JPWO2019155929A1 - Fiber reinforced resin composition and its manufacturing method - Google Patents

Abstract

An object of the present invention is to provide a fiber-reinforced resin composition capable of obtaining a molded product having sufficient strength and rigidity. The present invention provides a fiber-reinforced resin composition containing a thermoplastic resin, cellulose fibers, and at least one water-soluble polysaccharide.

Description

The present invention relates to a fiber-reinforced resin composition and a method for producing the same, and a coated fiber and a method for producing the same.

Since the thermoplastic resin has excellent moldability, it is molded by various molding methods such as injection molding, extrusion molding, and blow molding, and is used for various purposes. Composite materials with improved strength and rigidity by dispersing a filler in such a thermoplastic resin are known. For example, in the methods of Patent Documents 1 and 2, an inorganic material such as talc or glass fiber is filled. As an agent, it improves strength and rigidity.

However, since inorganic materials such as talc and glass fiber have a large specific gravity of 2.5 to 2.7, they deprive the resin of its light weight, leave residues as sludge when incinerated, and of resin. It is being considered to convert the filler to another material because the composite inorganic material may be scattered in the living space due to deterioration.

As such a material, Patent Document 3 uses fibers such as polyacrylonitrile fiber, aliphatic nylon fiber, aromatic nylon fiber, cellulose fiber, and polyvinyl alcohol fiber as a filler.

Among the fibers, cellulose fibers have a specific gravity of about 1.5, which is lighter than that of inorganic materials, can be sintered by combustion, and their use as a plant-derived renewable material is being studied.

Japanese Unexamined Patent Publication No. 2005-264033 JP-A-2017-61595 Japanese Unexamined Patent Publication No. 05-247263

However, the strength and rigidity (elastic modulus) of the molded product obtained from the conventional fiber-reinforced resin composition in which the cellulose fibers are dispersed in the thermoplastic resin are not sufficient.

Therefore, an object of the present invention is to provide a fiber-reinforced resin composition capable of obtaining a molded product having sufficient strength and rigidity.

As a result of diligent studies, the present inventors unexpectedly added a water-soluble polysaccharide to the fiber-reinforced resin composition containing the cellulose fiber and the thermoplastic resin composition, thereby unexpectedly adding the fiber-reinforced resin composition. The present invention has been completed by finding that the strength and rigidity of a molded product obtained from a product are improved.

That is, the present invention provides a fiber-reinforced resin composition containing a thermoplastic resin, cellulose fibers, and at least one water-soluble polysaccharide.

According to the present invention, the strength and rigidity of the molded product are improved as compared with the fiber reinforced resin composition containing cellulose fibers and not containing water-soluble polysaccharides. The mechanism of action is not clear, but the following reasons can be considered, for example.

Water-soluble polysaccharides form a film on the surface of cellulose fibers. Therefore, when the molten thermoplastic resin and the cellulose fibers are kneaded, the rebonding of the cellulose fibers is suppressed by the coating of the polysaccharide, the aggregation of the cellulose fibers is reduced, and the cellulose fibers are contained in the thermoplastic resin. It is considered that the cellulose fibers are easily defibrated during kneading.

It is also conceivable that the film of the water-soluble polysaccharide enhances the adhesion between the thermoplastic resin and the cellulose fiber, thereby improving the strength and rigidity of the molded product.

The polysaccharide can be at least one selected from the group consisting of pullulan and dextrins.

In particular, the polysaccharide is preferably pullulan. Since pullulan has excellent film properties and adhesiveness among polysaccharides, it is possible to efficiently form a film firmly adhered to cellulose fibers. Furthermore, pullulan has excellent lubricity, which makes it easier for cellulose fibers to be uniformly dispersed in the thermoplastic resin. Further, since pullulan is a Newtonian fluid having a relatively low viscosity among polysaccharides, it has an advantage that the thermoplastic resin and the cellulose fiber can be easily kneaded.

The thermoplastic resin is preferably a polyolefin resin or a polyamide resin. While the polyolefin resin and the polyamide resin have the advantages of low specific gravity and light weight, there is room for improvement in the strength and rigidity of the molded product. Therefore, in the present invention, the strength and rigidity of the molded product are strengthened by reinforcing with cellulose fibers. The effect of improvement is more pronounced. Further, the polyolefin resin has advantages that the molecular weight can be easily controlled, various modifications can be made by a copolymer, and a synthetic method has been established.

In the fiber-reinforced resin composition, the water-soluble polysaccharide may coat the surface of the cellulose fiber.

The fiber-reinforced resin composition can contain 0.1 to 30 parts by weight of a water-soluble polysaccharide with respect to 100 parts by weight of cellulose fibers.

