Biodegradable resin microbeads

Abstract

To provide an ultraviolet inhibitor which overcomes weaknesses of ultraviolet scattering agents and ultraviolet absorbers that have been used conventionally, and which also reduces environmental load.SOLUTION: Biodegradable resin microbeads whose mean particle diameter is several hundreds nm to several hundreds μm are used as an ultraviolet screening agent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to microbeads made of biodegradable resins such as polylactic acid-based resins, starch-based resins, and cellulose-based resins. More specifically, the biodegradable resin microbeads according to the present invention have an ultraviolet ray blocking ability. [Background technology]

[0002] When plastic products are used outdoors, they are subject to deterioration such as deformation and discoloration due to sunlight (especially ultraviolet rays), rainwater, oxidation, and temperature changes. Therefore, plastic products are required to be weather resistant. In particular, when plastic products are exposed to ultraviolet light, the hydrogen atoms of the polymer material are broken down through absorption of the ultraviolet light, generating radicals. These radicals then combine with oxygen in the air to generate peroxy radicals, which then remove hydrogen atoms from the polymer to generate radicals and hydroperoxides. The radicals and hydroperoxides thus generated further accelerate the deterioration of plastic materials. UV rays break down the polymer, reducing its molecular weight, causing a drop in melting point and a deterioration in mechanical properties. It is common to see plastic products left outdoors lose their luster, discolor, and become brittle.

[0003] Therefore, it is important to take measures to prevent deterioration of plastic products due to ultraviolet rays. Considering the above mechanism, it is effective to use, as ultraviolet blocking agents, either (1) ultraviolet scattering agents that scatter ultraviolet rays and reduce the amount of ultraviolet rays that plastic products receive, or (2) ultraviolet absorbers that absorb ultraviolet rays and reduce their reaction with the materials of plastic products.

[0004] Inorganic substances such as titanium oxide and zinc oxide are primarily used as UV scattering agents. Organic substances such as ethylhexyl methoxycinnamate, ethylhexyl dimethyl para-aminobenzoate, and t-butyl methoxydibenzoylmethane are primarily used as UV absorbers for plastics. A major disadvantage of UV scattering agents is that they are white powders, causing plastic products to become cloudy. Furthermore, titanium oxide and zinc oxide are also photocatalytic materials, which can accelerate the deterioration of plastics due to UV rays (Non-Patent Document 1). On the other hand, a major disadvantage of UV absorbers is that they may affect the material as a side reaction of their own reaction. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Ge et al. Photocatalytic degradation of (micro)plastics using TiO2-based and other catalysts: Properties, influencing factors, and mechanism, Environmental Research, 209, 112729 (2022). Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an ultraviolet protection agent which overcomes the drawbacks of conventionally used ultraviolet scattering agents and ultraviolet absorbers. In recent years, marine microplastic pollution has become a major global issue. At the G7 Charlevoix Summit held in Canada in June 2018, the Ocean Plastics Charter was adopted to encourage countries to take measures to address the problem of marine pollution caused by plastic waste. Meanwhile, in Japan, the Ministry of the Environment formulated the Plastic Resource Circulation Strategy in May 2019 regarding microbead management, and the Act on Promotion of Plastic Resource Circulation (abbreviated as the Plastic Resource Circulation Promotion Act) came into effect in April 2022. The Plastic Resource Circulation Promotion Act aims to improve the circulation of plastic resources in Japan through cooperation and collaboration between all businesses, local governments, and consumers involved in the entire process of plastic products, from design to disposal (i.e., the life cycle of plastic products). [Means for solving the problem]

[0007] To address these problems, the present inventors have combined their own particle dispersion technology, cellulose nanofiber composite technology, and biodegradable resin technology to develop biodegradable resin microbeads with ultraviolet light blocking properties.

[0008] The present invention provides microbeads made of polylactic acid-based resin, starch-based resin, and cellulose-based biodegradable resin. These microbeads have an average particle size of several hundred nanometers to several tens of micrometers, and despite being organic, they exhibit ultraviolet light scattering properties.

