Composite resin molded body with controlled decomposition rate and manufacturing method thereof

Abstract

To provide a composite resin molded body which has a high elastic modulus and a controlled biodegradation rate.SOLUTION: A composite resin molded body contains a main ingredient resin and a plurality of natural fibers dispersed in the main ingredient resin. The natural fibers contain microorganisms or enzymes. A content of the natural fibers is 10-99 mass% based on 100 mass% of the composite resin molded body. A portion of the natural fibers is exposed on surfaces of the composite resin molded body, and at least a portion of the surfaces of the natural fibers is coated with a hydrolyzable coating resin.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[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 plastic waste after use is increasing year by year, and because it is a substance with characteristics that make it difficult to decompose, it accumulates in the natural environment, causing pollution problems such as the destruction and contamination of the natural environment. In recent years, biodegradable plastics that decompose into water and carbon dioxide in the natural environment have been proposed as one of the measures to solve these problems, and it is expected that their use will expand, replacing general-purpose plastics that use petroleum-based raw materials.

[0004] However, biodegradable plastics have disadvantages, such as insufficient mechanical strength, compared to general-purpose plastics. Therefore, biodegradable plastics do not have sufficient properties required for materials used in various industrial products, including mechanical products such as automobiles, and electrical, electronic, and information products, and the current situation is that their range of application is limited. In addition, many biodegradable plastics are easily decomposed by their nature, and hydrolysis progresses during use, resulting in a deterioration in rigidity, which is an issue.

[0005] On the other hand, 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 long time for them to decompose completely, 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] For example, there have been disclosed a method of coating or blending microorganisms having enzymatic activity that decomposes biodegradable plastics with the material (see, for example, Patent Document 1), and a method of microencapsulating microorganisms in advance and incorporating them into biodegradable plastics (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-209587 A [Patent Document 2] JP 2020-520794 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, 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. On the other hand, in the method described in Patent Document 2, the molded body needs to be physically destroyed in order to release the microorganisms from the microcapsules, and there is a problem that the rigidity of the molded body decreases as the microcapsule content increases.

[0009] The present invention is devised to solve the above-mentioned problems of the conventional art, and has an object to provide a composite resin molding that maintains high rigidity during use and that is accelerated in biodegradation in humid environments such as the ocean or soil after disposal. [Means for solving the problem]

[0010] The composite resin molding of the present invention is a composite resin molding containing a main resin and a plurality of natural fibers dispersed in the main resin, wherein the natural fibers contain microorganisms or enzymes, and when the composite resin molding is taken as 100% by mass, the content of natural fibers containing microorganisms or enzymes is 10% by mass or more and 99% by mass or less, a portion of the natural fibers is exposed on the surface of the composite resin molding, and at least a portion of the surface of the natural fibers is coated with a hydrolyzable coating resin.

[0011] The manufacturing method of the present invention for producing a composite resin molding includes the steps of preparing microorganisms or enzymes, natural fibers, a hydrolyzable coating resin, and a base resin, impregnating the natural fibers with the microorganisms or enzymes, melt-kneading the natural fibers containing the microorganisms or enzymes together with the coating resin to proceed with defibration from the end in the fiber length direction of the natural fibers containing the microorganisms or enzymes and to increase the surface area of ​​the defibrated portion at the end, and kneading the coated natural fibers, at least a portion of whose surface is coated with the coating resin, together with the base resin, and then molding a composite resin molding. Effect of the Invention

[0012] According to the composite resin molding of the present invention, it is possible to realize a composite resin molding that has a high elastic modulus and a controlled biodegradation rate in a humid environment, as compared with a simple resin. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic cross-sectional view showing a cross-sectional structure of a composite resin molded body according to a first embodiment. [Diagram 2] 1 is a schematic cross-sectional view showing a cross-sectional structure of a natural fiber that is a constituent member of a composite resin molded product according to embodiment 1. FIG. [Diagram 3] 1 is a schematic cross-sectional view showing a cross-sectional structure of a composite resin molding containing natural fibers having defibrated portions according to embodiment 1. FIG. [Figure 4] 1A to 1C are schematic diagrams illustrating a manufacturing process of the composite resin molded body according to the first embodiment. [Diagram 5] 5A to 5C are diagrams showing the configurations and measurement results of composite resin molded bodies in examples and comparative examples according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The composite resin molding of the first aspect is a composite resin molding containing a base resin and a plurality of natural fibers dispersed in the base resin, wherein the natural fibers contain microorganisms or enzymes, and when the composite resin molding is 100% by mass, the content of natural fibers containing microorganisms or enzymes is 10% by mass or more and 99% by mass or less, a portion of the natural fibers is exposed on the surface of the composite resin molding, and at least a portion of the surface of the natural fibers is coated with a hydrolyzable coating resin.