The present invention also provides a method for producing a fiber-reinforced resin composition, which comprises a step of kneading a molten thermoplastic resin, a cellulose fiber, and at least one water-soluble polysaccharide. According to the method of the present invention, it is not necessary to control a complicated reaction, and the fiber-reinforced resin composition of the present invention can be produced easily and efficiently.

Here, the surface of the cellulose fiber to be subjected to the step of kneading the molten thermoplastic resin, the cellulose fiber, and the water-soluble polysaccharide may be coated with the water-soluble polysaccharide in advance. it can. Water is unlikely to exist at the temperature at which the thermoplastic resin melts, and it is not easy to coat the cellulose fibers with water-soluble polysaccharides. Therefore, it is preferable to coat the cellulose fibers before melting the thermoplastic resin.

In this case, a step of heating a mixture containing the thermoplastic resin, the cellulose fibers, the water-soluble polysaccharide, and water to remove water from the mixture can be included before the kneading step. ..

As a result, the water-soluble polysaccharide can be spread over a wider area on the surface of the cellulose fiber and adhere to the cellulose fiber to form a film. From the obtained fiber-reinforced resin composition, a molded product having higher strength and rigidity can be produced.

The step of heating the mixture and the step of kneading can be performed in the kneader. On the other hand, the heating step of the mixture may be performed outside the kneader.

Here, the mixture before heating can contain 5 to 100 parts by weight of water with respect to 1 part by weight of the water-soluble polysaccharide.

The present invention also provides a coated fiber comprising a cellulose fiber and a film of at least one water-soluble polysaccharide that coats the surface of the cellulose fiber. By using the coated fiber of the present invention, the fiber-reinforced resin composition of the present invention can be efficiently produced. Further, from the obtained fiber-reinforced resin composition, a molded product having excellent strength and rigidity can be molded.

The present invention also provides a method for producing a coated fiber, which comprises the step of coating the cellulose fiber with at least one water-soluble polysaccharide. According to this method, the coated fiber of the present invention can be efficiently produced.

In the above method, the coating step preferably includes contacting the cellulose fibers with an aqueous solution containing the polysaccharide, and drying the aqueous solution in contact with the cellulose fibers. By dissolving the water-soluble polysaccharide in water to form an aqueous solution and then contacting it with the cellulose fibers, the polysaccharides can be spread over a wider area on the surface of the cellulose fibers.

According to the present invention, there is provided a fiber reinforced resin composition capable of imparting sufficient strength and rigidity.

Hereinafter, embodiments of the present invention will be specifically described.

(Fiber Reinforced Resin Composition)
The fiber-reinforced resin composition of the present invention contains a thermoplastic resin, cellulose fibers, and a water-soluble polysaccharide. Hereinafter, each component will be described.

(Thermoplastic resin)
In the fiber-reinforced resin composition of the present invention, the thermoplastic resin constitutes a base material in which cellulose fibers are dispersed. The type of thermoplastic resin is not particularly limited, but for example, polyolefin resin, polyamide resin, polycarbonate resin, vinyl acetate resin, aromatic polyester resin, aliphatic polyester resin, polyether resin, vinyl chloride resin, fluororesin, acrylic resin, etc. Examples thereof include polystyrene resin and polyacetal resin. As the thermoplastic resin, one kind or a combination of two or more kinds of resins can be used.

The thermoplastic resin used in the present invention preferably has a processing temperature of 280 ° C. or lower. When the processing temperature is 280 ° C. or lower, when mixing the thermoplastic resin, the cellulose fiber, and the water-soluble polysaccharide at the processing temperature of the thermoplastic resin, and from the obtained fiber-reinforced resin composition, a molded product Since the cellulose fibers are not deteriorated or decomposed and are likely to remain in the resin composition during the production of the above, it is easy to obtain a molded product having further improved strength. Examples of the resin having such a processing temperature include polyolefin resins, polyamide resins, and the like among the resins listed above. Among the thermoplastic resins, crystalline resins such as polyolefin resins and polyamide resins are preferable.
The thermoplastic resin includes a crystalline resin and an amorphous resin. Generally, the crystalline resin is processed at a melting point of +20 to 50 ° C., and the amorphous resin is processed at a glass transition temperature of + 100 to 120 ° C. ..
Therefore, in the present specification, the processing temperature refers to a melting point of +20 to 50 ° C. in the case of a crystalline resin, and a glass transition temperature of +100 to 120 ° C. in the case of an amorphous resin.
Therefore, for example, when the thermoplastic resin is a crystalline resin, it preferably has a melting point of 260 ° C. or lower, and more preferably 230 ° C. or lower. Further, for example, when the thermoplastic resin is a non-crystalline resin, it preferably has a glass transition temperature of 180 ° C. or lower, and more preferably 160 ° C. or lower.
It is preferable to adjust the processing temperature to 280 ° C. or lower according to the melting point of the thermoplastic resin used or the glass transition temperature.
The melting point and glass transition temperature of the thermoplastic resin can be adjusted by modifying the functional groups of the monomers constituting the thermoplastic resin.

