Patent Application
20240409701
The present disclosure relates to a composite resin molded article having excellent mechanical properties and a controlled biodegradation rate in a humid environment, and a method for producing the same.
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 have a weight as small as a fraction of that of metal or ceramics. Therefore, general-purpose plastics are often used as materials of various daily commodities such as bags, various packaging, various containers, and sheets, and as materials for industrial components such as automobile components and electrical components, daily necessities, and miscellaneous goods.
Under such circumstances, the amount of plastic waste after use is increasing year by year, and plastic waste, which is a substance having a property of being hardly decomposed, accumulates in a natural environment and causes pollution problems such as destruction and pollution in the natural environment. In recent years, biodegradable plastics that are decomposed into water and carbon dioxide in the natural environment have been proposed as one of measures to solve such various problems, and expanded use of the biodegradable plastics instead of general-purpose plastics produced using petroleum-based raw materials is expected.
However, biodegradable plastics have disadvantages such as insufficient mechanical strength as compared with general-purpose plastics. Therefore, biodegradable plastics do not have sufficient properties required for materials used for machine products such as automobiles and various industrial products including electric/electronic/information products, and the application range thereof is currently limited.
On the other hand, the biodegradation rate of the biodegradable plastics after disposal is greatly affected by the environment. In an environment with a small number of microorganisms, such as in the ocean, it takes significantly long time to completely decompose the biodegradable plastics, and the properties of biodegradability are not sufficiently utilized. In order to solve such problems, various methods have been proposed to accelerate the decomposition of the biodegradable plastics after disposal.
In order to solve such problems, a product obtained by combining a biodegradable plastic with a microorganism having an enzyme activity of decomposing the material (see, for example, PTL 1), and a method of microencapsulating a microorganism in advance to incorporate the microorganism into a biodegradable plastic are disclosed (see, for example, PTL 2).
A composite resin molded article according to one aspect of the present disclosure is a composite resin molded article including: a base resin; a plurality of natural fibers dispersed in the base resin; and at least one of a microorganism and an enzyme, the microorganism and the enzyme being supported on each of the plurality of natural fibers, wherein at least one of the plurality of natural fibers includes a portion exposed on a surface of the composite resin molded article, and at least a part of a surface of each of the plurality of natural fibers is coated with a coating resin.
A method for producing a composite resin molded article according to one aspect of the present disclosure includes: a step of preparing at least one of a microorganism and an enzyme, a natural fiber, a water-soluble coating resin, and a base resin; a step of supporting at least one of the microorganism and the enzyme on the natural fiber; a step of dispersing the natural fiber on which at least one of the microorganism and the enzyme is supported and the coating resin in water, and performing drying and pulverization to obtain a coated natural fiber having at least a part coated with the coating resin on a surface of the natural fiber; a step of melt-kneading the coated natural fiber and the base resin to promote defibration of the coated natural fiber from an end portion in a fiber length direction, thus obtaining a composite resin material having a defibrated portion of the end portion, the defibrated portion having an enlarged surface area; and a step of molding the composite resin material to obtain a composite resin molded article.
In the method described in PTL 1, since the microorganism is directly kneaded into the biodegradable plastic, the material is limited to biodegradable plastics that can be molded at a temperature at which the microorganism can survive.
On the other hand, the method described in PTL 2 has a problem that the molded article needs to be physically broken in order to release the microorganism from a microcapsule, and the rigidity of the molded article decreases as the content of the microcapsule increases.
One aspect of the present disclosure is to solve the above-described conventional problems, and an object of the present disclosure is to provide a composite resin molded article that maintains high rigidity during use and promotes biodegradation in a humid environment such as in the ocean or the soil after disposal.
A composite resin molded article according to a first aspect is a composite resin molded article according to one aspect of the present disclosure is a composite resin molded article including: a base resin; a plurality of natural fibers dispersed in the base resin; and at least one of a microorganism and an enzyme, the microorganism and the enzyme being supported on each of the plurality of natural fibers, wherein at least one of the plurality of natural fibers has a portion exposed on a surface of the composite resin molded article, and at least a part of a surface of each of the plurality of natural fibers is coated with a coating resin.
