JP2009144262A - Surface modified cellulose short fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-modified cellulose short fiber redispersible to an organic polymer and an organic solvent and a method for producing the same. <P>SOLUTION: The surface-modified cellulose short fiber is obtained by subjecting a water dispersion of cellulose short fiber, a water-soluble polyvinyl alcohol having a polymerization degree of 500-2,000 and a saponification value of 85-95 mol% and at least one of an aldehyde selected from the group consisting of acetaldehyde, propionaldehyde and n-butylaldehyde to an acetal reaction using an acid catalyst. The method for producing the same is provided. The reinforcing material for a polymer composite material contains the surface-modified cellulose short fiber. The filler includes the surface-modified cellulose short fiber. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface-modified cellulose short fiber and a method for producing the same. More specifically, at least one selected from the group consisting of an aqueous dispersion of short cellulose fibers, a water-soluble polyvinyl alcohol having a polymerization degree of 500 to 2000 and a saponification degree of 85 to 95 mol%, and acetaldehyde, propionaldehyde, or normal butyraldehyde. The present invention relates to a surface-modified cellulose short fiber characterized by causing an acetal reaction of a seed aldehyde with an acid catalyst and a method for producing the same.

  As a polymer composite material that requires high physical properties (hardness, strength, elasticity, etc.), a glass fiber reinforced resin (hereinafter referred to as GFRP) is generally used and widely used.

  However, when glass fiber is used as a reinforcing material, the glass fiber damages the polymer material body due to the load applied to the GFRP, which causes deterioration of the polymer composite material, or the glass fiber becomes finer by impact, resulting in reinforcement. There is a problem that the effect is reduced. Further, GFRP has a problem that disposal and recycling after use are not easy.

  On the other hand, in recent years, studies have been made on the possibility of using cellulose short fibers, particularly cellulose nanofibers whose fiber diameter is refined to sub-micron or even nano level, for polymer composite materials.

  A cellulose short fiber is a fibrous substance in which cellulose molecular chains are assembled. Most of the cellulose is produced by higher plants such as trees, but there are also microorganisms that produce cellulose short fibers in addition to plants. In plant cellulose, a large number of cellulose molecular chains are concentrated, and first, very thin fibers called microfibrils are formed. These microfibrils are further bundled to form a higher-order structure in stages with fibrils, lamellae, and fiber cells. In bacterial cellulose, cellulose microfibrils secreted from fungal cells form a fine network structure with the same thickness. Although microfibrils depend on the production method, the diameter is usually several to several tens of nm, and the length is several hundreds to several tens of μm. The cellulose molecular chain constituting this microfibril has a feature that it has a strength more than five times that of steel, a high elastic modulus, and a low thermal expansion property even though it is lightweight because it is an extended chain crystal. Have. In addition, since cellulose short fibers are naturally derived raw materials, they can be recycled and biodegraded by microorganisms, so that the environmental load is small.

  Cellulose short fibers are conventionally used as fillers for polymer composite materials, and these are usually pulp and straw fibers having a fiber diameter of several tens of μm or more. In order to realize performance comparable to GFRP, it is necessary to refine the cellulose short fiber.

  Patent Document 1 discloses that a cellulose short fiber composite material in which pulp is made into nanofibers and hardened with an adhesive is much stronger than GFRP, and has a strength comparable to that of a magnesium alloy.

  However, the diameter of the cellulose short fiber which can be normally used in a dry state is several tens of μm or more. Cellulose short fibers made by dispersing these cellulose short fibers in water and mechanically or chemically defibrating them to several μm or less, once dried, become keratinous like ceramics due to enormous hydrogen bonding between the fibers, Since it cannot be dispersed again, it is difficult to form a composite with a polymer material.

  In order to use the micronized short cellulose fibers in a composite material, even if water as a dispersant is removed, adhesion due to strong hydrogen bonding between fibers is prevented, and further, it is easily dispersed in a polymer material. It is necessary to form an interface bond.

  As a method for achieving such an object, the following surface treatment method for cellulose short fibers has been proposed. Patent Document 2 discloses surface modification by latex polymerization, and Patent Document 3 discloses a surface modification method by emulsion polymerization. Patent Document 4 discloses a method of surface modification by etherifying hydroxyl groups on the surface of cellulose short fibers to reduce the hydroxyl groups on the fiber surface. Patent Document 5 discloses surface modification by esterification. A method of obtaining the same effect as is disclosed. Patent Document 6 discloses a method of dispersing in an organic solvent by surface treatment using a surfactant.