In the present invention, the thermoplastic resin is preferably a polyolefin resin or a polyamide resin. While polyolefin resins and polyamide resins have the advantages of low specific gravity and light weight, there is room for improvement in the strength and rigidity of the molded product. Therefore, in the present invention, the strength and rigidity of the molded product are increased by reinforcing with cellulose fibers. The effect of improvement is more pronounced. In addition, polyolefin resins and polyamide resins have advantages such as easy control of molecular weight, various modifications with copolymers, and established synthetic methods.

Examples of the polyolefin resin include olefin polymers such as low-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, and cyclic polyolefins, copolymers thereof, and modified products thereof. Further, the polyolefin resin may be a copolymer of ethylene and / or propylene and an α-olefin having 4 or more carbon atoms, such as an ethylene α-olefin copolymer or a propylene α-olefin copolymer. Among the polyolefin resins, polypropylene is particularly preferable because it is lightweight and has excellent heat resistance, chemical resistance, and moldability. Examples of polypropylene include ethylene / propylene block copolymers, ethylene / propylene random copolymers, propylene / butene copolymers, and the like, in addition to homopolymers.

Thermoplastic resins are polyolefins having an acid group, such as acid-modified polyolefins to which maleic anhydride has been added in order to improve adhesion to cellulose fibers, and copolymers of maleic anhydride and olefins such as α-olefins. Can be included.

The amount of polyolefin having an acid group is preferably 0.5 to 50% by weight based on the total amount of the thermoplastic resin.

Examples of the polyamide resin include polyamide-based polymers such as nylon 6, nylon 66, nylon 12, nylon 6, 66 copolymers, nylon 6, 12 copolymers, and metaxylene adipamide / nylon 6 copolymers, and their products. Modified products can be mentioned. Among the polyamide resins, it is preferable to use nylon 6 and nylon 66.

The content of the thermoplastic resin in the fiber-reinforced resin composition of the present invention is preferably 60 to 99 parts by weight with respect to 100 parts by mass of the fiber-reinforced resin composition. When the content of the thermoplastic resin is in the above range, the strength of the molded product obtained from the fiber-reinforced resin composition can be increased while maintaining the excellent moldability of the fiber-reinforced resin composition. The content of the thermoplastic resin is preferably 65 to 99 parts by weight, more preferably 75 to 90 parts by weight.

(Cellulose fiber)
In the fiber-reinforced resin composition of the present invention, the cellulose fibers are dispersed in the thermoplastic resin to increase the strength and rigidity of the molded product. The cellulose fiber used in the present invention is a fiber containing cellulose as a main component.

The cellulose fiber source is not particularly limited, and various known ones can be used. Specifically, wood, plants other than wood (cotton, hemp, bamboo, kenaf, hemp, seaweed, etc.); animal fiber produced by squirrel; bacterial cellulose produced by bacteria such as acetic acid bacteria; waste paper; rayon, polynosic, Regenerated cellulose such as cupra, lyocell, acetate; etc. Cellulose fibers may be used alone or in combination of two or more.

The form of the cellulose fiber used in the present invention is not particularly limited, and may be, for example, cellulose nanofiber, microfibrillated cellulose, or pulp.

An example of pulp is kraft pulp (KP), which is obtained by mechanically crushing hardwood (L material) or softwood (N material) into chips and removing lignin and oil components. KP is also advantageous in terms of cost. On the other hand, since KP leaves hemicellulose in pulp, it is easily decomposed by acid or alkali, and undergoes heat denaturation to cause discoloration. In order to avoid this problem, pulp having a shape close to that of α-cellulose may be used. Examples of such pulp are sulfide pulp (SP) in wood-based pulp, DKP in which chips are previously treated with hydrochloric acid and then kraft pulped, or non-wood-based pulp. Since hemp and cotton, which are typical examples of non-wood pulp, have long fiber lengths, they are often entangled with the fibers themselves when they are combined with resin. Cotton linter pulp, which is a type of cotton pulp, is easy to handle because it has a fiber length similar to that of wood pulp. The pulp is preferably defibrated.