In the composite resin molded article according to a second aspect, in the first aspect, each of the plurality of natural fibers may have a moisture content, as measured by a method defined in JIS L0105:2020, of 5% or more.
In the composite resin molded article according to a third aspect, in the first or second aspect, the base resin may be a biodegradable resin containing any one selected from the group consisting of a polyhydroxy acid, a polyhydroxyalkanoate, a polyalkylene dicarboxylate, and a modified starch.
In the composite resin molded article according to a fourth aspect, in any one of the first to third aspects, the coating resin may be any water-soluble resin selected from the group consisting of polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose, and a starch-based resin.
In the composite resin molded article according to a fifth aspect, in any one of the first to fourth aspects, A+B+C=100, 0.01B≤ C≤0.5B, 10≤B+C≤99, and C≤ A may be satisfied, where A is a volume % of the base resin, B is a volume % of natural fiber 2 on which at least one of the microorganism and the enzyme is supported, and C is a volume % of coating resin 3, based on 100 volume % of the composite resin molded article.
In the composite resin molded article according to a sixth aspect, in any one of the first to fifth aspects, each of the plurality of natural fibers may support at least one of the microorganism and the enzyme on a surface of each of the plurality of natural fibers.
In the composite resin molded article according to a seventh aspect, in any one of the first to sixth aspects, each of the plurality of natural fibers may be celluloses.
In the composite resin molded article according to an eighth aspect, in any one of the first to seventh aspects, each of the plurality of natural fibers may have a defibrated site at an end portion in a fiber length direction.
A method for producing a composite resin molded article according to a ninth aspect includes: a step of preparing at least one of a microorganism and an enzyme, a natural fiber, a water-soluble coating resin, and a base resin; a step of supporting at least one of the microorganism and the enzyme on the natural fiber; a step of dispersing the natural fiber on which at least one of the microorganism and the enzyme is supported and the coating resin in water, and performing drying and pulverization to obtain a coated natural fiber having at least a part coated with the coating resin on a surface of the natural fiber; a step of melt-kneading the coated natural fiber and the base resin to promote defibration of the coated natural fiber from an end portion in a fiber length direction, thus obtaining a composite resin material having a defibrated portion of the end portion, the defibrated portion having an enlarged surface area; and a step of molding the composite resin material to obtain a composite resin molded article.
Hereinafter, a composite resin molded article according to an exemplary embodiment and a method of producing the same will be described with reference to the accompanying drawings. In the following description, the same components are denoted by the same reference marks, and the description thereof is appropriately omitted.
Composite resin molded article 10 according to the exemplary embodiment is formed of a melt-kneaded product of base resin 1 and natural fiber 2 that supports microorganism and/or enzyme 4 (at least one of microorganism and enzyme) and is coated with coating resin 3. In composite resin molded article 10, as illustrated in the schematic view illustrating the cross-sectional structure of
Further, as illustrated in the schematic view illustrating the cross-sectional structure of composite resin molded article 10 containing natural fiber 2 having a defibrated site according to the exemplary embodiment of
According to composite resin molded article 10, since at least one natural fiber 2 is exposed on a surface of the composite resin molded article, and natural fibers 2 have contact points with each other, the composite resin molded article has high elastic modulus and high water absorbency. When coating resin 3 is dissolved by water absorption of natural fiber 2 in a humid environment, microorganism and/or enzyme 4 supported on natural fiber 2 is released, and decomposition of base resin 1 is promoted. Therefore, it is possible to realize composite resin molded article 10 which maintains high rigidity during use and has excellent biodegradability in a humid environment such as in the ocean or the soil after disposal.
Hereinafter, each member constituting the composite resin molded article will be described.