  However, in the above-mentioned method, it is necessary to replace the water content of the cellulose short fiber aqueous dispersion with an organic solvent before treating the cellulose short fibers, which is complicated from the viewpoint of cost and environment. There is a problem.

  In addition, in order to improve the modification degree of the hydroxyl group on the fiber surface, the cellulose short fiber is exposed to a strong acid and high temperature conditions, so that the crystal structure and molecular structure of cellulose are destroyed and the original function is deteriorated. There is a fear.

  Regarding compounding of cellulose short fiber and hydrophobic organic polymer, Patent Document 7 discloses a method for producing a polymer composite material by processing cellulose short fiber into a sheet, adding a resin, laminating, and heating pressing. Is disclosed.

  Patent Document 8 discloses a method for preparing a film by mixing and casting cellulose short fibers in an aqueous solution with a water-soluble polymer such as water-soluble polyvinyl alcohol (hereinafter referred to as PVA) or polyethylene glycol. ing.

  However, as described above, the short cellulose fibers cannot be redispersed in an organic solvent because once dried, they become keratinous like ceramics due to enormous hydrogen bonds between the fibers. Therefore, it could not be melt kneaded with a thermoplastic resin like glass fiber.

JP 2003-201695 A JP 9-509694 A US Pat. No. 6,103,790 US Pat. No. 6,703,497 Japanese National Patent Publication No. 11-513425 US Pat. No. 6,967,027 JP 2007-51266 A Japanese Patent Laid-Open No. 11-117120

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a surface-modified cellulose short fiber that can be redispersed in an organic polymer or an organic solvent, and a method for producing the same.

  The method for producing surface-modified cellulose short fibers of the present invention comprises an aqueous dispersion of cellulose short fibers, a water-soluble polyvinyl alcohol having a polymerization degree of 500 to 2000 and a saponification degree of 85 to 95 mol%, and acetaldehyde, propionaldehyde or normal butyl. An acetal reaction is performed with at least one aldehyde selected from the group consisting of aldehydes using an acid catalyst.

  The acetal reaction may be performed by freezing the reaction solution before the water-soluble polyvinyl alcohol is completely precipitated from the reaction solution due to an increase in the degree of acetalization, and then heating the reaction solution to 50 to 90 ° C. It is preferable to complete the conversion.

  Moreover, it has the 1st process which carries out the acetal reaction of the aqueous dispersion of the said cellulose short fiber, and the said aldehyde using an acid catalyst, and also adds the said water-soluble polyvinyl alcohol, and has a 2nd process which consists of an acetal reaction. It is preferable.

  Moreover, it is preferable that the said aldehyde is 2 or more types of aldehydes.

  The aldehyde is preferably propionaldehyde or normal butyraldehyde.

  Moreover, it is preferable that the average fiber diameter of the said cellulose short fiber is 3-5000 nm.

  The present invention is a surface-modified cellulose short fiber produced by the method according to claim 1, 2, 3, 4, 5 or 6.

  Further, the present invention is characterized in that it is a reinforcing material of a polymer composite material containing the surface-modified cellulose short fibers.

  Moreover, it is a filler of a polymer composite material containing the surface-modified cellulose short fibers.

  The surface-modified cellulose short fibers of the present invention can be easily combined with a polymer material because the surface is formed and / or physically coated with a polyvinyl acetal graft. In addition, polyvinyl acetal on the surface of short cellulose fibers is heat-meltable and can improve affinity with the resin by controlling the degree of acetalization, so it exhibits excellent dispersibility when combined with resin. High interfacial adhesion with resin matrix. Moreover, since it can be redispersed after drying, it can be combined with a thermoplastic resin by melt kneading in the same manner as a normal fibrous filler.

  Therefore, the obtained surface-modified cellulose short fibers can be used as they are, but can also be used as pellets or powders. It is also possible to perform solution casting. Moreover, the cellulose short fiber surface is modified with tough polyvinyl acetal, so that the fiber surface is prevented from being damaged in the melt processing process, and a high reinforcing effect is obtained.

