Biomass-resin composite and method for producing same

Abstract

This biomass-resin composite has non-chemically modified biomass nanofibers dispersed in at least one resin, and does not contain, as a dispersant, a dispersant soluble in water or a water-soluble alcohol other than the biomass nanofibers.

Description

Biomass Resin Composite and Method for Producing the Same

[0001] The present invention relates to a biomass resin composite which is a composite of biomass nanofibers having excellent dispersibility and a resin, and a method for producing the same.

[0002] Biomass nanofibers typified by cellulose nanofibers and chitin nanofibers are natural polymers composed of polysaccharides, and can be obtained by mechanically treating raw materials such as cellulose and chitin to perform microfibrillation. Since biomass nanofibers have excellent properties such as low weight, high strength, and high elasticity, many attempts have been made to improve the physical properties of the resin by mixing it with other materials, particularly resins.

[0003] Since a hydrophilic portion exists on the surface of biomass nanofibers and they are compatible with water, it is reasonable to disperse them in water in order to maintain the nanofibered structure, and many are provided as aqueous dispersions.

[0004] As described above, biomass nanofibers are compatible with water, while many resins are hydrophobic substances. Therefore, in mixing them, it has been an issue to uniformly disperse biomass nanofibers in the resin, and various studies have been made. For example, when water is removed from the aqueous dispersion of biomass nanofibers during mixing, the biomass nanofibers may aggregate with each other and the effect of nanofiber formation may be lost, or separation from the resin may occur.

[0005] In Patent Document 1, a method of powdering while suppressing aggregation in a drying process without performing special chemical modification or the like has been reported, and it is described that the dried product of biomass nanofibers obtained thereby can be highly dispersed in a hydrophobic resin.

[0006] Further, in Non-Patent Document 1, it has been reported that the polymerization of polystyrene was attempted by suspension polymerization in an aqueous dispersion of cellulose nanofibers that had not been chemically modified.

[0007] On the other hand, in order to mix biomass nanofibers with resin, it is also being considered to chemically modify the biomass nanofibers by changing the hydroxyl groups on the surface of the biomass nanofibers to other functional groups, thereby suppressing aggregation between biomass nanofibers and facilitating mixing with resin.

[0008] Patent Document 2 reports a method for obtaining a high-strength composite in which cellulose nanofibers are uniformly dispersed in a copolymer by copolymerizing ethylenically unsaturated monomers in a cellulose nanofiber dispersion made from chemically treated cellulose. In this method, an emulsifier is used to ensure that the polymerization of monomers is uniform in the reaction solution, and as a result, the dispersed anionically modified cellulose nanofibers and copolymer form a composite.

[0009] Japanese Patent Publication No. 2019-131772 Japanese Patent Publication No. 2016-155897

[0010] ACS Appl. Mater. Interfaces 2016, 8, 21, 13520-13525

[0011] Although the method described in Patent Document 1 allows for the dispersion of biomass nanofibers in a hydrophobic resin, it presents challenges due to the added step of drying and pulverizing the biomass nanofibers, which are generally provided as an aqueous dispersion, using a special method, and the burden of the process of blending organic components with the biomass nanofibers. Furthermore, compounding with resin requires the use of mixing methods commonly found in general compounding, and the use of compatibilizers is common. In compounding of thermally molten polymers and biomass nanofibers, it can be difficult to determine whether the nanofibers are dispersed under a microscope if voids are present.

[0012] Non-patent document 1 attempts to composite unmodified cellulose nanofibers with polystyrene, but reports that a sufficient composite product could not be obtained. In reactions in which polymerization is initiated by a polymerization initiator, the outcome of polymerization depends on where the polymerization initiator acts. The polymerization initiator used in Non-patent document 1 was AIBN (azobisisobutyronitrile), and since it is supported on cellulose nanofibers, which are used as a dispersant, it is thought that a large proportion of it migrates into the monomer droplets. However, polymerization on the dispersant and polymerization in the monomer droplets have different polymerization rates, and these rates also vary depending on the type of monomer, which is why a good composite product could not be obtained.

[0013] Methods such as those described in Patent Document 2, which involve chemically modifying biomass nanofibers and using emulsifiers to disperse hydrophobic monomers in an aqueous solvent, require chemicals, emulsifiers, and processes for the chemical modification, which often leads to increased costs and the burden of process control to ensure dispersibility.

[0014] This invention has been made in view of the above circumstances, and aims to provide a biomass resin composite in which biomass nanofibers dispersed in water do not require chemical modification, while maintaining their structure, and a method for producing the same.

[0015] Based on the concept of polymerization using a dispersant as the polymerization site (dispersion polymerization), the inventors discovered that unmodified biomass nanofibers themselves can function as a dispersant. They found that by polymerizing monomers in an aqueous dispersion of these nanofibers without using other dispersants soluble in water or water-soluble alcohol, a biomass resin composite that maintains the nanofiber structure can be obtained, leading to the present invention.

