanthomonas microorganisms.

[0044] Examples of enzymes used in this embodiment include various enzymes extracted from the microorganisms listed above. Specifically, examples of enzymes for decomposing polylactic acid include proteinase K; examples of enzymes for decomposing polyvinyl alcohol include polyvinyl alcohol dehydrogenase, polyvinyl alcohol oxidase, and secondary alcohol oxidase; examples of enzymes for decomposing poly-3-hydroxybutyric acid include PHB depolymerase; and examples of enzymes for decomposing polyurethane include cholesterol esterase, chitopearl cholesterol esterase, and urease. The above microorganisms and / or enzymes may be used alone or in combination of two or more. Note that the materials are not limited to those listed above, as long as they are capable of decomposing the base resin 1.

[0045] <Method for Manufacturing Composite Resin Molded Product> Next, a method for manufacturing the composite resin molded product 10 will be described. Fig. 4 is a flow diagram illustrating an example of a manufacturing process for the composite resin molded product 10 according to this embodiment.

[0046] (1) Microorganisms and / or enzymes 4 are supported in advance on the surface of the natural fibers 2. Methods for supporting the microorganisms and / or enzymes 4 include physical adsorption by dry blending, impregnation of natural fibers using a dispersion solvent, crosslinking, and entrapment. The support method is not limited to the above, as long as it can retain the microorganisms and / or enzymes 4 on the surface of the natural fibers 2.

[0047] (2) The natural fibers 2 carrying the microorganisms and / or enzymes 4 and the water-soluble coating resin 3 are dispersed in water, dried, and then pulverized using a cutter or a grinder to obtain the natural fibers 2 at least partially coated with the coating resin 3 of this embodiment. Specific methods include a pelletizer, a ball mill, a roll mill, a hammer mill, a wonder crusher, a jet grinder, and combinations thereof. Any other cutting or grinding method may be used as long as it can maintain the state in which at least a portion of the natural fibers 2 is coated with the coating resin 3.

[0048] (3) After dry-blending the base resin 1 and the natural fibers 2 coated with the coating resin 3, the fibers are placed in a melt-kneading treatment device and melt-kneaded within the device. Because the natural fibers are coated with the coating resin 3, thermal damage to the microorganisms and / or enzymes carried by the natural fibers is suppressed. This promotes defibration of agglomerates of the natural fibers 2 by the shearing action of the device, allowing the coated natural fibers 2 to be finely dispersed within the base resin 1. By adjusting the shearing conditions, it is possible to defibrate the ends of the natural fibers 2, thereby obtaining defibrated regions, as shown in Figure 3.

[0049] Conventionally, when fibers are compounded with resin, fibers are first defibrated through pretreatment such as wet dispersion. However, when natural fibers are defibrated in the solvent used in wet dispersion, the fibers swell due to the solvent. Therefore, to ensure that the natural fibers absorb water and expand sufficiently in the composite resin molding material, it is necessary to dry out the solvent in the natural fibers before mixing them with the base resin. Furthermore, because the fibers are more easily defibrated by wet dispersion than when defibrated in a molten base resin, it is difficult to defibrate only the ends, and the entire natural fiber ends up defibrated. Furthermore, adding pretreatment increases the number of processes, resulting in reduced productivity.

[0050] In contrast, in the manufacturing process for the composite resin molded body 10 in this embodiment, the natural fibers 2 are melt-kneaded together with the base resin 1 (all-dry method) without undergoing pretreatment by wet dispersion for the purpose of defibrating the natural fibers 2. In this method, by not performing wet dispersion treatment of the natural fibers 2, swelling of the natural fibers 2 during the manufacturing process can be suppressed, and the water absorption rate of the natural fibers 2 in the composite resin molded body 10 can be improved. By drying the natural fibers 2 beforehand or during kneading, the water absorption rate in a humid environment in the composite resin molded body 10 can be further improved. Furthermore, since the natural fibers 2 have defibrated regions as described above, there are many contact points between the fibers within the composite resin molded body 10, and the water absorption rate of the composite resin molded body 10 can be increased via the contact points between the fibers.

[0051] To produce the natural fibers 2 of this embodiment using an all-dry method, it is preferable to apply high shear stress during kneading. Specific kneading methods include a single-screw kneader, a twin-screw kneader, a roll kneader, a Banbury mixer, and combinations thereof. From the viewpoint of ease of applying high shear and high mass productivity, a continuous twin-screw kneader and a continuous roll kneader are particularly preferred. Other kneading methods may also be used as long as they can apply high shear stress.

