JP2013011026A - High-strength material including cellulose nanofiber as main component and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-strength and light-weight material that forms no combustion residue during disposal.SOLUTION: A high-strength and light-weight material having a density of 1.2 g/cmor more to 1.4 g/cmor less, a flexural strength of 200 MPa or more, and a flexural modulus of 14 GPa or more is provided by pressing cellulose nanofibers having an average fiber diameter of 10-100nm and an average aspect ratio of 1000 or more at high temperature under high pressure.

Description

  The present invention relates to a high-strength material derived from biomass. More specifically, the present invention relates to a high-strength and lightweight material mainly composed of cellulose nanofibers.

  Conventionally, as a resin-based high-strength material, a fiber-reinforced plastic in which glass fiber or carbon fiber is added to a resin, so-called FRP has been known. However, there is a problem that combustion residues are generated at the time of disposal when FRP is heavy or glass fiber is added. Therefore, in recent years, high-strength materials using biomass-derived fibers have attracted attention. For example, Japanese Unexamined Patent Application Publication No. 2005-60680 (Patent Document 1) discloses a high-strength material using bacterial cellulose, and Japanese Unexamined Patent Application Publication No. 2003-201695 (Patent Document 2) uses cellulose microfibrils. A high strength material was disclosed.

  JP-A-2005-60680 (Patent Document 1) contains fibers having an average fiber diameter of 4 to 200 nm and a matrix material, and has a light transmittance of 60% or more at a wavelength of 400 to 700 nm in terms of a thickness of 50 μm. Fiber reinforced composite materials have been proposed. This document describes that as a fiber having an average fiber diameter of 4 to 200 nm, bacterial cellulose, in particular, a bacterial cellulose structure having a three-dimensional cross structure that has not been disaggregated is preferable. Further, this document describes that the fiber content in the fiber-reinforced composite material is preferably 10% by weight or more, particularly 30% by weight or more, particularly 50% by weight or more, and the content in the examples is 70% by weight. is there. Furthermore, this document describes that the matrix material is preferably an amorphous synthetic polymer having a high glass transition temperature, and in the examples, phenol resin and acrylic resin are used.

  Japanese Unexamined Patent Application Publication No. 2003-201695 (Patent Document 2) proposes a high-strength material composed of cellulose microfibrils and additives. In this document, as a method for obtaining cellulose microfibrils, it is disclosed that pulp is made into fine fibers. As a method for making pulp into fine fibers, medium stirring mill treatment, vibration mill treatment, and high-pressure homogenization apparatus are used. And mortar-type grinding treatment.

  However, the material using bacterial cellulose of Patent Document 1 is satisfactory in terms of strength, but bacterial cellulose has a problem that it takes a long time for culturing and has low productivity. On the other hand, when the pulp disclosed in Patent Document 2 is made into nanofibers by medium stirring mill treatment, vibration mill treatment, treatment with a high-pressure homogenizer, or stone mill type pulverization treatment, the resulting nanofibers are often cut into fibers. Since the fiber length with respect to the fiber diameter is short, it is not suitable as a reinforcing material.

JP 2005-60680 A JP 2003-201695 A

  Accordingly, an object of the present invention is to provide a high-strength material derived from biomass and excellent in industrial productivity and a method for producing the same.

  As a result of intensive studies to achieve the above object, the present inventor dehydrated, dried and pressed plant-derived cellulose microfibers having a maximum fiber diameter of 100 nm or less and a relatively long fiber length. Thus, it was found that an excellent high-strength material can be obtained, and the present invention has been completed.

That is, the high-strength material of the present invention is a high-strength material having a density of 1.2 g / cm ³ or more and 1.4 g / cm ³ or less, a bending strength of 200 MPa or more, and a flexural modulus of 14 GPa or more. The high-strength material may contain cellulose nanofibers as a main component. The cellulose nanofiber may have a maximum fiber diameter of 100 nm or less and an average aspect ratio of 1000 or more. The cellulose nanofibers may be derived from pulp composed of wood fibers and / or seed hair fibers. The cellulose nanofibers were produced in a dispersion preparation step in which raw fibers were dispersed in a solvent to prepare a dispersion, and in a homogenization step in which the dispersion was homogenized with a homogenizer equipped with a crushing type homovalve sheet. May be. The crush-type homovalve seat is composed of a hollow disk-shaped main body part and a hollow cylindrical convex part extending in a downstream direction from the inner wall of the disk-shaped main body part, and the inner wall of the hollow cylindrical convex part is In addition, on the downstream side, a tapered portion whose inner diameter is enlarged with respect to the downstream direction may be formed. The ratio of the inner diameter of the downstream end of the hollow cylindrical convex portion and the thickness of the ring-shaped end surface in the crushing type homovalve seat may be the former / the latter = 100/1 to 5/1. The high-strength material of the present invention may be produced by pressing the cellulose nanofibers at a high temperature and a high pressure.