[0015] A composite resin molded product according to a second aspect may be the above-mentioned first aspect, wherein the moisture content of the natural fibers is 5% or more as measured by the method defined in ASTM D 1909.

[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 base resin is a biodegradable resin containing any one selected from the group consisting of polyhydroxy acid, polyhydroxyalkanoate, polyalkylene dicarboxylate, and modified starches.

[0017] A composite resin molded product according to a fourth aspect is any one of the first to third aspects, wherein the melting point of the coating resin is equal to or higher than the melting point of the base resin and equal to or lower than the carbonization temperature of the natural fibers.

[0018] A composite resin molded product according to a fifth aspect is any one of the first to fourth aspects, wherein the natural fibers have microorganisms or enzymes supported on the surfaces of the fibers.

[0019] A composite resin molded product according to a sixth aspect is any one of the first to fifth aspects, wherein the natural fibers are cellulose fibers.

[0020] A composite resin molded product according to a seventh aspect is any one of the first to sixth aspects, wherein the natural fibers may have defibrated portions at ends in the fiber length direction.

[0021] The manufacturing method of the composite resin molding according to the eighth aspect includes the steps of preparing microorganisms or enzymes, natural fibers, a hydrolyzable coating resin, and a base resin; impregnating the natural fibers with the microorganisms or enzymes; melt-kneading the natural fibers containing the microorganisms or enzymes together with the coating resin, proceeding with defibration from the end in the fiber length direction of the natural fibers containing the microorganisms or enzymes and increasing the surface area of ​​the defibrated portion at the end; and kneading the coated natural fibers, at least a portion of the surface of which is coated with the coating resin, together with the base resin, and then forming a composite resin molding.

[0022] The manufacturing method of the composite resin molded body according to the ninth aspect is the eighth aspect, wherein in the step of molding the composite resin molded body, the molding temperature may be 125% or less of the melting point of the coating resin.

[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 will be omitted as appropriate.

[0024] (Embodiment 1) Fig. 1 is a schematic cross-sectional view showing the cross-sectional structure of a composite resin molded product 10 according to embodiment 1. Fig. 2 is a schematic cross-sectional view showing the cross-sectional structure of a natural fiber which is a constituent member of the composite resin molded product 10 according to embodiment 1. The composite resin molding 10 according to the first embodiment is made of a molten mixture of a base resin 1 and natural fibers 2 containing microorganisms or enzymes 4 coated with a coating resin 3. As shown in the schematic cross-sectional view of FIG. 1, the composite resin molding 10 has the natural fibers 2 containing microorganisms or enzymes 4 coated with a coating resin 3 dispersed in the base resin 1. In this composite resin molded body 10, some of the natural fibers 2 are exposed on the surface of the molded body, and the natural fibers 2 are in contact with each other, so that the body has high elastic modulus and high water absorption. In a humid environment, when the coating resin 3 is hydrolyzed by the absorption of water by the natural fibers 2, the microorganisms or enzymes 4 supported by the natural fibers 2 are released, accelerating the decomposition of the base resin 1. Therefore, a composite resin molded body 10 can be realized that maintains high rigidity during use, and has excellent biodegradability in humid environments such as the ocean or soil after disposal.

[0025] Each of the members constituting this composite resin molded product will be described below.