[0016] Accordingly, the present invention provides the following biomass resin composites and methods for producing the same: [1] A biomass resin composite in which chemically unmodified biomass nanofibers are dispersed in at least one resin, and which does not contain a dispersant other than the biomass nanofibers that is soluble in water or water-soluble alcohol as a dispersant. [2] The biomass resin composite according to [1], wherein the biomass nanofibers are at least one selected from cellulose nanofibers and chitin nanofibers. [3] The biomass resin composite according to [1] or [2], wherein the monomer forming the resin is liquid at room temperature or soluble in water at room temperature. [4] The biomass resin composite according to [3], wherein the monomer is at least one selected from vinyl aromatic compounds and vinyl esters. [5] The biomass resin composite according to [4], wherein the monomer is methyl methacrylate and styrene monomer. [6] The biomass resin composite according to [4] or [5], further comprising another type of monomer. [7] A resin composition obtained by kneading the biomass resin composite described in [1] above with a resin. [8] The resin composition according to [7] above, wherein the resin kneaded with the biomass resin composite is a different resin from the resin in the biomass resin composite, and further comprises a compatibilizer. [9] The resin composition according to [8] above, wherein the resin kneaded with the biomass resin composite is a thermoplastic resin.

[10] A method for producing a biomass resin composite, comprising mixing at least one monomer and a polymerization initiator soluble in water with an aqueous dispersion of unmodified biomass nanofibers and polymerizing them.

[11] The method for producing a biomass resin composite according to

[10] above, wherein the polymerization initiator soluble in water is a persulfate.

[12] The method for producing a biomass resin composite according to

[10] or

[11] above, wherein the biomass nanofiber is at least one selected from cellulose nanofibers and chitin nanofibers.

[13] A method for producing a biomass resin composite according to any one of

[10] to

[12] above, wherein the monomer is liquid at room temperature or soluble in water at room temperature.

[14] A method for producing a biomass resin composite according to any one of

[10] to

[13] above, wherein the aqueous dispersion of unmodified biomass nanofibers is obtained by mechanical defibration of an aqueous mixture of biomass, and no additional chemical modification treatment is performed.

[15] A method for producing a biomass resin composite according to any one of

[10] to

[14] above, wherein the polymerization temperature is above the freezing point and below the boiling point of the aqueous dispersion.

[16] A method for producing a biomass resin composite according to any one of

[10] to

[15] above, wherein a monomer other than the monomer is mixed after the start of polymerization.

[17] A method for producing a resin composition, comprising mixing at least one monomer and a polymerization initiator soluble in water with an aqueous dispersion of unmodified biomass nanofibers, polymerizing the mixture, and further kneading a resin into the resulting biomass resin composite.

[18] A method for producing a resin composition according to

[17] above, wherein the kneading of the biomass resin composite and the resin is performed by adding the biomass resin composite to a thermoplastic resin and subjecting it to thermal melting and mechanical shearing.

[0017] According to the present invention, a biomass resin composite in which biomass nanofibers are uniformly dispersed in the resin can be manufactured in a low-cost and labor-saving process.

[0018] (a) An image of the biomass resin composite obtained in Example 1, taken with an electron microscope at a magnification of 20,000x. (b) An image of (a) magnified by approximately 5x. (a) An image of the dried product from the aqueous dispersion of cellulose nanofibers obtained in Example 1, taken with an electron microscope at a magnification of 20,000x. (b) An image of (a) magnified by approximately 5x. Results of thermal differential analysis of the biomass resin composite obtained in Example 2. Results of thermal differential analysis of the biomass resin composite obtained in Comparative Example 1, (a) the filtered portion and (b) the portion with the stirring bar attached. Results of measuring the tensile strength of the film sample obtained in Example 5.

[0019] The biomass resin composite of the present invention is a biomass resin composite in which chemically unmodified biomass nanofibers are dispersed in at least one type of resin, and does not contain any dispersant other than the biomass nanofibers that is soluble in water or water-soluble alcohol.

[0020] The process of dividing fibrous material in the direction of its fiber alignment is called fibrillation (or defibrillation). The smallest units created by bundling the molecules that make up biomass due to their crystalline properties are usually called microfibrils or nanofibers, but in this invention, they are referred to as nanofibers. In particular, nanofibers formed by fibrillating biomass such as cellulose and chitin are called biomass nanofibers.

[0021] Cellulose is found in wood pulp, cotton, linters, hemp, bacterial cellulose, and the fibrous material contained in parenchyma cells. While there are no particular limitations on the raw materials used for the nanofibers in this invention, it is preferable to use crystalline cellulose from which lignin and hemicellulose have been removed as the raw material, from the viewpoint of suitably performing microfibrillation.

[0022] Chitin is a fibrous material found in the exoskeletons of crustaceans such as crabs, shrimp, and krill, as well as insects, the midbones and cartilage of cephalopods such as squid and octopus, the cell walls of microorganisms, and mushrooms. The chitin used in this invention is not particularly limited, but deproteinized and decalcified chitin is preferred. Chitosan, obtained by hydrolyzing chitin, can also be used.

[0023] In this invention, biomass nanofibers obtained from cellulose as described above are referred to as cellulose nanofibers, and biomass nanofibers obtained from chitin as described above are referred to as chitin nanofibers. The biomass nanofibers used in this invention are preferably at least one selected from cellulose nanofibers and chitin nanofibers.

