CN108299701B - Fiber material and method for producing same, and composite material and method for producing same - Google Patents

Abstract

The invention provides a fiber material having excellent processability of a composite material using cellulose nanofibers, a method for producing the fiber material, and a composite material and a method for producing the composite material. The method for producing a fiber material according to the present invention includes a mixing step (S10) of mixing cellulose nanofibers, a metal salt, and an aqueous solvent to obtain a CNF dispersion, and a drying step (S12) of removing the aqueous solvent from the CNF dispersion obtained in the mixing step (S10) to obtain a fiber material. The mass ratio of the metal salt in the CNF dispersion to the cellulose nanofibers is 0.1 to 2 times.

Description

Fiber material and method for producing same, and composite material and method for producing same

Technical Field

The present invention relates to a fiber material using cellulose nanofibers, a method for producing the fiber material, a composite material, and a method for producing the composite material.

Background

In recent years, a cellulose nanofiber obtained by defibrating a natural cellulose fiber into a nano size has been attracting attention. Natural cellulose fibers are biomass using pulp such as wood as a raw material, and it is expected that the environmental load can be reduced by effectively utilizing the biomass.

Cellulose nanofibers are provided on the market as aqueous dispersions, but processing for compounding with elastomers and synthetic resins is difficult. Since the cellulose nanofibers are aggregated by forming hydrogen bonds in the drying step of removing water from the aqueous dispersion, the cellulose nanofibers cannot be present in a state of being highly defibrated in the composite forming step, and the composite material cannot be sufficiently reinforced by the cellulose nanofibers.

Therefore, a method of mixing an aqueous dispersion of cellulose nanofibers with a latex or a resin emulsion has been proposed (see patent documents 1 and 2).

However, the composite materials produced by these methods are affected by the characteristics of the latex or resin emulsion. Further, as the latex or the resin emulsion, it is impossible to apply the latex or the resin emulsion to rubbers and resins which are not distributed in the market.

Documents of the prior art

Patent document

Patent document 1: japanese patent application laid-open No. 2015-98576

Patent document 2: japanese patent application laid-open No. 2016-29169.

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide a fiber material having excellent processability for use in composite cellulose nanofibers, and a method for producing the same. Further, an object of the present invention is to provide a composite material using the fiber material and a method for producing the same.

Means for solving the problems

[ application example 1]

The method for producing a fiber material according to the present application example is characterized by including: a mixing step of mixing the cellulose nanofibers, the metal salt, and the aqueous solvent to obtain a CNF dispersion; and a drying step of removing an aqueous solvent from the CNF dispersion obtained in the mixing step to obtain a fiber material, wherein the mass ratio of the metal salt in the CNF dispersion to the cellulose nanofibers is 0.1 to 2 times.

[ application example 2]

In the method for producing a fiber material according to the application example, the metal salt may include at least one of a monovalent metal salt and a divalent metal salt.

[ application example 3]

In the method for producing a fiber material according to the application example, the metal salt is a monovalent metal salt, and a mass ratio of the monovalent metal salt to the cellulose nanofibers in the CNF dispersion liquid is 0.2 to 2 times.

[ application example 4]

In the method for producing a fiber material according to the application example, the metal salt is a divalent metal salt, and a mass ratio of the divalent metal salt to the cellulose nanofibers in the CNF dispersion liquid is 0.1 to 2 times.

[ application example 5]

In the method for producing a fiber material according to the application example, the fiber material obtained in the drying step is a swollen fiber material containing a predetermined amount of water.

[ application example 6]

The method for producing a fiber material according to the application example further includes a swelling step of swelling the fiber material obtained in the drying step with water to obtain a swollen fiber material containing a predetermined amount of water.

[ application example 7]

The method for producing a composite material according to this application example is characterized by comprising a kneading step of mixing the swollen fiber material described in the above application example with an elastomer to obtain a composite material, wherein the kneading step comprises a step of passing through an open roll having a roll interval of 0.1 to 0.5mm and a roll temperature of 0 to 50 ℃.

[ application example 8]

The method for producing a composite material according to the application example is characterized by including a kneading step of mixing the swollen fiber material described in the application example with a synthetic resin to obtain a composite material.

[ application example 9]

In the method for producing a composite material according to the application example, the synthetic resin may be a thermoplastic resin, and the kneading step may include a step of kneading at a temperature within a range from a working region development temperature of storage modulus of the thermoplastic resin composition in the vicinity of a melting point (Tm ℃) of the thermoplastic resin to a temperature 1.06 times (T3 ℃ x 1.06) higher than a flat region development temperature (T3 ℃) of the storage modulus.

[ application example 10]

In the method for producing a composite material according to the application example, the synthetic resin is a thermosetting resin, and the kneading step may further include a step of mixing the swelling fiber material with a main agent of the thermosetting resin, kneading the mixture at a kneading temperature in a range from a temperature lower by 20 ℃ than a softening point of the main agent to a temperature higher by 10 ℃ than the softening point, and then mixing the curing agent.

[ application example 11]

The method of manufacturing a composite material according to the application example may further include a dehydration step of dehydrating the composite material obtained in the kneading step.

[ application example 12]

The present application example relates to a cellulose nanofiber comprising a fiber material in which a metal derived from a metal salt is bonded.

[ application example 13]

In the fiber material according to the application example, the metal salt may include at least one of a monovalent metal salt and a divalent metal salt.

[ application example 14]

The composite material according to the application example is characterized by comprising cellulose nanofibers obtained by fiber separation from the fiber material of the application example, and an elastomer or a synthetic resin.

[ application example 15]

In the composite material according to the application example, the composite material may not contain cellulose nanofiber aggregates having a maximum width of 50 μm or more.

Effects of the invention

According to the present invention, a fiber material having excellent processability for use in composite cellulose nanofibers and a method for producing the same can be provided. Further, according to the present invention, a composite material using the fiber material and a method for manufacturing the same can be provided.

Drawings

Fig. 1 is a flowchart illustrating a method for manufacturing a fiber material according to an embodiment.

Fig. 2 is a flowchart illustrating a method for manufacturing a composite material according to an embodiment.

Fig. 3 is a view schematically showing a kneading step in the method for producing a composite material according to one embodiment.

Fig. 4 is a diagram schematically illustrating a kneading step in the method for producing a composite material according to one embodiment.

Fig. 5 is a view schematically showing a kneading step in the method for producing a composite material according to one embodiment.

Fig. 6 is a view showing an electron micrograph of a tensile fracture surface of the composite material of example 2.

Fig. 7 is a view showing an electron micrograph of a tensile fracture surface of the composite material of example 4.

Fig. 8 is a view showing an electron micrograph of a tensile fracture surface of the composite material of example 11.

Fig. 9 is a view showing an electron micrograph of a tensile fracture surface of the composite material of comparative example 3.

Fig. 10 is a view showing an electron micrograph of a tensile fracture surface of the composite material of comparative example 6.

FIG. 11 is a photograph showing an electron micrograph of a tensile fracture surface of the composite material of comparative example 14.

Fig. 12 is a graph showing stress-strain graphs of the composite materials of examples 21, 22.

Fig. 13 is a graph showing a linear expansion coefficient versus temperature graph of the composite material of example 23.

Fig. 14 is a graph showing the relationship of storage modulus and temperature of the sample of example 24 illustrating the method for obtaining the range of the second temperature.