[0026] <Main resin> In this embodiment, the base resin 1 is preferably a biodegradable plastic containing any one selected from the group consisting of polyhydroxy acid, polyhydroxyalkanoate, polyalkylene dicarboxylate, and modified starch. In addition, in order to ensure good moldability, it is preferably a thermoplastic resin, and the above resins may be used alone or in combination of two or more. Note that the base resin 1 is not limited to the above materials as long as it has biodegradability.

[0027] In the present embodiment, the term "biodegradable plastic" refers to a resin that has the same function as conventional petroleum-derived resins during use, and is eventually decomposed into water and carbon dioxide by microorganisms in the soil or ocean in the natural world 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, and modified starch. Polyester resins include homopolymers of polyester monomers, copolymers of polyester monomers such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and copolymers of polyester monomers and other copolymerizable monomers. These polyester resins may be used alone or in combination of two or more.

[0028] <Natural fibers> Next, the natural fibers 2 will be described. The first main purpose of adding the natural fibers 2 (hereinafter, sometimes simply referred to as "fibers") contained in the composite resin molded body 10 in this embodiment is to allow the coating resin 3 to come into contact with water and be hydrolyzed by absorbing water in soil or ocean without placing a burden on the environment when the composite resin molded body 10 is discarded after use. For this purpose, it is preferable that the natural fibers 2 have high water absorption, and the moisture content of the natural fibers 2 is preferably 5% or more by the method specified by ASTM D 1909. Specifically, pulp, cellulose, cellulose nanofiber, lignocellulose, lignocellulose nanofiber, cotton, silk, hemp, etc. are preferable.

[0029] The second purpose of adding the natural fibers 2 is to improve mechanical properties and improve 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 nanofiber, lignocellulose, lignocellulose nanofiber, cotton, silk, wool, and hemp. Among these, celluloses are particularly preferable in terms of availability, high elastic modulus, and low linear expansion coefficient. The natural fibers 2 are not limited to the above materials as long as they can improve mechanical properties and have water absorption.

[0030] After the microorganisms or enzymes 4 are contained in the natural fibers 2, the content of the natural fibers 2 containing the microorganisms or enzymes 4 in the composite resin molding 10 is preferably 10% by mass or more and 99% by mass or less when the composite resin molding 10 is taken as 100% by mass. If the content of the natural fibers 2 containing the microorganisms or enzymes 4 is less than 10% by mass, the natural fibers 2 are unlikely to come into contact with each other inside the composite resin molding 10, and the composite resin molding 10 does not have sufficient water absorbency. On the other hand, if the content of the natural fibers 2 containing the microorganisms or enzymes 4 is more than 99% by mass, the proportions of the main resin 1 and the coating resin 3 become small, so that the effect of bonding the natural fibers 2 together is lost and moldability is deteriorated.

[0031] The form of the natural fiber 2 in the composite resin molded body 10 will be described. The larger the bonding interface between the natural fiber 2 and the coating resin 3, the more the hydrolysis of the coating resin 3 is promoted when the natural fiber 2 absorbs water, so it is preferable that the specific surface area of ​​the natural fiber 2 is high. On the other hand, in order to improve the water absorption of the composite resin molded body 10, it is preferable that the natural fiber 2 is exposed on the surface of the composite resin molded body 10. By exposing the natural fiber 2 on the surface of the composite resin molded body 10, the natural fiber 2 absorbs water from the exposed part, and absorbs water into the composite resin molded body 10 due to the capillary phenomenon of the fibers constituting the natural fiber. The smaller the specific surface area of ​​the natural fiber 2 exposed on the surface of the composite resin molded body, the higher the water absorption. This is because when the specific surface area of ​​the natural fiber 2 exposed on the surface is large, the water repellency is increased due to the effect of fine unevenness. Furthermore, as shown in FIG. 3, by having a defibrated part at the end of the natural fiber 2, the specific surface area of ​​the defibrated part is increased, and the number of contact points between the natural fibers 2 is increased, so that it is possible to increase the water absorption rate through the contact points of the natural fibers 2 in a humid environment.

[0032] The central portion of the undefibrated natural fibers 2, which have a small specific surface area, is less entangled with the base 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 base resin 1 and penetrate into the interior together with the base resin 1. This makes it possible to obtain a composite resin molded product 10 in which the central portions of the natural fibers 2, not including both end portions, are exposed on the surface.