  The surface-modified cellulose short fibers of the present invention have light weight, high strength, high elastic modulus, and low thermal expansion compared to glass fibers. In addition, since it can be recycled with naturally-derived raw materials, it can be biodegraded by microorganisms and has little environmental impact. In addition, the manufacturing process is simple, and since it is performed in an aqueous solution, it is environmentally friendly.

  The use of the surface-modified cellulose short fibers of the present invention is not particularly limited, but can be used as, for example, thermoplastic polymers, thermosetting polymers, fibers, paint reinforcing agents, fillers, and structural materials. .

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a photograph of an electron microscope (hereinafter referred to as SEM) of a serisch used in the present invention, and FIG. 2 is a surface-modified cellulose short fiber of Example 1 of the present invention and its tetrahydrofuran (hereinafter referred to as THF). 3) The appearance of the dispersion and the sheet, FIG. 3 is the appearance of the surface-modified cellulose short fiber of Example 4 of the present invention and its THF dispersion, and FIG. 3 is a hot press sheet of a product obtained from Comparative Example 2.

(Cellulose short fiber)
The cellulose short fibers used in the present invention are not particularly limited, but those having an average fiber diameter of 3 to 5000 nm, preferably 3 to 500 nm are used. An example of the fiber structure is shown in FIG. 1, but is not particularly limited to this structure. When the average fiber diameter exceeds 5000 nm, the reinforcing effect tends to decrease due to a decrease in the surface area and aspect ratio of the fiber. The production cost of cellulose fibers having an average fiber diameter of less than 3 nm is high and not suitable for practical use. The cellulose short fibers may contain fibers having a fiber diameter of 5000 nm or more, but from the viewpoint of the reinforcing effect, the proportion is preferably 15% by weight or less.

  Although it does not specifically limit about the fiber length of a cellulose short fiber, 100 nm-100 micrometers of average fiber length are preferable. This is because if the average fiber length is shorter than 100 nm, the aspect ratio is low, the reinforcing effect is low, and the strength of the fiber-reinforced composite material becomes insufficient. When the average fiber length exceeds 100 μm, the fibers are difficult to uniformly disperse when complexed with the matrix resin. The cellulose short fibers may contain fibers having a fiber length of less than 100 nm, but the proportion is preferably 30% by weight or less from the viewpoint of the reinforcing effect.

  As the cellulose short fibers, those separated from plants and those produced by bacterial cellulose can be used, and the cellulose short fibers are not particularly limited thereto.

(PVA)
PVA has a degree of polymerization of 500 to 3000, preferably a degree of polymerization of 500 to 2000, and a degree of saponification of 80 to 95% because of the high dispersibility of the modified cellulose short fibers, but as long as it can be dissolved in water, In particular, it is not limited to these.

(aldehyde)
The aldehyde is not particularly limited as long as it can acetal-react the hydroxyl groups on the surfaces of PVA and cellulose short fibers. In view of reactivity and cost, formaldehyde, acetaldehyde, propionaldehyde, and normal butyraldehyde are preferred. The lower the number of carbons in the aldehyde, the higher the hydrophilicity. Therefore, the aldehyde tends to react with the hydroxyl group on the surface of the short cellulose fiber and the graft rate tends to increase. On the other hand, aldehydes with a large number of carbons have high hydrophobicity and are well dispersed in organic solvents, thus contributing to melt processability. Therefore, it is preferable to use two or more aldehydes having different carbon numbers in combination. The aldehyde may be normal or iso. An aromatic aldehyde having excellent heat resistance and flame retardancy can also be used.

  The mixing ratio of two or more aldehydes is not particularly limited. For example, the mixing ratio of normal butyraldehyde and acetaldehyde is preferably 1.5: 1, and the mixing ratio of normal butyraldehyde and propionaldehyde is 1 .5: 1 is preferred.

(Acid catalyst)
As the acid catalyst, for example, an inorganic acid such as hydrochloric acid, sulfuric acid, and phosphoric acid, or an organic acid such as acetic acid, formic acid, and paratoluenesulfonic acid can be used. Sulfuric acid is preferred. Moreover, an acid catalyst may be used individually by 1 type, or may use 2 or more types together. These acid catalysts are generally added in an appropriate amount at once or divided into several times according to the progress of the reaction so that the pH of the reaction solution is 0.2-3.

(Other)
In the production of the surface-modified cellulose short fibers, other additives such as a surfactant may be added.

(Method for producing surface-modified cellulose short fibers)
The surface-modified cellulose short fibers of the present invention are produced by subjecting an aqueous dispersion of cellulose short fibers, an aqueous PVA solution, and an aldehyde to an acetal reaction using an acid as a catalyst. At this time, the dry weight ratio of the short cellulose fiber and PVA is 95: 5 to 1:99, and preferably 90:10 to 3:97. When it exceeds 95: 5, the obtained surface-modified cellulose short fibers tend to deteriorate the dispersibility with respect to the organic resin. On the other hand, if it is less than 1:99, a sufficient reinforcing effect cannot be obtained.

  The degree of acetalization is 35 to 95 mol%, preferably 40 to 75 mol%. When the degree of acetalization is lower than 35 mol%, the hydrophilicity of the cellulose short fiber surface tends to be high, and the dispersibility in organic solvents and organic polymers tends to deteriorate. When the degree of acetalization is higher than 95 mol%, the productivity of the surface-modified cellulose short fibers tends to decrease.

  The acetal reaction occurs between the hydroxyl group on the cellulose surface and / or the hydroxyl group of PVA and the aldehyde. The aldehyde first reacts with one hydroxyl group to form a semiacetal, and then reacts with another hydroxyl group to form an acetal. When the two hydroxyl groups are composed of a hydroxyl group on the cellulose surface and a hydroxyl group of PVA, cellulose A graft of polyvinyl acetal is formed on the surface. In addition, the polyvinyl acetal may be simply coated on the cellulose surface without forming a graft.

  When the graft is formed on the surface of the short cellulose fiber, better interfacial adhesion can be obtained than when it is coated, and thus the acetal reaction can be divided into two stages in order to increase the graft ratio. That is, first, the cellulose short fibers and aldehyde are allowed to undergo an acetal reaction (first step), and then water-soluble PVA is added to cause further reaction (second step).

  The acetal reaction is carried out by reacting cellulose short fibers within a temperature range of 30 to 90 ° C. using an aldehyde and an acid as a catalyst for 30 minutes to several hours, and then lowering the temperature in the reaction system to 0 to 15 ° C. PVA is added and the reaction is allowed to proceed. Thereafter, in order to increase the degree of acetalization, the reaction temperature is raised to 55 ° C. or higher, and the reaction is completed in several minutes to several hours.

  PVA increases in hydrophobicity as the acetalization progresses and precipitates from the reaction solution, but since the specific gravity of the precipitated polyvinyl acetal resin is different from that of cellulose short fibers, the resin and cellulose short fibers do not adhere to the surface of cellulose short fibers. And uniform surface-modified cellulose short fibers may not be obtained. As a method of overcoming this problem, before the PVA is precipitated from the reaction solution due to the progress of acetalization, the reaction mixture is frozen and water-soluble PVA is deposited around the short cellulose fibers, and then heated again. Thus, uniform surface-modified cellulose short fibers can be obtained without separating the polyvinyl acetal and the cellulose short fibers.

  Examples of the reaction equipment include a tank reactor equipped with a stirrer, a reactor equipped with a tubular loop reactor and a tank reactor equipped with a stirrer, and a homogenizer reactor. From the viewpoint of convenience, a homogenizer reactor is preferable, but is not particularly limited thereto.

  Moreover, when using a low boiling point aldehyde, it reacts, pressurizing within the completely sealed reactor.

  If a manufacturing process is a manufacturing process of general polyvinyl acetal, it will be performed using the said reactor, and it will not specifically limit.

  After completion of the reaction and aging, the acid catalyst contained in the reaction solution is neutralized. The pH of the reaction product solution is preferably adjusted to an alkalinity of about 9 for the reason that the higher the pH value is, the higher the pH value, the higher the stability of the acetal structure, and the less the decomposition when compounded with the resin. Neutralization is performed by adding an aqueous solution of caustic soda or sodium bicarbonate while stirring.

  After neutralization, the solid component and the aqueous solution are separated in order to remove the neutralized salt, acid, alkali, and aldehyde that are water-soluble components. Dehydration is performed by a conventional solid-liquid separation method such as pressure filtration, centrifugal filtration, and freeze dehydration. The solid concentration of the reaction solution is 0.1 to 50%, preferably 1 to 10 in terms of the performance and cost of the obtained surface-modified cellulose short fibers.