  The high-strength material of the present invention is lightweight (low density) and particularly excellent in bending strength.

  In the present invention, the use of plant-derived cellulose nanofibers (cellulose microfibers) having a maximum fiber diameter of 100 nm or less and a ratio of the average fiber length to the average fiber diameter of 1000 or more enables light weight and particularly bending strength. High-strength material with excellent resistance can be obtained.

  The high-strength material of the present invention is composed of plant-derived cellulose microfibers.

[Production method of microfiber]
The method for producing microfibers of the present invention includes a dispersion preparation step in which raw fibers are dispersed in a solvent to prepare a dispersion, and a homogenization step in which the dispersion is homogenized with a homogenizer equipped with a crushing type homovalve sheet.

(Dispersion preparation process)
As the raw material fibers, natural fibers (for example, cellulose, silk, wool fibers, etc.), regenerated fibers (for example, protein or polypeptide fibers, alginic acid fibers, etc.), bituminous carbonaceous fibers (pitch fibers, etc.), synthetic fibers (for example) Organic fibers such as thermosetting resin fibers and thermoplastic resin fibers) are used. Of these organic fibers, natural fibers, thermosetting resin fibers (epoxy fibers, phenol fibers, unsaturated polyester fibers, polyimide fibers, polyamide imide fibers) because microfibrillation with a homogenizer is likely to proceed. , Polybenzimidazole fiber, polyurethane fiber, etc.), thermoplastic resin fiber (polyamide fiber, polyester fiber, polycarbonate fiber, polyphenylene oxide fiber, polyphenylene sulfide fiber, olefin fiber, acrylic fiber, fatty acid vinyl) Ester-based fibers and the like are preferable, and cellulose-based fibers are particularly preferable.

  Cellulose fibers are not particularly limited as long as they are polysaccharides having a β-1,4-glucan structure, and cellulose fibers derived from higher plants [for example, wood fibers (wood pulp of conifers, hardwoods, etc.), bamboo, etc. Natural cellulose fibers such as fiber, sugarcane fiber, seed hair fiber (cotton linter, Bombax cotton, kapok, etc.), gin leather fiber (eg, hemp, mulberry, mitsumata), leaf fiber (eg, Manila hemp, New Zealand hemp) (Pulp fibers, etc.), animal-derived cellulose fibers (such as squirt cellulose), bacterial-derived cellulose fibers, chemically synthesized cellulose fibers [cellulose acetate (cellulose acetate), cellulose propionate, cellulose butyrate, cellulose Acetate propionate, cellulose acetate Organic acid esters such as tyrates; inorganic acid esters such as cellulose nitrate, cellulose sulfate, and cellulose phosphate; mixed acid esters such as cellulose nitrate acetate; hydroxyalkyl celluloses (eg, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose, etc.); carboxyalkyls Cellulose (carboxymethyl cellulose (CMC), carboxyethyl cellulose, etc.); alkyl cellulose (methyl cellulose, ethyl cellulose, etc.); and cellulose derivatives such as regenerated cellulose (rayon, cellophane, etc.). The cellulose fiber is a high-purity cellulose having a high α-cellulose content, for example, an α-cellulose content of 70 to 100% by weight (for example, 95 to 100% by weight), preferably 98 to 100, depending on applications. It may be about wt%. Furthermore, in the present invention, by using high-purity cellulose having a low lignin or hemicellulose content, cellulose fibers having nanometer size and uniform fiber diameter can be prepared even when wood fibers or seed hair fibers are used. As a cellulose fiber with low lignin or hemicellulose content, in particular, the kappa number (kappa number) is 30 or less (for example, 0 to 30), preferably 0 to 20, more preferably about 0 to 10 (particularly 0 to 5). There may be. The kappa number can be measured by a method based on “Pulp-Kappa number test method” of JIS P8211. These cellulosic fibers may be used alone or in combination of two or more.

  Of these cellulosic fibers, pulps such as wood fibers (wood pulp such as conifers and hardwoods) and seed hair fibers (such as cotton linter pulp) are widely used from the viewpoint of productivity, and when using pulp, Pulp obtained by mechanical methods (crushed wood pulp, refiner ground pulp, thermomechanical pulp, semi-chemical pulp, chemiground pulp, etc.), or pulp obtained by chemical methods (craft pulp, sulfite pulp, etc.) Or beating fiber (beating pulp or the like) subjected to beating (preliminary beating) if necessary. The cellulosic fiber may be a fiber that has been subjected to a conventional purification treatment such as degreasing (for example, absorbent cotton). In the present invention, from the viewpoint of suppressing the entanglement of raw material fibers, realizing efficient microfibril formation by homogenization treatment, and obtaining uniform nanometer-sized microfibers, never dry pulp, that is, pulp having no drying history (dried) Pulp that retains its wet state without being) is particularly preferred. The never dry pulp is a pulp composed of wood fibers and / or seed hair fibers, and may be a pulp having a copper number of 30 or less (particularly about 0 to 10). Such pulp may be prepared by bleaching wood fibers and / or seed hair fibers with chlorine.

  The average fiber length of the raw material fibers is, for example, about 0.01 to 5 mm, preferably 0.03 to 4 mm, more preferably about 0.06 to 3 mm (particularly 0.1 to 2 mm), and usually 0.1 to 5 mm. It is about 5 mm. Moreover, the average fiber diameter of raw material fibers is 0.01-500 micrometers, Preferably it is 0.05-400 micrometers, More preferably, it is about 0.1-300 micrometers (especially 0.2-250 micrometers).

The solvent is not particularly limited as long as it does not cause chemical or physical damage to the raw fiber. For example, water, organic solvents [alcohols (C _1-4 alkanols such as methanol, ethanol, 2-propanol, isopropanol, etc.), Ethers (diC _1-4 alkyl ethers such as diethyl ether and diisopropyl ether, cyclic ethers such as tetrahydrofuran (cyclic C _4-6 ethers and the like)), esters (alkanoic esters such as ethyl acetate), ketones (acetone, DiC _1-5 alkyl ketones such as methyl ethyl ketone and methyl butyl ketone, C _4-10 cycloalkanones such as cyclohexanone), aromatic hydrocarbons (toluene, xylene, etc.), halogenated hydrocarbons (methyl chloride, fluoride) Methyl etc.)] and the like.

These solvents may be used alone or in combination of two or more. Of these solvents, water is preferable from the viewpoint of productivity and cost, and a mixed solvent of water and an aqueous organic solvent (C _1-4 alkanol, acetone, etc.) may be used if necessary.

  The raw material fiber to be subjected to the homogenization treatment may be in a state of coexisting at least in the solvent, and the raw material fiber may be dispersed (or suspended) in the solvent prior to the homogenization treatment. Dispersion may be performed using, for example, a conventional disperser (such as an ultrasonic disperser, a homodisper, or a three-one motor). The disperser may include mechanical stirring means (such as a stirring bar and a stirring bar).

  The concentration of the raw fiber in the solvent is, for example, 0.01 to 20% by weight, preferably 0.05 to 10% by weight, more preferably 0.1 to 5% by weight (particularly 0.5 to 3% by weight). It may be.

(Homogenization process)
As the homogenizer, the one described in JP 2011-146132 A was used. Further, the homogenization process was also performed according to the process described in JP 2011-146132 A.

(Refiner process)
In the present invention, the dispersion may be refined as a pre-process (preliminary process) of the homogenization process.

  In the refiner process, a disk refiner (single disk refiner, double disk refiner, etc.) can be used. The disc refiner has a disc clearance of about 0.1 to 0.3 mm, preferably about 0.12 to 0.28 mm, more preferably about 0.13 to 0.25 mm (for example, 0.14 to 0.23 mm). May be.

  The number of rotations of the disk is not particularly limited, and can be selected from a wide range of 1,000 to 10,000 rpm. For example, 1,000 to 8,000 rpm, preferably 1,300 to 6,000 rpm, more preferably 1, It may be about 600 to 4,000 rpm.

  In the refiner process, the number of processes (pass number) may be 1 to 20 times, preferably 2 to 15 times, and more preferably about 3 to 10 times (for example, 4 to 9 times).

  The degree of the raw fiber beating process can be adjusted by the disk clearance and the number of refiner processes. If the disk clearance is too narrow or the number of treatments is too high, the raw fiber will receive a large shearing force, fibrillation will proceed, twisting and roughening of the surface will occur, and the fibers will tend to get entangled. The dispersibility of the fibrillated fibers is reduced. On the other hand, if the disk clearance is too wide, the shearing force applied to the raw fiber becomes small, and an undivided portion remains.

  Cellulose nanofibers obtained by microfibrillation of such raw material fibers have a uniform nanometer size and do not substantially contain micron-order size fibers. That is, the maximum fiber diameter of cellulose nanofiber is 100 nm or less, for example, about 20 to 100 nm, preferably about 30 to 90 nm, and more preferably about 40 to 80 nm (particularly about 50 to 70 nm).

  The average fiber diameter of a cellulose nanofiber is 10-90 nm, for example, Preferably it is 15-80 nm, More preferably, it is a 20-60 nm (especially 25-50 nm) grade. Furthermore, the standard deviation of the fiber diameter distribution is, for example, about 80 nm or less (for example, 1 to 80 nm), preferably 3 to 50 nm, more preferably about 5 to 40 nm (particularly 10 to 30 nm).

  In the present invention, the average fiber diameter, the standard deviation of the fiber diameter distribution, and the maximum fiber diameter are values calculated from a fiber diameter (about n = 20) measured based on an electron micrograph.

  The average fiber length of the cellulose nanofiber can be selected from a range of about 10 to 1000 μm. However, from the viewpoint of improving the mechanical properties of the fiber reinforced resin composition, for example, 100 to 500 μm, preferably 110 to 400 μm, and more preferably 120 It may be about ˜300 μm (particularly 130 to 200 μm). Furthermore, the ratio of the average fiber length to the average fiber diameter (average fiber length / average fiber diameter) (average aspect ratio) is 1000 or more, for example, 1000 to 15000, preferably 2000 to 10000, more preferably 3000 to 8000 ( In particular, it is about 4000 to 7000). In the present invention, the use of cellulose nanofibers having a relatively long fiber length and aspect ratio in spite of having a nano-sized average diameter, the fibers are appropriately intertwined, or dimensional stability. And a resin composition and sheet excellent in mechanical properties such as strength and strength.

  The cross-sectional shape (cross-sectional shape perpendicular to the longitudinal direction of the fiber) of the cellulose nanofiber may be an anisotropic shape (flat shape) like bacterial cellulose, but it has optical properties such as transparency and low haze. Therefore, a substantially isotropic shape is preferable. Examples of the substantially isotropic shape include a perfect circle shape and a regular polygon shape. In the case of a substantially circular shape, the ratio of the major axis to the minor axis (average aspect ratio) is, for example, 1-2, preferably 1-1. 0.5, more preferably about 1 to 1.3 (particularly 1 to 1.2).

  The dehydration time of the cellulose nanofiber is, for example, 1000 seconds or more, preferably 1200 to 10000, when measured using a fiber slurry having a concentration of 0.5% by weight in accordance with a test method for dehydration amount of API standard. Second, more preferably about 1500 to 8000 seconds (especially 1800 to 7000 seconds). The longer the dehydration time, the higher the average fiber length / average fiber diameter ratio, and the higher the water retention, the better the mechanical properties.

  Cellulose nanofibers are highly dispersible in water and can form a stable dispersion (or suspension). For example, the viscosity of the suspension obtained by suspending cellulose nanofibers in water to a concentration of 2% by weight is 3000 mPa · s or more, preferably 4000-15000 mPa · s, more preferably about 5000-10000 mPa · s. It is. The viscosity was measured using a B-type viscometer using a rotor No. 4 is a value measured as an apparent viscosity at 25 ° C. at a rotation speed of 60 rpm. If the degree of fibrillation is small or the fiber diameter is large, the dispersibility in water decreases, a uniform suspension cannot be obtained, and the viscosity cannot be measured.

[Method of manufacturing high-strength material]
The high-strength material of the present invention is produced by pressing the cellulose nanofibers at a high temperature and a high pressure. For example, the slurry liquid of the cellulose nanofiber is drained so as to have a solid content of 30%, thereby preparing a hard cake. Subsequently, the hard cake is dried with a dryer, and then pressed at a high temperature to obtain a high-strength material. For example, a pressure dehydrator can be used to remove the slurry. Moreover, although it is press conditions, it is preferable to press at a pressure of 2 MPa to 30 MPa under a temperature condition of 80 ° C. to 200 ° C.

The density of the high strength material thus obtained is preferably 1.2 g / cm ³ or more and 1.4 g / cm ³ or less. Similarly, the bending strength is 200 MPa or more and 300 MPa or less, preferably 220 MPa or more and 260 MPa or less. The flexural modulus is 10 GPa or more and 20 GPa or less, preferably 13 GPa or more and 18 GPa or less.

  Example

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The test pieces obtained in Examples and Comparative Examples were evaluated by the following methods.

[density]
The density was calculated from the volume and weight of the test pieces obtained in the examples and comparative examples.

[Bending strength]
In accordance with ISO178, the bending strength of the test pieces obtained in Examples and Comparative Examples was measured by a three-point bending measurement method.

[Bending elastic modulus]
According to ISO178, the bending elastic modulus was measured by the 3 point | piece bending measuring method for the test piece obtained by the Example and the comparative example.

Example 1
Using NBKP pulp (manufactured by Marusumi Paper Co., Ltd., solid content of about 50% by weight, copper number of about 0.3), 100 liters of a slurry liquid containing 1% by weight of pulp was prepared. Subsequently, using a disk refiner (SUPERFIBRATER 400-TFS, manufactured by Hasegawa Tekko Co., Ltd.), a refiner-treated product was obtained by beating 10 times with a clearance of 0.15 mm and a disk rotation speed of 1750 rpm. This refiner-treated product was converted into a first homogenizer (manufactured by Gorin, 15M8AT) equipped with a normal non-crushing type homovalve seat (inner diameter at the downstream end of the hollow cylindrical projection / thickness of the ring-shaped end surface = 1.9 / 1). ) Was used 20 times at a processing pressure of 50 MPa. Furthermore, using a second homogenizer (manufactured by Nirosoavi, PANDA2K) equipped with a crushing type homovalve seat (inner diameter of the downstream end of the hollow cylindrical convex portion / thickness of the ring-shaped end face = 16.8 / 1) The treatment was performed 20 times at 120 MPa. Furthermore, Table 1 shows the average fiber diameter, average fiber length, and aspect ratio (average fiber length / average fiber diameter) of the obtained microfibers.

  The 1% slurry solution of cellulose nanofibers thus obtained was drained using a pressure dehydrator so that the solid content was 30%, and a hard cake was prepared. This hard cake was dried with a dryer at 120 ° C. for 2 hours, and then pressed at 120 ° C. and 30 MPa for 30 minutes to obtain a molded piece having a thickness of 2 mm. This molded piece was cut into a strip having a width of 10 mm, and the bending strength and the bending elastic modulus were measured by a three-point bending measurement method. Table 1 shows the evaluation results of the obtained test pieces.

Example 2
Example 1 was performed except that the hard cake after drying was pressed at 120 ° C. and 100 MPa for 30 minutes. Table 1 shows the evaluation results of the obtained test pieces.

Comparative Example 1
A 10-pass treatment was performed on a serish KY-100G (manufactured by Daicel Chemical Industries, Ltd.) using a grinder (manufactured by Masuyuki Sangyo Co., Ltd., Super Mass Colloid) and a No. 80 grindstone. The 1% slurry was drained using a pressure dehydrator so that the solid content was 30%, and a hard cake was prepared. This hard cake was dried with a dryer at 120 ° C. for 2 hours, and then pressed at 120 ° C. and 30 MPa for 30 minutes to obtain a molded piece having a thickness of 2 mm. This molded piece was cut into a strip having a width of 10 mm, and the bending strength and the bending elastic modulus were measured by a three-point bending measurement method. Table 1 shows the evaluation results of the obtained test pieces.