[0033] The tip defibrated portion is preferably 5% or more and 50% or less of the entire fiber length L of the natural fibers 2. If the defibrated portion is less than 5% of the entire fiber length L, the specific surface area is small and no improvement in elastic modulus is observed, whereas if it is longer than 50%, the defibrated portion with a large aspect ratio is exposed on the surface of the composite resin molding, resulting in poor water absorbency.

[0034] Next, the characteristics of the natural fiber 2 will be described. The types of the main resin 1 and the natural fiber 2 are as described above. However, if the natural fiber 2 is too soft relative to the main resin 1, i.e., if the elastic modulus is small, the composite resin molding 10 will have a small elastic modulus as a whole, resulting in a decrease in strength. On the other hand, if the natural fiber 2 is too hard relative to the main resin 1, i.e., if the elastic modulus is large, shock waves generated upon impact will not be propagated but will be absorbed at the interface between the main resin 1 and the natural fiber 2, making it easier for cracks and crazes to occur near the interface, resulting in a decrease in impact resistance. Therefore, in the relationship between the elastic modulus of the main resin 1 and the natural fiber 2, it is preferable that the elastic modulus of the natural fiber 2 is higher, and the difference between them is as small as possible. The optimal relationship is calculated from the results of a simulation, and it is preferable that the difference in elastic modulus between the main resin 1 and the natural fiber 2 is within 20 GPa.

[0035] In addition, 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. However, 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.

[0036] <Additives> Additives may be used as necessary for the purpose of improving the affinity between the base resin 1 and the natural fibers 2. Any additives that are commonly used may be used.

[0037] <Coating resin> Next, the coating resin 3 will be described. The coating resin 3 in this embodiment is used for the purpose of protecting the microorganisms or enzymes 4 supported on the natural fibers 2 and preventing contact with the base resin 1 during the use of the composite resin molded body 10. After the composite resin molded body 10 is discarded, the coating resin 3 needs to be decomposed and release the microorganisms or enzymes 4 supported on the natural fibers 2 in order to promote biodegradation in a humid environment, so it is preferable that the coating resin 3 is a hydrolyzable resin that decomposes in an environment with a humidity of 50% or more. Specifically, polyester resins such as polylactic acid, polybutylene terephthalate, and polycarbonate can be mentioned. In addition, in order to ensure good moldability, it is preferable that the resin is a thermoplastic resin, and the above resins may be used alone or in combination of two or more kinds. The coating resin 3 is not limited to the above materials as long as it has hydrolytic properties.

[0038] 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 molding 10, it is preferable that the melting point of the coating resin 3 is equal to or higher than the melting point of the base resin 1 and is within a range lower than the carbonization temperature of the natural fibers 2. If the melting point of the coating resin 3 is equal to or higher than the melting point of the base resin 1, it will not melt during molding of the composite resin molding 10, and if the melting point is lower than the carbonization temperature of the natural fibers 2, it can coat the natural fibers 2 without deteriorating them.

[0039] The state of the coating resin 3 in the composite resin molding 10 will be described. By controlling the coverage of the natural fibers 2 with the coating resin 3, it is possible to delay the release of the microorganisms or enzymes 4 supported on the natural fibers 2 and control the decomposition rate.

[0040] <Microorganisms or enzymes> Next, the microorganism or enzyme 4 will be described. The microorganism or enzyme 4 in this embodiment is used for the purpose of accelerating the decomposition of the composite resin molded body 10 in a humid environment. The microorganism or enzyme 4 in this embodiment varies depending on the main resin 1, and specifically, as polylactic acid decomposition substances and polybutylene succinate decomposition substances, Amulatopsis genus microorganisms, as poly 3-hydroxybutyric acid decomposition substances, Streptomyces genus microorganisms, Pseudomonas genus microorganisms such as Pseudomonas lemonygnei, Alcaligenes genus microorganisms, Alcaligenes paradoxus, etc., as decomposition substances of polyethers such as polyethylene glycol, Pseudomonas genus microorganisms such as Pseudomonas sutzeri, Pseudomonas aeruginosa, Pseudomonas vesicularis, Alcaligenes genus microorganisms, Acinetobacter genus microorganisms, Xanthomonas genus microorganisms, etc., can be mentioned.