In the present exemplary embodiment, base resin 1 is preferably a biodegradable plastic containing any one selected from the group consisting of a polyhydroxy acid, a polyhydroxyalkanoate, a polyalkylene dicarboxylate, and a modified starch. Further, in order to ensure good moldability, a thermoplastic resin is preferable, and the above resins may be used alone or in combination of two or more thereof. Note that base resin 1 is not limited to the above materials as long as it has biodegradability.
In the present exemplary embodiment, the term “biodegradable plastic” refers to “resin that has a function similar to that of a conventional petroleum-derived resin at the time of use, and is finally decomposed into water and carbon dioxide by microorganisms in the soil and the ocean in nature after use”. Specific examples of the biodegradable plastic include polyhydroxyalkanoates such as polyhydroxybutyrate and polyhydroxyvalerate; polyhydroxy acids such as polylactic acid, polyglycolic acid, and polycaprolactone; polyester-based resins including polyalkylene dicarboxylates such as polybutylene adipate terephthalate, polyethylene succinate, and polybutylene succinate; polyamides; and modified starches. Examples of the biodegradable plastic include, in addition to a homopolymer of a monomer of the resins described above, a copolymer of a monomer, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and a copolymer of a monomer and another copolymerizable monomer.
Next, natural fiber 2 will be described. The main first purpose of adding natural fiber 2 (hereinafter, may be simply referred to as “fiber”) contained in composite resin molded article 10 according to the present exemplary embodiment is to cause composite resin molded article 10 to absorb water in the soil and the ocean without imposing a load on the environment when composite resin molded article 10 is discarded after use, to thereby bring coating resin 3 into contact with water and dissolve coating resin 3. For this purpose, natural fiber 2 preferably has high water absorbency, and the moisture content of natural fiber 2 is preferably 5% or more by a method defined in JIS L0105:2020. Specifically, pulp, cellulose, cellulose nanofibers, lignocellulose, lignocellulose nanofibers, cotton, silk, and hemp are preferable.
The second purpose of adding natural fiber 2 is to improve mechanical properties and to improve dimensional stability by decreasing the linear expansion coefficient. For this purpose, natural fiber 2 preferably has a higher elastic modulus than base resin 1. Specific examples thereof include pulp, cellulose, cellulose nanofibers, lignocellulose, lignocellulose nanofibers, cotton, silk, wool, and hemp. Further, among them, celluloses are particularly preferable from the viewpoint of availability, high elastic modulus, and low linear expansion coefficient. Note that natural fiber 2 is not limited to the above materials as long as it can improve mechanical properties and has water absorbency.
After microorganism and/or enzyme 4 is supported on natural fiber 2 and at least a part of the natural fiber is coated with coating resin 3, the content of natural fiber 2 on which microorganism and/or enzyme 4 is supported and coating resin 3 in composite resin molded article 10 is preferably 10 volume % or more and 99 volume % or less based on 100 volume % of composite resin molded article 10. When the content of natural fiber 2 on which microorganism and/or enzyme 4 is supported and coating resin 3 is less than 10 volume %, natural fibers 2 are less likely to have a contact point with each other in composite resin molded article 10, and thus sufficient water absorbency is not attained. On the other hand, when the content of natural fiber 2 on which microorganism and/or enzyme 4 is supported and coating resin 3 is more than 99 volume %, the proportion of base resin 1 decreases, so that the effect of bonding natural fibers 2 to each other is lost and moldability is thus deteriorated.