[0052] (4) The composite resin composition extruded from the melt kneading device is injection molded to produce the composite resin molding 10 as an injection molded product.

[0053] Hereinafter, examples and comparative examples of the experiments conducted by the inventors will be described.

[0054] Example 1 In Example 1, a cellulose-composite poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) resin molded article was produced by the following production method.

[0055] Softwood pulp (manufactured by Mitsubishi Paper Mills, product name: NBKP Celgar) was used as the starting material for the natural fiber. PHB depolymerase extracted from the culture broth of a Streptomyces microorganism was used as the PHBV-degrading enzyme. Softwood pulp and PHB depolymerase were dry-blended at a volume ratio of 90:10 and pulverized using a roll mill to obtain an enzyme-loaded cellulose filler.

[0056] Polyvinyl alcohol (PVA) (manufactured by Kuraray, product name: PVA-217) as a coating resin and the above enzyme-supported cellulose filler were weighed out in a volume ratio of 10:90, dispersed in pure water, and formed into a sheet using a stretching machine (manufactured by Imoto Machinery Co., Ltd., model IMC-1124), which was then dried. The resulting cellulose PVA sheet was pulverized using a Wonder Crusher (manufactured by Osaka Chemical, model WC-3) to obtain a cellulose filler coated with PVA resin. The pulverization conditions were a rotation speed of 15,000 rpm.

[0057] The cellulose filler coated with PVA resin and PHBV (manufactured by TianAn Biopolymer, product name: Y1000P) as the base resin were weighed to a volume ratio of 90:10 and dry-blended. The mixture was then melt-kneaded in a twin-screw kneader (KRC Kneader, manufactured by Kurimoto Iron Works). The screw was a medium shear type. The melt-kneading conditions were a material temperature of 180°C and a rotation speed of 50 min. －１ The composite resin composition discharged from the twin-screw kneader was hot-cut to prepare cellulose-composite PHBV resin pellets with a volume ratio of base resin, enzyme-supported natural fiber, and coating resin of 10:81:9.

[0058] Then, test pieces of cellulose-composite PHBV resin molded bodies were prepared using an injection molding machine (180AD manufactured by Japan Steel Works). The test piece preparation conditions were: base resin temperature 200°C, mold temperature 50°C, injection speed 100 mm / s, and holding pressure 100 Pa. The total heating time for the melt-kneading and injection molding was set to within 5 minutes. The shape of the test piece was changed depending on the evaluation items described below.

[0059] (Evaluation of Water Absorbency of Fibers) The water absorbency of fibers was evaluated by measuring the moisture content of the fibers according to the method specified in JIS L0105:2020. Specifically, the weight of the fibers dried at 80°C for 24 hours was measured, and this was used as the reference weight. Then, the weight of the fibers maintained at a temperature of 20°C and a humidity of 65% for 24 hours was measured. The weight increase from the reference weight was taken as the moisture content, and the moisture content was calculated. A moisture content of less than 5% was rated B, and a moisture content of 5% or more was rated A. In the composite resin molding according to Example 1, the moisture content of the softwood pulp was 6.5%, and the evaluation was A.

[0060] (Fiber end defibration) The obtained cellulose-composite PHBV resin molded body was immersed in chloroform and pure water to dissolve the PHBV and PVA, and the shape of the remaining cellulose fibers was observed by SEM. In the composite resin molded body of Example 1, the fiber ends were defibrated.

[0061] (Evaluation of Elastic Modulus of Composite Resin Molded Article) A three-point bending test was carried out using the obtained JIS K7139 Type A12 size dumbbell-shaped test piece. Here, the evaluation method for the elastic modulus was such that a value less than 200 MPa was rated as B and a value 200 MPa or more was rated as A. The elastic modulus of the composite resin molded article of Example 1 was 605 MPa, and the evaluation was A.

[0062] (Degradation test of composite resin molded body) A degradation test was conducted using the obtained JIS K7139 Type A12 size dumbbell-shaped test piece. The test piece was kept at a temperature of 60°C and a humidity of 40% for 48 hours. The 60°C environment is an accelerated test that is about 50 times faster than in a normal atmosphere at room temperature. A three-point bending test was conducted using the test piece after the degradation test. As a degradation evaluation method, a decrease in the elastic modulus of less than 10% compared to before the accelerated test was evaluated as A, and a decrease in the elastic modulus of 10% or more was evaluated as B. For the composite resin molded body of Example 1, the decrease in the elastic modulus of the test piece was 5%, and it was evaluated as A.