[0041] Examples of the enzyme in this embodiment include various enzymes extracted from the above microorganisms. Specifically, the enzyme for decomposing polylactic acid includes proteinase K, the enzyme for decomposing polyvinyl alcohol includes polyvinyl alcohol dehydrogenase, polyvinyl alcohol oxidase, secondary alcohol oxidase, etc., the enzyme for decomposing poly 3-hydroxybutyric acid includes PHB depolymerase, and the enzyme for decomposing polyurethane includes cholesterol esterase, chitopearl cholesterol esterase, urease, etc. The above microorganisms or enzymes may be used alone or in combination of two or more kinds. Note that the materials are not limited to the above as long as they have decomposability to the base resin 1.

[0042] <Method of manufacturing composite resin molded body> Next, a description will be given of a method for manufacturing the composite resin molded body 10. Fig. 4 is a flow diagram illustrating an example of a manufacturing process for the composite resin molded body 10 in this embodiment. (1) The microorganisms or enzymes 4 are supported in advance on the surface of the natural fibers 2. Methods for supporting the microorganisms or enzymes 4 include physical adsorption by dry blending, impregnation of natural fibers using a dispersion solvent, crosslinking, and entrapment. The method for supporting is not limited to the above as long as it can hold the microorganisms or enzymes 4 on the surface of the natural fibers 2.

[0043] (2) The natural fibers 2 and the coating resin 3 are fed into a melt-kneading processing device and melt-kneaded within the device. This melts the coating resin 3, and the natural fibers 2 are dispersed in the molten coating resin 3. At the same time, the shearing action of the device promotes defibration of agglomerates of the natural fibers 2, allowing the natural fibers 2 to be finely dispersed in the coating resin 3. By adjusting the shearing conditions at this time, it is also possible to defibrate the ends of the natural fibers 2 and obtain defibrated areas, as shown in Figure 3.

[0044] Conventionally, when fibers are compounded with resin, fibers that have been defibrated in advance by pretreatment such as wet dispersion have been used. However, when natural fibers are defibrated in the solvent used in wet dispersion, the fibers swell due to the solvent, so in order for the natural fibers to absorb water and expand sufficiently in the composite resin molding, it is necessary to dry the solvent in the natural fibers before kneading them with the base resin. In addition, defibration by wet dispersion is easier than defibration in a molten base resin, so it is difficult to defibrate only the ends, and the entire natural fiber ends up in a defibrated state. In addition, adding pretreatment increases the number of processes, which reduces productivity.

[0045] In contrast, in the manufacturing process of the composite resin molded body 10 in this embodiment, the natural fibers are not pretreated by wet dispersion for the purpose of defibrating the natural fibers, but are melt-kneaded together with the coating resin 3 (all-dry method). In this method, by not carrying out 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 in advance or during kneading, the water absorption rate in the composite resin molded body 10 in a humid environment can be further improved. In addition, by having the natural fibers 2 have defibrated regions as described above, the fibers have many contact points inside 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.

[0046] To produce the natural fiber 2 of the present embodiment by the all-dry method, it is preferable to apply high shear stress during kneading, and 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 easy application of high shear and high mass productivity, a continuous twin-screw kneader and a continuous roll kneader are particularly preferable. Any kneading method other than those mentioned above may be used as long as it is a method capable of applying high shear stress.

[0047] (3) The composite resin composition of the natural fibers 2 and the coating resin 3 extruded from the melt kneader is pulverized by a cutter or a crusher to obtain the natural fibers 2 at least partially coated with the coating resin 3 of the present embodiment. Specific methods include a pelletizer, a ball mill, a roll mill, a hammer mill, a wonder crusher, a jet crusher, and combinations thereof. Any other cutting or crushing 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] (4) The base resin 1 and the natural fibers 2 coated with the coating resin 3 are dry-blended, then kneaded and injection-molded to produce an injection-molded product as a composite resin molded body 10. The molding temperature during injection molding is preferably 125% or less of the melting point of the coating resin 3. If the molding temperature is higher than 125% of the melting point of the coating resin 3, the coating resin 3 will melt during molding and be dispersed in the base resin 1.

