JP7829864B2 - Polymer composite cellulose and its manufacturing method, resin body, carbon fiber - Google Patents

Description

This invention relates to polymer composite cellulose, a method for producing the same, a resin body containing polymer composite cellulose, and carbon fiber which is a carbonized product of polymer composite cellulose.

Cellulose nanofibers (CNF), obtained from plants, are materials obtained by defibrating cellulose fibers to the extreme. Due to their high elasticity, high strength, and low thermal expansion properties, they have recently attracted attention as a reinforcing material for resins. However, CNF is inherently hydrophilic, and its strong hydroxyl groups cause aggregation during mixing with resins, reducing the resin's impact strength. Therefore, introducing hydrophobic functional groups into CNF to improve compatibility with resins has been proposed (see, for example, Patent Document 1).

Japanese Patent Publication No. 2019-137711

When introducing hydrophobic functional groups into cellulose, various chemical treatments are performed, such as using bases as catalysts. Such chemical treatments can damage the sugar chains of CNF, potentially reducing the strength of the hydrophobic CNF.

In view of the aforementioned problems relating to the prior art, this invention was proposed to suitably solve these problems, and aims to provide polymer composite cellulose with good strength, a method for producing the same, a resin body, and carbon fibers.

A first aspect of the polymer-composite cellulose according to the present invention is:
Celluloses and,
The cellulose has an aromatic polymer attached to its surface,
The gist of this is that the aromatic polymer has a cross-linked structure.

As a second embodiment of the polymer composite cellulose according to the present invention, in the first embodiment of the polymer composite cellulose,
The celluloses may be coated with the aromatic polymer.

As a third embodiment of the polymer composite cellulose according to the present invention, in the first embodiment of the polymer composite cellulose or the second embodiment of the polymer composite cellulose,
The aromatic polymer may be linked together to form a network structure.

A first aspect of the method for producing polymer-compound cellulose according to the present invention is:
A mixture is prepared by dispersing cellulose, cyclic amines, and aromatic hydrocarbons in a water-free solvent.
By heating the aforementioned mixture, the cyclic amine and the aromatic hydrocarbons react to form an aromatic polymer.
The gist of this method is to attach the aromatic polymer to the surface of the cellulose.

As a second aspect of the method for producing polymer composite cellulose according to the present invention, in the first aspect of the method for producing polymer composite cellulose,
The solvent may be an alcohol.

One embodiment of the resin body according to the present invention is:
The gist of the invention is that it comprises a polymer composite cellulose according to any of the first, second, and third embodiments, and a synthetic resin.

One embodiment of the carbon fiber according to the present invention is:
The gist of the invention is that the polymer composite cellulose is carbonized according to any of the first, second, or third embodiments.

According to the first embodiment of the polymer-composite cellulose of the present invention, it has good strength.
According to a first embodiment of the method for producing polymer composite cellulose according to the present invention, polymer composite cellulose having good strength can be obtained.
According to one embodiment of the resin body of the present invention, the strength can be improved by polymer composite cellulose having good strength.
According to one embodiment of the carbon fiber of the present invention, the shape based on polymer composite cellulose is maintained.

This shows the monomers of the examples and the structural formulas of the resulting aromatic polymers. This is a graph showing the infrared absorption spectrum. This is a photograph showing the adhesion status of the aromatic polymer in Example 4. This is a photograph showing the adhesion status of the aromatic polymer in Comparative Example 1. This is a photograph showing filter paper before the aromatic polymer was applied. This graph shows the infrared absorption spectrum, illustrating the effect of reaction temperature. This graph shows the infrared absorption spectrum, illustrating the effect of reaction time. This is an electron microscope image of the polymer composite cellulose of Example 11, observed at 100,000x magnification. This is an electron microscope image of the polymer composite cellulose of Example 11, observed at 50,000x magnification. This is an electron microscope image of CNF observed at 100,000x magnification. This is an electron microscope image of CNF observed at 50,000x magnification. (a) is a graph showing the results of differential scanning calorimetry for the TMTA-DHN polymer in Test Example 1, and (b) is a graph showing the results of differential scanning calorimetry for Example 11 and CNF. (a) is a graph showing the results of differential scanning calorimetry of CNF, and (b) is a graph showing the results of differential scanning calorimetry of TMTA-DHN polymer in Test Example 2. (a) shows the dispersion state of CNF in a mixture of hexane and water, and (b) shows the dispersion state of the polymer composite cellulose of Example 11 in a mixture of hexane and water. This is a photograph showing the results of a drying test. This graph shows the results of the heat resistance test between the polymer-compound cellulose of Example 11 and CNF. This is an electron microscope image of polypropylene particles adsorbed with the polymer composite cellulose of Example 11, observed at 30x magnification. This is an electron microscope image of polypropylene particles adsorbed with the polymer composite cellulose of Example 11, observed at 5000x magnification. This is an electron microscope image of polypropylene particles with CNF adsorbed onto them, observed at 30x magnification. This is an electron microscope image of polypropylene particles with CNF adsorbed onto them, observed at 5000x magnification. This is an electron microscope image of polypropylene particles observed at 30x magnification. This is an electron microscope image of polypropylene particles observed at 5000x magnification. This is an illustrative diagram of the polymer composite cellulose in the resin body of the example. This graph shows the results of a bending strength test on a resin body. This is an electron microscope image of the carbon fiber used in the example, observed at 100,000x magnification. This is an electron microscope image of the carbon fiber used in the example, observed at 50,000x magnification. This is an electron microscope image of the carbon fiber used in the example, observed at 20,000x magnification. This is an electron microscope image of the comparative carbon fiber observed at 50,000x magnification. This is an electron microscope image of the comparative carbon fiber observed at 20,000x magnification.

(Polymer-complexed cellulose)
The polymer-compound cellulose according to this disclosure comprises celluloses and aromatic polymers attached to the surface of the celluloses. The aromatic polymers are not introduced into the celluloses as functional groups, nor are they crosslinked with the celluloses; the celluloses are not modified in order to attach the aromatic polymers. The polymer-compound cellulose is reinforced by the aromatic polymer while maintaining the structure of the celluloses before the attachment of the aromatic polymer, such as sugar chains and functional groups. In other words, the polymer-compound cellulose has the properties and strength of the celluloses before the attachment of the aromatic polymer, plus the properties and strength of the aromatic polymer. It is thought that the aromatic polymers are positioned on the surface of the celluloses by physical adsorption, chemical adsorption such as hydrogen bonding, or a combination of physical and chemical adsorption. The polymer-compound cellulose may be in the form of aggregates of multiple materials, such as threads or paper.

In polymer-compound cellulose, aromatic polymers coat part or all of the surface of the cellulose. The degree of adhesion of the aromatic polymer to the cellulose surface can be easily controlled by adjusting the reaction temperature and reaction time of the monomers, as described later. For example, by lowering the reaction temperature or shortening the reaction time of the monomers, the aromatic polymer can be positioned over a portion of the cellulose surface. By raising the reaction temperature or lengthening the reaction time of the monomers, the aromatic polymer can be positioned over the entire surface of the cellulose.

In polymer-compound cellulose, aromatic polymers may be fused together at their contact points. Furthermore, the polymer-compound cellulose may have a network-like structure in which the aromatic polymers are interconnected. The fusion of aromatic polymers and the networking of the polymer-compound cellulose can be easily controlled by adjusting the reaction temperature and reaction time of the monomers, as described later. For example, lowering the reaction temperature of the monomers or shortening the reaction time can suppress the fusion of aromatic polymers and inhibit the growth of the network structure in the polymer-compound cellulose. Conversely, increasing the reaction temperature of the monomers or lengthening the reaction time can promote the fusion of aromatic polymers and accelerate the formation of the network structure in the polymer-compound cellulose.

The surface shape of the aromatic polymer may be smooth, or it may be uneven. Furthermore, the surface shape of the aromatic polymer may have granular raised areas, and multiple raised areas may be linked together in a bead-like pattern. The surface shape of the aromatic polymer can be easily controlled by adjusting the reaction temperature and reaction time of the monomer, as described later. For example, by lowering the reaction temperature of the monomer or shortening the reaction time of the monomer, the surface shape of the aromatic polymer can be made smooth. Conversely, by raising the reaction temperature of the monomer or lengthening the reaction time of the monomer, the surface of the aromatic polymer can be raised to create a bead-like pattern.

In polymer-compound cellulose, the aromatic polymer has a cross-linked structure. Because the aromatic polymer molecules are linked together in the cross-linked aromatic polymer, the strength of the aromatic polymer itself can be improved compared to non-cross-linked aromatic polymers.

(Celluloses)
Celluloses may be cellulose itself (unmodified cellulose) or chemically modified (introduced functional groups) cellulose derivatives. Celluloses may also be bamboo-derived cellulose, wood-derived cellulose, bacterial cellulose, or ascidian cellulose. Examples of cellulose derivatives include TEMPO-oxidized cellulose, carboxymethyl cellulose, and sulfated cellulose. Celluloses may be fibrous, thread-like, or paper-like aggregates. Examples of fibrous celluloses include microfibers, nanofibers (sometimes specifically called cellulose nanofibers or CNF), nanocrystals, or amorphous materials. It is also acceptable to use a single type of cellulose or a combination of multiple types. Celluloses with fiber widths in the range of 1 nm to 999 nm are sometimes specifically called nanocelluloses, and celluloses with fiber widths in the range of 1 μm to 999 μm are sometimes specifically called microcelluloses.

(Size of cellulose compounds)
The cellulose can be either microcellulose or nanocellulose, but nanocellulose is preferred when compounded into a resin. If nanocellulose is used, its fiber width is preferably 10 nm to 50 nm. The cellulose is preferably 200 nm to 15,000 nm in length. In nanocellulose, fibers with a fiber width of approximately 3 nm to 1,500 nm and a fiber length of approximately 200 nm to 10,000 nm are sometimes called nanofibers, and fibers with a fiber width of approximately 1 nm to 10 nm and a fiber length of approximately 100 nm to 300 nm are sometimes called nanocrystals. In addition, cellulose with a fiber width of approximately 1 nm to 10 nm and a fiber length of approximately 100 nm to 300 nm are sometimes called amorphous. For example, as cellulose undergoes nanofibrillation beyond the nanocrystalline state, it tends to become amorphous and its degree of crystallinity decreases. For example, when mixed with resin, cellulose is preferably in the form of nanofibers or nanocrystals, and more preferably in the form of nanofibers.

(Aromatic polymers)
The aromatic polymers of this disclosure are preferably polymers obtained by the reaction of aromatic hydrocarbons having hydroxyl groups with cyclic amines. Aromatic polymers can be broadly defined as phenolic resins, including those synthesized using organic compounds belonging to phenols such as cresol. As aromatic polymers, for example, those consisting of oxazine resins, resol resins, resorcinol resins, novolacs, and derivatives thereof can be used. Among these, benzoxazine resins as shown in Chemical Formula 1 below, or naphthoxazine resins as shown in Chemical Formula 2 below, are preferred.

In chemical formulas 1 and 2 above, _R1 refers to hydrogen or a hydrocarbon. Also, in chemical formulas 1 and 2 above, n indicates the repetition of the expression in parentheses.

(Aromatic hydrocarbons)
Aromatic hydrocarbons having hydroxyl groups include cresol, phenol, alkylphenol, dihydronaphthalene, dihydroanthracene, and bisphenol A. Among these, dihydronaphthalene (DHN), such as 1,5-dihydronaphthalene and 2,6-dihydronaphthalene, is preferred, and more preferably, 1,5-dihydronaphthalene (DHN) as shown in the following chemical formula 5.

(Cyclic amine)
Examples of cyclic amines include hexamine, quinuclidine, DACO(1,4-diazabicyclo[2.2.2]octane), and their derivatives. For example, hexamethylenetetramine (HMT) (also called hexamine), as shown in chemical formula 3 below, is an example.

Examples of cyclic amines include pyridine-based saturated cyclic amines such as piperidine, piperideine, piperazine, triazinane, tetrazinane, and pentadinane, as well as their derivatives. Among the aforementioned cyclic amines, triazinane is preferred, and among triazinanes, 1,3,5-triazinane, as shown in the following chemical formula 4, is preferred. Examples of 1,3,5-triazinanes include 1,3,5-trimethyl-1,3,5-triazinane, 1,3,5-triphenyl-1,3,5-triazinane, 1,3,5-triheptyl-1,3,5-triazinane, and 1,3,5-tripentyl-1,3,5-triazinane, among which 1,3,5-trimethylhexahydro-1,3,5-triazinane (TMTA) is preferred. It is preferable to use a cyclic amine with high solubility in the reaction solvent. For example, triazinanes are more soluble in water-free organic solvents than hexamines. Therefore, when using a water-free organic solvent as the reaction solvent, it is preferable to use triazinane as the cyclic amine.

(Method for producing polymer-compound cellulose)
The polymer-compound cellulose described above can be produced by reacting monomers in a solvent containing cellulose to form an aromatic polymer. More specifically, a mixture is prepared by dispersing cellulose and cyclic amines and aromatic hydrocarbons as monomers in a water-free solvent. The order in which the cellulose, cyclic amines, and aromatic hydrocarbons are added to the solvent is not particularly limited, but adding the cyclic amines and aromatic hydrocarbons to the solvent containing the cellulose makes it easier for the monomers to react on the surface of the cellulose. Next, the mixture is heated to react the cyclic amines and aromatic hydrocarbons to form an aromatic polymer. At this time, once the mixture is heated to a predetermined temperature, it is preferable to maintain the mixture at the predetermined temperature (reaction temperature) and stir it for a predetermined time (reaction time). The cyclic amines and aromatic hydrocarbons react, and polycondensation occurs simultaneously with the ring opening of the cyclic amine, forming an aromatic polymer. The aromatic polymer generated near the interface of the cellulose then adheres to the surface of the cellulose, and polymer-compound cellulose is obtained.

When using nanocellulose, which has a small fiber width, as the cellulose, it is preferable to prepare a cellulose alcohol dispersion by adding an organic solvent other than water to a cellulose aqueous dispersion containing nanocellulose, and then replacing the water with the organic solvent by centrifugation. Here, it is preferable to use the same organic solvent as the reaction solvent used in the monomer reaction; for example, if an alcohol (e.g., ethanol) is used as the reaction solvent, the water should be replaced with the alcohol (ethanol). Then, a mixture can be prepared by adding aromatic hydrocarbons and cyclic amines to the cellulose organic solvent dispersion.

Celluloses may be in fibrous form, or they may be aggregates formed into predetermined units, such as paper or cloth.

(Reaction solvent)
The reaction solvent to which the monomer is added is an organic solvent that does not contain water. The reaction solvent is preferably a liquid with polar molecules, which is less polar than water but close in polarity to water (a polar organic solvent). The reaction solvent has an affinity for cellulose and can disperse the added cellulose. The reaction solvent may also be one that does not dissociate protons under neutral pH conditions. Examples of reaction solvents include alcohols, amphiphilic solvents such as acetone, and aprotic polar solvents such as tetrahydrofuran (THF), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). Examples of alcohols include ethanol, isopropyl alcohol, methanol, and butanol. The reaction solvent may be a single solvent or a mixed solvent of multiple types, but it is required that it does not contain water in order to efficiently attach the aromatic polymer to the surface of the cellulose. Alcohols are preferred as the reaction solvent because they are easy to handle, can appropriately disperse the cellulose, and can moderately suppress the reaction rate of the monomer.

(Reaction temperature)
The reaction temperature for reacting monomers is not particularly limited as long as the reaction proceeds at a temperature within which it can take place. The reaction of monomers can proceed at room temperature in the range of 15°C to 30°C, or even at low temperatures below 15°C. From an industrial standpoint, the reaction temperature for reacting monomers is preferably 20°C or higher, more preferably 40°C or higher, and even more preferably 60°C or higher. Setting the reaction temperature as described above allows the reaction to proceed efficiently, and a reaction temperature of 60°C or higher is particularly preferable because it shortens the reaction time. The reaction temperature for reacting monomers is preferably 100°C or lower, more preferably 80°C or lower, and even more preferably 78°C or lower. Setting the reaction temperature as described above prevents the reaction from proceeding too quickly, and allows for the appropriate placement of aromatic polymers on the surface of celluloses.

(Reaction time)
There is no particular limit to the reaction time for reacting the monomers, but the longer the reaction time, the more aromatic polymer can be obtained. From an industrial standpoint, the reaction time for reacting the monomers is preferably 1 hour or more, more preferably 3 hours or more, and even more preferably 6 hours or more. By setting the reaction time as described above, the aromatic polymer can be appropriately arranged on the surface of the cellulose, and a reaction time of 6 hours or more is particularly preferable because it allows the cellulose to be coated with the aromatic polymer. There is no particular upper limit to the reaction time for reacting the monomers, but from an industrial standpoint, it is preferably 24 hours or less.

By changing conditions such as the amount of monomer added, reaction temperature, and reaction time, the thickness and shape of the resulting aromatic polymer can be appropriately controlled. Similarly, by changing these conditions, the degree of growth of the network structure in the resulting polymer-compound cellulose can be appropriately controlled. The aromatic polymer addition process can be repeated multiple times to form multiple layers of aromatic polymer.

When forming multiple layers of aromatic polymers by repeating the aromatic polymer application process multiple times, the type of aromatic polymer can be changed depending on the layer. For example, it is possible to combine different materials, such as forming one layer with an aromatic polymer derived from dihydronaphthalene and another layer with an aromatic polymer derived from dihydroanthracene.

Polymer-compound cellulose is reinforced by aromatic polymers attached to the surface of the cellulose, resulting in improved strength compared to cellulose alone. Furthermore, because the aromatic polymers in polymer-compound cellulose have a cross-linked structure, the aromatic polymers themselves are stronger than those without cross-linking, resulting in superior overall strength. Therefore, when polymer-compound cellulose is used as a filler in materials such as resins, even a smaller amount than that used for cellulose alone can effectively improve the mechanical strength of the resin material.

Polymer-compound cellulose is hydrophobic because aromatic polymers are attached to the surface of the cellulose particles, improving its affinity with materials such as resins, which was difficult with cellulose alone. Therefore, when polymer-compound cellulose is used as a filler in materials such as resins (resin bodies), it can be appropriately dispersed in the resin body. Furthermore, polymer-compound cellulose can be adsorbed onto resin particles. By molding a resin body from resin particles adsorbed with polymer-compound cellulose, the polymer-compound cellulose can be appropriately dispersed within the resin body. Moreover, by molding a resin body from resin particles adsorbed with polymer-compound cellulose, the polymer-compound cellulose can be dispersed in a network-like structure within the resin body, thereby uniformly improving the strength of the resin body.

Polymer-compound cellulose is reinforced by aromatic polymers attached to the surface of the cellulose, making it less prone to deformation and shrinkage when dried compared to cellulose alone.

Polymer-compound cellulose exhibits improved heat resistance compared to pure cellulose due to aromatic polymers adhering to its surface. Therefore, using polymer-compound cellulose as a filler in materials such as resins can improve the heat resistance of those materials. Furthermore, carbonizing polymer-compound cellulose to produce carbon fibers maintains the fiber shape of the carbon fibers based on the polymer-compound cellulose and suppresses fiber adhesion. Moreover, carbonizing polymer-compound cellulose with nano-sized fiber widths allows for the production of carbon fibers with nano-sized fiber widths. While commercially available carbon fibers typically have a lower limit of around 100 nm in fiber width, it becomes possible to easily produce carbon fibers with widths of 10 nm or less.

Polymer-compound cellulose can be produced through a simple process involving the reaction of monomers with celluloses in a water-free solvent to form aromatic polymers. Thus, a polymer-compound cellulose with good strength can be obtained through a so-called one-step and one-pot process, without the need for complicated steps. Furthermore, unlike the process of hydrophobizing cellulose by introducing functional groups (chemical modification), there is no need to use chemicals such as acids or alkalis, which require careful handling. Because acids and alkalis are not used, the sugar chains of the celluloses are not damaged, thus preserving the strength of the celluloses themselves. This, combined with the reinforcement provided by the aromatic polymers attached to the surface of the celluloses, improves the strength of the resulting polymer-compound cellulose.

When aromatic polymers coat celluloses, the strength of the polymer-compound cellulose can be improved. Furthermore, when the parts of the aromatic polymers in the polymer-compound cellulose are fused together, the strength of the polymer-compound cellulose can be improved. Additionally, when the aromatic polymers form a network structure, the strength of the polymer-compound cellulose can be improved. Moreover, when the aromatic polymers form a beaded structure, the strength of the polymer-compound cellulose can be improved.

(Resin body)
A resin body can be constructed that includes the aforementioned polymer composite cellulose and a resin. The resin body of this disclosure can also be said to use the aforementioned polymer composite cellulose as a filler to impart a predetermined function (e.g., improved strength) to the resin body. The shape of the resin body is not particularly limited and can be formed in various shapes such as film, sheet, or block, depending on the application.

(resin)
The resin constituting the resin body may be thermoplastic, thermosetting, or engineering plastic, as long as it is a resin that can be compounded with polymer composite cellulose. Specifically, for example, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyethylene, polypropylene, polyethylene-vinyl acetate copolymer, polyethylene-vinyl acetate alcohol copolymer, poly(meth)acrylic resin, silicone resin, polyamide such as nylon-6, nylon-6,6, nylon-6,10, and nylon-6,12, polyimide resin, polyurethane, epoxy resin, phenolic resin, melamine resin, polycarbonate, cellulose triacetate, cellulose acetate butyrate, vinylon, polyvinyl butyral, etc. can be used.

(Percentage of polymer-complexed cellulose)
The blending ratio of polymer composite cellulose to the resin is not particularly limited, but is preferably 0.01 wt% or more, and more preferably 5 wt% or more. As mentioned above, polymer composite cellulose has excellent strength, so the amount blended can be relatively small. The blending ratio of polymer composite cellulose to the resin is not particularly limited, but is preferably 95 wt% or less, and more preferably 90 wt% or less. If the amount of polymer composite cellulose blended is too high, problems such as brittleness of the resin body are likely to occur.

A known method can be used to manufacture the resin body. As mentioned above, polymer composite cellulose can be adsorbed onto resin, so for example, the resin body can be manufactured using a particle adsorption method in which polymer composite cellulose is adsorbed onto resin particles, which are made by granulating resin. By molding the resin particles on which polymer composite cellulose has been adsorbed, the polymer composite cellulose can be dispersed in the resin. Furthermore, the polymer composite cellulose can be arranged in a network pattern within the resin (see Figure 23). When manufacturing a resin body from resin particles on which polymer composite cellulose has been adsorbed, compression molding is preferable. By compression molding, the gaps between resin particles are eliminated, and a network of polymer composite cellulose can be formed in the resin.

Thus, by incorporating polymer-compound cellulose as a filler into the resin, a resin body with good strength can be obtained. Furthermore, because the polymer-compound cellulose is dispersed in the resin body, its strength is uniform. The strength of the resin body is further improved when a network of polymer-compound cellulose is formed.

(Carbon fiber)
Carbon fibers can be manufactured by carbonizing the aforementioned polymer composite cellulose. The carbon fibers, which are the carbonized product of polymer composite cellulose, have a fiber shape based on the polymer composite cellulose. For example, if the carbonized polymer composite cellulose has some aromatic polymers fused to it, the resulting carbon fibers will have some fibers connected together. Also, if the carbonized polymer composite cellulose has a network structure connected by aromatic polymers, the resulting carbon fibers will have a network-like structure. The carbon fibers, which are the carbonized product of polymer composite cellulose, have a fiber width based on the fiber width of the polymer composite cellulose. For example, if the carbonized polymer composite cellulose has a micro-sized fiber width, the resulting carbon fibers will have a micro-sized fiber width, and if the carbonized polymer composite cellulose has a nano-sized fiber width, the resulting carbon fibers will have a nano-sized fiber width.

The carbonization treatment of polymer composite cellulose can be performed using known methods. For example, carbon fibers can be obtained by carbonizing the polymer composite cellulose by heating it in an atmosphere of an inert gas such as nitrogen. More specifically, for example, a flame-retardant treatment process is performed to make the material infusible and stabilize it by heat-treating it in air at 200°C to 350°C for several hours. Next, a carbonization process is performed by heat-treating it at 600°C to 1500°C in an atmosphere of an inert gas such as nitrogen. This yields carbon fibers. After the carbonization process, a graphitization process may be performed as needed, by heat-treating it at 2000°C to 3000°C in an atmosphere of an inert gas such as nitrogen. The elasticity of the carbon fibers can be improved by undergoing the graphitization process. Carbon fibers that have undergone the graphitization process are sometimes called graphite fibers.

Carbon fibers produced by carbonizing polymer-compound cellulose maintain their shape due to the high heat resistance of the polymer-compound cellulose, which suppresses adhesion between fibers. Furthermore, the high heat resistance of the polymer-compound cellulose improves the recovery rate of the resulting carbon fibers. Additionally, carbon fibers produced by carbonizing polymer-compound cellulose can be formed with a fiber diameter of 10 nm or less, making them extremely fine.

As shown in Table 1, Examples 1 to 10 and Comparative Example 1 use 0.10 g of chemical analysis filter paper (equivalent to JIS P 38015 Type 1, model number 101, size: 9 cm x 9 cm, ash content: 0.15%, weight: 80 ± 4 g/ ^m² , maximum pore size: 20 μm to 25 μm, fiber width: approximately 20 μm) as the cellulose. The filter paper is mainly composed of cotton fibers, and the cotton is mainly composed of cellulose. Example 11 uses 6.0 g of cellulose nanofiber (manufactured by Chuetsu Pulp & Paper Co., Ltd., product name: nanoforest-s-BBC10, fiber width: 10 nm to 20 nm, fiber length: 15 μm, degree of defibration: C defibration) as the cellulose. In Examples 1 to 11 and Comparative Example 1, naphthoxazine (an aromatic polymer) is formed by the reaction of TMTA (1,3,5-trimethylhexahydro-1,3,5-triazinane) as a cyclic amine with DHN (1,5-dihydronaphthalene) as an aromatic hydrocarbon. In Examples 1 to 11, ethanol alone is used as the solvent for reacting the cyclic amine with the aromatic hydrocarbon. In Comparative Example 1, a mixed solvent of water and ethanol is used as the solvent for reacting the cyclic amine with the aromatic hydrocarbon.

(Examples 1-10)
Specifically, in Examples 1 to 10, polymer composite cellulose was prepared as follows: A filter paper was placed in 200 ml of ethanol solvent. 2 mmol of TMTA (1,3,5-trimethylhexahydro-1,3,5-triazinane) and 2 mmol of 1,5-DHN (1,5-dihydronaphthalene) were added to the solvent containing the filter paper to prepare a mixture. The mixture was heated and maintained at the reaction temperature shown in Table 1, and while stirring at a rotation speed of 50 rpm for the reaction time shown in Table 1, TMTA and DHN underwent an addition-condensation reaction, forming an aromatic polymer, naphthoxazine (sometimes called TMTA-DHN polymer), on the surface of the fibers (cellulose) constituting the filter paper, thereby adhering the polymer to the cellulose constituting the filter paper. The obtained polymer composite cellulose was then washed with water, ethanol, and methanol as a post-treatment, and then dried under reduced pressure. Figure 1 shows naphthoxazine (TMTA-DHN polymer), an aromatic polymer obtained by the reaction of TMTA and DHN.

(Example 11)
Ethanol was added to a cellulose aqueous dispersion containing 6.0 g of cellulose nanofibers, and centrifugation was performed to replace the water with ethanol, yielding 500 ml of cellulose ethanol dispersion. 10 mmol of TMTA (1,3,5-trimethylhexahydro-1,3,5-triazinane) and 10 mmol of DHN (1,5-dihydronaphthalene) were added to the cellulose ethanol dispersion to prepare a mixture. The mixture was heated and maintained at a reaction temperature of 70°C, and while stirring at 50 rpm for 6 hours, TMTA and DHN were subjected to an addition-condensation reaction to form naphthoxazine (TMTA-DHN polymer), an aromatic polymer, on the surface of the cellulose nanofibers, yielding the polymer composite cellulose of Example 11. The obtained polymer composite cellulose was then washed with water, ethanol, and methanol as a post-treatment, and then dried under reduced pressure.

(Comparative Example 1)
A filter paper is placed in a mixed solvent consisting of 100 ml of water and 100 ml of ethanol. Two mmol of TMTA (1,3,5-trimethylhexahydro-1,3,5-triazinane) and two mmol of 1,5-DHN (1,5-dihydronaphthalene) are added to the solvent containing the filter paper to prepare a mixture. The mixture is heated and maintained at a reaction temperature of 70°C, and while stirring at a rotation speed of 50 rpm for a reaction time of 6 hours, the TMTA and DHN undergo an addition-condensation reaction to form naphthoxazine on the surface of the fibers (cellulose) constituting the filter paper, thereby obtaining the filter paper of Comparative Example 1. The filter paper of Comparative Example 1 is then washed with water, ethanol, and methanol as a post-treatment, and then dried under reduced pressure.

The infrared absorption spectra of the polymer composite cellulose from Examples 4 and 11, and the filter paper from Comparative Example 1, were measured using a Fourier transform infrared spectrometer. Separately, TMTA-DHN polymer particles were prepared by reacting TMTA and DHN in a solvent consisting only of ethanol at a reaction temperature of 70°C for 24 hours. The infrared absorption spectra of these TMTA-DHN polymer particles were measured using a Fourier transform infrared spectrometer. Furthermore, the infrared absorption spectra of the filter paper used in Examples 1-10 and the CNF used in Example 11 were also measured using a Fourier transform infrared spectrometer. The infrared spectrometer used was a FT/IR-6300 manufactured by JASCO Corporation. The results are shown in Figure 2.

As shown in Figure 2, the infrared absorption spectra of Examples 4 and 11 show that an absorption of aromatic C=C stretching vibration appears at 1602 ^cm⁻¹ , and an absorption of cyclic amine CH bending vibration appears at 1502 ^cm⁻¹ . The absorptions appearing at 1602 ^cm⁻¹ and 1502 ^cm⁻¹ in the spectra of TMTA-DHN polymer particles match the aforementioned absorptions of Examples 4 and 11. This indicates that in Example 4, the TMTA-DHN polymer is attached to the fibers constituting the filter paper, and similarly, in Example 11, the TMTA-DHN polymer is attached to the CNF. Note that no absorptions appear at 1602 ^cm⁻¹ and 1502 ^cm⁻¹ for filter paper and CNF that have not undergone polymer application treatment.

As shown in Figure 2, unlike Examples 4 and 11 which used ethanol as the solvent, Comparative Example 1, which used a mixed solvent of water and ethanol, did not show absorption at 1602 ^cm⁻¹ and 1502 ^cm⁻¹ . In other words, in Comparative Example 1, it can be seen that the TMTA-DHN polymer did not adhere to the cellulose constituting the filter paper. It is thought that when water is present in the reaction solvent, as in Comparative Example 1, the reaction between TMTA and DHN occurs quickly, and the TMTA-DHN polymer is not distributed to the surface of the filter paper. From this, it is inferred that the TMTA-DHN polymer is dispersed in the solvent, making it difficult for the TMTA-DHN polymer to adhere to the filter paper.

In the preparation of Example 4, the mixture gradually changed from brown to green over time, and after 6 hours, it turned dark green. The filter paper obtained after 6 hours in Example 4 had also changed to a dark green color, similar to the color of the mixture (see Figure 3). In contrast, in the preparation of Comparative Example 1, the mixture immediately changed to red and then to dark green, but even after 6 hours, the filter paper did not change color and remained white, indistinguishable from the filter paper before polymer application shown in Figure 5 (see Figure 4). This also indicates that in Comparative Example 1, the TMTA-DHN polymer did not adhere to the cellulose constituting the filter paper.

Figure 6 shows the results when the reaction temperature is varied under the same conditions, with the reaction time set to 6 hours and the amounts of solvent and monomer remaining the same. As shown in Figure 6, it can be seen that the higher the reaction temperature, the easier it is for the TMTA-DHN polymer to adhere to the cellulose constituting the filter paper. In particular, according to the results in Figure 6, a reaction temperature of 60°C or higher is preferable, and 70°C or higher is more preferable. Note that even with a lower reaction temperature, the TMTA-DHN polymer can be adhered to the cellulose by increasing the reaction time.

Figure 7 shows the results when the reaction temperature is set to 70°C and the amounts of solvent and monomer are kept the same, but the reaction time is varied. As shown in Figure 7, it can be seen that the longer the reaction time, the more the TMTA-DHN polymer adheres to the cellulose constituting the filter paper. In particular, according to the results in Figure 7, a reaction time of 6 hours or more is preferable, 12 hours or more is more preferable, and 24 hours or more is even more preferable. Note that even with a shorter reaction time, the TMTA-DHN polymer can be adhered to the cellulose by setting a higher reaction temperature.

Figures 8 and 9 are electron microscope images of the surface of the polymer-composite cellulose of Example 11, which underwent polymer-conjugation treatment. Figures 10 and 11 are electron microscope images of the surface of the CNF used in Example 11. As shown in Figures 10 and 11, the surface of the CNF that has not undergone polymer-conjugation treatment is smooth. In contrast, as shown in Figures 8 and 9, it can be seen that in Example 11, the CNF is completely coated with the TMTA-DHN polymer. Furthermore, in Example 11, it can be seen that the parts of the TMTA-DHN polymer that are in contact with each other are fused together, and the TMTA-DHN polymers are connected to form a network, resulting in a reticular structure for the resulting polymer-composite cellulose. The TMTA-DHN polymer in Example 11 has granular raised portions, and multiple raised portions are linked together in a bead-like shape. In this disclosure, an electrolytic emission scanning electron microscope (Hitachi High-Technologies Corporation, model SU8000) was used as the electron microscope.

In a solvent consisting solely of ethanol, TMTA and DHN were reacted at a reaction temperature of 70°C for 24 hours to obtain TMTA-DHN polymer particles of Test Example 1. Similarly to Comparative Example 1, TMTA and DHN were reacted in a mixed solvent of water and ethanol at a reaction temperature of 70°C for 24 hours to obtain TMTA-DHN polymer particles of Test Example 2. Differential scanning calorimetry (DSC) was then performed on the polymer composite cellulose of Example 11, the TMTA-DHN polymer of Test Example 1, the TMTA-DHN polymer of Test Example 2, and CNF. In differential scanning calorimetry, the temperature difference between the sample and the reference substance was detected while increasing the temperature at a rate of 2°C/min in a nitrogen stream, and this difference was converted to heat flow. The results of the differential scanning calorimetry are shown in Figures 12 and 13.

As shown in Figure 12(a), the TMTA-DHN polymer in Test Example 1 exhibits an exothermic peak, indicating that crosslinking has occurred in the TMTA-DHN polymer (Furukawa et al., Adhesion Society of Japan, pp. 89-96, Vol. 43, No. 3 2007). Thus, it can be seen that a TMTA-DHN polymer with a crosslinked structure can be obtained by reacting TMTA and DHN in a solvent consisting only of ethanol without water. As shown in Figure 12(b), the polymer composite cellulose in Example 11 exhibits an exothermic peak similar to that of the TMTA-DHN polymer in Test Example 1 shown in Figure 12(a), indicating that the TMTA-DHN polymer coating the CNF in Example 11 has a crosslinked structure.

In Test Example 2, where TMTA and DHN were reacted in a mixed solvent of water and ethanol, the TMTA-DHN polymer did not exhibit an exothermic peak, as shown in Figure 13(b), indicating that it did not have a crosslinked structure. Furthermore, the CNF measurement results in Figures 12(b) and 13(c) show that the exothermic peak was not due to CNF. Thus, it is evident that by reacting monomers in a water-free solvent, a crosslinked structure of aromatic polymers can be formed in polymer-compound cellulose.

A CNF dispersion was prepared by mixing hexane and water in a 1:1 ratio and adding the CNF used in Example 11 to a concentration of 0.5 wt%. A polymer composite cellulose dispersion was also prepared by mixing hexane and water in a 1:1 ratio and adding the polymer composite cellulose from Example 11 to a concentration of 0.5 wt%. As shown in Figure 14(a), in the CNF dispersion, the CNF is dispersed in the water separated at the bottom of the test solution. In contrast, as shown in Figure 14(b), in the polymer composite cellulose dispersion, the polymer composite cellulose is dispersed in the hexane separated at the top of the test solution. Thus, it can be seen that the polymer composite cellulose of Example 11 is hydrophobic, not hydrophilic.

In a test tube, a CNF aqueous dispersion was prepared by adding 2.4 wt% of the CNF used in Example 11 to water. A polymer-compound cellulose aqueous dispersion was also prepared by adding 2.4 wt% of the polymer-compound cellulose from Example 11 to water. The CNF aqueous dispersion and the polymer-compound cellulose aqueous dispersion were freeze-dried in test tubes. As shown in Figure 15, the polymer-compound cellulose formed a cylindrical shape conforming to the internal shape of the test tube, and no deformation or shrinkage occurred. In contrast, as shown in Figure 15, the CNF deformed from the internal shape of the test tube and also shrunk. It can be seen that the polymer-compound cellulose from Example 11 has improved strength compared to CNF.

The thermal weight loss rate was measured for the polymer-compound cellulose of Example 11 and the CNF used in Example 11. In the thermal weight loss test, the sample was heated in a nitrogen gas atmosphere at a heating rate of 10°C/min from 30°C to 900°C, and then allowed to cool naturally once 900°C was reached. The weight of the sample was measured at each temperature, and the weight loss rate from the starting weight was calculated. The results are shown in Figure 16.

As shown in Figure 16, the polymer-compound cellulose of Example 11 has a higher decomposition completion temperature and improved heat resistance compared to CNF. While chemically modified hydrophobic CNF generally only shows a decomposition completion temperature increase of about 10°C compared to CNF, the polymer-compound cellulose of Example 11 shows a decomposition completion temperature increase of about 26°C compared to CNF, demonstrating superior heat resistance. Furthermore, the higher decomposition completion temperature of the polymer-compound cellulose of Example 11 improves the yield of residual carbon during carbonization, which is advantageous when producing carbon fibers as described later.

(Resin body)
The resin body of the example will now be described. The resin body of the example contains the polymer composite cellulose of Example 11 and polypropylene (PP) as the resin. A dispersion is prepared by adding polypropylene particles (average particle size 500 μm) and the polymer composite cellulose of Example 11 to water. Here, the polymer composite cellulose of Example 11 is blended to be 0.4 wt% relative to the polypropylene particles. The dispersion is shaken with a shaker to mix the polypropylene particles and the polymer composite cellulose, thereby adsorbing the polymer composite cellulose onto the surface of the polypropylene particles. The mixture is sieved through a mesh with a mesh size of 500 μm to remove the polymer composite cellulose that has not been adsorbed onto the polypropylene particles, and the polypropylene particles with polymer composite cellulose adsorbed on their surface are collected and dried. The polypropylene particles with adsorbed polymer composite cellulose (2.3 g) are set in a hot press mold, pre-pressed at 155°C for 5 minutes with a pressure of 20 MPa, and then pressed at 200°C for 3 minutes with a pressure of 20 MPa. This resulted in obtaining the resin body of the embodiment, which is in the form of a film with dimensions of 50 mm in length and width and 1 mm in thickness.

Examples, Comparative Examples, and Reference Examples: The hot press mold used for molding the resin body has a structure in which a polyimide sheet is laid on a metal plate, a stainless steel spacer is placed in the center, another polyimide sheet is placed on top of the spacer, and then a metal plate is placed on top of that. Polypropylene particles placed within the spacer are then compressed and molded.

The comparative example resin was molded using the CNF used in Example 11. A dispersion was prepared by adding polypropylene particles (average particle size 500 μm) and CNF (without polymer-adding treatment) to water. The CNF was blended at a concentration of 0.4 wt% relative to the polypropylene particles. The dispersion was shaken to mix the polypropylene particles and CNF, causing the CNF to adsorb onto the surface of the polypropylene particles. The mixture was then sieved through a 500 μm mesh to remove any CNF not adsorbed onto the polypropylene particles. The polypropylene particles with adsorbed CNF were collected and dried. The CNF-adsorbed polypropylene particles (2.3 g) were placed in a hot press mold, pre-pressed at 155°C for 5 minutes under a pressure of 20 MPa, and then pressed at 200°C for 3 minutes under a pressure of 20 MPa. This yielded the comparative example resin, which was a film with dimensions of 50 mm x 50 mm and a thickness of 1 mm.

The same polypropylene particles (2.3 g) as in the examples and comparative examples were placed in a hot press mold, pre-pressed at 155°C for 5 minutes under a pressure of 20 MPa, and then pressed at 200°C for 3 minutes under a pressure of 20 MPa. This yielded a reference example resin body in the form of a film with dimensions of 50 mm in length and width and 1 mm in thickness.

As shown in Figure 18, it can be seen, compared to Figure 22, that polymer-compound cellulose is adsorbed onto the surface of the polypropylene particles. The amount of polymer-compound cellulose adsorbed onto the polypropylene particles is greater in Figure 18 compared to Figure 20, where CNF is adsorbed onto the polypropylene particles. This is because the presence of the aromatic polymer TMTA-DHN polymer on the surface of the CNF in the polymer-compound cellulose improves its affinity to the polypropylene particles compared to the case of CNF alone.

As shown in Figure 23, when polypropylene particles with polymer composite cellulose adsorbed on their surface are compressed and molded, the polymer composite cellulose adsorbed on the surface of the polypropylene particles is positioned between the crushed polypropylene particles. This is thought to cause the polymer composite cellulose to form a network within the polypropylene.

For each of the resin bodies in the examples, comparative examples, and reference examples, test specimens measuring 50 mm horizontally and 10 mm vertically were prepared, and their bending strength was measured. Bending strength was measured by supporting the test specimen at points 32 mm apart horizontally, and applying a load at a speed of 1.0 mm/min to the horizontal center of the support points. Figure 24 shows the relationship between bending strain (horizontal axis) and stress (vertical axis).

As shown in Figure 24, the resin body of the example containing polymer-compound cellulose shows improved flexural strength compared to the comparative example containing CNF and the reference example containing only PP. Despite the small amount of polymer-compound cellulose (0.4 wt%) relative to the polypropylene particles, the resin body of the example showed approximately 1.1 times greater strength than the comparative example and the reference example.

(Carbon fiber)
The carbon fibers in the example were produced by carbonizing the polymer composite cellulose of Example 11. First, the polymer composite cellulose of Example 11 was placed in a heating furnace and heated at 200°C for 3 hours while the air inside the furnace was sucked out. Next, carbonization treatment was performed by sintering in the heating furnace under a nitrogen gas atmosphere until it reached 900°C, and then it was allowed to cool naturally. The carbon fibers in the comparative example were produced by carbonizing the CNF used in Example 11. First, the CNF was placed in a heating furnace and heated at 200°C for 3 hours while the air inside the furnace was sucked out. Next, carbonization treatment was performed by sintering in the heating furnace under a nitrogen gas atmosphere until it reached 900°C, and then it was allowed to cool naturally.

As shown in Figures 25 to 27, the carbon fibers of the example maintain a fiber shape similar to that of the unfired polymer composite cellulose shown in Figures 8 and 9. The fiber width of the unfired polymer composite cellulose shown in Figures 8 and 9 is approximately 10 nm, and the fiber width of the obtained carbon fibers of the example is also approximately 10 nm. In other words, the carbon fibers of the example can be formed with a fiber width similar to that of the unfired polymer composite cellulose.

As shown in Figures 25 to 27, the carbon fibers in the examples maintain their fiber shape because they are made from polymer-compound cellulose, which is reinforced with the aromatic polymer TMTA-DHN polymer to improve heat resistance. Furthermore, using polymer-compound cellulose with excellent heat resistance as the raw material improves the yield of the resulting carbon fibers. As shown in Figures 28 and 29, the carbon fibers in the comparative example, where CNF was calcined, show adhesion between the CNF fibers, indicating that maintaining the fiber shape is difficult with CNF alone.

Claims (8)

Celluloses and,
A polymer composite cellulose having an aromatic polymer attached to the surface of the cellulose,
The aforementioned aromatic polymer is a benzoxazine resin of the following chemical formula 1 or a naphthoxazine resin of the following chemical formula 2, all of which have a cross-linked structure.
The polymer composite cellulose is characterized by being hydrophobic.
In the above chemical formulas 1 and 2, R1 _refers to hydrogen or hydrocarbons. The polymer-composite cellulose according to claim 1, wherein the cellulose is coated with the aromatic polymer. The polymer-composite cellulose according to claim 1, wherein the polymer-composite cellulose has a network structure, with the aromatic polymer attached to the surface of the fibrous celluloses connecting them. The polymer-composite cellulose according to claim 2, wherein the polymer-composite cellulose has a network structure, with the aromatic polymer attached to the surface of the fibrous celluloses connecting them. A mixture is prepared by dispersing cellulose, cyclic amines, and aromatic hydrocarbons in a water-free solvent.
By heating the aforementioned mixture, the cyclic amine and the aromatic hydrocarbons react to form an aromatic polymer.
A method for producing polymer-composite cellulose, comprising attaching the aromatic polymer to the surface of fibrous cellulose,
A method for producing polymer-compound cellulose, characterized in that the aromatic polymer is a benzoxazine resin of the following chemical formula 1 or a naphthoxazine resin of the following chemical formula 2.
In the above chemical formulas 1 and 2, R1 _refers to hydrogen or hydrocarbons. The method for producing polymer-compound cellulose according to claim 5, wherein the solvent is an alcohol. A resin body comprising a polymer-composite cellulose according to any one of claims 1 to 4, and a synthetic resin. A carbon fiber which is a carbonized polymer composite cellulose according to any one of claims 1 to 4.