Regenerated cellulose is characterized by easy control of fiber length.

The cellulose nanofibers mean cellulose having a fiber diameter of 3 nm to 35 nm or less, and it is also said that the diameter of the carboxylic acid-modified cellulose nanofibers produced by a TEMPO-based catalyst is 3 to 6 nm. Microfibrillated cellulose is obtained by mechanically defibrating cellulose fibers such as pulp, and means cellulose fibers from the micro to nano level, and such a material can also be used as a cellulose fiber in the present invention. ..

The average fiber length of the cellulose fibers in the resin is not particularly limited, but for example, the average fiber length of the cellulose fibers can be 0.2 to 20 mm. When the average fiber length of the cellulose fibers is in the above range, the strength and rigidity of the molded product obtained from the fiber-reinforced resin composition can be sufficiently increased. Preferably, the average fiber length of the cellulose fibers is 0.2 to 3 mm, more preferably 0.8 to 2 mm. The fiber length of the cellulose fiber can be appropriately adjusted by selecting the raw material of the cellulose fiber, the method of defibration treatment, and the like.

The average fiber diameter of the cellulose fibers in the resin is not particularly limited, but for example, the average fiber diameter of the cellulose fibers can be 15 nm to 30 μm. The fiber diameter of the cellulose fiber can be appropriately adjusted by selecting the raw material of the cellulose fiber, the method of defibration treatment, and the like.

The fiber length and fiber diameter of the cellulose fibers can be measured by, for example, a scanning electron microscope (SEM), an optical microscope, or the like.

The content of the cellulose fiber in the fiber-reinforced resin composition of the present invention is not particularly limited, but may be 0.5 to 75 parts by weight with respect to 100 parts by weight of the thermoplastic resin. When the content of the cellulose fibers is within the above range, the tensile strength, bending strength, strength and rigidity, impact resistance, etc. of the molded product molded from the resin composition are likely to be improved. The content of the cellulose fiber is more preferably 1 to 50 parts by weight, still more preferably 10 to 50 parts by weight.

(Water-soluble polysaccharide)
In the fiber-reinforced resin composition of the present invention, the water-soluble polysaccharide forms a film on the surface (for example, side surface) of the cellulose fiber.

A "polysaccharide" is a sugar in which a large number (for example, 10 or more) of monosaccharide molecules are polymerized by glycosidic bonds. It is considered that a coating / coating effect that cannot be obtained with a monosaccharide and a disaccharide having a small molecular weight (molecular length) can be obtained by using a polysaccharide having a large molecular weight (molecular length).

"Water-soluble" means that when 1 g of a solid is powdered, put into water, and vigorously shaken at 100 ° C. or lower every 5 minutes for 30 seconds, it dissolves in less than 30 mL of water within 30 minutes. To say. Even if the polysaccharide does not dissolve when the water temperature is low, if it dissolves when the water is heated, a film can be formed on the cellulose fibers by heating. In the invention, it is said to be "water-soluble".

From the viewpoint of easiness of forming a film on the cellulose fiber, the weight average molecular weight of the water-soluble polysaccharide used in the present invention based on GPC is preferably 100,000 or more, more preferably 200,000 or more, and the upper limit is particularly high. Although not, it is preferably 400,000 or less.

The type of water-soluble polysaccharide is not particularly limited, but any of synthetic polysaccharide, natural polysaccharide and natural modified polysaccharide can be used, for example, α-1,4-glucan (amylose, amylopectin, glycogen), α-. 1,6-Glucan (Dextran), β-1,6-Glucan (Pustulan), β-1,3-Glucan (eg Cardran, Sizophyllan, etc.), α-1,3-Glucan, β-1,2- Glucan, β-1,4-galactan, β-1,4-mannan, α-1,6-mannan, β-1,2-fractane (inulin), β-2,6-fractan (levan), β- Examples thereof include 1,4-xylan, β-1,3-xylan, glucan, agarose, alginic acid and the like, as well as salts and derivatives thereof. Moreover, you may use starch containing amylose. Moreover, you may use dextrins. The water-soluble polysaccharide may be used alone or in combination of two or more. Since cellulose is not water-soluble, it is not included in the "water-soluble polysaccharide" in the present invention.

Among the above-mentioned polysaccharides, pullulan is preferable. Pullulan is a water-soluble compound having a structure in which maltotriose in which three molecules of glucose are linked by α-1,4 bonds is a constituent unit, and maltotrioses are linked via α-1,6 bonds. Since pullulan has excellent film properties and adhesiveness among polysaccharides, it is possible to efficiently form a film that is firmly adhered to the cellulose fibers, and the effect of preventing aggregation of the cellulose fibers becomes higher. Furthermore, pullulan has excellent lubricity, which makes it easier for cellulose fibers to be uniformly dispersed in the thermoplastic resin. Further, since it is a Newtonian fluid having a relatively low viscosity among polysaccharides, it has an advantage that it is easy to knead when the thermoplastic resin and the cellulose fiber are kneaded.