[0049] Hereinafter, examples and comparative examples of the experiments conducted by the inventors will be described.

[0050] 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.

[0051] Softwood pulp (manufactured by Mitsubishi Paper Mills, product name: NBKP Celgar) was used as the starting material for natural fibers. PHB depolymerase extracted from the culture solution of Streptomyces microorganisms was used as the PHBV decomposition enzyme. Softwood pulp and PHB depolymerase were dry-blended in a mass ratio of 90:10 and pulverized by a roll mill to obtain an enzyme-loaded cellulose filler.

[0052] Polylactic acid (manufactured by Unitika, product name: TE-2000) as a coating resin and the enzyme-supported cellulose filler were weighed out in a mass ratio of 50:50 and dry-blended. Then, the mixture was melt-kneaded in a twin-screw kneader (Kurimoto Iron Works, KRC Kneader). The screw was of medium shear type. The melt-kneading conditions were: material temperature 200°C, rotation speed 50 min -1 The composite resin composition discharged from the twin-screw kneader was hot-cut to prepare cellulose-composite polylactic acid resin pellets.

[0053] The cellulose-composite polylactic acid pellets thus prepared were pulverized using a Wonder Crusher (Osaka Chemical Co., Ltd., WC-3) to obtain cellulose fibers coated with polylactic acid resin. The pulverization conditions were a rotation speed of 15,000 rpm.

[0054] The cellulose fiber coated with polylactic acid resin and PHBV (manufactured by TianAn Biopolymer, product name: Y1000P) as the base resin were weighed out in a mass ratio of 50:50 and dry blended. Then, they were melt-kneaded in a twin-screw kneader (Kurimoto Iron Works, KRC Kneader). The screw was of medium shear type. The melt-kneading conditions were material temperature 180°C, rotation speed 50 min -1 The composite resin composition discharged from the twin-screw kneader was hot-cut to produce cellulose-composite PHBV resin pellets having a mass ratio of base resin, enzyme-containing natural fiber, and coating resin of 50:25:25.

[0055] Then, test pieces of cellulose-composite PHBV resin molded bodies were prepared using an injection molding machine (Japan Steel Works, Ltd. 180AD). The conditions for preparing the test pieces were: base resin temperature 200°C, mold temperature 50°C, injection speed 100mm / s, and holding pressure 100Pa. The shape of the test pieces was changed depending on the evaluation items described below.

[0056] (Evaluation of fiber water absorbency) The water absorption of the fibers was evaluated by measuring the moisture content of the fibers according to the method specified in ASTM D 1909. Specifically, the weight of the fibers dried at 80°C for 24 hours was measured and used as the reference weight. The weight of the fibers maintained at a temperature of 20°C and a humidity of 65% for 24 hours was then measured. The increase in weight from the reference weight was taken as the moisture content and the moisture content was calculated. Moisture content of less than 5% was rated as x, and moisture content of 5% or more was rated as o. The moisture content of softwood pulp was 6.5%, and was rated as o.

[0057] (Fiber end defibrability) The obtained cellulose-composite PHBV resin molded body was immersed in chloroform solvent to dissolve the PHBV and polylactic acid, and the shape of the remaining cellulose fibers was observed by SEM. The ends of the fibers were in a defibrated state.

[0058] (Evaluation of elastic modulus of composite resin molding) A three-point bending test was carried out using the obtained JIS K7139 Type A12 size dumbbell-shaped test piece. Here, the elastic modulus was evaluated as being less than 200 MPa as x and 200 MPa or more as ◯. The elastic modulus of the test piece was 259 MPa, and the evaluation was ◯.

[0059] (Deterioration test of composite resin molding) 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 the 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 marked as ○, and a decrease of 10% or more was marked as ×. The decrease in the elastic modulus of the same test piece was 5%, and it was rated as ○.