Comparative Example 2
Bacterial cellulose (manufactured by Fujicco Co., Ltd.) was pulverized for 10 minutes with a juicer mixer, and washed with water three times to remove acetic acid and acetic acid bacteria. Subsequently, the bacterial cellulose 1% slurry thus treated was dehydrated using a pressure dehydrator so as to have a solid content of 30%, thereby preparing a hard cake. This hard cake was dried with a dryer at 120 ° C. for 2 hours, and then pressed at 120 ° C. and 30 MPa for 30 minutes to obtain a molded piece having a thickness of 2 mm. This molded piece was cut into a strip having a width of 10 mm, and the bending strength and the bending elastic modulus were measured by a three-point bending measurement method. Table 1 shows the evaluation results of the obtained test pieces.

Comparative Example 3
A 1% slurry solution of powdered cellulose (KC Flock W-300G, manufactured by Nippon Paper Industries Co., Ltd.) was treated 20 times with a counter collision type homogenizer (Starburst, manufactured by Sugino Machine Co., Ltd.). Subsequently, this 1% slurry was dehydrated using a pressure dehydrator so that the solid content was 30%, and a hard cake was prepared. Furthermore, this hard cake was dried at 120 ° C. for 2 hours with a dryer, and then pressed at 120 ° C. and 30 MPa for 30 minutes to obtain a molded piece having a thickness of 2 mm. This molded piece was cut into a strip having a width of 10 mm, and the bending strength and the bending elastic modulus were measured by a three-point bending measurement method. Table 1 shows the evaluation results of the obtained test pieces.

Comparative Example 4
A 1% slurry solution of Celish KY-100G (manufactured by Daicel Chemical Industries, Ltd.) was dehydrated using a pressure dehydrator so that the solid content was 30%, and a hard cake was prepared. This hard cake was dried with a dryer at 120 ° C. for 2 hours, and then pressed at 120 ° C. and 30 MPa for 30 minutes to obtain a molded piece having a thickness of 2 mm. This molded piece was cut into a strip having a width of 10 mm, and the bending strength and the bending elastic modulus were measured by a three-point bending measurement method. Table 1 shows the evaluation results of the obtained test pieces.

   As is clear from the results in Table 1, the high-strength materials obtained in the examples are excellent in bending strength and bending elastic modulus.

  The high-strength material of the present invention is excellent in bending strength and flexural modulus, is lightweight, and does not generate toxic gas or combustion residue when incinerated, and thus can be widely used as a high-strength material.

Claims (8)

A high-strength material having a density of 1.2 g / cm ³ or more and 1.4 g / cm ³ or less, a bending strength of 200 MPa or more, and a flexural modulus of 14 GPa or more.   The high-strength material according to claim 1, comprising cellulose nanofiber as a main component.   The high-strength material according to claim 1, wherein the cellulose nanofiber has a maximum fiber diameter of 100 nm or less and an average aspect ratio of 1000 or more.   The high-strength material according to any one of claims 1 to 3, wherein the cellulose nanofibers are derived from pulp composed of wood fibers and / or seed hair fibers.   Cellulose nanofibers are manufactured in a dispersion preparation step in which a raw material fiber is dispersed in a solvent to prepare a dispersion, and in a homogenization step in which the dispersion is homogenized with a homogenizer equipped with a crushing type homovalve sheet. The high-strength material according to claim 1.   The crushing type homo-valve seat is composed of a hollow disc-shaped main body portion and a hollow cylindrical convex portion extending in a downstream direction from the inner wall of the disc-shaped main body portion, and the inner wall of the hollow cylindrical convex portion is The high-strength material according to claim 5, wherein a taper portion whose inner diameter is increased in the downstream direction is formed on the downstream side.   The high-strength material according to claim 6, wherein the ratio of the inner diameter of the downstream end of the hollow cylindrical convex portion and the thickness of the ring-shaped end surface of the crushing type homovalve seat is the former / the latter = 100/1 to 5/1.   The method for producing a high-strength material according to claim 1, wherein the cellulose nanofiber is pressed at a high temperature and a high pressure.