[0063] (Biodegradability Evaluation of Composite Resin Molded Articles) A ​​biodegradation test was conducted using bar-shaped test pieces made of the obtained cellulose composite resin molded articles. 50 g of compost inoculum (YK-11 manufactured by Yawata Bussan) was placed in a plastic container, and a bar-shaped test piece measuring 20 mm in height, 10 mm in width, and 3 mm in thickness, the weight of which had been measured in advance, was buried in the inoculum. The test piece was kept at a temperature of 58°C and a humidity of 50%, and the weight loss after two months was evaluated. The biodegradation rate was evaluated as follows: AA for a weight loss of 50% or more, A for a weight loss of 40% or more but less than 50%, and B for a weight loss of less than 40%. The biodegradation rate of the composite resin molded article of Example 1 was 41%, and the test piece was rated A.

[0064] In Example 2, the volume ratio of the base resin, the enzyme-supported natural fiber, and the coating resin was changed to 40:40:20, and the other material conditions and process conditions were the same as in Example 1 to produce a cellulose-composite PHBV resin molded product. Evaluations similar to those in Example 1 were also carried out.

[0065] In Comparative Example 1, a cellulose-composite PHBV resin molded body was produced without using a coating resin, except that the volume ratio of the base resin to the enzyme-supported cellulose filler was changed to 19:81, and the other material and process conditions were the same as in Example 1. Evaluation was also performed in the same manner as in Example 1.

[0066] In Comparative Example 2, a PHBV composite resin molding was produced without using natural fibers, except that the volume ratio of the base resin, enzyme, and coating resin was changed to 82.9:8.1:9, and the other material and process conditions were the same as in Example 1. Evaluation was also performed in the same manner as in Example 1.

[0067] In Comparative Example 3, the volume ratio of the base resin, the enzyme-supported natural fiber, and the coating resin was changed to 10:40:50, and the other material conditions and process conditions were the same as in Example 1 to produce a cellulose-composite PHBV resin molded product. The evaluation was also performed in the same manner as in Example 1.

[0068] Comparative Example 4 In Comparative Example 4, enzyme-supported PET fibers were produced using PET fibers with a fiber diameter of 20 μm and a fiber length of 100 μm instead of softwood pulp. The other material and process conditions were the same as in Example 1 to produce a PHBV composite resin molding. The evaluation was also the same as in Example 1.

[0069] The structures and measurement results of the composite resin moldings in Examples 1 and 2 and Comparative Examples 1 to 4 are shown in FIG.

[0070] As is clear from Figure 5, in Examples 1 and 2, in which the enzyme carried on the natural fiber was protected by a coating resin, the elastic modulus was high at 200 MPa or more, and Example 1, which had a higher proportion of natural fiber, showed a higher elastic modulus compared to Example 2. In a low humidity environment of 40%, the decrease in elastic modulus was also suppressed compared to Comparative Example 3. The biodegradation rate was accelerated compared to the comparative examples.

[0071] As described above, it has been confirmed that when natural fibers carrying enzymes on their surfaces are composited, the natural fibers are coated with a water-soluble resin on at least a portion of their surfaces, the fibers are exposed on the surface of the composite resin molding, and the natural fibers have a high water absorption rate, a composite resin with a high elastic modulus, high durability, and high biodegradability can be obtained.

[0072] Comparative Example 1, which was produced without using a coating resin, had an improved elastic modulus compared to Comparative Example 2 due to the use of natural fibers, but the enzyme was not protected by the coating resin during molding, and the enzyme was significantly damaged by heat during kneading and molding, so the biodegradation rate was lower than that of Example 1 and the product was rated B.

[0073] In Comparative Example 2, which was produced without using natural fibers, the natural fibers did not absorb water into the composite resin molding, so the dissolution of the PVA did not progress, and the biodegradation rate was lower than in Example 1, and the product was evaluated as B.

[0074] In Comparative Example 3, in which the volume ratio of the coating resin to the base resin was high, dissolution of the water-soluble coating resin progressed in the deterioration test, the modulus of elasticity decreased, and the rate of decrease in modulus of elasticity was evaluated as B.