Description of the symbols

2, open milling roller; 10 a first roller; 20 a second roller; 30 an elastomer; 34 stacking; 36 intermediate mixture; 50 a composite material; 80 swell the fibrous material.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments described below do not unreasonably limit the contents of the present invention described in the claims. It should be noted that not all of the structures described below are essential structural elements of the present invention.

1. Method for producing fiber material

A method for producing a fiber material according to an embodiment will be described with reference to fig. 1. Fig. 1 is a flowchart illustrating a method for manufacturing a fiber material according to an embodiment.

As shown in fig. 1, the method for producing a fiber material according to the present embodiment includes a mixing step (S10) of mixing cellulose nanofibers, a metal salt, and an aqueous solvent to obtain a CNF dispersion, and a drying step (S12) of removing the aqueous solvent from the CNF dispersion obtained in the mixing step (S10) to obtain a fiber material. Here, the mass ratio of the metal salt in the CNF dispersion liquid to the cellulose nanofibers is 0.1 to 2 times.

1-1. mixing procedure

The mixing step (S10) is a step of mixing the cellulose nanofibers, the metal salt, and the aqueous solvent to obtain a CNF dispersion.

In the mixing step (S10), the metal salt may be added to the cellulose nanofiber dispersion as a raw material, and the mixture may be mixed by using a known mixer, for example, a propeller mixer, a rotary mixer, or three rolls. The cellulose nanofiber dispersion liquid and the metal salt dispersion liquid in which the metal salt is dissolved or dispersed may be mixed.

1-1-1. cellulose nanofiber dispersion

As the cellulose nanofiber dispersion as a raw material, those commercially available from first industrial pharmaceutical companies and the like can be used. In general, cellulose nanofibers available on the market are provided in a state of being dispersed in an aqueous solution, for example, at a concentration of 2%.

The cellulose nanofiber dispersion as a raw material can be obtained by a production method including, for example, an oxidation step of oxidizing natural cellulose fibers to obtain oxidized cellulose fibers and a refining step of refining the oxidized cellulose fibers. Here, a method for producing a cellulose nanofiber dispersion using an oxidation step is described, but a dispersion obtained by another production method may be used.

First, in the oxidation step, water is added to natural cellulose fibers as a raw material, and the mixture is treated with a stirrer or the like to prepare a slurry in which the natural cellulose fibers are dispersed in the water.

Examples of the natural cellulose fibers include wood pulp, cotton pulp, and bacterial cellulose. More specifically, examples of the wood pulp include conifer pulp, hardwood pulp, and the like; examples of cotton pulp include cotton linters (cotton linters) and cotton lint (cotton linters); examples of the non-wood pulp include straw pulp, bagasse pulp (bagass pulp), and the like. At least one of them may be used as the natural cellulose fiber.

Natural cellulose fibers have a structure composed of cellulose microfibril bundles and lignin and hemicellulose embedded therebetween. That is, it is assumed that the cellulose microfibrils and/or cellulose microfibril bundles are covered with hemicellulose and further covered with lignin. The plant fibers are formed by firmly linking together the lignin, the cellulose microfibrils and/or the cellulose microfibril bundles. Therefore, it is preferable to remove lignin from the plant fiber as much as possible because aggregation of the cellulose fiber in the plant fiber can be prevented. Specifically, the lignin content in the plant fiber-containing material is usually about 40% by mass or less, and preferably about 10% by mass or less. The lower limit of the lignin removal rate is not particularly limited, but is preferably as close to 0 mass%. The measurement of the lignin content can be measured by the Klason method.

The cellulose microfibrils are those having a width of about 4nm as the minimum unit, and may be referred to as single cellulose nanofibers. In the present invention, the term "cellulose nanofibers" refers to cellulose microfibrils and/or cellulose microfibril bundles in which natural cellulose fibers and/or oxidized cellulose fibers are opened to a nano-size level, and the average fiber diameter may be 1nm to 200nm, further 1nm to 150nm, and particularly 1nm to 100 nm. That is, the cellulose nanofibers may comprise individual single cellulose nanofibers or a bundle in which a plurality of single cellulose nanofibers are aggregated.

The average value of the aspect ratio (fiber length/fiber diameter) of the cellulose nanofibers may be 10 to 1000, further 10 to 500, and particularly 100 to 350.

The average value of the fiber diameter and the fiber length of the cellulose nanofiber is an arithmetic average value measured for at least 50 or more cellulose nanofibers within the line of sight of an electron microscope.

Next, as an oxidation step, natural cellulose fibers are subjected to oxidation treatment using an N-oxyl compound in water as an oxidation catalyst to obtain oxidized cellulose fibers. Examples of the N-oxyl compound usable as an oxidation catalyst for cellulose include 2,2,6,6, -tetramethyl-1-piperidine-N-oxide (hereinafter, also referred to as TEMPO), 4-acetamido-TEMPO, 4-carbonyl-TEMPO, and 4-phosphonooxy-TEMPO.

After the oxidation step, for example, the purification step may be performed by repeating washing with water and filtration to remove impurities other than the oxidized cellulose fibers contained in the slurry, such as unreacted oxidizing agent and various by-products. The solvent containing oxidized cellulose fibers is, for example, in a state of being immersed in water, and at this stage, the oxidized cellulose fibers are not defibrated into units of cellulose nanofibers. The solvent may be water, but for example, a water-soluble organic solvent (alcohols, ethers, ketones, etc.) other than water may be used depending on the purpose.

In the oxidized cellulose fiber, a part of the hydroxyl groups of the cellulose nanofibers is modified with a substituent having a carboxyl group, and the modified cellulose nanofibers have a carboxyl group. The oxidized cellulose fibers may have an average fiber diameter of 10 μm to 30 μm. The average value of the fiber diameter of the oxidized cellulose fibers is an arithmetic average value measured for at least 50 or more oxidized cellulose fibers in a field of an electron microscope. The oxidized cellulose fibers may be bundles of cellulose microfibrils. The oxidized cellulose fiber can be defibrated into cellulose nanofibers in the fining step.

In the refining step, the oxidized cellulose fibers may be stirred in a solvent such as water to obtain cellulose nanofibers.

In the fining step, the solvent as the dispersant may be water. As the solvent other than water, water-soluble organic solvents such as alcohols, ethers, ketones and the like can be used alone or in combination.

Examples of the stirring treatment in the fining step include a disintegrator, a beater, a low-pressure homogenizer, a high-pressure homogenizer, a grinder, a coarse grinder, a ball mill, a jet mill, a short-axis extruder, a two-axis extruder, an ultrasonic mixer, and a home-use juicer mixer.

In the refining treatment, the solid content concentration of the solvent containing the oxidized cellulose fibers may be, for example, 50 mass% or less. When the solid content concentration exceeds 50 mass%, a higher energy is required for dispersion.

By the fine-sizing step, a cellulose nanofiber dispersion containing cellulose nanofibers can be obtained. The cellulose nanofiber dispersion may be a colorless transparent or translucent suspension. In the suspension, cellulose nanofibers, which are fine fibers whose surfaces are oxidized and subjected to fiber separation, are dispersed in water. That is, in this dispersion, the strong cohesive force between fibrils (hydrogen bonds between surfaces) is weakened by the carboxyl groups introduced in the oxidation step, and further, cellulose nanofibers can be obtained by going through the refining step. Further, the carboxyl group content, polarity, average fiber diameter, average fiber length, average aspect ratio, and the like can be controlled by adjusting the conditions of the oxidation step.