[0024] The above-mentioned method for producing biomass nanofibers (microfibrillation method) typically involves dispersing the raw material biomass in water to form a slurry, i.e., a biomass-water mixture, and then physically separating it in the fiber direction using mechanical defibrillation methods such as high-pressure homogenizers, disc mills, and ball mills. Specific methods that can be employed to apply these physical forces include, in the case of high-pressure homogenizers, a type that utilizes the shear force generated when the pressure is released by adjusting the flow channel diameter with a valve opening, resulting in shear force from the impact of the pressure colliding with the valve and subsequent pressure release (valve type, e.g., LAB1000 / 2000 manufactured by SMT Corporation), and a type that applies pressure through turbulence generated by flow diversion intersection (nozzle type, e.g., NanoMeister manufactured by Okawara Seisakusho Co., Ltd., NanoVaster series manufactured by Yoshida Machinery Industry Co., Ltd.). There is also a type that causes opposing flow diversions to collide (underwater counter-collision type, e.g., Starburst series manufactured by Sugino Machine Co., Ltd.). In the case of disc mills, one method is to pulverize the raw material slurry by passing it between two grinding wheels using a grinder or crusher (e.g., Super Mascolloider manufactured by Masuko Sangyo Co., Ltd.). The above methods are merely examples of fibrillation methods, and the method is not limited to any method as long as nanofibers can be created.

[0025] The mechanical fibrillation of biomass as described above allows for adjustment of the degree of fibrillation by adjusting the number of passes. The degree of fibrillation affects the dispersibility of the nanofibers in water. The diameter of the biomass nanofibers of the present invention is usually 3 nm or more, and is often between 10 nm and 50 nm depending on the degree of fibrillation, but is not particularly limited. The diameter of the biomass nanofiber is the diameter of the cross-section perpendicular to the length direction. When the diameter of the nanofibers is within the above range, the viscosity of the aqueous dispersion also increases, so the slurry concentration of the biomass raw material is preferably 10% by weight or less, and more preferably 3% by weight or less, depending on the microfibrillation method. Within this range, compounding with resin can be carried out smoothly. Not chemically modified biomass nanofibers are those obtained by the above method, without undergoing additional chemical modification steps, and can be obtained as an aqueous dispersion of biomass nanofibers.

[0026] A commonly used chemical modification is TEMPO oxidation, which is performed before cellulose defibrillation. This process converts the hydroxyl groups of cellulose molecules on the surface of cellulose microfibrils into carboxyl groups through oxidation, thereby facilitating the separation between microfibrils. The amount of carboxyl groups in the resulting cellulose nanofibers can reach, for example, 1.3 mmol / g (pulp). In contrast, the amount of carboxyl groups in unmodified cellulose nanofibers is significantly lower, for example, less than 0.1 mmol / g (pulp). When the amount of carboxyl groups is high, compounding with resin through polymerization may not be successful.

[0027] The biomass resin composite of the present invention can be obtained by adding a monomer and a polymerization initiator to an aqueous dispersion in which biomass nanofibers as described above are dispersed in water and polymerizing it.

[0028] The polymerization method of the present invention does not use emulsifiers and therefore differs from emulsion polymerization. Furthermore, in monomer polymerization, the presence of a substance that acts as a nucleation site for polymerization initiation facilitates polymerization; this is sometimes referred to as seed polymerization or dispersion polymerization. However, in such methods, the nucleation site for polymerization initiation needs to have affinity for the monomer and be dispersed in the solvent. In contrast, the present invention allows polymerization to proceed even if the monomer does not exhibit sufficient affinity for biomass nanofibers. The polymerization method of the present invention utilizes biomass nanofibers as a dispersant, differing from the known methods described above. This method of the present invention does not require chemical modification of the biomass nanofibers and does not require a dispersant soluble in water or water-soluble alcohol other than the biomass nanofibers. In the present invention, an emulsifier refers to a substance that forms micelles through emulsification and is intended for use in dispersing monomer droplets into a dispersion (polymerization solution). A dispersant, on the other hand, does not form micelles itself but helps disperse other substances and is itself dispersed in the solvent. Furthermore, the compatibilizers described later are materials that mediate between resins, and include copolymers (graft resins, etc.) that combine each resin into a single material.

[0029] In reactions in which polymerization is initiated by a polymerization initiator, as described above, the outcome of polymerization and the properties of the polymer are determined by where the polymerization initiator acts. Both emulsion polymerization and suspension polymerization control the polymerization reaction by dispersing monomer droplets in water, but the difference in the polymer is caused by whether the polymerization initiator is in the water or in the monomer droplets. In the present invention, biomass nanofibers are dispersed in water, and the biomass nanofibers support the polymerization initiator. With this configuration, polymerization occurs near the biomass nanofibers, forming a composite with the polymer. If the polymerization initiator migrates into the monomer droplets during this polymerization, polymers will also be formed there. In this case, if these are recovered, the composite with the biomass nanofibers and the polymers in the monomer droplets will be mixed, and a sufficient composite will not be obtained. The polymerization initiator used in Non-Patent Document 1 mentioned above was AIBN, which, unlike the present invention, is thought to have been a polymerization initiator that migrated into the monomer droplets. In this invention, good compounding was achieved by using a polymerization initiator that is soluble in water.