The form of natural fiber 2 in composite resin molded article 10 will be described. When the bonding interface between natural fiber 2 and coating resin 3 is large, the dissolution of coating resin 3 is promoted during water absorption of natural fiber 2, and therefore, the specific surface area of natural fiber 2 is preferably high. On the other hand, in order to improve the water absorbency of composite resin molded article 10, natural fiber 2 is preferably exposed on the surface of composite resin molded article 10. Since natural fiber 2 is exposed on the surface of composite resin molded article 10, water is absorbed from an exposed portion of natural fiber 2, and water is absorbed into the inside of composite resin molded article 10 by a capillary phenomenon of fibers constituting the natural fiber. The exposed portion of natural fiber 2 exposed on the surface of composite resin molded article 10 has higher water absorbency as the specific surface area is smaller. This is because when the specific surface area of the exposed portion of natural fiber 2 exposed on the surface is large, water repellency is enhanced by the effect of fine irregularities. Further, as illustrated in
The central portion of natural fiber 2, which has a small specific surface area and is not defibrated, is less entangled with base resin 1 and is easily exposed to the surface of the composite resin molded article depending on the molding conditions. On the other hand, the tip portion of defibrated natural fiber 2 is highly entangled with base resin 1, and enters the inside together with base resin 1. As a result, it is possible to obtain composite resin molded article 10 in which the central portion not including both ends of natural fiber 2 is exposed to the surface.
The total length of the tip defibrated sites at both ends of natural fiber 2 is preferably 5% or more and 50% or less of fiber length L of entire natural fiber 2. When the length of the defibrated site is less than 5% of total fiber length L, the clastic modulus is not improved because the specific surface area is small, and when the length of the defibrated site is more than 50%, the defibrated site having a high aspect ratio is exposed on the surface of the composite resin molded article, so that water absorbency is deteriorated.
Next, properties of natural fiber 2 will be described. The types of base resin 1 and natural fiber 2 are as described above, but when natural fiber 2 is too soft, that is, has a small elastic modulus with respect to base resin 1, composite resin molded article 10 has a small elastic modulus as a whole, resulting in a decrease in strength. On the other hand, when natural fiber 2 is too hard, that is, has a large elastic modulus with respect to base resin 1, shock waves generated at the time of impact are not propagated but absorbed at the interface between base resin 1 and natural fiber 2, so that cracks and creases are likely to occur in the vicinity of the interface, and as a result, impact strength is deteriorated. Therefore, in the relationship between the elastic modulus of base resin 1 and the elastic modulus of natural fiber 2, the elastic modulus of natural fiber 2 is higher than the elastic modulus of base resin 1, and the difference between the elastic moduli is preferably as small as possible. The optimum relationship is calculated from simulation results, and the difference in elastic modulus between base resin 1 and natural fiber 2 is preferably within 20 GPa.
Further, these natural fibers 2 may be subjected to a surface treatment for the purpose of, for example, improving adhesion to base resin 1 and coating resin 3 or dispersibility in composite resin molded article 10, but when the water absorbency of natural fibers 2 is impaired by the surface treatment, it is preferable not to perform the surface treatment in advance.
An additive may be used as necessary for the purpose of, for example, improving the affinity between base resin 1 and natural fiber 2. Note that additives that are usually used can be used.
Next, coating resin 3 will be described. Coating resin 3 in the present exemplary embodiment protects microorganism and/or enzyme 4 supported on natural fiber 2, and suppresses thermal damage to microorganism and/or enzyme 4 received from molten base resin 1 at the time of producing composite resin molded article 10. In addition, during use of composite resin molded article 10, coating resin 3 is used for the purpose of protecting microorganism and/or enzyme 4 supported on natural fiber 2 and preventing contact with base resin 1. After disposal of composite resin molded article 10, in order to promote biodegradation in a humid environment, coating resin 3 needs to be dissolved to release microorganism and/or enzyme 4 supported on natural fiber 2. Therefore, coating resin 3 is preferably a water-soluble resin that is soluble in water at a temperature of 20° C. Specific examples thereof include polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose, and a modified starch. The above resins may be used alone or in combination of two or more thereof. Note that coating resin 3 is not limited to the above materials as long as it has water solubility.
In addition, as for coating resin 3 in composite resin molded article 10, in order to maintain a state in which at least a part of the surface of natural fiber 2 is coated, A+B+C=100, 0.01B≤ C≤0.5B, and C≤ A are preferably satisfied, where A is the volume % of base resin 1, B is the volume % of natural fiber 2 on which microorganism and/or enzyme 4 is supported, and C is the volume % of coating resin 3, based on 100 volume % of composite resin molded article 10. When 0.5B<C, the volume % of coating resin 3 is too large with respect to natural fiber 2, and it is difficult to maintain the contact point between natural fibers 2. When C<0.01B, the volume % of coating resin 3 is too small with respect to natural fiber 2, and it is difficult to protect microorganism and/or enzyme 4 supported on natural fiber 2. When A<C, the volume % of coating resin 3 is too large, and water-soluble coating resin 3 exposed on the surface of composite resin molded article 10 is easily deteriorated, so that it is difficult to maintain durability.
The presence state of coating resin 3 in composite resin molded article 10 will be described. By controlling the volume % of natural fiber 2, coating resin 3 can delay the release of microorganism and/or enzyme 4 supported on natural fiber 2, to thereby control the decomposition rate.
<Microorganism and/or Enzyme>
Next, microorganism and/or enzyme 4 will be described. Microorganism and/or enzyme 4 in the present exemplary embodiment is used for the purpose of accelerating decomposition of composite resin molded article 10 in a humid environment.
Microorganism and/or enzyme 4 in the present exemplary embodiment varies depending on base resin 1, and specific examples include Amycolatopsis microorganisms as polylactic acid degradants and polybutylene succinate degradants. Examples of poly(3-hydroxybutyric acid) degradants include Streptomyces microorganisms, Pseudomonas microorganisms such as Pseudomonas lemoignei, and Alcaligenes microorganisms such as Alcaligenes paradoxus. Further, examples of degradants of polyether such as polyethylene glycol include Pseudomonas microorganisms such as Pseudomonas stutzeri, Pseudomonas aeruginosa, and Pseudomonas vesicularis, Alcaligenes microorganisms, Acinetobacter microorganisms, and Xanthomonas microorganisms.
Examples of the enzyme in the present exemplary embodiment include various enzymes extracted from the above-described microorganisms. Specific examples thereof include Proteinase K as an enzyme for decomposing polylactic acid; polyvinyl alcohol dehydrogenase, polyvinyl alcohol oxidase, secondary alcohol oxidase, and the like as an enzyme for decomposing polyvinyl alcohol; PHB depolymerase as an enzyme for decomposing poly(3-hydroxybutyric acid); and cholesterol esterase, Chitopearl cholesterol esterase, urease, and the like as an enzyme for decomposing polyurethane. The above-described microorganisms and/or enzymes may be used alone or in combination of two or more thereof. Note that microorganism and/or enzyme 4 is not limited to the above materials as long as it has decomposability with respect to base resin 1.
Next, a method of producing composite resin molded article 10 will be described.
(1) Microorganism and/or enzyme 4 is supported on the surface of natural fiber 2 in advance. Examples of the method for supporting microorganism and/or enzyme 4 include physical adsorption by dry blending, an impregnation method of natural fibers using a dispersion solvent, a crosslinking method, and an entrapment method. The method for supporting microorganism and/or enzyme 4 is not limited to the above-described methods as long as it is a method capable of holding microorganism and/or enzyme 4 on the surface of natural fiber 2.
(2) Natural fiber 2 on which microorganism and/or enzyme 4 is supported and water-soluble coating resin 3 are dispersed in water, dried, and then pulverized by a cutting machine or a pulverizer, whereby natural fiber 2 having a surface at least partially coated with coating resin 3 in the present exemplary embodiment can be obtained. Specific examples of the method include a pelletizer, a ball mill, a roll mill, a hammer mill, a wonder crusher, a jet pulverizer, and a combination thereof. Any cutting or pulverizing method other than the above may be employed as long as it is a method capable of maintaining a state in which at least a part of natural fiber 2 is coated with coating resin 3.