The cellulose nanofiber dispersion thus obtained may contain 0.1 to 10 mass% of cellulose nanofibers. For example, the solid content of the cellulose nanofibers may be diluted to 1 mass% to obtain a dispersion. The light transmittance of the dispersion may be 40% or more, further 60% or more, particularly 80% or more. Transmittance of dispersion the transmittance at a wavelength of 660nm was measured using an ultraviolet-visible spectrophotometer.

1-1-2. Metal salts

The metal salt is mixed with the cellulose nanofiber dispersion liquid, and metal ions can be ionically combined with the cellulose nanofiber. The metal salt may comprise at least one of a monovalent metal salt, a divalent metal salt, and a trivalent metal salt. The metal salt is preferably a monovalent metal salt or a divalent metal salt. The monovalent metal salt is a salt containing sodium, potassium, and silver, and examples thereof include unsaturated metal salt monomers such as sodium acrylate, potassium acrylate, sodium methacrylate, and potassium methacrylate. The divalent metal salt is a salt containing magnesium, calcium, barium, zinc, copper, iron, lead, nickel, manganese, tin, etc., and examples thereof include unsaturated metal salt monomers such as zinc acrylate, magnesium acrylate, calcium acrylate, zinc methacrylate, magnesium methacrylate, calcium methacrylate, etc. Examples of the trivalent metal salt include neodymium methacrylate and aluminum chloride (AlCl)₃) Iron chloride (FeCl)₃) And the like. The metal salt may be eitherThe water-soluble may be water-insoluble.

The mass ratio of the metal salt in the CNF dispersion to the cellulose nanofibers is 0.1 to 2 times. When the mass ratio of the metal salt to the cellulose nanofibers is less than 0.1 times, the workability in the kneading step described later is lowered. That is, in the kneading step, it is difficult to separate the aggregated cellulose nanofibers into fibers. Further, when the mass ratio of the metal salt to the cellulose nanofibers exceeds two times, the metal salt not bound to the cellulose nanofibers precipitates at the stage of the fiber material. The precipitated metal salt may affect the physical properties of the elastomer or the like in the kneading step described later. The mass ratio of the metal salt to the cellulose nanofibers may be 0.2 to 1.5 times.

In the case where the metal salt is a monovalent metal salt, the mass ratio of the monovalent metal salt to the cellulose nanofibers in the CNF dispersion may be 0.2 to 2 times, and further may be 0.5 to 1.5 times. In the case where the metal salt is a divalent metal salt, the mass ratio of the divalent metal salt to the cellulose nanofibers in the CNF dispersion may be 0.1 to 2 times, and further may be 0.2 to 1.5 times. From the results of the experiment, it is presumed that the addition amount of the monovalent metal salt or the divalent metal salt and the cellulose nanofibers has an influence on the processability in the kneading step described later.

The aqueous solvent may be water or an aqueous solution containing a water-soluble component.

1-1-3.CNF dispersions

The CNF dispersion is a mixture of cellulose nanofibers, a metal salt, and an aqueous solvent, and it is considered that a water-soluble metal salt ionizes to bond metal ions to the cellulose nanofibers, and a water-insoluble metal salt also bonds metal ions to the cellulose nanofibers. The CNF dispersion is expressed as a "CNF dispersion" for the purpose of distinguishing it from a cellulose nanofiber dispersion as a raw material not containing a metal salt. Metal ion and Na combined with carboxyl ion of cellulose nano fiber⁺And substitution to make ionic bonding. It is considered that the water-soluble metal ions in the CNF dispersion are formed by aggregation of a plurality of metal ions into ion clusters. Moreover, the separation is considered to beCellulose nanofibers are bonded to the sub-clusters. Further, even when a water-insoluble metal salt is used, the physical properties of the composite material are improved in the same manner as the water-soluble metal salt, and therefore, metal ions form ion clusters, and cellulose nanofibers are bonded to the ion clusters. The size of the ion cluster is several tens to several hundreds of nanometers.

The water-soluble metal ions are bonded to the cellulose nanofibers in the CNF dispersion liquid in a defibrated state, and dispersed as a whole. The water-insoluble metal ions are bonded to the cellulose nanofibers in the state after the fiber separation, but a part of the aqueous solvent of the CNF dispersion is dispersed in the CNF dispersion in a separated state.

1-2. drying procedure

The drying step (S12) is a step of removing the aqueous solvent from the CNF dispersion obtained in the mixing step (S10) to obtain a fiber material. The CNF dispersion may be dried by a known method, for example, by heating.

For example, the CNF dispersion is allowed to flow into a container (square pan, etc.), and the container is put into an oven to evaporate the aqueous solvent at 30 to 100 ℃. The fiber material obtained in the drying step may be a swollen fiber material containing a predetermined amount of water. When the fiber material is used in the method for producing a composite material described later, the fiber material may be dried until the fiber material contains a predetermined amount of water to be used as a swollen fiber material. The method may further comprise a swelling step of swelling the fiber material obtained in the drying step with water to obtain a swollen fiber material containing a predetermined amount of water. The swelling step and the swollen fiber material will be described in the section of the swelling step described later.

1-3. fiber material

The fibrous material obtained from the drying process comprises cellulose nanofibers to which a metal from a metal salt has been bonded.

The fiber material may be pulverized into powder in consideration of the workability in the kneading step.

The cellulose nanofibers in the fiber material are reformed into hydrogen bonds on the surface of the cellulose nanofibers by removing the aqueous solvent, and are thus reformed into, for example, a sheet-like solid material. The fiber material is mixed as it is in the elastomer or the like without fiber separation into cellulose nanofibers, and only the pulverized solid matter is dispersed in the elastomer.

In order to obtain effects such as reinforcement of cellulose nanofibers, which are nano-sized fibers, by mixing a fiber material with an elastomer or the like, it is necessary to disperse the cellulose nanofibers in the composite material in a state in which the cellulose nanofibers are unwound one by one, as in the CNF dispersion liquid.

2. Method for producing composite material

A method for producing a composite material according to an embodiment will be described with reference to fig. 2. Fig. 2 is a flowchart illustrating a method of manufacturing a composite material according to an embodiment.

The method for producing a composite material according to the present embodiment further includes a kneading step (S16) of kneading the swollen fiber material with an elastomer or a synthetic resin to obtain a composite material. The swollen fiber material used in the kneading step (S16) may be a swollen fiber material obtained in the drying step (S12) and containing a predetermined amount of water, or a swollen fiber material obtained in the swelling step. Further, for example, as shown in fig. 2, the method for producing the composite material may include a swelling step (S14) of swelling the fiber material with water, a kneading step (S16) of mixing the swollen fiber material with an elastomer or a synthetic resin to obtain a composite material, and a dehydration step (S18) of removing water from the composite material.

2-1. swelling step

The swelling step (S14) is a step of swelling the fiber material with water.

By adding a predetermined amount of water to the fiber material, the releasability between the cellulose nanofibers firmly bonded to the fiber material is improved. It is believed that the metal bound to the cellulose nanofibers is re-ionized by water absorbed in the fiber material, weakening the hydrogen bonds between the cellulose nanofibers and the ionic bonds with the metal ion clusters.