[0030] The monomers used in this invention can be monomers commonly used in polymerization and are not particularly limited, but examples include methyl acrylate (melting point -75°C, boiling point 80°C), methyl methacrylate (melting point -48°C, boiling point 100°C), ethyl acrylate (melting point -71°C, boiling point 99°C), ethyl methacrylate (melting point -75°C, boiling point 120°C), and n-butyl acrylate (melting point -64.6°C, boiling point 14°C). (meth)acrylic acid esters such as n-butyl methacrylate (melting point -50°C, boiling point 163°C), 2-ethylhexyl acrylate (melting point -90°C, boiling point 213.5°C), and 2-ethylhexyl methacrylate (melting point -50°C, boiling point 218°C); vinyl esters such as vinyl acetate (melting point -93.2°C, boiling point 72°C), vinyl propionate (melting point -80°C, boiling point 95°C), and tertiary vinyl carboxylates; Aromatic vinyl compounds such as styrene (melting point -30°C, boiling point 145°C), α-methylstyrene (melting point -23°C, boiling point 166°C), vinyltoluene (melting point -77°C, boiling point 170°C); acrylonitrile (melting point -84°C, boiling point 77°C), ethyl vinyl ether (melting point -115°C, boiling point 36°C), methyl vinyl ketone (melting point -7°C, boiling point 81°C), vinylacetamide (melting point 54°C, boiling point 96°C), vinyl chloride Vinylidene halides such as 175°C (melting point -153.7°C, boiling point -13.3°C), vinylidene chloride (melting point -122°C, boiling point -32°C), and vinylidene fluoride (melting point -144°C, boiling point -82°C); α-olefins such as ethylene (melting point -169.2°C, boiling point -104°C) and propylene (melting point -185°C, boiling point -48°C); and dienes such as butadiene (melting point -109°C, boiling point -4°C) can be used.

[0031] Furthermore, esterified compounds such as acrylic acid (melting point 14°C, boiling point 141°C), methacrylic acid (melting point 16°C, boiling point 159°C), itaconic acid (melting point 172°C, soluble in water, upper limit concentration 8.3% by weight), maleic acid (melting point 131°C, solubility in water 78 g / 100 ml), fumaric acid (melting point 300°C, solubility in water 0.63 g / 100 ml), crotonic acid (melting point 71.5°C, boiling point 169°C, solubility in water 94 g / kg), dimethyl maleate (melting point -18°C, boiling point 201°C); and esterified compounds such as maleic anhydride (melting point 53°C, boiling point 202°C), itaconic anhydride, etc. Ruboxyl group-containing monomers; α,β-ethylenically unsaturated acid amides such as acrylamide (melting point 84.5°C, solubility in water 204 g / 100 ml), methacrylamide (melting point 111°C, boiling point 225°C, solubility in water 202 g / L), maleamide (melting point 166°C, slightly soluble in water); glycidyl group-containing monomers such as glycidyl methacrylate (melting point -41.5°C, boiling point 189°C), allyl glycidyl ether (melting point -100°C, boiling point 154°C); 2-hydroxylethyl acrylate (melting point -60.2°C, boiling point 191°C), Hydroxyl group-containing monomers such as 2-hydroxylethyl methacrylate (melting point -60°C, boiling point 67°C); amino group-containing monomers such as dimethylaminoethyl methacrylate (melting point -30°C, boiling point 186°C); substituted amides of unsaturated carboxylic acids such as N-methylolacrylamide (melting point 75°C, boiling point 277°C, solubility in water 188 g / 100 ml), N-methylolmethacrylamide (melting point -37°C, boiling point 100°C, solubility in water 600 g / L), and diacetoneacrylamide (melting point 57°C, boiling point 120°C, readily soluble in water); 3-methacryloxy Silane compounds containing unsaturated bonds, such as propyltrimethoxysilane (KBM-503, manufactured by Shin-Etsu Chemical, liquid at room temperature, boiling point 255°C); monomers having two or more unsaturated bonds in one molecule, such as diallylphthalate (melting point -70°C, boiling point 290°C), divinylbenzene (melting point -52°C, boiling point 195°C), allyl methacrylate (melting point -75°C, boiling point 141°C), trimethylolpropane trimethacrylate (melting point -25°C, boiling point 200°C), and ethylene glycol dimethacrylate (melting point -75°C, boiling point 80.7°C), can also be applied.

[0032] Among these monomers, monomers that are liquid at room temperature or soluble in water at room temperature are preferred because they facilitate mechanical mixing during polymerization and make it easier to obtain resin composites in which biomass nanofibers are uniformly dispersed in the resin. Here, "room temperature" usually refers to a range of 20 to 25°C. Furthermore, monomers that are liquid at the polymerization temperature, regardless of their solubility in water, are even more preferred.

[0033] Among such monomers, it is preferable to use at least one monomer selected from vinyl aromatic compounds and vinyl esters from the viewpoint of polymerization control.

[0034] The monomers mentioned above may be polymerized individually or as a mixture of multiple types. The method of polymerization is not particularly limited; for example, one type of monomer can be polymerized first, and then another type of monomer can be added and polymerized. Furthermore, from the viewpoint of dispersibility, it is preferable to divide the monomer to be added into fixed amounts and add them as the polymerization progresses.

[0035] The monomers mentioned above may be selected to have a composition that facilitates miscibility when further kneading with resin after forming the biomass resin composite described later. While the specific composition can be selected as appropriate and is not limited, polystyrene produced when styrene is selected as the monomer is preferred because it is easily miscible with various resins. As an example, it is preferable to select methyl methacrylate and styrene as monomers and form a copolymer through biomass resin compounding.