The pullulan used in the present invention is not particularly limited in terms of acquisition method and type, but preferably has a weight average molecular weight of 5,000 to 500,000 based on GPC, and more preferably has a weight average molecular weight of 50,000 to 400,000. .. By using pullulan having a weight average molecular weight in the above range, it is considered that the coating effect of the pullulan coating on the cellulose fibers becomes better.

Among the polysaccharides, dextrins are also preferable. Dextrins are compounds that can be obtained by hydrolysis of starch or glycogen and have a molecular structure in which α-glucose is polymerized by α-1,4 or α-1,6 glycosidic bonds. Dextrins include dextrins, maltodextrins and powdered candy. Since dextrins also have excellent film properties and adhesiveness, it is possible to efficiently form a film that is firmly adhered to the cellulose fibers, and the effect of preventing aggregation of the cellulose fibers is enhanced. The dextrins used in the present invention are not particularly limited in terms of acquisition method and type, but those having a dextrose equivalent (DE) of 10 or less are preferable, and those having a dextrin equivalent (DE) of 3.0 or less are more preferable. Further, a GPC-based weight average molecular weight of 5,000 to 500,000 is preferable, and a weight average molecular weight of 50,000 to 400,000 is more preferable. By using dextrins having a weight average molecular weight in the above range, it is considered that the coating effect of the dextrins on the cellulose fibers becomes better.

The content of the water-soluble polysaccharide in the fiber-reinforced resin composition of the present invention is not particularly limited, but is preferably 0.1 to 30 parts by weight with respect to 100 parts by weight of the cellulose fiber. When the content of the water-soluble polysaccharide in the cellulose fiber is within the above range, the polysaccharide can efficiently form a film on the cellulose fiber. The water-soluble polysaccharide is more preferably 0.2 to 10 parts by weight based on 100 parts by weight of the cellulose fiber.

(Other ingredients)
If necessary, the fiber-reinforced resin composition of the present invention may contain components other than the above-mentioned thermoplastic resin, cellulose fiber, and water-soluble polysaccharide. Such components include various additives commonly used in thermoplastic resin compositions, such as antioxidants, light stabilizers, UV absorbers, neutralizers, lubricants, antiblocking agents, dispersants, fluidity. Additives such as improvers, mold release agents, flame retardants, foaming agents, colorants, fillers, thickeners, low thickeners, and crystal nucleating agents can be mentioned. The content ratio of the fiber-reinforced resin composition of these additives is preferably 30 parts by weight or less when the entire fiber-reinforced resin composition is 100 parts by weight.

(Action)
According to the fiber-reinforced resin composition according to the embodiment of the present invention, the strength and rigidity of the molded product are higher than those of the fiber-reinforced resin composition containing cellulose fibers but not containing water-soluble polysaccharides. The reason is not clear, but the following can be considered.

Water-soluble polysaccharides form a film on the surface of cellulose fibers. Therefore, when the molten thermoplastic resin and the cellulose fibers are mixed, the rebonding of the cellulose fibers is suppressed by the coating of the polysaccharide, the aggregation of the cellulose fibers is reduced, and the cellulose fibers are contained in the thermoplastic resin. It is considered that the cellulose fibers are easily defibrated during mixing.

It is also conceivable that the film of the water-soluble polysaccharide enhances the adhesion between the thermoplastic resin and the cellulose fiber, thereby improving the strength and rigidity.

(Manufacturing method of fiber reinforced resin composition)
The method for producing a fiber-reinforced resin composition of the present invention includes a step of kneading a molten thermoplastic resin, cellulose fibers, and a water-soluble polysaccharide. According to the method of the present invention, it is not necessary to control a complicated reaction, and the above-mentioned fiber-reinforced resin composition can be produced easily and efficiently.

The above kneading can be carried out by various kneaders such as a single-screw or twin-screw extruder, a roll, a Banbury mixer, a kneader, and a lavender. The cellulose fibers to be put into the kneader may be an aqueous dispersion or a dried product.

The temperature at which the molten thermoplastic resin and the cellulose fibers are kneaded may be any temperature as long as the temperature at which the thermoplastic resin melts. For example, the melting point of the crystalline thermoplastic resin can be +20 to 50 ° C., and the glass transition temperature of the amorphous thermoplastic resin can be +100 to 120 ° C.