  In order to further remove the water-soluble component remaining on the surface and voids of the surface-modified cellulose, washing and drying are performed at room temperature to 50 ° C. after dehydration. This is because this temperature range is efficient for dehydration.

  Since the surface-modified cellulose short fibers of the present invention can be redispersed after drying, they can be combined with a thermoplastic resin by melt-kneading in the same manner as ordinary fibrous fillers. Therefore, the obtained surface-modified cellulose short fibers can be used as they are, but can also be used as pellets or powders. It is also possible to perform solution casting.

  Cellulose short fibers have high strength and high elasticity, are not easily broken, and have high interfacial adhesiveness with a polymer material. Therefore, the cellulose short fiber has a high reinforcing effect on the polymer material and uses GFRP, for example, It can be used as a thermoplastic polymer, thermosetting polymer, fiber and paint reinforcement, filler or structural material.

  The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

Various chemicals used in Examples and Comparative Examples are described below.
Microfibril cellulose (hereinafter referred to as MFC): Celish FG-100 manufactured by Daicel Corporation.
Bacterial cellulose: manufactured by Fujicco Corporation. Distilled water was added to the sterilized bacterial cellulose, and a bacterial cellulose aqueous dispersion having a solid content of 0.5% by weight was prepared with a homogenizer.
Polyvinyl alcohol A: average polymerization degree 500, saponification degree 85 mol%.
Polyvinyl alcohol B: average polymerization degree 2000, saponification degree 95 mol%.

Example 1
10 parts by weight of PVA having an average polymerization degree of 500 and a saponification degree of 85 mol% in a reaction vessel equipped with a temperature controller and a stirrer was dissolved in 790 parts by weight of water under stirring, and serisch water was made 2% by weight. 500 parts by weight of the dispersion and 10 parts by weight of 35% by weight aqueous hydrochloric acid were added and stirred until uniform, and then the temperature was adjusted to 10 ° C. The pH of the mixed solution at that time was 0.5. Next, while stirring the mixed liquid maintained at 10 ° C., 4.2 parts by weight of normal butyraldehyde and 2.8 parts by weight of acetaldehyde were continuously added and mixed while adjusting the temperature to 10 to 15 ° C. Stirring was stopped about 15 minutes after the start of the addition. Thereafter, the reaction system was heated to 60 ° C. and held for 1 hour. After completion of the reaction, the mixture was cooled to 40 ° C., and 1 mol% aqueous sodium hydroxide solution was added to adjust the mixture to pH 9. Washing and dehydration were carried out by filtration. Next, in order to completely remove moisture, the dehydrated product was further dried with a 40 ° C. blower dryer.

As shown in FIG. 2, the obtained surface-modified cellulose short fibers were dispersed in THF, a mixed solvent of ethanol and toluene (ethanol: toluene = 2: 1 (weight ratio)) and distilled water, and their dispersion. The sex was confirmed. The obtained surface-modified cellulose short fibers were not dispersed in water, but were dispersed in a mixed solvent of THF, ethanol and toluene with stirring. The obtained dispersion did not phase separate when observed after 48 hours at room temperature. When this powder was hot-pressed at 190 ° C. and 200 kg / cm ² , a translucent sheet as shown in FIG. 2 was obtained. Moreover, the heat formability was also confirmed by forming the sheet with a hot press.

Example 2
In a 500 mL beaker, 2.5 parts by weight of PVA having an average degree of polymerization of 500 and a saponification degree of 85 mol% was dissolved in 197.5 parts by weight of water with stirring, and 125 parts by weight of a 2% by weight serisch aqueous dispersion was dissolved in 2.5 parts by weight of 35% by weight hydrochloric acid aqueous solution was added, and the mixture was stirred using a homogenizer until uniform, and then the temperature was adjusted to 10 ° C. Next, 1.05 parts by weight of normal butyraldehyde and 0.7 parts by weight of propionaldehyde were added to the mixed liquid maintained at 10 ° C. while stirring with a homogenizer. After the addition, the mixture was stirred for 15 minutes and the resulting intermediate reaction was rapidly frozen. Then, it moved to the 60 degreeC water bath, and when it heat-processed for 60 minutes, the white deposit precipitated. After completion of the reaction, the reaction solution was cooled to 40 ° C. and 1 mol% aqueous sodium hydroxide solution was added to adjust the reaction solution to pH 9. Washing and dehydration were carried out by filtration, and the dehydrated product was further dried with a 40 ° C. blower dryer in order to completely remove moisture.