[0075] In Comparative Example 4, which was made using PET fiber instead of softwood pulp, the PET fiber had a low moisture content and was not water absorbent, so in the biodegradability evaluation, the dissolution of PVA did not progress and the biodegradation rate was lower than in Example 1, resulting in a rating of B.

[0076] From the above evaluations, it was confirmed that a composite resin molding with high elastic modulus, high durability, and high biodegradability can be obtained by using water-absorbent natural fibers and biodegradable plastics, carrying enzymes on the surface of the natural fibers, coating at least a portion of the fiber surface with a water-soluble coating resin, and exposing the fibers on the surface of the composite resin molding. Furthermore, because the microorganisms and / or enzymes carried on the natural fibers are covered with the coating resin, the microorganisms and / or enzymes carried on the natural fibers can be protected from heat damage caused by the molten base resin during melt-kneading in the production of the composite resin molding.

[0077] It should be noted that the present disclosure includes appropriate combinations of any of the various embodiments and / or examples described above, and can achieve the effects of each embodiment and / or example.

[0078] A composite resin molded body according to one aspect of the present disclosure can realize a composite resin molded body that not only has a high elastic modulus compared to a resin alone, but also has a controlled biodegradation rate in a humid environment.

[0079] According to one aspect of the present disclosure, a composite resin molded article can be provided that has better mechanical strength and a more controllable biodegradation rate than conventional biodegradable plastics. The composite resin molded article according to one aspect of the present disclosure can improve the properties of the base resin, and thus can be used as a substitute for petroleum-derived general-purpose plastics. Therefore, the environmental impact of various industrial products or household goods made from petroleum-derived general-purpose plastics can be significantly reduced. Furthermore, the composite resin molded article can be used for packaging materials, daily necessities, home appliance housings, building materials, etc.

[0080] REFERENCE SIGNS LIST 1 Base resin 2 Natural fiber 3 Coating resin 4 Microorganism and / or enzyme 10 Composite resin molded body

Claims

1. A composite resin molding comprising a base resin, a plurality of natural fibers dispersed in the base resin, and at least one of a microorganism and an enzyme supported on each of the plurality of natural fibers, At least one of the plurality of natural fibers has a portion exposed on a surface of the composite resin molding, At least a portion of the surface of each of the plurality of natural fibers is coated with a coating resin.

2. The composite resin molding according to claim 1, wherein the moisture content of each of the plurality of natural fibers is 5% or more as determined by the method specified in JIS L0105:2020.

3. 2. The composite resin molding according to claim 1, wherein the main resin in the composite resin molding is a biodegradable resin containing any one selected from the group consisting of polyhydroxy acid, polyhydroxyalkanoate, polyalkylene dicarboxylate, and modified starch.

4. 2. The composite resin molding according to claim 1, wherein the coating resin is a water-soluble resin selected from the group consisting of polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose, and starch-based resins.

5. 2. The composite resin molding of claim 1, wherein, when the composite resin molding is 100% by volume, the volume percentage of the base resin is A, the volume percentage of the natural fibers carrying at least one of the microorganisms and enzymes is B, and the volume percentage of the coating resin is C, then A + B + C = 100, 0.01B ≦ C ≦ 0.5B, 10 ≦ B + C ≦ 99, and C ≦ A are satisfied.

6. 2. The composite resin molding according to claim 1, wherein each of the plurality of natural fibers in the composite resin molding carries at least one of the microorganisms and the enzymes on a surface of the fiber.

7. The composite resin molding according to claim 1 , wherein each of the plurality of natural fibers is a cellulose fiber.

8. The composite resin molding according to claim 1 , wherein each of the plurality of natural fibers has an open portion at an end in the fiber length direction.

9. A step of preparing at least one of a microorganism and an enzyme, natural fibers, a water-soluble coating resin, and a base resin; A step of supporting at least one of the microorganisms and the enzymes on the natural fibers; a step of dispersing the natural fibers carrying at least one of the microorganisms and the enzymes and the coating resin in water, drying and pulverizing the fibers to obtain coated natural fibers having at least a portion of the surface of the natural fibers coated with the coating resin; a step of melting and kneading the coated natural fibers together with the main resin, and proceeding with defibration from the end portions in the fiber length direction of the coated natural fibers, thereby obtaining a composite resin member with an expanded surface area of ​​the defibrated portions at the end portions; a step of molding the composite resin member to obtain a composite resin molded body; A method for producing a composite resin molded product, comprising: