JP7237165B2 - Composite material - Google Patents

Description

The present invention relates to a composite material containing polyacetal resin and cellulose nanofibers.

BACKGROUND ART Conventionally, polyacetal resins have been used as materials for various products because they have excellent mechanical strength and are inexpensive. For example, polyacetal resin is used as a material for gears, zippers, etc., because it has excellent slidability.

Moreover, in recent years, resin materials such as polyacetal resin have been used as fiber-reinforced plastics (FRP) that are enhanced in strength by being combined with fibers. Fiber materials contained in FRP include glass fiber, carbon fiber, cellulose nanofiber, and the like. Among these, cellulose nanofiber is a preferred fiber material from the viewpoint of excellent lightness, ease of recycling, low environmental load, and the like.

In order for a composite material containing cellulose nanofibers to exhibit expected functions, dispersibility of cellulose nanofibers in resin is important. However, cellulose nanofibers have high hydrophilicity due to the presence of many hydroxyl groups in cellulose, and thus cellulose nanofibers are generally difficult to mix with highly hydrophobic resins. In order to overcome this problem, a composite material has been proposed in which a resin contains modified cellulose nanofibers in which the hydroxyl groups of cellulose are modified with organic groups.

As such a composite material, Patent Literature 1 describes a composite material containing a polyacetal resin and modified cellulose nanofibers in which some of the hydroxyl groups of cellulose are acetylated. Hydrophobicity of the acetylated modified cellulose nanofibers is improved because some of the hydroxyl groups of cellulose are acetylated. As a result, the acetylated modified cellulose nanofibers have improved affinity with polyacetal resins, and can exhibit better dispersibility in polyacetal resins compared to unmodified cellulose nanofibers.

Japanese Patent No. 6091589

However, the composite material described in Patent Document 1 has a problem that the effect due to the addition of cellulose nanofibers is not sufficiently exhibited. In particular, the composite material has a problem that the functions required when it is molded into various products are insufficient. For example, the composite material suffers from insufficient dimensional stability and high shrinkage during molding, which entails difficulties in molding.

In view of the above circumstances, an object of the present invention is to provide a composite material capable of exhibiting superior functions as compared with the prior art.

In general, cellulose nanofibers are reduced in crystallinity by chemical modification such as acetylation. In addition, since the amorphous portion is thermally unstable compared to the crystalline portion, the cellulose nanofibers with reduced crystallinity are likely to be thermally decomposed.

In contrast, the present inventors have found that among cellulose nanofibers, cotton-derived cellulose nanofibers have a relatively high degree of crystallinity. The inventors have found that the degree of crystallinity does not easily decrease, and have completed the present invention.

The composite material according to the present invention is
Containing polyacetal resin and cellulose nanofibers,
In the cellulose nanofiber, part of the hydroxyl groups of cellulose are acylated,
The cellulose nanofiber is a composite material derived from cotton.

Also preferably, in the composite material according to the present invention, the acylation is acetylation.

Preferably, the composite material according to the present invention further contains an amide-based dispersant.

Preferably, in the composite material according to the present invention, the amide-based dispersant is polyoxyethylene alkylamide.

FIG. 1 is an SEM image of CNF of Production Example 1 in Examples. FIG. 2 is an SEM image of CNF of Production Example 2 in Example. FIG. 3 is an SEM image of CNF of Production Example 3 in Example. FIG. 4 is an IR spectrum of CNF of Production Examples 1 to 3 in Examples. FIG. 5 is an XRD chart of CNFs of Production Examples 1 to 5 in Examples. FIG. 6 is a TG chart of CNFs of Production Examples 1 to 5 in Examples. FIG. 7 is a diagram showing an example of a DMA chart and a method of obtaining the softening temperature from the DMA chart.

An embodiment of the composite material according to the present invention will be described below with reference to the drawings.

A composite material according to the present embodiment contains a polyacetal resin, cellulose nanofibers, and an amide-based dispersant, and the cellulose nanofibers have cellulose hydroxyl groups partially acylated. In addition, the cellulose nanofibers are made from cellulose fibers obtained from cotton.