The obtained surface-modified cellulose short fibers were dispersed in THF, a mixed solvent of ethanol and toluene (ethanol: toluene = 2: 1 (weight ratio)) and distilled water, and their dispersibility was confirmed. The obtained surface-modified cellulose short fibers were not dispersed in water, but were dispersed in a mixed solvent of THF, ethanol and toluene with stirring. When the obtained dispersion was observed after 48 hours at room temperature, no phase separation occurred. When this powder was hot pressed at 190 ° C. and 200 kg / cm ² , a translucent sheet as shown in FIG. 2 was obtained. Thermoformability was also confirmed by forming the sheet with a hot press.

Example 3
The same procedure as in Example 2 was performed except that the heating temperature of the mixed solution was changed to 90 ° C.

The obtained surface-modified cellulose short fibers were dispersed in THF, a mixed solvent of ethanol and toluene (ethanol: toluene = 2: 1 (weight ratio)) and distilled water, and their dispersibility was confirmed. The obtained surface-modified cellulose short fibers were not dispersed in water, but were dispersed in a mixed solvent of THF, ethanol and toluene with stirring. When the obtained dispersion was observed after 48 hours at room temperature, no phase separation occurred. When this powder was hot pressed at 190 ° C. and 200 kg / cm ² , a translucent sheet was obtained. Thermoformability was also confirmed by forming the sheet with a hot press.

Example 4
The same procedure as in Example 2 was performed except that a polymerization degree of 2000 and a saponification degree of 90 mol% were used instead of the PVA polymerization degree of 500.

The obtained surface-modified cellulose short fibers were dispersed in THF, a mixed solvent of ethanol and toluene (ethanol: toluene = 2: 1 (weight ratio)) and distilled water, and their dispersibility was confirmed. The obtained surface-modified cellulose short fibers were not dispersed in water, but were dispersed in a mixed solvent of THF, ethanol and toluene with stirring. When the obtained dispersion was observed after 48 hours at room temperature, no phase separation occurred. When this powder was hot pressed at 190 ° C. and 200 kg / cm ² , a translucent sheet was obtained. Thermoformability was also confirmed by forming the sheet with a hot press.

Example 5
The same procedure as in Example 2 was performed except that a 0.2 wt% serisch aqueous dispersion was used instead of the 2 wt% serisch aqueous dispersion. About the obtained product, the dispersibility to THF was confirmed. The product obtained in this example is a polyvinyl butyral composite material containing 5% by weight cellulose short fiber, and can be used directly as a composite material. A sheet was formed from the obtained product by hot pressing, and a tensile test and surface hardness were measured. The results of sheeting by hot pressing are shown in Table 1, FIG. 3 and FIG.

Example 6
The same procedure as in Example 2 was performed except that a 0.1 wt% serisch aqueous dispersion was used instead of the 2 wt% serisch aqueous dispersion. About the obtained product, the dispersibility to THF was confirmed. The product obtained in this example is a polyvinyl butyral composite material containing 2.5% by weight of short cellulose fibers and can be directly used as a composite material. The obtained product was formed into a sheet by hot pressing, and a tensile test and a surface height were measured. The result of forming into a sheet by hot pressing is shown in Table 1 and FIG.

Example 7
The same procedure as in Example 2 was carried out except that a 0.5 wt% bacterial cellulose aqueous dispersion was used instead of the 2 wt% serisch aqueous dispersion. The obtained surface-modified bacterial cellulose was dispersed in THF to obtain a uniform and stable dispersion. It was also confirmed that the sheet was formed by hot pressing.

Example 8
The same procedure as in Example 2 was performed except that 0.6 part of acetaldehyde was used instead of 0.7 part by weight of propionaldehyde. The obtained surface-modified cellulose short fibers were dispersed in THF to obtain a uniform and stable dispersion. It was also confirmed that the sheet could be formed by hot pressing at 190 ° C.

Comparative Example 1
A 2% by weight serisch FG-100 aqueous dispersion was dehydrated by filtration and then further dried with a 40 ° C. blower dryer. The dried serisch was pulverized and dispersed in distilled water or THF, but both precipitated as particles. Further, hot pressing was performed in the same manner as in Example 1, but the sheet could not be formed.