The swelling step (S14) is a step of placing the fiber material and a predetermined amount of water in a closed container, and heating the container for a predetermined time and holding the container. For example, about one hour at 70 ℃. The water saturated with water vapor in the closed container is absorbed by the fiber material, and the fiber material swells. For the closed vessel, a glass vessel may be used, and an apparatus for an autoclave may be used.

In the swelling step (S14), the mass ratio of the predetermined amount of water contained in the fiber material to the cellulose nanofibers contained in the fiber material may be 0.5 to 4 times. When the mass ratio of water to the cellulose nanofibers is less than 0.5 times, the workability in the kneading step (S16) is lowered. When the mass ratio of water to the cellulose nanofibers exceeds 4 times, the fibers are not easily mixed with an elastomer or the like, and the processing time is long. Further, in the swelling step (S14), the mass ratio of the predetermined amount of water contained in the fiber material to the cellulose nanofibers may be 1 to 3.5 times, and particularly, the mass ratio to the cellulose nanofibers may be 1 to 3 times.

The swelling step (S14) is a step for improving the processability and defibering properties in the kneading step. Therefore, even if the swelling step (S14) is not performed, the fiber material used in the kneading step may contain a predetermined amount of water, and water is removed in the drying step (S12) until the predetermined amount of water is obtained, for example. Fibrous materials containing a specified amount of water are called swollen fibrous materials. The predetermined amount of water in the swollen fiber material is the same as the amount of water contained in the swollen fiber material obtained in the swelling step (S14) even in the case where the swollen fiber material is obtained in the drying step (S14).

2-2. kneading step

The kneading step (S16) differs depending on the conditions of the material to be the matrix of the composite material. Thermoplastic resins and thermosetting resins will be described as elastomers and synthetic resins, respectively.

2-2-1. kneading step Using elastomer

A mixing and kneading step (S16) of mixing and kneading the fiber material and the elastomer will be described with reference to fig. 3 to 5. Fig. 3 to 5 are diagrams schematically illustrating a method of manufacturing a composite material according to an embodiment. The kneading step (S16) is characterized by comprising a step of performing thin-passing using open rolls having a roll interval of 0.1 to 0.5mm and a roll temperature of 0 to 50 ℃.

First, before the thin-pass step, as shown in fig. 3, mastication of the elastic body 30 wound around the first roll 10 may be performed, and the molecular chains of the elastic body 30 may be appropriately sheared to generate radicals. The free radicals of the elastomer 30 generated by mastication are in a state of being easily bonded to the cellulose nanofibers. As the elastomer 30, natural rubber, synthetic rubber, and thermoplastic elastomer can be used.

Next, as shown in fig. 4, a step of gradually charging the swollen fiber material 80 into the pile 34 of the elastic body 30 wound around the first roll 10 and kneading the same to obtain an intermediate mixture may be performed. The swelling fibrous material 80 may contain, for example, a crosslinking agent, a vulcanizing agent, a vulcanization accelerator, a vulcanization retarder, a softener, a plasticizer, a curing agent, a reinforcing agent, a filler, an age resistor, a colorant, an acid acceptor, and the like, in addition to the cellulose nanofibers. Compounding agents other than these cellulose nanofibers may be added to the elastomer 30 at an appropriate time in the mixing process.

The intermediate mixture obtained in fig. 3 and 4 is not limited to the open mill method, and for example, an internal kneading method or a multi-axis extrusion kneading method may be used.

Further, as shown in fig. 5, a thin pass process may be performed. The thin-passing step may be a step of obtaining an uncrosslinked composite material 50 by thin-passing at 0 to 50 ℃ using an open roll 2 having a roll interval of 0.5mm or less. In this step, the roll interval d between the first roll 10 and the second roll 20 is set to, for example, 0.5mm or less, more preferably 0.1mm to 0.5mm, and the intermediate mixture 36 obtained in FIG. 2 may be fed to the open roll 2 to be passed through the open roll 2 once or more than once. The number of thin passes may be, for example, about 1 to 10. When the surface speed of the first roller 10 is V1 and the surface speed of the second roller 20 is V2, the surface speed ratio (V1/V2) of the two rollers for passing through may be 1.05 to 3.00, and further may be 1.05 to 1.2. By using such a surface velocity ratio, a desired shear force can be obtained.

The composite material 50 extruded from the narrow roll gap is largely deformed as shown in fig. 5 by the restoring force due to the elasticity of the elastic body, and at this time, the cellulose nanofibers move largely together with the elastic body. The composite material 50 obtained by the thin pass is separated into a sheet shape having a prescribed thickness of, for example, 100 μm to 500 μm by roll casting.

In the thin pass step, in order to obtain as high a shear force as possible, the roll temperature may be set to, for example, 0 ℃ to 50 ℃, or may be set to a relatively low temperature of 5 ℃ to 30 ℃. The measured temperature of the composite material 50 may also be adjusted to 0 ℃ to 50 ℃, and further to 5 ℃ to 30 ℃.

By adjusting the temperature to such a range, the cellulose nanofibers can be defibrated by the elasticity of the elastomer, and the defibrated cellulose nanofibers can be dispersed in the composite material 50.

By the high shear force in the thin-pass step, a high shear force acts on the elastomer, and the cellulose nanofibers in the swollen fiber material are separated from each other so as to be pulled out one by one in the molecules of the elastomer, and are dispersed in the elastomer. This is because the metal bound to the cellulose nanofibers is ionized by swelling of the fiber material, and the binding force between the cellulose nanofibers is weakened. Especially, the elastic body has elasticity and viscosity, so that the cellulose nano-fiber can be subjected to fiber separation and dispersion. Further, the composite material 50 excellent in dispersibility and dispersion stability of the cellulose nanofibers (the cellulose nanofibers are less likely to reaggregate) can be obtained.

More specifically, when the elastomer and the cellulose nanofibers are mixed by the open roll, the elastomer having tackiness invades between the cellulose nanofibers. The surface of the cellulose nanofibers is suitably highly active by, for example, oxidation treatment, and in particular can be easily bonded to molecules of the elastomer. Then, when a strong shearing force acts on the elastomer, the cellulose nanofibers move along with the movement of the molecules of the elastomer, and the aggregated cellulose nanofibers are separated by the restoring force of the elastomer due to the elasticity after shearing, and become dispersed in the elastomer. In particular, the open mill method is preferable because it can control not only the roll temperature but also the actual temperature of the mixture.

Next, a method for producing a composite material using a synthetic resin will be described.

2-2-2 mixing and kneading step Using thermoplastic resin

A kneading step using a thermoplastic resin as a synthetic resin will be described. The kneading step includes a step of kneading at a kneading temperature within a range from a working region development temperature of the storage modulus of the thermoplastic resin composition in the vicinity of the melting point (Tm ℃) of the thermoplastic resin to a temperature 1.06 times (T3 ℃ C. times.1.06) the flat region development temperature (T3 ℃) of the storage modulus.

In the kneading step, a device for melting the thermoplastic resin and molding the molten thermoplastic resin may be used, for example, an open roll, an internal kneading machine, an extruder, an injection molding machine, or the like. For example, it can be carried out by using an extruder having a conical screw, and the open roll 2 shown in FIGS. 3 to 5.