[0009] More specifically, the present invention provides: (1) Biodegradable resin microbeads comprising a biodegradable resin or a biodegradable resin composition containing cellulose nanofibers; (2) The biodegradable resin is selected from the group consisting of polylactic acid (PLA), microbial polysaccharides such as pullulan and curdlan, polycaprolactone (PCL), starch-based biodegradable polymers, polyhydroxyalkanoates (PHAs) such as polyhydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), and polyhydroxybutyrate valerate (PBAV), and all biodegradable plastics derived from microorganisms; polyvinyl alcohol; polyamino acids; chitin and chitosan; all cellulose-based biodegradable plastics including cellulose acetate, hydroxyethyl cellulose (HEC), and hydroxypropyl methylcellulose (HPMC); polyglycolic acid; polyethylene terephthalate succinate (PETS); polybutylene succinate (PBS), and polybutylene adipate-co-terephthalate. (PBAT) and mixtures thereof; (3) Biodegradable resin microbeads according to (1) above, wherein the cellulose nanofibers are produced by a production method comprising, in this order, a step of subjecting wood pieces or wood chips, or pulp to a solvothermal treatment, a step of crushing the solvothermal-treated wood chips, and a step of subjecting the crushed wood chips to a chemical treatment to obtain cellulose nanofibers (CNF); (4) The biodegradable resin microbeads according to (3) above, wherein the solvothermal treatment is carried out under subcritical or supercritical conditions; (5) Biodegradable resin microbeads according to (3) or (4) above, wherein the wood chips or wood chips are those of softwood or hardwood; (6) Biodegradable resin microbeads according to any one of (3) to (5) above, wherein the chemical treatment is any treatment selected from the group consisting of oxidation, phosphate, acetic acid, and sulfation; (7) A molded article containing the biodegradable resin microbeads described in any one of (1) to (6) above; and (8) Cosmetics containing the biodegradable resin microbeads described in any one of (1) to (6) above. to provide. [Effects of the Invention]

[0010] According to the present invention, biodegradable resin microbeads having ultraviolet shielding properties are provided which reduce the disadvantages of both ultraviolet scattering agents and ultraviolet absorbers, which are representative of conventional ultraviolet shielding agents, and which also take environmental pollution into consideration, and which can be used in a variety of technical fields. DETAILED DESCRIPTION OF THE INVENTION

[0011] The biodegradable resin microbeads according to the present invention are made of a biodegradable resin composition containing a polylactic acid (PLA), starch, cellulose, or other biodegradable resin, or a biodegradable resin composition containing a composite material in which the biodegradable resin is combined with cellulose nanofibers. [Example]

[0012] 1. Biodegradable resin microbeads (1) Preparation of biodegradable resin Examples of biodegradable resins that can be used in the present invention include polylactic acid (PLA); microbial polysaccharides such as pullulan and curdlan; polycaprolactone (PCL); starch-based biodegradable polymers; all microbially derived biodegradable plastics including polyhydroxyalkanoates (PHAs) such as polyhydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), and polyhydroxybutyrate valerate (PBAV); polyvinyl alcohol; polyamino acids; chitin and chitosan; all cellulose-based biodegradable plastics including cellulose acetate, hydroxyethyl cellulose (HEC), and hydroxypropyl methylcellulose (HPMC); polyglycolic acid; polyethylene terephthalate succinate (PETS); polybutylene succinate (PBS), and polybutylene adipate-co-terephthalate (PBAT), and any and all biodegradable resins, and combinations thereof.

[0013] (2) Preparation of cellulose nanofibers The cellulose nanofibers (CNFs) of the present invention that can be used in biodegradable composite materials containing CNFs and biodegradable resins differ from those produced by conventional manufacturing methods (e.g., Patent Documents 4 and 5), and are obtained by solvothermal treatment of wood pieces the size of wood chips or the like, without any prior chemical treatment. More specifically, the CNF used in the present invention is produced by a manufacturing method including the steps of subjecting wood chips to solvothermal treatment, crushing the solvothermal-treated wood chips, and subjecting the crushed wood chips to chemical treatment. As used herein, solvothermal treatment refers to a treatment in which raw materials such as wood chips are immersed in a solvent and exposed to a subcritical to supercritical state under high-temperature and high-pressure conditions for a certain period of time, and is sometimes referred to as hydrothermal treatment when water is used as the solvent.

[0014] The wood chips used as raw materials in the above-mentioned production method may be any raw material from which natural cellulose can be extracted, for example, wood chips of broad-leaved trees or conifers, as well as herbaceous plants. The wood chips used in the present invention include wood chips preferably having a size of 0.5 x 0.5 cm to 2.0 x 2.0 cm, more preferably 0.7 x 0.7 cm to 1.5 x 1.5 cm, and most preferably 0.8 x 0.8 cm to 1.2 x 1.2 cm.