Cellulose fibers are preferably defibrated in advance. The method of defibration treatment is not particularly limited, and for example, physical treatment such as grinding method, high-pressure homogenizer method, underwater opposition method, refiner method, ultrasonic homogenizer method, biaxial kneading method, TEMPO oxidation method, ozone. Chemical treatment such as oxidation method and enzyme treatment method, and a combination thereof can be performed.

When defibrating sheet-shaped pulp, there are generally two methods, one of which is the dry method. In the dry method, defibrated fibers can be obtained by recovering the crushed material with an air blow while crushing the pulp sheet with a hammer mill or the like, but the crystallinity of cellulose decreases due to a strong impact, and the fibers Obstacles such as shortening of the length may appear. Further, since the obtained defibrated product becomes a low-density cotton-like product, a special device may be required when it is put into the kneader together with the resin.

Another method for defibrating sheet pulp is the wet method. Pulp is usually well compatible with water and can be defibrated into fibers with a weak force in water, for example, with a normal stirrer or pulper (stirring device). When excess water is removed from this state by suction filtration method, centrifugation method, belt press method, etc., defibrated water-containing cellulose fibers (aqueous dispersion) can be obtained. When kneading with a resin, a kneader having a function of removing residual water such as a vent is required, but the crystallinity does not decrease during defibration and the fiber length can be preserved.

Generally, the cellulose fiber concentration obtained by the wet defibration method is about 15 to 30% by weight in the case of KP, about 20 to 35% by weight in the case of cotton linter, and 5 to 20% by weight in the case of microfibrillated cellulose. In the case of cellulose nanofibers, it can be 0.3 to 3% by weight.

When cellulose nanofibers, microfibrillated cellulose, or the like are dried, they interact strongly with each other. Therefore, it is generally preferable to knead the cellulose nanofibers, microfibrillated cellulose, or the like with the resin in a water-containing state without drying.

When the molten thermoplastic resin and the cellulose fiber are kneaded, it is preferable that a film of a water-soluble polysaccharide is formed on the surface of the cellulose fiber in advance. In order to do so, for example, it is preferable to coat the surface of the cellulose fiber with a water-soluble polysaccharide to form a film before putting it into the kneader.

Specifically, the cellulose fibers and the cellulose fibers are obtained by contacting the cellulose fibers with an aqueous solution A containing a water-soluble polysaccharide, and by drying the aqueous solution A in contact with the cellulose fibers by heating, reducing pressure, or the like. It is possible to obtain a coated fiber having a water-soluble polysaccharide film that coats the surface of the above. The aqueous solution A can be dried by a known method such as heating, depressurization, and natural drying.

In addition, coating of cellulose fibers with water-soluble polysaccharides can also be performed in a kneader.
Specifically, a mixture B of a solid thermoplastic resin, cellulose fibers, a water-soluble polysaccharide, and water may be kneaded in a kneader. In the kneader, the mixture B is heated by the kneading of the mixture B, and the water in the mixture B can be removed from the system as steam. In this case, it is preferable to use a kneader having a vent. When water is removed from the mixture B, a film of water-soluble polysaccharides is formed on the surface of the cellulose fibers. After that, if the mixture from which water has been removed is further kneaded, the thermoplastic resin is melted, and the melted thermoplastic resin and the cellulose fiber having a coating of polysaccharides are kneaded.

The cellulose fiber contains 5 to 9% by weight of adsorbed water even if it is a dried product. Therefore, even when liquid water is not added to the kneader, the mixture containing the thermoplastic resin, the cellulose fibers, and the water-soluble polysaccharide is heated by shearing in the kneader, and the adsorbed water is discharged from the cellulose fibers. Since it is desorbed to form free water, a mixture of thermoplastic resin, cellulose fibers, water-soluble polysaccharides, and water can be formed in the kneader. Therefore, the above-mentioned fiber-reinforced resin composition can be produced without adding liquid water.

In order to efficiently coat the surface of the cellulose fiber with the water-soluble polysaccharide, the aqueous solution A and the mixture B should be 5 to 100 parts by weight based on 1 part by weight of the water-soluble polysaccharide. It is preferable to contain water.

(Molded body)
A molded product can be produced from the fiber-reinforced resin composition of the present invention described above. As the molding method, various known methods can be used without particular limitation, and examples thereof include compression molding, injection molding, extrusion molding, extrusion laminating molding, rotary molding, calendar molding, vacuum molding, blow molding and the like. .. Further, the shape of the molded product is not particularly limited. The molded product obtained from the fiber-reinforced resin composition of the present invention has sufficient strength and rigidity.