The kneading step may include, for example: a first temperature mixing step of kneading a thermoplastic resin and a swollen fiber material at a first temperature to obtain a first mixture; a low-temperature step of adjusting the temperature of the first mixture to a second temperature; and a low-temperature kneading step of kneading the first mixture at the second temperature. The first temperature is higher than the second temperature, and the second temperature is in a range from a temperature at which a processed region of the storage modulus of the composite material in the vicinity of the melting point (Tm ℃) of the thermoplastic resin develops to a temperature that is 1.06 times (T3 ℃ C.. times.1.06) the temperature at which a flat region of the storage modulus develops (T3 ℃).

2-2-2-1. first temperature mixing procedure

The first temperature mixing step is to mix and knead the thermoplastic resin and the swollen fiber material at a first temperature to obtain a first mixture.

The first temperature mixing step is a step until the completion of charging the thermoplastic resin with the swollen fiber material in a predetermined amount, and preferably, a step until the operator can visually recognize that the cellulose nanofibers are mixed in the entire thermoplastic resin. The present invention can be implemented as shown in fig. 3 and 4, similarly to the case of the elastic body described above.

The first temperature is a temperature higher than the melting point (Tm) of the thermoplastic resin. The first temperature is a higher temperature than the second temperature. The first temperature is a temperature that can be higher by 25 ℃ or more than the melting point (Tm) of the thermoplastic resin. The first temperature may be a temperature higher by 25 ℃ to 70 ℃ than the melting point (Tm) of the thermoplastic resin and higher by 25 ℃ to 60 ℃ than the melting point (Tm). The first temperature is the actual temperature of the thermoplastic resin in the first temperature mixing step, and is not the temperature of the processing apparatus. The molding temperature of the thermoplastic resin is generally indicated by the set temperature of the heating cylinder if it is a processing device such as an extruder or an injection molding machine, but generally, the actual resin temperature is higher than the set temperature of the processing device due to shear heat generated during kneading. Since the first temperature is a temperature during processing, it is preferable to measure the actual surface temperature of the resin as much as possible, but if it cannot be measured, the surface temperature of the resin immediately after the first mixture is taken out from the processing apparatus may be measured as the actual surface temperature. The first temperature is not only a temperature immediately after the resin is fed into the processing apparatus but also a temperature at which the feeding of the swollen fiber material is completed and the mixture is mixed.

The "melting point (Tm)" in the present invention is a melting peak measured using Differential Scanning Calorimetry (DSC) based on JIS K7121.

The cellulose nanofibers in the first mixture obtained in the first temperature mixing step are dispersed and present as a whole in the same state as the raw material in the form of aggregates. Therefore, the first mixture has defects in its material, such as a significantly reduced elongation at break when compared to the thermoplastic resin monomer of the raw material when subjected to a tensile test or the like.

2-2-2-2. Low temperature Process

The low-temperature step is a step of adjusting the temperature of the first mixture to a second temperature.

Here, the second temperature will be explained.

The normal processing set temperature of the first temperature mixing step, i.e., the set temperature of the processing device, is a temperature higher than the recommended processing set temperature of the thermoplastic resin, for sufficiently melting the thermoplastic resin in a short time and rapidly processing the thermoplastic resin. Therefore, the thermoplastic resin is not processed in the vicinity of its melting point. As described above, the surface temperature of the thermoplastic resin during processing is higher than such a processing set temperature.

In particular, when a filler such as cellulose nanofibers is blended in a thermoplastic resin, it is normal to process the thermoplastic resin at a temperature higher than a normal processing set temperature. When the amount of cellulose nanofibers added increases, the temperature of the first mixture in the first temperature mixing step rapidly increases due to heat generation caused by shearing.

Therefore, in order to perform the low-temperature kneading step, the temperature of the first mixture needs to be lowered. Since the temperature of the first mixture rises when the kneading is performed, there is a difficulty in lowering the temperature while continuing the kneading. For this reason, the low-temperature step may stop the kneading machine for a predetermined time after kneading, or may take out the first mixture from the kneading machine and cool it to the second temperature. Further, the first mixture may be actively cooled using a cooling device provided with a cooling mechanism such as a fan, a spot cooler, or a cooler. The processing time can be shortened by active cooling.

The second temperature is within a range from a temperature at which a processed region of the composite material having a storage modulus develops near the melting point (Tm ℃) of the thermoplastic resin used in the production method to a temperature that is 1.06 times (T3 ℃ C.. times.1.06) the temperature at which a flat region of the storage modulus develops (T3 ℃).

As a result of studies by the inventors, it has been found that a composite material shows a behavior different from that of a thermoplastic resin as a raw material when subjected to a dynamic viscoelasticity test (hereinafter, referred to as a DMA test). The thermoplastic resin of the raw material has a storage modulus (E') sharply decreased in the vicinity of the melting point (Tm) and flows. However, it is known that a composite material in which cellulose nanofibers are mixed exhibits a flat region in which the storage modulus (E') is hardly decreased even when the storage modulus exceeds the melting point, that is, a rubber elastic region such as an elastomer, by dispersing cellulose nanofibers in a predetermined amount or more.

The low-temperature kneading step separates fibers from the temperature in the vicinity of the melting point to a part of the flat region to disentangle the aggregated cellulose nanofibers, and disperses the fibers in the thermoplastic resin. In order to set the second temperature range, a DMA test needs to be performed on a sample of the composite material to which the second temperature range is added. Specifically, the following is shown.

First, the first temperature mixing step of 2-2-2-1 was carried out with a predetermined mixing ratio to obtain a first mixture. Next, a composite material sample is obtained by performing the same process as the low-temperature kneading process described later, with respect to the first mixture, using a temperature near the melting point of the thermoplastic resin to be the matrix (for example, a processable range of +10 ℃ to +20 ℃ of the melting point) as the kneading temperature. In this sample, it is preferable that cellulose nanofibers or the like are dispersed by defibration, and even if defibration is not sufficiently performed, a clear change in characteristics can be confirmed in the vicinity of the inflection point or flat region developing temperature. The DMA test was performed on the composite material sample, the relationship between the storage modulus (E') and the temperature (c) was graphed, and the DMA test result was used if a flat area was confirmed. Further, if no flat region was confirmed in this composite material sample, the composite material sample was newly obtained by the above-described method with the temperature around the inflection point as the second temperature, subjected to the DMA test, and similarly mapped. Such operations are repeated until a flat area is found unambiguously.

The method of setting the kneading temperature (second temperature) in the low-temperature kneading step will be described using the DMA test results of the composite material sample of example 24 described later prepared using the kneading temperature thus obtained. Fig. 14 is a graph showing the DMA measurement results (temperature dependence of storage modulus E') of the sample of example 24. In fig. 14, the abscissa is temperature (deg.c), the ordinate on the left side is the logarithm (log (E ')) of the storage modulus (E '), and the graph of log (E ') is represented by a solid line. In FIG. 14, the vertical axis on the right side represents the differential value (d (log (E '))/dT) of the logarithmic value (log (E')) of the storage modulus (E '), and the graph of d (log (E'))/dT is represented by a broken line.

The thermoplastic resin of example 24 was a linear short chain branched polyethylene (LLDPE) having a melting point of 115 ℃ and the plot of log (E') had an inflection point P1 at 121.5 ℃. Inflection point P1 appears explicitly in the graph of d (log (E'))/dT. The inflection point appears at a slightly different temperature by changing the amount of cellulose nanofibers incorporated. The inflection point P1 differs depending on the melting point of the thermoplastic resin.

Next, from the graph of log (E ') of fig. 14, "processing region developing temperature T2" of storage modulus (E') was obtained. The graph of log (E ') is 78 ℃ or lower, the gradient of the graph is constant, and the storage modulus (E') sharply decreases and starts flowing in the vicinity of 115 ℃ which is the melting point (Tm). In the thermoplastic resin monomer not compounded with the cellulose nanofibers, when the flow is started, the storage modulus (E ') continues to decrease and flow while maintaining this state, but the sharp decrease of the graph of log (E') in the composite material stops becoming a flat region and does not flow. It is understood that the first region W1 in which the gradient of the region smaller than the melting point before the start of the flow is constant is clearly shown in the graph of d (log (E'))/dT, and is in the range of 62 ℃ to 78 ℃. The temperature of the first intersection point P2 of the line L1 of the graph of the extrapolation line L2 and the log (E ') of the inflection point P1 of the graph of the log (E') of the first region W1 is the processing region development temperature T2(108 ℃). The processing area appearance temperature T2 is the lower limit temperature of the kneading-possible processing in the low-temperature kneading step.

Further, the "flat region (rubber elastic region) appearance temperature T3" of the storage modulus (E ') was obtained from the graph of log (E') of fig. 14. In fig. 14, the inclination is constant in the range of 128 ℃ to 142 ℃. The second region W2 in which the inclination is constant from the end of the sharp decrease of the graph of log (E ') at the temperature exceeding the melting point is clearly shown in the graph of d (log (E'))/dT. The temperature of the second intersection point P3 of the line L1 of the graph of the extrapolation line L3 and the log (E ') of the inflection point P1 of the graph of the log (E') of the second region W2 is the flat region developing temperature T3.

The region (W1, W2) in which the inclination of the graph of log (E') becomes constant is a region in which a temperature range of at least 10 ℃ or higher exists. The flat area is the second area W2.

A temperature higher than the temperature T1 of the inflection point P1 thus obtained and at which the viscosity of the composite material sample becomes low to the extent of no flow-out, for example, a temperature T4(132.5 ℃ C. in FIG. 14) at which the flat region developing temperature T3(125 ℃ C. in FIG. 14) is 1.06 times (T3 ℃ C. x 1.06) is set as the upper limit of the kneading temperature. It is considered that the agglomerated masses of cellulose nanofibers can be defibrated from all thermoplastic resins up to a temperature T4 that is 1.06 times (T3 ℃x1.06 times) the flat region development temperature T3.

The second mixture has appropriate elasticity and appropriate viscosity in a temperature range from the processing region development temperature T2 to a temperature T4 that is 1.06 times (T3 ℃x1.06) the flat region development temperature T3, and therefore can be processed and cellulose nanofibers can be defibrated. It has been found through studies by the present inventors that the temperature range from T3 to T4 tends to be large as the melting point becomes higher.

The lower limit of the kneading temperature in the low-temperature kneading step may be not less than the inflection point temperature T1 of the inflection point P1. This is to make the processing of the second mixture easier. The temperature T2 and the temperature T4 are slightly different temperatures because the amount of cellulose nanofibers to be blended is changed.

The inventors of the present invention have found that by performing the low-temperature kneading step at a kneading temperature in a range from a temperature slightly lower than the inflection point temperature T1 to a temperature T4 which is 1.06 times (T3 ℃x1.06) the flat region developing temperature T3, the fibers can be separated so that the aggregated cellulose nanofibers are disentangled and dispersed in the thermoplastic resin.

The second temperature is a relatively low temperature not employed as the processing temperature of the thermoplastic resin, particularly as a low temperature range heretofore not employed as the processing temperature of the second mixture.

The first mixture whose temperature is lowered to the second temperature may be fed into an oven set to the second temperature, for example, and the prescribed temperature may be maintained in the second temperature range. The first mixture taken out of the kneading machine is cooled for the purpose of stabilizing the processing quality.

When using particles (pellet) containing commercially available cellulose nanofibers as the first mixture, a reheating step is required between the first temperature mixing step and the low temperature step. The reheating step may be performed by heating the thermoplastic resin to a temperature equal to or higher than the melting temperature of the thermoplastic resin.

2-2-2-3. Low-temperature kneading step

The low-temperature kneading step is to knead the first mixture at the second temperature.

As the first mixture, a mixture obtained by the above-described first temperature mixing step of 2-2-2-1 can be used.

In this step, for example, conditions other than the roll temperature may be set to be equal to or less than 0.5mm, more preferably, 0mm to 0.5mm, in the same manner as in fig. 5 using an elastomer, with respect to the roll gap d between the first roll 10 and the second roll 20, and the first mixture obtained in the first temperature mixing step may be introduced into the open roll 2 and kneaded.

Since the second temperature is in a temperature range having appropriate elasticity and appropriate viscosity, the first mixture extruded from the narrow space between the rolls is largely deformed by the restoring force due to the elasticity of the thermoplastic resin, and the cellulose nanofibers move largely together with the deformation of the thermoplastic resin at this time.

The second temperature is the surface temperature of the first mixture in the low-temperature kneading step, and is not the set temperature of the processing apparatus. As described above with reference to the first temperature, it is preferable that the second temperature is the actual surface temperature of the resin as much as possible, but if the second temperature cannot be measured, the surface temperature of the resin immediately after the composite material is taken out from the processing apparatus may be measured, and the second temperature during processing may be determined from the measured surface temperature.

In the case of the open roll 2, the surface temperature may be measured using a non-contact thermometer, and the non-contact thermometer 40 may be disposed at a position other than the position just passing through the nip, and is preferably disposed above the first roll 10. It is preferred to avoid the first mixture immediately after passing through the nip because it is an unstable temperature that changes dramatically.

Further, when the surface temperature of the first mixture in the low-temperature mixing and kneading step cannot be measured like an internal mixer, an extruder, or the like, it can be confirmed that the surface temperature of the composite material immediately after mixing and kneading taken out from the apparatus is within the range of the second temperature.

The low-temperature kneading step may be performed at the second temperature for, for example, 4 to 20 minutes, and further 5 to 12 minutes. By making the kneading time at the second temperature sufficient, the cellulose nanofibers can be more reliably defibrated.

Since the cellulose nanofibers are blended, the workability of the first mixture is lowered, and the temperature of the first mixture is higher than the set temperature of the apparatus by the shear heat generated by kneading the mixture. For this reason, in order to maintain the surface temperature of the first mixture in the second temperature range suitable for the low-temperature kneading step, the temperature of the rolls is adjusted so that the temperature of the first mixture does not become high in the case of open rolls, and it is necessary to actively adjust the temperature for cooling. Similarly, in the internal kneading machine, the extruder, the injection molding machine, or the like, the surface temperature of the first mixture can be maintained in the second temperature range for a certain period of time by adjusting the processing set temperature of the apparatus so as to be actively cooled. For example, in the extruder, the set temperature of the heating cylinder in the vicinity of the feed material may be set to a temperature higher than the normal processing temperature, the other region may be set to a temperature lower than the second temperature, and the surface temperature of the resin during processing may be adjusted so as to be the second temperature.

The composite material obtained in the low-temperature kneading step may be, for example, cast into a mold and pressed, or further processed into pellets using an extruder, and molded into a desired shape by a known processing method for thermoplastic resins.