[0015] In the solvothermal treatment step of the above-described production method, raw wood chips or herbaceous materials are immersed in a solvent and subjected to subcritical to supercritical conditions under high temperature and pressure. Examples of solvents used here include water, pyrrolidone solvents such as methanol, ethanol, propanol, and N-methylpyrrolidone, acetate solvents such as butyl acetate, glycol ether solvents such as diethylene glycol monomethyl ether, ketone solvents such as methyl ethyl ketone, aromatic solvents such as toluene and xylene, and hydrocarbon solvents such as paraffin. The immersed wood chips are then treated at 1 to 300 atmospheres and up to 400°C, preferably 2 to 250 atmospheres and 5 to 350°C, more preferably 25 to 100 atmospheres and 100 to 300°C, and preferably 40 to 80 atmospheres, for 60 to 180 minutes at a temperature ranging from 150 to 250°C, where the temperature is in the subcritical to supercritical state. These solvothermal treatments turn chips into a soft, swollen, pulverized wood material. The production method of the present invention is characterized by subjecting wood chips directly to the solvothermal treatment process. While conventional CNF production methods first chemically treat wood chips, the above production method is characterized by subjecting cellulose raw materials of a certain size, such as wood chips, to solvothermal treatment first without chemical treatment. When mixed with resin, CNF produced by this production method improves the physical properties of composite materials.

[0016] Next, the obtained pulverized wood is subjected to a crushing process to further reduce the pulp of the pulverized wood. This crushing process can be performed using a ball mill, disc mill, wet cutter mill, pressure homogenizer, etc. This crushing process reduces the wood to smaller pulverized wood particles of 0.05 to 0.5 mm.

[0017] Finally, the crushed wood pulverized material is chemically treated. Examples of chemical treatments include oxidation treatment, hydrolysis treatment, base treatment, or a combination thereof. For oxidation treatment, oxidizing agents such as ozone, hypochlorous acid, acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid or a salt thereof, persulfuric acid or a salt thereof, and perorganic acid or a salt thereof can be used. For this oxidation treatment, an oxidation catalyst such as an N-oxyl compound can be used in combination. For hydrolysis treatment, hydrolases such as cellulase enzymes and hemicellulase enzymes can be used. For base treatment, caustic soda, KOH, etc. can be used.

[0018] Lignin can also be added to wood chips or the like before the solvothermal treatment. Adding lignin hydrophobizes the surface of the resulting CNF (hydrophobized CNF). A composite material produced by mixing hydrophobized CNF with resin is preferable because it has higher tensile strength than a composite material made with non-hydrophobized CNF without lignin. The mixing ratio of wood pulverized material to lignin (wood pulverized material / lignin by weight) is preferably 0.5 to 2, preferably 0.7 to 1.5, and more preferably 0.8 to 1.2. (3) Preparation of microbeads Either polylactic acid (PLA), starch-based biodegradable polymer, or cellulose acetate biodegradable resin was ground in a grinder such as a food processor. After that, large biodegradable resin particles were passed through a mesh to remove them, and only biodegradable resin beads with the target average particle size (0.3-500 μm) were selected to prepare control biodegradable resin microbeads. Wood, wood chips, pulp, etc. that had been subjected to solvothermal oxidation treatment were mixed with biodegradable resins such as polylactic acid (PLA), starch-based biodegradable polymers, or cellulose acetate in a twin-screw extruder, as described above, and composited. The biodegradable resin composited with CNF was then pulverized in a grinder such as a food processor. Larger biodegradable resin particles were then passed through a mesh to remove them, and only biodegradable resin beads with the target average particle size (0.3 to 500 μm) were selected to produce CNF-composite biodegradable resin microbeads. The average particle size was measured using a laser diffraction / scattering particle size distribution analyzer manufactured by Microtrac, with the sample suspended in water as a dispersion medium so that the sample concentration was 0.5% by weight.

[0019] 2. Plastic products The effect of the biodegradable resin microbeads of the present invention on plastic products will be confirmed. The biodegradable resin microbeads obtained above were added to thermoplastic resins and thermosetting resins (acrylic, polycarbonate, vinyl chloride, polyethylene) used to mold plastic products, and mixed by kneading with a twin-screw extruder or stirring with various stirrers to obtain various resin materials containing biodegradable resin microbeads.

[0020] Using a HAAKE (trademark) MiniJet Pro Piston Injection Molding System from Thermo Fisher, the various biodegradable resin microbead-containing resin materials were molded into flat plates (20 mm long x 30 mm wide, 0.2 mm thick).

[0021] The reflectance spectra of the flat plates of the resin material containing the various biodegradable resin microbeads were obtained by the reflectance method (specular reflection) using a V-700 series ultraviolet-visible-near-infrared spectrophotometer manufactured by JASCO Corporation. The reflectance of all the flat plate samples was good, ranging from 60 to 90%.