[0036] In this invention, polymerization preferably proceeds in the form of particles stabilized as colloids in water. In this state, the mixing ratio of biomass nanofibers and polymers between particles can be kept constant. Similarly, it is preferable that the particles become mixable in water through mechanical operations such as stirring or shaking. To achieve this, it is preferable that the total concentration of monomers in the aqueous dispersion be 30% by weight or less, so as not to make the density of the polymers excessively high. However, this range is not limited as it depends on the type of monomer, the degree of polymerization, and the conversion rate, and as long as the particles can be dispersed in water through mechanical operations such as stirring or shaking during polymerization.

[0037] The polymerization initiator used in this invention can be any that is commonly used in polymerization. Polymerization in this invention preferably uses a polymerization initiator that generates radicals. Examples of radical polymerization initiators include thermal polymerization initiators and photopolymerization initiators, and are not particularly limited, but thermal polymerization initiators are preferred from the viewpoint of productivity. As mentioned above, since the composite formation using biomass nanofibers as a dispersant is carried out in water, and the polymerization is carried out in the vicinity of the dispersant, polymerization initiators used in emulsion polymerization that are soluble in water are preferred.

[0038] Specific examples of polymerization initiators include organic peroxides such as benzoyl peroxide (abbreviated as BPO), methyl ethyl ketone peroxide (abbreviated as MEKP), and cumene hydroperoxide (abbreviated as CHP); persulfates such as potassium peroxodisulfate (abbreviated as KPS, also known as potassium persulfate), ammonium persulfate, and sodium persulfate; 2,2'-azobis(2-amidinopropane) dihydrochloride (also known as V-50), 4,4'-azobis(4-cyanovaleric acid) (also known as V-501), and azo-based initiators such as water-soluble 2,2'-azobis[2-(imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[2-(carboxyethyl)propane] dihydrochloride, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride.

[0039] In the present invention, from the viewpoint of using a polymerization initiator that matches the difference in polymerization temperature and polymerization rate between monomers, persulfates are preferably used as polymerization initiators from among the above-mentioned compounds, and among them, potassium peroxodisulfate is preferably selected.

[0040] Radical polymerization can also be performed as redox polymerization, which involves combining a reducing agent to control the generation of radicals. Examples include a binary system with CHP and iron(divalent) ions, a ternary system with CHP, iron(divalent) ions, and tetraethylenetetraamine, a combination of CHP, iron(divalent) ions, ethylenediaminetetraacetic acid, and hydrazine, and a quaternary system with KPS, iron(divalent) ions, ethylenediaminetetraacetic acid, and sodium formaldehyde hyposulfite.

[0041] The amount of polymerization initiator added can be adjusted as appropriate according to the type of polymer to be obtained as a biomass resin composite, and is not particularly limited. For example, 0.1 to 10 parts by weight of radical polymerization initiator can be used per 100 parts by weight of monomer. Parts by weight is indicated in comparison to the weight of the value, and the same number of parts by weight means that the same weight is given. Depending on the polymerization time, an additional amount of the same amount of polymerization initiator may be added to replenish the amount consumed. The polymerization temperature also needs to be adjusted according to the type of polymer to be obtained, and is not particularly limited. For example, from the viewpoint of using an aqueous dispersion of biomass nanofibers, it is preferable that the temperature is above the freezing point of water and below the boiling point, more preferably 30°C to 90°C, and even more preferably 40°C to 70°C.

[0042] As described above, the biomass nanofibers in the present invention are obtained as an aqueous dispersion, to which monomers and polymerization initiators necessary for polymerization are added to carry out polymerization. Before polymerization, water may be added to dilute the aqueous dispersion of biomass nanofibers to the required concentration. In addition, solvents that are miscible with water, such as alcohols like methanol and ethanol, ketones like acetone, amide solvents like dimethylformamide and dimethylacetamide, and solvents like dimethyl sulfoxide and acetonitrile may be added to control polymerization.

[0043] In the polymerization of the present invention, it is preferable to stir the polymerization solution. Even for monomers that are insoluble in water as the polymerization medium, stirring is effective for a small amount of solubility and the transfer to polymerization nuclei due to its diffusion. However, although this is an operation that affects the progress of polymerization, it is not an operation that determines polymerization. Therefore, as long as it is a physical or mechanical operation such as stirring by a stirring blade, stirring by a water flow pump, shaking of the reaction vessel, or by ultrasonic waves, the method is not limited.

[0044] The method for recovering the biomass resin composite after polymerization in the present invention is not particularly limited. However, since its processing and subsequent kneading with the resin can be performed well, it is preferable to dehydrate by filtration and then dry. The filtration operation is not particularly limited, and examples include vacuum filtration dehydration, sealed pressure filtration, filter press, centrifugal filtration dehydration, decanter type centrifugal dehydration, centrifugal thin film evaporation, belt press, screw press, rotary pressure dehydration, multiple disk dehydration, etc.

[0045] In addition, a step of washing the polymerization solution with water may be added in combination with the filtration operation. In order to perform the water washing a predetermined number of times, a step by centrifugation can also be added. Similarly, a method of adding alcohols, etc. and replacing them to facilitate drying can also be applied. In addition, filtration drying can also be performed as one step. Specifically, spray drying or freeze drying can also be performed to obtain a dried product.