The thermoplastic resin is subjected to a high shearing force by the shearing force obtained in the low-temperature kneading step, and the aggregated cellulose nanofibers are separated from each other so as to be pulled out one by one in the molecules of the thermoplastic resin, separated from the fibers, and dispersed in the thermoplastic resin. This is because the metal bound to the cellulose nanofibers is ionized by swelling of the fiber material, and the binding force between the cellulose nanofibers is weakened. In particular, since the thermoplastic resin has elasticity and viscosity in the second temperature range, the cellulose nanofibers can be separated and dispersed. Further, a composite material excellent in dispersibility and dispersion stability of the cellulose nanofibers (cellulose nanofibers are less likely to reaggregate) can be obtained.

2-2-3. kneading Process Using thermosetting resin

A kneading step using a thermosetting resin as a synthetic resin will be described. Here, a two-liquid mixing type resin using a main agent such as an epoxy resin, a phenol resin, or a urethane resin and a curing agent as a thermosetting resin will be described, but the present invention is not limited thereto.

The kneading step may further include a step of mixing the swelling fiber material with the main agent of the thermosetting resin, kneading the mixture at a kneading temperature in a range from a temperature lower by 20 ℃ than the softening point of the main agent to a temperature higher by 10 ℃ than the softening point, and then mixing the curing agent. If the temperature is around the softening point of the base product, the base product is not completely liquid, and according to the test results, the base product can have appropriate elasticity and viscosity at a kneading temperature ranging from a temperature 20 ℃ lower than the softening point to a temperature 10 ℃ higher than the softening point.

In the case of an epoxy resin, for example, bisphenol a type epoxy resins which are solid at room temperature and have a softening point of 100 ℃ or lower can be used as the main component. The softening point of the base compound can be determined by the ring and ball method. The ring and ball method can be, for example, the softening point test method defined in JIS K7234. As the curing agent for the epoxy resin, for example, amines, amidoamines, and the like which are liquid at room temperature can be used. The fiber material mixed with the main agent of the thermosetting resin may be a swollen fiber material.

In the case of a phenol resin, for example, a novolac resin can be used as a main agent, and hexamethylenetetramine or the like can be used as a curing agent. The softening point of the base compound can be determined by the ring and ball method.

The main component is solid at room temperature and has a softening point of 100 ℃ or lower, and therefore, the kneading workability is excellent, and particularly, the main component is easily worked by a restoring force due to the elasticity of the main component by applying a shearing force during kneading.

In the kneading step, for example, an open roll, an internal kneader, an extruder, or the like can be used. For example, it can be carried out by using the open roll 2 shown in FIGS. 3 to 5.

The basic procedure is the same as in the case of the elastomer, but here, the case of the epoxy resin will be described by taking a bisphenol A type main agent (the solid softening point is 64 ℃ C. at normal temperature) as an example. First, the first roll 10 is masticated at 60 ℃ to 70 ℃ and the second roll 20 is masticated at a temperature of 50 ℃ to 60 ℃ in fig. 3. Next, the swollen fiber material was slowly charged into the main agent shown in fig. 4 and mixed. Thereafter, the thin-pass process shown in fig. 5 may be performed, for example, with the roller interval d set to 0mm to 0.5 mm. The surface speed of the roller is the same as in the case of the elastic body. The method is used for defibrating cellulose nanofibers by utilizing appropriate elasticity and appropriate viscosity of the base material, as in the thin-pass process using an elastomer.

The roll temperature was controlled to be around the softening point of the main agent, and the roll 10 and the roll 20 were made to have a temperature difference of about 10 ℃ depending on the workability of the main agent. Since such a base compound is easily attached to the rolls, when the two rolls 10 and 20 are at the same temperature, the base compound is simply separated from the rolls 10 and 20 and attached to the rolls. For this reason, a shearing force is not easily applied to the main agent, and thus the cellulose nanofibers are not easily defibrated. Therefore, by setting such a temperature difference, the main agent can be wound around the second roller 20 on the low temperature side, and a desired shearing force can be applied to the main agent, and as a result, the cellulose nanofibers can be effectively defibrated.

In the kneading step, the moisture of the swollen fiber material ionizes the metal bound to the cellulose nanofibers. Therefore, the shearing force of kneading is added in a state where the binding force between the cellulose nanofibers is weakened by the metal ions, and further, the interval between the cellulose nanofibers can be widened by the restoring force due to the elasticity of the main agent in the thin-pass step, and uniform fiber separation and dispersion of the cellulose nanofibers can be performed.

The step of mixing the curing agent is preferably performed after the dehydration step. This is to improve the quality of the processed product.

After the main agent and the cellulose nanofibers are kneaded, a curing agent (for example, polyamidoamine) is added, and then the main agent and the curing agent are kneaded by the same method and under the same conditions as those of the main agent to uniformly mix the curing agent. The method of mixing the curing agent is also performed in the same manner as the method of mixing and kneading the main agent, and the cellulose nanofibers in the main agent are uniformly mixed and dispersed without deteriorating the fiber separation state. Thereafter, the resulting mixture is molded (e.g., press molded, compression molded, or extrusion molded), left to stand at room temperature for one day to cure the mixture, and then post-baked (80 ℃ C., 15 hours) to obtain a composite material.

2-3. dehydration step

The dehydration step (S18) is a step of dehydrating the composite material obtained in the kneading step (S16). In the method for producing a composite material using a thermosetting resin, as described above, it is preferable that the composite material is obtained by mixing the curing agent after the step of kneading the main agent and the cellulose nanofibers and then the step of dehydrating (S18).

The dehydration step (S18) may be performed by heating the composite material to evaporate water. For example, the composite material is placed in an oven, and the interior of the oven is evacuated while heating.

In addition, when water in the fiber material is removed in the middle of the kneading step (S16), the dewatering step (S18) is not required. For example, in the case of the mixing step (S16) using an open roll, the water may be removed by heating the roll after the thin pass, or a device having a dewatering function may be used in the case of a closed type mixing and kneading machine.

When the elastomer composite material is used, a known rubber chemical such as a vulcanization accelerator, a vulcanizer, an antioxidant, a reinforcing agent, and a coupling agent is further added, and vulcanization molding is performed by heating and pressing to form a desired shape. In order to obtain desired physical properties of the rubber product, known reinforcing agents such as carbon black, silica, and carbon nanotubes may be added to the elastomer in the kneading step (S16).

2-4. composite material

The composite material is characterized by not containing cellulose nanofiber aggregates having a maximum width of 50 [ mu ] m or more. The cellulose nanofiber aggregate is a substance in which a plurality of cellulose nanofibers are aggregated and dispersed in a matrix in a state of aggregated particles. The maximum width of the cellulose nanofiber aggregate was measured by observing the cut surface of the composite material with a scanning electron microscope, observing the particulate aggregate dispersed in the matrix material, and measuring the maximum width.

The composite material comprises cellulose nanofibers bonded with a metal from a metal salt in a CNF dispersion. Since the composite material has high rigidity, metals derived from metal salts in the composite material exist close to each other, forming ion clusters. It is speculated that a reinforced structure through the fibers can be obtained by building a three-dimensional simulated network in the composite material by cellulose nanofibers bonded to the metal forming the ion clusters. This is because, in the polymer that does not react with the silane coupling agent, the rigidity of the composite material is not improved even when the composite material is produced in a state where the cellulose nanofibers are defibrated by the silane coupling agent or the like that does not form ion clusters.