[0022] 3. Cosmetics Such ultraviolet screening agents can also be used in cosmetics for absorbing ultraviolet light. For example, microbeads with average particle sizes ranging from several micrometers to several hundred micrometers are used as scrubbing agents in various personal care and skin care products, such as facial cleansers, body shampoos, toothpastes, sunscreens, and boosters. The microbeads used in scrubbing agents have traditionally been made from natural materials such as crushed seeds and shells of almonds, walnuts, and rice bran, pigments such as silica, semi-synthetic materials such as crystalline cellulose, and synthetic materials such as polyethylene, polypropylene, polystyrene, and polyvinyl chloride. Previously, these materials were hard and irregularly shaped, posing a risk of skin damage. Subsequently, spherical resin particles with smooth surfaces were developed, enabling stable formulations. Microbeads made from these synthetic resins became mainstream. However, scrubbing agents made from synthetic resins, such as polyethylene and polypropylene, are discharged in huge quantities into sewers from baths, showers, and toilets around the world every day, contributing significantly to marine microplastic pollution. Therefore, in the field of cosmetics containing microbeads that constitute scrubbing agents, research and development is being conducted into replacing the material of the microbeads with biodegradable resins.

[0023] Therefore, the effects of the biodegradable resin microbeads according to the present invention on cosmetics will be confirmed. 5g of each of the biodegradable resin microbeads obtained above was added to 100g of booster (an item that is applied as the first step in skin care after washing the face to prepare the skin's foundation, soften the skin, and make it easier to feel the effects of cosmetics used later), and the mixture was mixed by stirring using various stirrers to obtain various cosmetics containing biodegradable resin microbeads.

[0024] The absorption spectrum of any of the above cosmetics containing biodegradable resin microbeads was obtained using a V-700 series ultraviolet-visible-near-infrared spectrophotometer manufactured by JASCO Corporation, and the absorbance was measured at 290 / 320 / 350 / 380 nm. The index of absorbance of the booster containing biodegradable resin microbeads is the rate of change, with the absorbance of the booster without biodegradable resin microbeads set at 1. The measurement results are summarized in Table 1.

[0025] [Table 1]

[0026] In this way, simply adding biodegradable resin microbeads to conventional cosmetics improved their UV absorption ability, and when they were combined with the cellulose nanofibers developed by the inventors, the UV absorption ability was further increased.

[0027] The average particle size of the biodegradable resin microbeads according to the present invention is several hundred nm to several hundred μm, which is about 1 / 10 to 1 times the size of conventional scrubbing agents (average particle size = several μm to several hundred μm), and therefore exhibits ultraviolet scattering ability while maintaining the scrubbing effect. Furthermore, the biodegradable resin microbeads of the present invention do not suffer from the problems of inorganic UV scattering agents being weak to sweat, being less effective, not blending well with the skin and being sticky, or leaving a whitish cast, and do not place a burden on the skin as occurs when UV absorbers based on photochemical reactions are used. [Industrial Applicability]

[0028] The biodegradable resin microbeads according to the present invention can be applied to various products such as plastic products and cosmetics to protect against the effects of ultraviolet rays, and furthermore, can reduce the environmental load.

Claims

1. Biodegradable resin microbeads comprising a biodegradable resin or a biodegradable resin composition containing cellulose nanofibers.

2. The biodegradable resin may be any of polylactic acid (PLA), microbial polysaccharides such as pullulan and curdlan, polycaprolactone (PCL), starch-based biodegradable polymers, polyhydroxyalkanoates (PHAs) such as polyhydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polyhydroxybutyrate valerate (PBAV), and other biodegradable plastics derived from microorganisms, polyvinyl alcohol, polyamino acids, chitin and chitosan, cellulose-based biodegradable plastics including cellulose acetate, hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC), and other biodegradable plastics, polyglycolic acid, polyethylene terephthalate succinate (PETS), polybutylene succinate (PBS), and polybutylene adipate-co-terephthalate.

2. The biodegradable resin microbeads according to claim 1, selected from the group consisting of (PBAT) and mixtures thereof.

3. The biodegradable resin microbeads according to claim 1, wherein the cellulose nanofibers are produced by a production method comprising, in this order, a step of subjecting wood pieces or wood chips, or pulp to solvothermal treatment, a step of crushing the solvothermal-treated wood chips, and a step of subjecting the crushed wood chips to chemical treatment to obtain cellulose nanofibers (CNF).

4. The biodegradable resin microbeads according to claim 3, wherein the solvothermal treatment is carried out under subcritical or supercritical conditions.

5. 5. Biodegradable resin microbeads according to claim 3 or 4, wherein the wood chips are wood chips or wood chips of softwood or hardwood.

6. 4. The biodegradable resin microbeads according to claim 3, wherein the chemical treatment is any treatment selected from the group consisting of oxidation, phosphation, acetic acid, and sulfation.

7. A molded article comprising the biodegradable resin microbeads according to claim 1.

8. A cosmetic product containing the biodegradable resin microbeads according to claim 1.

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