[0046] Analysis of the biomass nanofibers and resin components contained in the obtained biomass resin composite is an important factor in determining the properties of the biomass resin composite and can ensure its quality when considering repeated manufacturing for commercialization. For example, acid decomposition is generally used as a quantitative method for cellulose nanofibers. On the other hand, in the present invention, weight change measurement by thermal decomposition can be suitably applied as a method for determining the biomass nanofiber fraction, resin fraction, and copolymerization ratio contained in the biomass resin composite. The specific procedure of this method is as follows: First, the weight change of a biomass resin composite sample is measured at a constant heating rate to determine the temperature at which the rate of change for each component is maximum. Subsequently, the heating is stopped at a temperature lower than the temperature at which each component's weight change is maximum, and higher than the temperature at which the weight change of another component is maximum on the low-temperature side, and the measurement conditions are set to heat at a constant temperature. The temperature holding time should be set according to the expected ratio of each component that can be calculated from the amount of material used. By performing this operation, the weight ratio of each component can be obtained from the difference between the temperature at which the weight change is maximum and the thermal decomposition temperature. This method makes it possible to distinguish between components with similar thermal decomposition temperatures in a way that is practical for real-world use.

[0047] The success or failure of polymerization can also be determined by the filtration properties after polymerization of the obtained biomass resin composite. The biomass nanofiber fraction contained in the biomass resin composite can be determined using the exemplified method. If the amount of biomass resin composite produced by the filtration operation is close to that biomass nanofiber fraction, it can be determined that there are almost no biomass nanofibers dissolved in the filtrate, and that the biomass resin composite has been uniformly polymerized while maintaining a homogeneous dispersion state similar to that of the aqueous dispersion of biomass nanofibers. On the other hand, for example, filtration is not possible even if the aqueous dispersion of biomass nanofibers itself is filtered. Therefore, it is possible to determine whether a uniformly polymerized biomass resin composite has been obtained by confirming that it can be filtered by the filtration operation.

[0048] The biomass resin composite of the present invention obtained by such a method is a biomass resin composite in which biomass nanofibers are uniformly dispersed in the resin while maintaining their structure, and it can be produced at a lower cost and with less labor than conventional methods.

[0049] The biomass resin composite of the present invention can be made into a resin composition by kneading it with the same resin or a different resin contained therein. The ratio of the biomass resin composite in the resin composition is not limited to the above range, but can be appropriately adjusted from the viewpoints of obtaining the effect of the biomass nanofibers contained in the biomass resin composite and imparting moldability to the resin composition. Preferably, it is 1 to 40% by weight, more preferably 1 to 25% by weight. The above-mentioned different resins can be appropriately selected according to the purpose of use of the resin obtained by kneading, and are not particularly limited, but a thermoplastic resin is preferably employed from the viewpoint of good processability of the kneaded product. Also, similar to kneading, a prepolymer of a thermosetting resin or a thermosetting monomer may be mixed and heat-processed. Regarding the kneading method, a known method can be applied and is not particularly limited, but for example, a method of applying heat melting and mechanical shear is preferable.

[0050] Since it is rare for different resins to be compatible by kneading, a compatibilizer can be added for the purpose of stabilizing the dispersion of the resin or the biomass resin composite by kneading. The compatibilizer stabilizes the interface generated between the resins and is also a surfactant. As long as the purpose is to stabilize the dispersion, the type and technique used are not particularly limited. The compatibilizer may be one that not only stabilizes the interface by a chemical reaction with the resin but also provides an adhesive force. When kneading the same resin as the resin contained in the biomass resin composite, there is no need to add a compatibilizer.

[0051] For example, when mixing polystyrene and polyimide, their block copolymers act as compatibilizers; however, block copolymers tailored to the type of resin may be used. Alternatively, graft copolymers may be used to take advantage of the effects of the resin's two-dimensional structure. Other examples of resins having substituents that induce chemical reactions include glycidyl methacrylate polyethylene copolymers having glycidyl groups, and polyethylene graft maleic anhydride copolymers having carboxylic acid anhydrides.

[0052] When a compatibilizer is used, the amount added can be adjusted as appropriate to the desired effect and is not particularly limited, but it is preferably 20 parts by weight or less, and more preferably 10 parts by weight or less, per 100 parts by weight of the resin composition.

[0053] In the present invention, various additives can be added to improve the processability and physical properties of the resin composition obtained by kneading. The effects may be contradictory depending on the type of resin, but examples include plasticizers such as diisononyl phthalate and diisononyl adipate, crystallization retarders such as carnauba wax, nigrosine, and silicone oil that delay the crystallization of the resin, crystallization nucleating agents such as metal benzoate salts that promote the crystallization of the resin, fillers such as carbon black, silica, talc, mica, and calcium carbonate, antioxidants such as phenolic antioxidants, and light stabilizers. Furthermore, the present invention is not limited to these, and known additives can be added depending on the purpose.

[0054] When additives are used, the amount added can be adjusted as appropriate to the desired effect and is not particularly limited, but for example, it is preferable to add plasticizers in an amount of 50 parts by weight or less per 100 parts by weight of the resin composition, and fillers in an amount of 50 parts by weight or less per 100 parts by weight of the resin composition.

[0055] The resin composition obtained in this manner, in which the biomass resin composite of the present invention is dispersed, can be suitably used in products that take advantage of the resin's properties, such as light transmittance, weather resistance, flame resistance, and impact resistance.