The composite material is used as a molding material for various parts, and can be molded into automobile parts, precision parts, and the like by injection molding, for example. The composite material is molded at a molding temperature of usually 180 to 220°C, preferably 180 to 200°C. Therefore, the composite material preferably has excellent moldability under such molding conditions. From this point of view, the coefficient of linear expansion of the composite material at 30 to 120°C is preferably 90 ppm/°C or less, more preferably 70 ppm/°C or less, and even more preferably 50 ppm/°C or less. Moreover, the linear expansion coefficient of the composite material is usually 10 ppm/° C. or more. The coefficient of linear expansion is measured by the measuring method described in Examples.

The storage modulus (E') of the composite material at 100°C is preferably 1000 MPa or more, more preferably 1100 MPa or more, still more preferably 1200 MPa or more, and still more preferably 1500 MPa or more. Thereby, the composite material can have excellent heat resistance and mechanical properties. In addition, the storage modulus (E') of the composite material at 100°C is usually 2500 MPa or less. In addition, the said storage elastic modulus is measured by the measuring method described in the Example.

The polyacetal resin is a polymer having an acetal structure —(—O—CRH—) _n — (R represents a hydrogen atom or an organic group) in a repeating structure. Usually, an oxymethylene group (--OCH ₂ --) in which R is a hydrogen atom is the main structural unit. The polyacetal resin may be a polyacetal homopolymer or a polyacetal copolymer. In addition, the polyacetal resin has a content of the polyacetal homopolymer or the polyacetal copolymer of usually 90% by mass or more, preferably 95% by mass or more, and may partially contain other polymer components. good.

The raw material is seed hair fiber collected from seeds of seed hair plants. Examples of seed-hair plants include cotton, acundo, and kapok, and among these, cotton is preferred. Cotton seeds are covered with fibers called cotton balls, which are made up of lint covering the seeds and lint covering the outside of the linters. Since lint has a longer fiber length than linter, lint is generally used as a raw material for cotton thread and cotton fabric, and linter is used as linter pulp and rayon. The cellulose nanofibers may be produced from lint, or may be produced from linter. In the present embodiment, the cellulose nanofibers are made from linter pulp produced from linter.

The cellulose nanofibers derived from cotton have a lower lignin content than cellulose nanofibers derived from other plants such as conifers. Here, since the lignin is easily decomposed by heat, the thermal stability of the cellulose nanofibers may be lowered when the content thereof is high. Therefore, composite materials containing the cellulose nanofibers derived from cotton can have excellent thermal stability. The lignin content in the cellulose nanofibers is preferably 500 ppm or less, more preferably 100 ppm or less. The lignin content is measured by the Klason method.

The cellulose nanofibers are defibrated to a nano level. The nano-level means that the average fiber diameter of the cellulose nanofibers is usually 15 to 800 nm, preferably 20 to 500 nm. In addition, the cellulose nanofiber should just have the said average fiber diameter in the said composite material. For example, cellulose fibers having an average fiber diameter of about several tens of micrometers may be defibrated to a nano level by being kneaded with the polyacetal resin. Also, the average fiber diameter is measured by the measuring method described in the Examples.

Moreover, the average fiber length of the cellulose nanofibers is usually 0.5 to 100 μm, preferably 1 to 80 μm. The average fiber length is measured by the measuring method described in Examples.

In the cellulose nanofiber, part of the hydroxyl groups of cellulose are acylated. In other words, part of the cellulose hydroxyl groups of the cellulose nanofibers are substituted with acyl groups represented by the chemical formula R ¹ COO. As the acyl group, R ¹ is preferably an alkyl group having 1 to 18 carbon atoms, preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms. preferable. For example, the acyl group is preferably an acetyl group, a butyryl group or a lauryl group. Among these, the cellulose nanofibers having an acetyl group are preferable from the viewpoint of exhibiting excellent thermal stability and reducing the manufacturing cost.

The ratio of acylated hydroxyl groups to the cellulose hydroxyl groups in the cellulose nanofibers is indicated as the average degree of substitution. The average degree of substitution is generally 0.1 to 0.5, preferably 0.2 to 0.45, in the case of wood pulp. On the other hand, in the case of cotton-derived linter pulp, it is 0.1 to 1.5, preferably 0.2 to 1.2, more preferably 0.3 to 1.0. Moreover, the preferred value of the average degree of substitution differs depending on the type of the acyl group. For example, in the case of an acetyl group, it is preferably 0.1 to 1.5, more preferably 0.2 to 1.2, and in the case of a butyryl group, it is preferably 0.05 to 1.3, more preferably It is preferably 0.1 to 1.2, and in the case of a lauryl group, it is preferably 0.05 to 1.2, more preferably 0.1 to 1.0. A lauryl group has 12 carbon atoms in R ¹ and has a relatively long alkyl side chain, which can cover the surface of cellulose. Therefore, cellulose nanofibers having lauryl groups can have excellent affinity with the polyacetal resin even when the average degree of substitution is relatively low. Moreover, when the average degree of substitution is low, it is preferable because the decrease in crystallinity of the cellulose nanofibers can be suppressed. The average degree of substitution is measured by the measuring method described in Examples.