(3) Base resin 1 and natural fiber 2 coated with coating resin 3 are dry-blended, and then the mixture is fed into a melt-kneading apparatus and melt-kneaded in the apparatus. At this time, since natural fiber 2 is coated with coating resin 3, thermal damage to the microorganism and/or enzyme supported on the natural fiber can be suppressed. As a result, the shearing action of the apparatus promotes defibration of aggregates of natural fibers 2, and coated natural fibers 2 can be finely dispersed in base resin 1. At this time, by adjusting the shear conditions, as illustrated in
Conventionally, when fibers are combined with a resin, fibers that have been defibrated in advance by a pretreatment such as wet dispersion have been used. However, when the natural fibers are defibrated in a solvent used in wet dispersion, the fibers swells due to the solvent. Therefore, in order for the natural fibers to sufficiently absorb water and expand in the composite resin molded material, the solvent in the natural fibers needs to be dried before being kneaded with the base resin. Further, in the defibration by wet dispersion, the fibers are easier to be defibrated than to be defibrated in the molten base resin, so that it is difficult to defibrate only the end portion, and the entire natural fiber is defibrated. In addition, there is a problem that the number of processes increases and productivity deteriorates by combining the pretreatment.
On the other hand, in the process of producing composite resin molded article 10 according to the present exemplary embodiment, a melt-kneading treatment (all-dry method) is performed together with base resin 1 without performing a pretreatment by wet dispersion for the purpose of defibrating natural fiber 2. In this method, since the wet dispersion treatment of natural fiber 2 is not performed, swelling of natural fiber 2 in the production process is suppressed, and the water absorption rate of natural fiber 2 in composite resin molded article 10 can be improved. By subjecting natural fiber 2 to a drying treatment in advance or during kneading, the water absorption rate in a humid environment in composite resin molded article 10 can be further improved. When natural fiber 2 has a defibrated site as described above, the fibers have many contact points inside composite resin molded article 10, and the water absorption rate of composite resin molded article 10 can be increased via the contact points between the fibers.
In order to produce natural fiber 2 of the present exemplary embodiment by the all-dry method, it is preferable to apply high shear stress during kneading. Specific examples of the kneading method include a single screw kneader, a twin screw kneader, a roll kneader, a Banbury mixer, and a combination 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. A kneading method other than the above may be used as long as high shear stress can be applied.
(4) By injection-molding the composite resin composition extruded from the melt-kneading apparatus, composite resin molded article 10 as an injection-molded article can be produced.
Hereinafter, examples and comparative examples in experiments performed by the inventors will be described.
In Example 1, a cellulose composite poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) resin molded article was produced by the following production method.
Softwood pulp (product name: NBKP Celgar, manufactured by Mitsubishi Paper Mills Limited) was used as a starting material for the natural fiber. PHB depolymerase extracted from a culture solution of a Streptomyces microorganism was used as a PHBV-degrading enzyme. The softwood pulp and the PHB depolymerase were dry-blended at a volume ratio of 90:10, and pulverized by a roll mill to obtain a cellulose filler on which an enzyme was supported.
Polyvinyl alcohol (PVA) (product name: PVA-217 manufactured by Kuraray Co., Ltd.) as a coating resin and the cellulose filler on which the above-described enzyme was supported were weighed at a volume ratio of 10:90, dispersed in pure water, formed into a sheet by a stretching machine (IMC-1124 manufactured by Imoto machinery Co., Ltd.), and dried. The obtained cellulose PVA sheet was pulverized by a wonder crusher (WC-3 manufactured by OSAKA CHEMICAL Co., Ltd.) to obtain a cellulose filler coated with a PVA resin. The pulverization condition was set to a rotation speed of 15000 rpm.
The cellulose filler coated with a PVA resin and PHBV (product name: Y1000P manufactured by TianAn Biopolymer) as a base resin were weighed at a volume ratio of 90:10, and then dry-blended. Thereafter, the mixture was melt-kneaded with a twin screw kneader (KRC kneader manufactured by Kurimoto, Ltd.). A screw was of a medium shear type. The conditions of the melt-kneading 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 produce cellulose composite PHBV resin pellets in which a volume ratio of the base resin, the natural fiber on which an enzyme was supported, and the coating resin was 10:81:9.
Thereafter, a test piece of a cellulose composite PHBV resin molded article was produced by an injection molding machine (180AD manufactured by The Japan Steel Works, Ltd.). The preparation conditions of the test piece were a base resin temperature of 200° C., a mold temperature of 50° C., an injection speed of 100 mm/s, and a holding pressure of 100 Pa. At this time, the total heating time in the melt-kneading and injection molding was set to 5 minutes or less. The shape of the test piece was changed according to the evaluation items described below.
The water absorbency of the fiber was evaluated by measuring the moisture content of the fiber according to the method defined in JIS L0105:2020. Specifically, the weight of the fiber dried at 80° C. for 24 hours was measured and taken as a reference weight. Thereafter, the weight of the fiber maintained at a temperature of 20° C. and a humidity of 65% for 24 hours was measured. The moisture content was calculated using the weight increase increased from the reference weight as moisture. A sample having a moisture content of less than 5% was rated as B, and a sample having a moisture content of 5% or more was rated as A. In the composite resin molded article according to Example 1, the moisture content of the softwood pulp was 6.5%, and the evaluation thereof was A.
The obtained cellulose composite PHBV resin molded article was immersed in chloroform and pure water to dissolve PHBV and PVA, and the shape of the remaining cellulose fibers was observed by SEM. In the composite resin molded article according to Example 1, the end portion of the fiber was in a defibrated state.
A three-point bending test was performed using the obtained dumbbell-shaped test piece of JIS K7139 type A12 size. Here, as a method for evaluating the elastic modulus, a sample having a numerical value of less than 200 MPa was rated as B, and a sample having a numerical value of 200 MPa or more was rated as A. In the composite resin molded article according to Example 1, the elastic modulus of the test piece was 605 MPa, and the evaluation thereof was A.
A degradation test was performed using the obtained dumbbell-shaped test piece of JIS K7139 type A12 size. The test piece was held at a temperature of 60° C. and a humidity of 40% for 48 hours. The environment of 60° C. is an accelerated test of about 50 times the normal atmosphere at normal temperature. A three-point bending test was performed using the test piece after the degradation test. As a degradation evaluation method, a sample having a reduction rate of the elastic modulus before the accelerated test of less than 10% was rated as A, and a sample having a reduction rate of 10% or more was rated as B. In the composite resin molded article according to Example 1, the reduction rate of the elastic modulus of the test piece was 5%, and the evaluation thereof was A.
A biodegradation test was performed using a bar-shaped test piece formed of the obtained cellulose composite resin molded article. Into a plastic container, 50 g of a compost planting source (YK-11 manufactured by Yawata Corporation) was placed, a bar-shaped test piece having a height of 20 mm, a width of 10 mm, and a thickness of 3 mm, the weight of which was measured in advance, was embedded in the planting source, this was held at a temperature of 58° C. and a humidity of 50%, and the weight loss after 2 months was evaluated. As a method for evaluating the biodegradation percentage, a sample having a weight loss value of 50% or more was rated as AA, a sample having a numerical value of weight loss of 40% or more and less than 50% was rated as A, and a sample having a weight loss value of less than 40% was rated as B. In the composite resin molded article according to Example 1, the biodegradation percentage of the test piece was 41%, and the evaluation thereof was A.
In Example 2, a cellulose composite PHBV resin molded article was produced under the same material conditions and process conditions as in Example 1 except that the volume ratio of the base resin, the natural fiber on which an enzyme was supported, and the coating resin was changed to 40:40:20. The evaluation was performed in the same manner as in Example 1.
In Comparative Example 1, a cellulose composite PHBV resin molded article was produced under the same material conditions and process conditions as in Example 1 except that the coating resin was not used, and the volume ratio of the base resin and the cellulose filler on which an enzyme was supported was changed to 19:81. The evaluation was performed in the same manner as in Example 1.
In Comparative Example 2, a PHBV composite resin molded article was produced under the same material conditions and process conditions as in Example 1 except that the natural fiber was not used, and the volume ratio of the base resin, the enzyme, and the coating resin was changed to 82.9:8.1:9. The evaluation was performed in the same manner as in Example 1.
In Comparative Example 3, a cellulose composite PHBV resin molded article was produced under the same material conditions and process conditions as in Example 1 except that the volume ratio of the base resin, the natural fiber on which an enzyme was supported, and the coating resin was changed to 10:40:50. The evaluation was performed in the same manner as in Example 1.
In Comparative Example 4, a PET fiber on which an enzyme was supported was produced using a PET fiber having a fiber diameter of 20 μm and a fiber length of 100 μm instead of softwood pulp. A PHBV composite resin molded article was produced under the same material conditions and process conditions as in Example 1 except for the above. The evaluation was performed in the same manner as in Example 1.
As is apparent from
As described above, it was confirmed that a composite resin having high elastic modulus, high durability, and high biodegradability was obtained when natural fibers on which an enzyme was supported on the surface were composited, at least a part of the surface of the natural fiber was coated with a water-soluble resin, the fibers were exposed on the surface of the composite resin molded article, and the water absorption rate of the natural fiber was high.
In Comparative Example 1 produced without using a coating resin, the elastic modulus was improved as compared with Comparative Example 2 due to the composite of the natural fibers, but the enzyme was not protected by the coating resin during molding, and the thermal damage of the enzyme during kneading and molding was large, so that the biodegradation rate was decreased as compared with Example 1, and the evaluation thereof was B.
In Comparative Example 2 produced without using natural fibers, water absorption into the inside of the composite resin molded article by the natural fibers did not proceed, so that the dissolution of PVA did not proceed, the biodegradation rate was decreased as compared with Example 1, and the evaluation thereof was B.
In Comparative Example 3 in which the volume ratio of the coating resin to the base resin was high, the dissolution of the water-soluble coating resin proceeded in the degradation test, the elastic modulus was decreased, and the evaluation of reduction rate of the elastic modulus was B.
In Comparative Example 4 produced using PET fibers instead of softwood pulp, the moisture content of the PET fibers was low and the water absorbency was absent, so that the dissolution of PVA did not proceed in the evaluation of the biodegradability, the biodegradation rate was decreased as compared with Example 1, and the evaluation thereof was B.
From the above evaluations, it was confirmed that a composite resin molded article having high elastic modulus, high durability, and high biodegradability was obtained when natural fibers having water absorbency and biodegradable plastics were used, an enzyme was supported on the surface of the natural fibers, at least a part of the surface of the fibers was coated with a water-soluble coating resin, and the fibers were exposed on the surface of the composite resin molded article. In addition, since the microorganisms and/or enzymes supported on the natural fibers are coated with the coating resin, the microorganisms and/or enzymes supported on the natural fibers can be protected from thermal damage caused by the molten base resin in melt-kneading during the production of the composite resin molded article.
Note that the present disclosure includes appropriate combination of arbitrary exemplary embodiments and/or examples among the various exemplary embodiments and/or examples described above, and effects of the respective exemplary embodiments and/or examples can be exhibited.
According to the composite resin molded article according to one aspect of the present disclosure, it is possible to realize a composite resin molded article having high elastic modulus and controlled biodegradation rate in a humid environment as compared with a resin alone.
The composite resin molded article according to one aspect of the present disclosure, it is possible to provide a molded article capable of controlling mechanical strength and biodegradation rate more than conventional biodegradable plastics. Since the properties of the base resin can be improved by the composite resin molded article according to one aspect of the present disclosure, the composite resin molded article according to one aspect of the present disclosure can be used as an alternative to petroleum-derived general-purpose plastics. Therefore, the environmental load of various industrial products or daily commodities made of petroleum-derived general-purpose plastics can be significantly reduced. Further, the composite resin molded article according to one aspect of the present disclosure can be used for packaging materials, daily necessities, housings for household electric appliances, building materials, and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-032074 | Mar 2022 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2022/035257 | Sep 2022 | WO |
| Child | 18811837 | US |