[0056] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0057] [Example 1] 1.2 g of cellulose (manufactured by Nippon Paper Industries Co., Ltd., KC Floc W-300G) was mixed with 118.8 g of distilled water to obtain an aqueous mixture. This aqueous mixture was treated 10 times at a pressure of 240 MPa using a Starburst (manufactured by Sugino Machine Co., Ltd., HJP-25005V2) to obtain an aqueous dispersion of cellulose nanofibers.

[0058] 90 g of the obtained aqueous dispersion of cellulose nanofibers was mixed with 2.7 g of vinyl acetate monomer and 0.02 g of polymerization initiator KPS (potassium peroxodisulfate). This mixture was placed in a reaction vessel (300 ml round-bottom flask) along with a stirring bar, its opening was closed with a condenser, and the vessel was placed in an oil bath. The mixture was reacted at an oil bath temperature of 70°C for 24 hours while stirring. After the reaction solution was cooled to room temperature, it was filtered to obtain a biomass resin composite of cellulose nanofibers and polyvinyl acetate as the reaction product. This was air-dried and weighed, yielding 2.7 g and a yield of 75%.

[0059] The obtained composite material was observed using an FE-SEM (JEOL Ltd., JSM-IT800SHL model) at an acceleration of 2 keV and a magnification of 20,000x. For comparison, a dried product from an aqueous dispersion of cellulose nanofibers was also observed. Figures 1 and 2 show the respective images (a) and images of each further magnified by approximately 5x (b).

[0060] The composite of cellulose nanofibers and polyvinyl acetate does not undergo aggregation upon drying, and it can be seen that the cellulose remains in a microfibril state due to mechanical defibrillation, and is uniformly dispersed when mixed with the resin.

[0061] [Example 2] 90 g of an aqueous dispersion of cellulose nanofibers obtained in the same manner as in Example 1 was mixed with 2.7 g of styrene monomer and 0.02 g of polymerization initiator V-501 (4,4'-azobis(4-cyanovaleric acid), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The mixture was placed in a reaction vessel (300 ml pear-shaped flask) along with a stirring bar, its opening was closed with a condenser, and it was placed in an oil bath. The mixture was reacted at an oil bath temperature of 70°C for 24 hours while stirring. After the reaction solution was cooled to room temperature, it was filtered to obtain a biomass resin composite of cellulose nanofibers and polystyrene as the reaction product. This was air-dried and its weight was measured, yielding 1.2 g and a yield of 33%.

[0062] The obtained composite was weighed out at a dose of 11 mg and measured by differential thermal analysis (Shimadzu Corporation, TGA-51). The results are shown in Figure 3. A peak derived from cellulose, with the maximum weight loss at 375°C, and a peak derived from polystyrene, with the maximum weight loss at 475°C, were observed. From the weight ratio, it was determined that the composite consisted of 70% cellulose and 30% polystyrene. From this, it can be determined that in 1.2 g of the obtained composite, the cellulose content was 0.84 g and the polystyrene content was 0.36 g.

[0063] [Example 3] 90 g of an aqueous dispersion of cellulose nanofibers obtained in the same manner as in Example 1 was mixed with 2.7 g of styrene monomer and 0.02 g of polymerization initiator KPS (potassium peroxodisulfate). The mixture was placed in a reaction vessel (300 ml pear-shaped flask) with a stirring bar, its opening was closed with a condenser, and it was placed in an oil bath. The mixture was reacted at an oil bath temperature of 70°C for 24 hours while stirring. After the reaction solution was cooled to room temperature, it was filtered to obtain a biomass resin composite of cellulose nanofibers and polystyrene as the reaction product. This was air-dried and its weight was measured, yielding 2.5 g and a yield of 70%. The obtained biomass resin composite was analyzed by differential thermal analysis in the same manner as in Example 2, and it was found to be 26% cellulose and 74% polystyrene.

[0064] [Example 4] 90 g of an aqueous dispersion of cellulose nanofibers obtained in the same manner as in Example 1 was mixed with 1.35 g of methyl methacrylate, 1.35 g of styrene monomer, and 0.015 g of polymerization initiator KPS (potassium peroxodisulfate). This mixture was placed in a reaction vessel (300 ml pear-shaped flask) with a stirring bar, its opening was closed with a condenser, and it was placed in an oil bath. The mixture was reacted at an oil bath temperature of 70°C for 20 hours while stirring. After the reaction solution was cooled to room temperature, it was filtered to obtain a biomass resin composite of cellulose nanofibers and polymethyl methacrylate and polystyrene copolymer as the reaction product. This was air-dried and its weight was measured, yielding 2.5 g and a yield of 70%.

[0065] [Evaluation of Biomass Resin Composites] The biomass resin composites obtained in Examples 1 to 4 were evaluated for the success of the composite formation based on the presence or absence of biomass resin composites recovered by filtration. The results are shown in Table 1. The biomass nanofiber aqueous dispersion had a gel-like state, and almost no water could be removed even after filtration. On the other hand, for the biomass composites, some water could be removed by filtration due to separation from water. As shown in Example 2, the biomass nanofiber content in the biomass resin composites could be analyzed by differential thermal analysis, and since this was equivalent to the content in the biomass nanofiber aqueous dispersion, it can be determined that the polymerization of the biomass resin composites was successful, as biomass nanofibers could be filtered out after polymerization, and the amount of biomass resin composites produced exceeded the amount of biomass nanofibers added. The filtration method was surface filtration (using Advantec Toyo's qualitative filter paper No. 2, φ150), and the recovered material was dried naturally at room temperature.