The cellulose nanofibers have cellulose type I crystals. The content of the cellulose type I crystals in the cellulose nanofibers is indicated as the degree of crystallinity. The cellulose nanofibers derived from cotton have a higher degree of crystallinity than other plant-derived cellulose nanofibers. Moreover, when the cellulose nanofibers are acylated, the acylated portion usually becomes amorphous, so the degree of crystallinity is lowered. In contrast, the cellulose nanofibers derived from cotton are less likely to lower the crystallinity due to acylation. The reason for this is thought to be that the cellulose nanofibers derived from cotton are difficult for the acylating agent to permeate inside, and the surface portion that greatly affects the affinity with the polyacetal resin is efficiently acylated. In addition, the fact that the acylating agent hardly penetrates into the inside of the cellulose nanofiber means that the cellulose in the inside is hardly acylated, that is, the crystallinity in the inside is hard to decrease. Cellulose nanofibers having a high degree of crystallinity have high thermal stability and are less likely to be thermally decomposed when kneaded with the polyacetal resin. Therefore, the composite material containing such cellulose nanofibers can exhibit excellent functions.

The crystallinity is preferably 45% or more, more preferably 50% or more, still more preferably 70% or more, still more preferably 75% or more, and most preferably 80% or more. . The crystallinity is measured by the measuring method described in Examples. In addition, as shown in FIG. 5, the cotton-derived cellulose nanofibers show specific peaks at 2θ=14.9° and 16.5° in a powder X-ray crystal diffraction (XRD) chart.

Here, since the polyacetal resin has a relatively high melting point, the kneading temperature is set to a relatively high temperature (usually 180 to 220° C., preferably 180 to 200° C.). In addition, the temperature of the kneaded product can be several tens of degrees Celsius higher than the set temperature due to heat generated during kneading. Therefore, the cellulose nanofibers preferably have heat resistance under such temperature conditions. From such a viewpoint, the thermal decomposition temperature (5% weight loss temperature) of the cellulose nanofibers is preferably 290°C or higher, more preferably 300°C or higher, and 310°C or higher. is more preferable, and 320° C. or higher is even more preferable. The cotton-derived cellulose nanofibers have higher heat resistance than other plant-derived cellulose nanofibers, that is, they can have the thermal decomposition temperature as described above. As a result, the cellulose nanofibers are less likely to be thermally decomposed when kneaded with the polyacetal resin, and the composite material can exhibit excellent functions. In addition, the thermal decomposition temperature of the cellulose nanofiber is usually 360° C. or lower. Also, the thermal decomposition temperature is measured by the measuring method described in the Examples.

The content of the cellulose nanofibers is generally 4 to 50% by mass, preferably 10 to 30% by mass, more preferably 10 to 20% by mass, relative to the total amount of the composite material.

The amide-based dispersant is a dispersant having an amide group in the molecule and is represented by the chemical formula R ² CONR ³ R ⁴ . The amide-based dispersant is preferably liquid under the temperature conditions during kneading, and is preferably less volatile under the temperature conditions during kneading. The melting point of the amide-based dispersant is usually 200°C or higher, preferably 250°C or higher. The boiling point of the amide-based dispersant is usually 200°C or higher, preferably 250°C or higher.

Examples of the amide dispersant include one or more selected from the group consisting of fatty acid amides, fatty acid alkanolamides, polyoxyethylene alkylamides and polyoxypropylene alkylamides. The ^R2 portion of such an amide-based dispersant preferably has a structure capable of exhibiting affinity with the polyacetal resin. From such a viewpoint, R ² is preferably an alkyl or alkenyl group having 3 to 25 carbon atoms, more preferably 5 to 20 carbon atoms.

Examples of the fatty acid amide include stearic acid monoamide, oleic acid monoamide, erucic acid monoamide, ethylenebisstearic acid amide, and ethylenebisoleic acid amide.