[0060] (Biodegradability evaluation of composite resin moldings) A biodegradation test was carried out using a bar-shaped test piece made of the obtained cellulose composite resin molded body. 50 g of compost inoculum (YK-11 manufactured by Yawata Bussan) was placed in a plastic container, and a bar-shaped test piece with a height of 20 mm, width of 10 mm, and thickness of 3 mm, the weight of which had been measured in advance, was buried in the inoculum, and the temperature was kept at 58°C and humidity at 50%, and the weight loss after 2 months was evaluated. The biodegradation rate was evaluated as follows: a weight loss of 50% or more was indicated as ◎, a weight loss of 40% or more but less than 50% was indicated as ○, and a weight loss of less than 40% was indicated as ×. The biodegradation rate of the test piece was 42%, and the evaluation was ◯.

[0061] Example 2 In Example 2, the mass ratio of the base resin, the enzyme-containing natural fiber, and the coating resin was changed to 67.5:25:7.5, and the other material conditions and process conditions were the same as in Example 1 to produce a cellulose-composite PHBV resin molded product. Evaluation was also performed in the same manner as in Example 1.

[0062] Comparative Example 1 In Comparative Example 1, an uncoated enzyme-supported cellulose filler was used. The mass ratio of the base resin to the enzyme-supported cellulose filler was changed to 25:75, and the other material conditions and process conditions were the same as in Example 1 to produce a cellulose-composite PHBV resin molded body. The evaluation was also performed in the same manner as in Example 1.

[0063] Comparative Example 2 In Comparative Example 2, no natural fibers were used, and the polylactic acid resin coating resin and the enzyme were melt-kneaded at a mass ratio of 95:5. The mass ratio of the base resin and the enzyme-containing polylactic acid resin was changed to 50:50, and the other material conditions and process conditions were the same as in Example 1 to produce a PHBV composite resin molding. The evaluation was also performed in the same manner as in Example 1.

[0064] Comparative Example 3 In Comparative Example 3, enzyme-supported PET fibers were prepared by using PET fibers with a fiber diameter of 20 μm and a fiber length of 100 μm instead of softwood pulp. The other material conditions and process conditions were the same as in Example 1 to prepare a PHBV composite resin molding. The evaluation was also performed in the same manner as in Example 1.

[0065] Comparative Example 4 In Comparative Example 4, a polylactic acid resin was used as the base resin instead of PHBV resin, and the other process conditions were the same as in Example 1 to produce a polylactic acid composite resin molded body.

[0066] Comparative Example 5 In Comparative Example 5, a PHBV resin molded body was produced using PHBV resin as a raw material without using natural fibers, coating resins, and enzymes, and the other process conditions were the same as in Example 1. The same evaluation as in Example 1 was also performed.

[0067] The structures and measurement results of the composite resin molded bodies in Examples 1 and 2 and Comparative Examples 1 to 5 are shown in FIG.

[0068] As is clear from Figure 5, in Examples 1 and 2 in which the enzyme supported on the natural fiber was protected by a coating resin, the elastic modulus was high at 200 MPa or more, and deterioration in stiffness in a low humidity environment of 40% was also suppressed compared to Comparative Example 2. The biodegradation rate was accelerated compared to Comparative Example 5. In the biodegradation evaluation, Example 2, which had a smaller proportion of coating resin, showed a higher biodegradation rate compared to Example 1.

[0069] As described above, it has been confirmed that when natural fibers carrying enzymes on their surfaces are composited, at least a portion of the fiber surface of the natural fibers is coated with a hydrolyzable resin, 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 high elastic modulus, high durability, and high biodegradability can be obtained.

[0070] Comparative Example 1, which was produced without using a coating resin, had an improved elastic modulus compared to Comparative Example 5 due to the incorporation of natural fibers. However, the enzyme was not protected by the coating resin during molding, and the enzyme was significantly damaged by heat during kneading and molding. As a result, the biodegradation rate was lower than that of Comparative Example 3, and the product was rated as ×.

[0071] In Comparative Example 2, which was produced without using natural fibers, the elastic modulus was improved by compounding with polylactic acid resin, but since the natural fibers did not absorb water into the inside of the composite resin molding, hydrolysis of the polylactic acid resin did not progress, and the biodegradation rate was lower than in Comparative Example 5, and the evaluation was poor.

[0072] In Comparative Example 3, which was made using PET fiber instead of softwood pulp, the moisture content of the PET fiber was low and it was not water absorbent, so in the biodegradability evaluation, hydrolysis of the polylactic acid resin did not progress and the biodegradation rate was lower than that of Comparative Example 5, and the product was rated as x.

[0073] In Comparative Example 4, which was produced using polylactic acid resin instead of PHBV resin as the main resin, hydrolysis of the main resin proceeded in the deterioration test, the elastic modulus decreased, and the evaluation was X. In the biodegradability evaluation, since the biodegradation rate of the main resin, polylactic acid resin, was slower than that of PHBV resin, the biodegradation rate also decreased, and the evaluation was X.

[0074] From the above evaluations, it was confirmed that if absorbent natural fibers and biodegradable plastics are used, enzymes are supported on the surface of the natural fibers, at least a portion of the fiber surface is coated with a hydrolyzable coating resin, and the fibers are exposed on the surface of the composite resin molding, a composite resin molding with high elastic modulus, high durability, and high biodegradability can be obtained.

[0075] In addition, 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. [Industrial Applicability]

[0076] According to the composite resin molding of the present invention, it is possible to provide a composite resin molding that has a higher mechanical strength and a more controllable biodegradation rate than conventional biodegradable plastics. Since the properties of the base resin can be improved by the present invention, it can be used as a substitute for general-purpose petroleum-derived plastics. Therefore, it is possible to significantly reduce the environmental load of various industrial products or daily necessities made of general-purpose petroleum-derived plastics. Furthermore, it is possible to use it for packaging materials, daily necessities, housings for home appliances, building materials, etc. [Explanation of symbols]

[0077] 1 Base resin 2. Natural Fibers 3. Coating resin 4. Microorganisms or enzymes 10 Composite resin molding

Claims

1. A biodegradable resin polyhydroxyalkanoate as the main resin; A plurality of natural fibers dispersed in the base resin; A composite resin molding comprising: The natural fiber contains a microorganism or an enzyme having decomposition ability to the base resin depending on the material of the base resin, When the composite resin molding is taken as 100% by mass, the content of the natural fiber containing the microorganism or the enzyme is 10% by mass or more and 99% by mass or less. A portion of the natural fibers is exposed on a surface of the composite resin molding, A composite resin molded product, in which at least a portion of the surface of the natural fiber is coated with a hydrolyzable coating resin.

2. 2. The composite resin molding according to claim 1, wherein the moisture content of the natural fibers is 5% or more as measured by the method specified in ASTM D 1909.

3. 3. The composite resin molding according to claim 1, wherein the melting point of the coating resin is within a range of not less than the melting point of the base resin and not more than the carbonization temperature of the natural fibers.

4. The composite resin molding according to claim 1 , wherein the natural fibers in the composite resin molding have the microorganisms or enzymes supported on the surfaces of the fibers.

5. The composite resin molding according to claim 1 , wherein the natural fibers are cellulose fibers.

6. The composite resin molding according to claim 1 , wherein the natural fibers have defibrated portions at ends in a fiber length direction.

7. A method for producing a biodegradable polyhydroxyalkanoate resin as a base resin, a microorganism or an enzyme having decomposition properties for the base resin depending on the material of the base resin, natural fibers, and a hydrolyzable coating resin; impregnating said natural fibers with said microorganisms or enzymes; a coating resin melt-kneading step in which the natural fibers containing the microorganisms or enzymes are melt-kneaded together with the coating resin, and defibration is advanced from the end in the fiber length direction of the natural fibers containing the microorganisms or enzymes, thereby expanding the surface area of ​​the defibrated portion at the end; a step of kneading the coated natural fibers, at least a part of the surface of which is coated with the coating resin, together with the base resin, and then forming a composite resin molding; A method for producing a composite resin molded product comprising the steps of:

8. 8. The method for producing a composite resin molded product according to claim 7, wherein in the step of molding the composite resin molded product, a molding temperature is set to a temperature in Celsius that is 125% or less of a melting point of the coating resin.

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