Comparative Example 2
The same procedure as in Example 2 was performed except that the 2 wt% serisch aqueous dispersion was not added. The obtained polyvinyl butyral containing no cellulose short fiber was formed into a sheet by hot pressing, and a tensile test and surface hardness were measured. The results are shown in Table 1 and FIG.

(Dynamic hardness)
The surface hardness of the hot press sheet was measured with a Shimadzu dynamic microphotometer DUH-200 using a triangular pyramid indenter with a ridge angle of 115 ° C.
Test force = 0.2 mN.

(Measurement of tensile properties)
The obtained strip-shaped body having a thickness of 0.1 mm was punched out with a dumbbell 28 described in JIS K 6251 to prepare a test piece. Using this test piece, 25 ° C., cutting tensile stress, cutting tensile elongation, and elastic modulus were measured with an AGS-20KNG strength tester manufactured by Shimadzu Corporation.
Load cell used: 1KN
Distance between grips: 30mm
Test speed: 5mm / min

  It can be seen from Table 1 that the hardness, tensile strength, and elastic modulus improved as the amount of MFC added increased. Moreover, it turns out that the sheet | seat of the surface modification cellulose short fiber of Example 5 and 6 is excellent in hardness and tensile strength compared with the sheet | seat of the comparative example 2, and has a high elasticity modulus.

It is a SEM photograph of serisch used for the present invention. The fiber diameter is estimated to be 10-500 nm. It is the external appearance of the surface-modified cellulose short fiber of Example 1 of this invention, its THF dispersion liquid, and a sheet | seat. It can be seen that the surface-modified cellulose short fibers produced in Example 1 are not keratinized and are in a powder state, as shown in the center photograph. In addition, the surface-modified cellulose short fibers produced according to Example 1 can be well dispersed in THF to form a 1% by weight THF dispersion as shown in the left figure, and highly dispersed in an organic solvent. Showed sex. Moreover, as the right figure shows, it turns out that the surface modification cellulose short fiber of Example 1 was able to become a sheet | seat by the hot press. It is the external appearance of the surface modified cellulose short fiber of Example 4 of this invention, and its THF dispersion liquid. It can be seen that the surface-modified cellulose short fibers of Example 4 are not keratinized even in a dry state and are in a powder state, as shown in the left figure. Further, as shown in the right figure, it was well dispersed in THF and could be a 5 wt% THF dispersion, which showed high dispersibility in organic solvents. It is a hot press sheet of the product obtained from Examples 5 and 6 and Comparative Example 2 of the present invention. It can be seen that the short cellulose fibers of Examples 5 and 6 were well dispersed in THF and could be formed into sheets by hot pressing.

Claims (9)

An aqueous dispersion of short cellulose fibers;
Water-soluble polyvinyl alcohol having a polymerization degree of 500 to 2000 and a saponification degree of 85 to 95 mol%;
At least one aldehyde selected from the group consisting of acetaldehyde, propionaldehyde, or normal butyraldehyde,
A method for producing a surface-modified cellulose short fiber, wherein an acetal reaction is carried out using an acid catalyst. The acetal reaction is carried out by freezing the reaction solution before the water-soluble polyvinyl alcohol is completely precipitated from the reaction solution due to an increase in the degree of acetalization, and then heating the reaction solution to 50 to 90 ° C. The method for producing surface-modified cellulose short fibers according to claim 1, wherein the method is completed. A first step in which an aqueous dispersion of the cellulose short fibers and the aldehyde are subjected to an acetal reaction using an acid catalyst;
Furthermore, the manufacturing method of the surface modification cellulose short fiber of Claim 1 or 2 which has a 2nd process consisting of adding the said water-soluble polyvinyl alcohol and making it acetal-react. The method for producing surface-modified cellulose short fibers according to claim 1, 2 or 3, wherein the aldehyde is two or more aldehydes. The method for producing surface-modified cellulose short fibers according to claim 1, 2, 3, or 4, wherein the aldehyde is propionaldehyde or normal butyraldehyde. The method for producing surface-modified cellulose short fibers according to claim 1, 2, 3, 4, or 5, wherein the cellulose short fibers have an average fiber diameter of 3 to 5000 nm. Surface-modified cellulose short fibers produced by the method according to claim 1, 2, 3, 4, 5 or 6. A reinforcing material for a polymer composite material comprising the surface-modified cellulose short fibers. A polymer composite filler comprising the surface-modified cellulose short fibers.