Examples of the fatty acid alkanolamide include coconut fatty acid monoethanolamide, coconut fatty acid diethanolamide, lauric acid isopropanolamide, beef tallow fatty acid diethanolamide, lauric acid diethanolamide, and oleic acid diethanolamide.

Examples of the polyoxyethylene alkylamide include polyoxyethylene coconut oil fatty acid monoethanolamide and polyoxyethylene lauric acid monoethanolamide.

Examples of the polyoxypropylene alkylamide include polyoxypropylene coconut oil fatty acid monoisopropanolamide.

At least one of R ³ and R ⁴ in the chemical formula of the amide-based dispersant is preferably a hydrogen atom. In such an amide-based dispersant, the hydrogen atom can form a hydrogen bond with the carbonyl oxygen atom of the acyl group in the cellulose nanofiber. Therefore, such an amide-based dispersant can exhibit affinity with the cellulose nanofibers.

Furthermore, it is preferable that R ³ in the chemical formula of the amide-based dispersant is a hydrogen atom and R ⁴ is —(C ₂ H ₄ O) _n H (polyoxyethylene alkyl group). Nimid (registered trademark) manufactured by NOF Corporation is an example of such an amide-based dispersant. In such an amide-based dispersant, the polyoxyethylene group portion exhibits a high affinity with the polyacetal resin, and the hydrogen atom forms a hydrogen bond with the carbonyl oxygen atom of the acyl group in the cellulose nanofiber. can form. That is, such an amide-based dispersant has a structure that exhibits affinity with the polyacetal resin and the cellulose nanofibers, respectively, so that it can function between them like a surfactant. Therefore, such an amide-based dispersant can facilitate the dispersion of the cellulose nanofibers in the composite material.

The content of the amide-based dispersant is generally 1 to 10% by mass, preferably 2 to 5% by mass, relative to the entire composite material.

Next, a method for manufacturing a composite material according to this embodiment will be described.

First, a method for producing the cellulose nanofiber will be described.

The raw material of the cellulose nanofiber is the linter pulp. The crystallinity of the linter pulp is preferably 50% or more, more preferably 70% or more, even more preferably 75% or more, and still more preferably 80% or more. A commercially available linter pulp can be used.

Conventionally known methods can be employed for the method of acylating and defibrating the cellulose fibers. A preferred method is to use a fibrillation device such as a supermasscolloider, and the cellulose fibers are treated with an acylating agent such as a carboxylic acid vinyl ester or a carboxylic anhydride, an acid or base catalyst, and an organic solvent such as DMSO. and a method of obtaining acylated cellulose fibers by treating with a treatment liquid containing. According to this method, the decrease in crystallinity of the cellulose fibers can be suppressed as compared with a mechanical defibration method using a refiner, a high-pressure homogenizer, or the like.

Examples of the acylating agent include carboxylic anhydrides such as acetic anhydride, butyric anhydride and lauric anhydride; carboxylic acids such as acetic acid, butyric acid and lauric acid; vinyl carboxylates such as vinyl acetate, vinyl butyrate and vinyl laurate; Examples include carboxylic acid halides such as halogenated acetic acid, halogenated butyric acid, and halogenated lauric acid.

As the organic solvent, in addition to DMSO, aprotic polar solvents such as formamide, dimethylacetamide, and N-methyl-2-pyrrolidone are preferred.

Further, a defibrating agent that promotes defibration of cellulose fibers may be added to the treatment liquid. Aldehydes represented by R ⁵ —CHO (R ⁵ represents a hydrogen atom, an alkyl group having 1 ^to 16 carbon atoms, an alkenyl group, a cycloalkyl group, or an aryl group); Examples thereof include carboxylic acid vinyl esters represented by CH=CH2 (R6 represents an alkyl group, alkylene group, cycloalkyl group or aryl group having 1 to 24 carbon atoms).

Next, the treatment liquid is removed from the acylated cellulose fibers by filtration, centrifugation, or the like, and the treated cellulose fibers are washed with 2-propanol and/or dimethylacetamide as a washing solvent, Part of the washing solvent is removed by concentration to obtain paste-like cellulose nanofibers. The content of cellulose nanofibers contained in the paste-like cellulose nanofibers is usually 5 to 30% of the total amount.

Next, a method for manufacturing the composite material will be described.

First, a generally used stirrer is used to mix the paste-like cellulose nanofibers and the amide-based dispersant to obtain dispersant-treated cellulose nanofibers.

Next, the dispersant-treated cellulose nanofibers and the polyacetal resin are dispersed in a kneading solvent and kneaded using a kneader to obtain a kneaded product. The kneading temperature is usually 180-195°C. Note that the number of revolutions of the kneader and the kneading time during kneading can be appropriately changed in consideration of the amount of the composite material to be obtained, the amount of cellulose nanofibers to be contained in the composite material, and the like.

As the kneading solvent, an alcohol solvent such as ethanol or 2-propanol, or an amide solvent such as dimethylacetamide or 2-methyl-2-pyrrolidone can be used. Moreover, you may use these solvent in mixture of 2 or more types. As the organic solvent, the amide solvent is preferable, and among these, dimethylacetamide is preferable.

Next, the kneaded material is dried using a vacuum dryer or the like to obtain the composite material. The drying temperature is usually 80-125°C.

As mentioned above, the composite material according to the present invention is
Containing polyacetal resin and cellulose nanofibers,
In the cellulose nanofiber, part of the hydroxyl groups of cellulose are acylated,
The cellulose nanofiber is derived from cotton.

Since the cellulose nanofiber is derived from cotton, it exhibits a higher crystallinity than other plant-derived cellulose nanofibers, and the crystallinity is less likely to decrease due to acylation. Therefore, according to such a configuration, the cellulose nanofibers are less likely to be thermally decomposed when kneaded with the polyacetal resin, so that the composite material can exhibit excellent functions. For example, the composite may have good dimensional stability and thereby good moldability.

In the composite material, the acylation may be acetylation.

With such a configuration, the composite material can have better functions and can be manufactured at a relatively low cost.

The composite material may further contain an amide-based dispersant.

According to such a configuration, when the cellulose nanofibers and the polyacetal are kneaded, the dispersion of the cellulose nanofibers is promoted, so that the composite material can exhibit even better functions.

In the composite material, the amide-based dispersant may be polyoxyethylene alkylamide.

According to such a configuration, when the cellulose nanofibers and the polyacetal are kneaded, the dispersion of the cellulose nanofibers is further promoted, so that the composite material can exhibit even better functions.

In addition, the composite material according to the present invention is not limited to the configuration of the above embodiment. Moreover, the composite material according to the present invention is not limited by the effects described above. Various modifications can be made to the composite material according to the present invention without departing from the gist of the present invention.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples.

[raw materials used]
・Linter pulp and coniferous wood pulp (manufactured by Georgia-Pacific) were used as raw materials for cellulose nanofibers (hereinafter also referred to as CNF).
- Vinyl acetate (manufactured by Nacalai Tesque), vinyl butyrate (manufactured by Nacalai Tesque), and vinyl laurate (manufactured by Nacalai Tesque) were used as acylating agents.
- A polyacetal resin (hereinafter also referred to as POM) manufactured by Polyplastics Co., Ltd. was used.
- Nimid (registered trademark) MT-215 (manufactured by NOF Corporation) was used as an amide-based dispersant.

[Production example of cellulose nanofiber]
CNF of Production Example 1 in Table 1 was produced as follows. 10 g of vinyl acetate, 1.5 g of sodium carbonate and 90 g of DMSO were placed in a three-necked flask and mixed to prepare a treatment liquid. 3 g of linter pulp was added to the obtained treatment liquid, reacted at 50° C. for 3 hours, and then washed with water. After that, the acetylated CNF of Production Example 1 was obtained by fibrillating using a supermasscolloider.

[Measuring method of average fiber diameter and average fiber length]
The average fiber diameter and average fiber length of CNF were measured using scanning electron microscopy (SEM). Specifically, using FE-SEM (JSM-6700F, manufactured by JEOL Ltd.), SEM images at a magnification of 100 to 100,000 times are acquired under the following measurement conditions, and fiber diameter and fiber length of any 50 fibers was measured, and each arithmetic mean value was defined as the average fiber diameter and the average fiber length. SEM images of the CNFs of Production Examples 1-3 are shown in FIGS.
(Measurement condition)
・Pt coating conditions: 10 mA, 60 seconds ・Acceleration voltage: 5 kV
・SEI: Secondary electron image ・LEI: Lower detector image (secondary electron image + backscattered electron image)

[Method for measuring average degree of substitution]
The average degree of substitution of cellulose nanofibers was measured by the following titration method.
(Titration method)
Acyl groups were hydrolyzed by dispersing 0.5 g of CNF in 100 mL of a mixture of sodium hydroxide (number of moles A)/ethanol/water and stirring at 23° C. for 4 hours. The ratio of sodium hydroxide, ethanol and water is adjusted according to the type of acyl group. For example, in the case of acetylated CNF, a mixture of 5 g sodium hydroxide/50 g ethanol/50 g water was used. On the other hand, in the case of laurylated CNF, a mixed solution of 5 g sodium hydroxide/80 g ethanol/20 g water was used. Filtration separated the residue (CNF in which the acyl group was converted to a hydroxyl group) and the reaction solution (mixed solution in which sodium carboxylate and sodium hydroxide were dissolved). The residue was vacuum dried at a set temperature of 105 ° C., and the drying was terminated when it was observed that the change in mass of the residue during drying per hour was 0.01% or less, and the mass of the dried residue ( W) was weighed. Also, the amount of sodium hydroxide in the reaction solution was titrated with an aqueous hydrochloric acid solution to determine the number of moles (C). The average degree of substitution was calculated by the following formula. The same CNF was measured three times, and the average value obtained from the three measurements was adopted.
Mole number of cellulose (M) = W/162
Number of moles of carboxylic acid generated by decomposition of acyl group B = AC
Average degree of substitution = B/M

[IR analysis of CNF]
CNF was analyzed using FT-IR. FIG. 4 shows the IR spectrum. In the IR spectrum, the spectrum near 1370 cm ⁻¹ is absorption due to C—H bonds of cellulose. Also, the spectrum near 1750 cm ⁻¹ is the absorption due to the C=O bond of the acyl group. From the IR spectrum in FIG. 4, it was confirmed that the CNFs of Production Examples 1 to 5 have acyl groups.

[Method for measuring crystallinity]
Powder X-ray crystal diffraction (XRD) of CNF was analyzed using a sample horizontal multi-purpose X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation). As shown in FIG. 5, the CNFs of Production Examples 1 to 5 showed a peak at 2θ=22.6°, indicating that they had cellulose type I crystals. In addition, CNFs made from linter pulp (Production Examples 1 to 4) showed specific peaks at 2θ=14.9° and 16.5°. On the other hand, CNF (manufacturing example 5) made from coniferous wood pulp did not show such a peak.
(Measurement condition)
・X-ray: Cu/40kV/40mA
・Scan speed: 10°/min ・Scan range: 2θ = 5 to 70°
(Method for calculating crystallinity)
The crystallinity was calculated by the following formula (see Textile Res. J.29:786-794, 1959).
Crystallinity (%) = [(I ₂₀₀ −I _AM )/I ₂₀₀ ]×100
I ₂₀₀ : Diffraction intensity at 2θ=22.6° I _AM : Diffraction intensity at 2θ=18.5°, which is the diffraction intensity of the amorphous portion

[Method for measuring thermal decomposition temperature]
The thermal decomposition behavior of CNF was analyzed using a simultaneous differential thermogravimetric analyzer (STA7200, manufactured by Hitachi High-Tech Science Co., Ltd.). FIG. 6 shows the measurement results.
(Measurement condition)
- Atmosphere: argon gas (flow rate 300 mL/min)
・Temperature range: 30 to 400°C
・Temperature increase rate: 10°C/min (thermal decomposition temperature = 5% weight loss temperature)
FIG. 6 shows the TG chart of CNF of Production Examples 1-5. In the TG chart, the mass decrease up to 100°C is due to the evaporation of water. Therefore, based on the mass at 200° C. on the TG chart, the temperature at which the mass decreased by 5% (5% mass loss temperature) was defined as the thermal decomposition temperature.

Table 1 shows the measurement results of CNF in Production Examples 1-5. The linters, cotton-derived CNFs, maintained around 80% crystallinity and exhibited high thermal decomposition temperatures. On the other hand, conifer-derived CNF showed relatively low crystallinity and thermal decomposition temperature. From these results, it was considered that cotton-derived CNF has relatively high thermal stability, and thus is unlikely to be thermally decomposed during kneading with the polyacetal resin when producing the composite material. Therefore, it was thought that a composite material containing such CNF could exhibit excellent functions.