[0066]

[0067] [Comparative Example 1] 90 g of an aqueous dispersion of cellulose nanofibers obtained in the same manner as in Example 1 was mixed with 2.7 g of styrene monomer and 0.02 g of polymerization initiator ADVN (2,2'-azobis(2,4-dimethylvaleronitrile)). The mixture was placed in a reaction vessel (300 ml round-bottom flask) along with a stirring bar, its opening was closed with a condenser, and it was placed in an oil bath. The mixture was reacted at an oil bath temperature of 70°C for 24 hours while stirring. After the reaction solution was cooled to room temperature and filtered, a portion that could be filtered out and a portion in which polymer had adhered to the stirring bar in a windmill-like manner were obtained. The filtered portion and the portion attached to the stirring bar were subjected to differential thermal analysis in the same manner as in Example 2. The results are shown in Figures 4(a) and (b), respectively. The filtered portion mainly contained cellulose nanofibers and showed signs of composite formation with a small amount of resin. On the other hand, the portion where polymerized material adhered to the stirring bar in a windmill-like pattern was a homopolymer (polystyrene) formed by polymerization of monomer particles mainly transported from the surface by the stirring flow, resulting in soap-free polymerization. As a result, a uniform biomass resin composite could not be obtained.

[0068] [Example 5] 3.0 g of the biomass resin composite of cellulose nanofiber and polystyrene obtained in Example 3 and 12.0 g of styrene polymer (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed together to facilitate mixing, and then put into a kneader (Xplore Compounder 15, manufactured by DSM Corporation) and kneaded. The kneader was pre-set to 215°C and kneaded at a rotation speed of 250 rpm for 10 minutes to obtain a kneaded resin composition.

[0069] The resulting mixture was extruded through a 5 cm wide T-die to obtain a film with a thickness of approximately 0.5 mm. This kneader is a circulating type, and by replenishing the extruded material with the same styrene polymer and repeating the kneading process, a low-concentration resin composition can be obtained. Through a total of three refilling operations, four different film samples with varying concentrations were obtained.

[0070] Each sample was cut to a width of 1 cm and a length of 15 cm using a hot knife (manufactured by Taiyo Electric Industry Co., Ltd.), and its tensile strength was measured at a speed of 100 mm / min using a Tensilon universal testing machine (RTF-2410, manufactured by A&D Company, Limited). The results are shown in Figure 5.

[0071] This relationship, where the tensile strength increases with the ratio of cellulose nanofibers, indicates that the resin mixing was successful.

Claims

1. A biomass resin composite in which chemically unmodified biomass nanofibers are dispersed in at least one type of resin, and which does not contain a dispersant other than the biomass nanofibers that is soluble in water or water-soluble alcohol as a dispersant.

2. The biomass resin composite according to claim 1, wherein the biomass nanofiber is at least one selected from cellulose nanofiber and chitin nanofiber.

3. The biomass resin composite according to claim 1 or 2, wherein the monomer forming the resin is liquid at room temperature or soluble in water at room temperature.

4. The biomass resin composite according to claim 3, wherein the monomer is at least one selected from vinyl aromatic compounds and vinyl esters.

5. The biomass resin composite according to claim 4, comprising methyl methacrylate and styrene monomer as the monomers.

6. The biomass resin composite according to claim 4, further comprising another type of monomer.

7. A resin composition obtained by kneading the biomass resin composite described in claim 1 with a resin.

8. The resin composition according to claim 7, wherein the resin kneaded with the biomass resin composite is a different resin from the resin in the biomass resin composite, and further comprises a compatibilizer.

9. The resin composition according to claim 8, wherein the resin kneaded with the biomass resin composite is a thermoplastic resin.

10. A method for producing a biomass resin composite by mixing at least one monomer and a polymerization initiator soluble in water with an aqueous dispersion of chemically unmodified biomass nanofibers and polymerizing them.

11. The method for producing a biomass resin composite according to claim 10, wherein the polymerization initiator having water solubility is a persulfate.

12. The method for producing a biomass resin composite according to claim 10, wherein the biomass nanofiber is at least one selected from cellulose nanofiber and chitin nanofiber.

13. The method for producing a biomass resin composite according to claim 10, wherein the monomer is liquid at room temperature or soluble in water at room temperature.

14. The method for producing a biomass resin composite according to claim 10, wherein the aqueous dispersion of unmodified biomass nanofibers is obtained by mechanical defibrillation of an aqueous mixture of biomass, and no additional chemical modification treatment is performed.

15. The method for producing a biomass resin composite according to claim 10, wherein the polymerization temperature is above the freezing point of the aqueous dispersion and below the boiling point.

16. The method for producing a biomass resin composite according to claim 10, wherein a monomer other than the monomer is mixed after polymerization has started.

17. A method for producing a resin composition, comprising mixing at least one monomer and a polymerization initiator soluble in water with an aqueous dispersion of chemically unmodified biomass nanofibers, polymerizing the mixture to obtain a biomass resin composite, and then kneading the resulting composite with a resin.

18. The method for producing a resin composition according to claim 17, wherein the kneading of the biomass resin composite and the resin is performed by adding the biomass resin composite to a thermoplastic resin and subjecting it to thermal melting and mechanical shearing.

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