(Preparation of an aqueous dispersion of cellulose fiber 1)
A water slurry containing 2% by weight of NBKP (bleached kraft pulp made from softwood) was prepared. This was mechanically defibrated with a pulper (stirring device) to obtain an aqueous dispersion of cellulose fibers 1. Then, excess water was removed by a centrifuge and concentrated to finally prepare an aqueous dispersion of cellulose fibers 1 having a concentration of cellulose fibers 1 of 25% by weight. The average fiber length of the cellulose fiber 1 was 2.8 mm, and the average fiber diameter was 25 μm.

(Preparation of Cellulose Fiber 2)
The sheet-shaped NBKP was crushed with a hammer mill to obtain a fluff-shaped cellulose fiber 2. The average fiber length of the cellulose fiber 2 was 1.8 mm, the average fiber diameter was 25 μm, and the water content was 7% by weight.

(Preparation of Cellulose Fiber 3)
1000 parts by weight of a 1.0% by weight aqueous pullulan solution is sprayed on 100 parts by weight of cellulose fibers 2, these are mixed well, and then dried at 60 ° C., and 10 parts by weight of 100 parts by weight of cellulose fibers are added. Cellulose fibers 3 coated with pullulan were produced.

(Examples 1 to 6)
In Examples 1 to 4, the aqueous dispersion of cellulose fiber 1 and polypropylene (BC06C, manufactured by Japan Polypropylene), acid-modified polypropylene (H1000P, manufactured by Toyo Boseki), and powdered pullulan (food grade "Pullulan", manufactured by Hayashihara) are used. The fibers are blended in the amounts shown in Table 1, supplied to a twin-screw kneader with a vent, kneaded while discharging water vapor from the vent, and further kneaded while melting polypropylene at 230 ° C. to prepare a fiber-reinforced resin composition. did. An injection-molded article was prepared from the obtained fiber-reinforced resin composition, and its flexural modulus was measured. In Table 1, "part" means "part by weight".
In Example 5, 20 parts by weight of a 10% by weight pullulan aqueous solution was blended in the same manner as in Example 2 except that the amount of water was increased.
In Example 6, 2 parts by weight of a 10% by weight pullulan aqueous solution was blended.

(Comparative Examples 1 to 4)
A fiber reinforced resin was prepared in the same manner as in Examples 1 to 4 except that pullulan was not added, according to the formulation shown in Table 1.

(Examples 7 to 11)
In Example 7, a fiber-reinforced resin was prepared by the formulation shown in Table 1 in the same manner as in Example 2 except that a fluff-like dried cellulose fiber 2 was used instead of the aqueous dispersion of the cellulose fiber 1. did. The cellulose fiber 2 does not contain liquid water, but contains 7% by weight of adsorbed water.
Examples 8 to 10 were the same as in Example 7 except that liquid water was further added according to the formulation shown in Table 1.
In Example 11, the same procedure as in Example 7 was carried out except that 20 parts by weight of a 10% by weight pullulan aqueous solution was blended.

(Comparative Example 5)
A fiber-reinforced resin was prepared by the formulation shown in Table 1 in the same manner as in Example 7 except that pullulan was not added.

(Example 12)
A cellulose fiber reinforced resin was prepared in the same manner as in Example 7 except that the cellulose fiber 3 coated with pullulan in advance was used instead of the combination of the powdered pullulan and the cellulose fiber 2. In addition, 20 parts of cellulose fibers are covered with 2 parts of pullulan.

(Comparative Example 6)
A fiber-reinforced resin was produced in the same manner as in Example 1 except that 10 parts by weight of powdered trehalose was blended in place of the powdered pullulan.

In Examples 1 to 6 and Comparative Examples 1 to 4, an aqueous dispersion of cellulose fibers 1 obtained by wet defibration treatment was used. According to the comparison between Examples 1 to 4 and Comparative Examples 1 to 4, the flexural modulus tends to increase as the amount of cellulose fibers increases regardless of the addition or absence of pullulan, but the amount of cellulose fibers When the value is constant, the flexural modulus is significantly improved in each example to which pullulan is added as compared with each comparative example to which pullulan is not added. It can also be seen that in the system to which pullulan is added, the crystallinity of the resin increases as the amount of cellulose fibers increases.
Further, from the comparison between Example 2 and Example 5, the degree of crystallization and the flexural modulus are different between the case where powdered pullulan is added to the aqueous cellulose fiber dispersion and the case where the aqueous pullulan solution is added to the aqueous cellulose fiber dispersion. It can be seen that it does not affect.
Further, when comparing Example 5 and Example 6, the amount of pullulan added was 1/10 of that of Example 5 in Example 6, but the crystallinity and flexural modulus of the resin were the same. It showed an effect.