[Manufacture of composite materials]
According to the formulation in Table 2, the composite material was produced as a sheet-like composite sheet. In addition, the compounding amount of CNF in Table 2 represents the compounding amount with respect to 100 mass parts of polyacetal resins. In the kneading of CNF and POM, ethanol (EtOH), 2-propanol (IPA), dimethylacetamide (DMAc) or N-methyl-2-pyrrolidone (NMP) was used as a kneading solvent (in Example 8, mixed solvent of DMAc/EtOH). An example of manufacturing a typical composite material is shown below.

In a preparation example of CNF containing an amide-based dispersant in a composite material, CNF was added to a solvent in which the amide-based dispersant was dissolved, and stirred using a stirrer or by mechanical stirring for 120 to 180 minutes at 20 to 30 ° C. Dispersed and dispersant-treated CNF were prepared.

CNF (or dispersant-treated CNF) and POM were kneaded using a Laboplastomill at 180 to 195° C. and 45 to 100 rpm for 20 to 70 minutes. Next, using a vacuum dryer, the obtained kneaded material was dried at 120° C. for 5 hours to obtain an unmolded composite material. Using a hot press, the unmolded composite material was heated at 190° C. for 4 minutes, pressurized at a pressure of 180 kg/cm ² for 1 minute, and allowed to cool at room temperature to prepare a composite sheet. For the obtained composite sheet, various data were obtained by the following measurement methods, and dimensional stability, dynamic viscoelasticity and tensile properties were evaluated.

[Measurement method of coefficient of linear expansion]
The coefficient of linear expansion of the composite sheet was measured using a dynamic viscoelasticity measuring device (Q800 DMA manufactured by TA Instruments Japan) equipped with a thermomechanical analysis (TMA) function.
(Measurement condition)
・Static load: 50mN
・Temperature range: 30 to 120°C (0% change in length at 30°C)
・Temperature increase rate: 3 ° C./min ・Test piece: rectangular shape with a width of 5 mm and a length of 25 to 30 mm, thickness of 0.1 to 0.3 mm

[Method for measuring dynamic viscoelasticity]
The dynamic viscoelasticity (DMA) of the composite sheet was measured using the dynamic viscoelasticity measurement device.
(Measurement condition)
・Measurement mode: Tensile ・Test piece: Rectangular with a width of 5 mm and a length of 25 to 30 mm, thickness of 0.1 to 0.3 mm
・Distance between grips: 15mm
・Temperature increase rate: 3°C/min ・Strain: 0.1%
・Measurement temperature: -100 to 160°C or room temperature to 160°C
(How to find the softening temperature)
As shown in FIG. 7, among the curves showing changes in storage modulus, the temperature indicated by the intersection of a straight line obtained by extending the straight line portion observed on the low temperature side and the tangent line of the portion where the rate of decrease in storage modulus is maximum. is the softening temperature.

[Method of tensile test]
A tensile test of the composite sheet was performed under the following measurement conditions.
(Measurement condition)
・Test piece: 5 mm wide strip ・Distance between grips: 20 mm
・Tensile speed: 5mm/min

From the measurement results shown in Table 2, it was confirmed that the composite material containing CNF derived from cotton exhibited a low coefficient of linear expansion and had excellent dimensional stability. In particular, the composite material containing the amide-based dispersant showed a remarkably low coefficient of linear expansion, indicating the possibility of being applied to precision parts.

In addition, the composite material containing cotton-derived CNF showed a relatively high value of storage elastic modulus at 100° C., and was recognized to have excellent heat resistance. In particular, a composite material containing an amide-based dispersant has a higher storage modulus than a composite material that does not contain an amide-based dispersant, and has superior heat resistance. .

Claims (2)

Containing a polyacetal resin, cellulose nanofibers , and an amide-based dispersant ,
In the cellulose nanofiber, part of the hydroxyl groups of cellulose are acetylated ,
The cellulose nanofibers are derived from cotton and have an average degree of substitution, which is the ratio of acetylated hydroxyl groups, of 0.3 to 1.0,
The amide-based dispersant is polyoxyethylene alkylamide,
A composite material, wherein the content of the cellulose nanofibers is 10 to 20% by mass, and the content of the amide-based dispersant is 2 to 5% by mass. The composite material according to claim 1, having a linear expansion coefficient of 50 ppm/°C or less at 30 to 120°C.

Images