In Comparative Example 6 in which 10 parts by weight of powdered trehalose was blended instead of powdered pullulan, unlike Examples 1 to 4, the effects of increasing the crystallinity of the resin and improving the flexural modulus were observed. There wasn't.

In Examples 7 to 11 and Comparative Example 5, dried cellulose fibers 2 obtained by the dry defibration treatment were used. Comparing Example 7 in which dried cellulose fibers 2 and pullulan in powder form were added and no liquid water was added, and Comparative Example 5 in which neither pullulan nor water was added, the crystallinity of polypropylene was compared. Was about the same, but the value of the flexural modulus of the molded product of Example 7 was slightly higher. Further, comparing Examples 7 to 10, when the same amount of cellulose fibers and the same amount of pullulan were used, the crystallinity of polypropylene increased as the amount of liquid water added increased, and further, bending of the molded product was performed. The elastic modulus increased.
As in Example 7, even when liquid water is not added, since the cellulose fibers contain water as adsorbed water, the purulan is released from the cellulose fibers in the process of heating to cause the pullulan to be on the surface of the cellulose fibers. However, it is considered that the effect of forming the film is enhanced by adding liquid water as in Examples 8 to 10.

In Example 11, pullulan was added in the form of an aqueous solution. Compared with Example 9 in which the same amount of powdered pullulan and substantially the same amount of water were added, the crystallinity of polypropylene and the flexural modulus of the molded product were significantly higher in Example 11. As described above, there was no difference between Example 2 and Example 5 of the wet defibrated cellulose fiber, whereas the reason why such a difference appears in the dry defibrated cellulose fiber is not clear, but the wet defibrated cellulose Unlike fibers, dry defibrated cellulose fibers are considered to be more effective when added as an aqueous solution from the beginning.

Example 12 is an example in which the cellulose fiber 3 in which the cellulose fiber 2 is pre-coated with pullulan is used for kneading. In Example 12, the crystallinity of polypropylene and the flexural modulus of the molded product similar to those in Examples 10 and 11 were obtained. That is, by using the cellulose fibers pre-coated with pullulan, the flexural modulus of the molded product could be effectively increased without adding water during kneading.

The present invention provides a fiber-reinforced resin composition capable of obtaining a molded product having excellent strength and rigidity, and can be used in various fields.

Claims (15)

A fiber-reinforced resin composition containing a thermoplastic resin, cellulose fibers, and at least one water-soluble polysaccharide. The fiber-reinforced resin composition according to claim 1, wherein the polysaccharide is at least one selected from the group consisting of pullulan and dextrins. The fiber-reinforced resin composition according to claim 1 or 2, wherein the polysaccharide is pullulan. The fiber-reinforced resin composition according to any one of claims 1 to 3, wherein the thermoplastic resin is a polyolefin resin or a polyamide resin. The fiber-reinforced resin composition according to any one of claims 1 to 4, wherein the water-soluble polysaccharide covers the surface of the cellulose fiber. The fiber-reinforced resin composition according to any one of claims 1 to 5, which contains 0.1 to 30 parts by weight of a water-soluble polysaccharide with respect to 100 parts by weight of cellulose fibers. A step of kneading the molten thermoplastic resin with the cellulose fibers and at least one water-soluble polysaccharide.
The method for producing a fiber-reinforced resin composition according to any one of claims 1 to 6. The method according to claim 7, wherein the surface of the cellulose fiber to be subjected to the step of kneading is previously coated with the water-soluble polysaccharide. Before the kneading step
8. The method of claim 8, comprising the step of heating a mixture containing the thermoplastic resin, the cellulose fibers, the water-soluble polysaccharide, and water to remove water from the mixture. The method according to claim 9, wherein the step of heating the mixture and the step of kneading are performed in a kneader. The method of claim 9 or 10, wherein the mixture before heating contains 5 to 100 parts by weight of water relative to 1 part by weight of the water-soluble polysaccharide. A coated fiber comprising a cellulose fiber and a film of at least one water-soluble polysaccharide that coats the surface of the cellulose fiber. The coating fiber according to claim 12, wherein the polysaccharide is pullulan. Including the step of coating the cellulose fibers with at least one water-soluble polysaccharide,
The method for producing a coated fiber according to claim 12 or 13. 15. The method of claim 14, wherein the coating step comprises contacting the cellulose fibers with an aqueous solution containing the polysaccharide and drying the aqueous solution in contact with the cellulose fibers.