The cellulose nanofibers contained in the fiber material in the composite material are separated into individual cellulose nanofibers and dispersed in the composite material against hydrogen bonds between the cellulose nanofibers in the kneading step.

The composite material may include cellulose nanofibers defibrated from a fibrous material and an elastomer or synthetic resin. The fiber material in the composite material exists as cellulose nanofibers in a state in which fibers are separated in a matrix of an elastomer or a synthetic resin. The cellulose nanofibers in the composite material are preferably all defibrated, but preferably at least when the stretch-broken surface is observed with an electron microscope, the cellulose nanofiber aggregates having a maximum width of 50 μm or more are not included. This is because when such aggregate is included, not only the reinforcing effect as a fiber cannot be obtained, but also there is a possibility that it may become a fracture starting point in a tensile test.

Examples

Examples of the present invention will be described below, but the present invention is not limited thereto.

(A) Preparation of sample Using elastomer

(A-1) preparation of samples of examples 1 to 20

A mixing procedure: a cellulose nanofiber dispersion (TEMPO-oxidized cellulose nanofibers at a concentration of 2% manufactured by first industrial pharmaceutical company) was diluted with water as a dispersion of cellulose nanofibers at a concentration of 1% (the solvent was water), and metal salts of the types shown in tables 1 to 5 were stirred and mixed in this dispersion using a propeller mixer to obtain a CNF dispersion.

In the context of tables 1 to 5,

"CNF": TEMPO oxidizing cellulose nanofibers (the cellulose nanofibers having an average fiber diameter of 3.3nm and an average aspect ratio of 225),

"sodium methacrylate": sodium methacrylate (metal component 19% to 21%, methacrylic acid component 75% to 80%) manufactured by shalian chemical industry,

"zinc methacrylate": zinc methacrylate R-20S (metal component 25% to 27%, methacrylic acid component 60% to 64%) manufactured by Mitsuita chemical industries,

"zinc acrylate": zinc acrylate RSS (metal content of 27% or more, acrylic acid content of 56% or more) manufactured by Shaitan chemical industries, Ltd,

"calcium acrylate": calcium acrylate (metal component 18-22%, acrylic acid component 60-75%) manufactured by Mitsuita chemical industry,

“CaCl₂": and calcium chloride (pharmaceutical specialty, purity 95% or more) manufactured by Wako pure chemical industries, Ltd.

The "blend of fiber materials" in tables 1 to 5 is represented by the ratio of the blend amounts when CNF in the swollen fiber materials after the swelling step is 1.

A drying procedure: the aqueous solvent was removed from the CNF dispersion to obtain a fiber material. More specifically, the CNF dispersion was poured into a square pan, and the aqueous solvent was dried off in an oven at 80 ℃ for 24 hours to obtain a fiber material. The fiber materials used in examples 1 to 20 were not visually observed to confirm the precipitation of the metal salt on the surface.

Swelling step: swelling the fibrous material with water to obtain a swollen fibrous material. More specifically, the fiber material and a predetermined amount of water were placed in a glass-made closed container, and the container was kept at 70 ℃ for 1 hour in the closed container to swell the fiber material, thereby obtaining a swollen fiber material. The amount of water is represented by the ratio of the amount of water added when the CNF shown in tables 1 to 5 is 1.

A mixing and kneading step: the swollen fiber materials were mixed into the elastomers shown in tables 1 to 5 to obtain composite materials. More specifically, a swollen fiber material was gradually charged into an elastomer kneaded with two rolls, and kneaded to obtain an intermediate mixture, which was then subjected to thin-passing (roll temperature 10 ℃ C. to 30 ℃ C., roll interval 0.3mm, roll speed ratio 1.1) to obtain a composite material.

The "blending of composite materials" in tables 1 to 5 represents the blending amount of cellulose nanofibers and metal salt contained in the swollen fiber material in the kneading step in parts by mass (phr). Samples of the composite were made using 100g of elastomer.

In the context of tables 1 to 5,

"HNBR": zetpol 2010(Zetpol is a registered trademark) manufactured by Zeon corporation of Japan (in combination with an acrylonitrile amount center value of 11 (%), an iodine value center value of 7 or less (mg/100mg), a Mooney viscosity (center value) of 85),

"EPDM": JSR EP24(JSR is a registered trademark) manufactured by JSR corporation (ENB content 4.5 (%), ethylene content 54 (%), Mooney viscosity 42(ML (1+4)100 ℃), oil charge 0 (PHR)).

A dehydration step: the composite material obtained in the kneading step is dehydrated. More specifically, the composite material was dried at 40 ℃ to 90 ℃ for 12 hours using an oven, and additional water was removed from the composite material during the swelling process.

A pressing procedure: after a crosslinking agent, an anti-aging agent and the like are compounded into the dehydrated composite material by using two rollers, the composite material is placed into a mold and is subjected to pressure forming under vacuum, and a sample is manufactured. Vacuum press molding was conducted by heating a mold at 165 ℃, press molding was conducted for 25 minutes while pressing (against the mold), the mold was moved to a cooling press, and cooling was conducted to room temperature while pressing (against the mold), to obtain sheet-like samples of examples 1 to 20 having a thickness of 1 mm.

(A-2) preparation of samples of comparative examples 1 to 15

Samples of comparative examples 1 to 15 were prepared in accordance with the compounding amounts shown in tables 6 to 9.

The samples of comparative examples 1 and 15 were obtained by compression molding of pure rubber in the same manner as in examples. Comparative example 1 is "HNBR" and comparative example 15 is "EPDM".

The samples of comparative examples 2 and 3 were samples to which no metal salt was added. Samples of comparative examples 2 and 3 were obtained in the same manner as in example 1 except that the mixing step (the swelling step was also omitted in comparative example 2) was omitted and a resin material containing no metal salt was used.

Samples of comparative examples 4 to 7 were obtained in the same manner as in example 1. Comparative example 4 is a case where the amount of the metal salt is small, and comparative examples 5 to 7 are cases where the amount of the metal salt is the same as the samples of examples 3 to 5 and the amount of water in the swelling step is changed. Comparative example 5 did not undergo the swelling step.

Samples of comparative examples 8 to 14 were obtained in the same manner as in example 1 except that a silane coupling agent was used instead of the metal salt.

In the case of tables 8 and 9,

coupling agent 1 is "3- (methacryloyloxy) propyltrimethoxysilane": KBM-503 manufactured by shin-Etsu chemical industries,

coupling agent 2 is "3-glycidoxypropyltrimethoxysilane": KBM-403 manufactured by shin-Etsu chemical industries,

coupling agent 3 is "N-2- (aminoethyl) -3-aminopropyltrimethoxysilane": KBM-603, manufactured by shin-Etsu chemical industries, Inc.,

coupling agent 4 is "3-isocyanatopropyltriethoxysilane": KBE-9007, manufactured by shin-Etsu chemical industries,

coupling agent 5 is "3-mercaptopropylmethyldimethoxysilane": KBM-803, manufactured by shin-Etsu chemical industries, Inc.

(B) Evaluation method

(B-1) measurement of hardness

Rubber hardness (hs (JIS a) measurement results are shown in tables 1 to 9 for samples of examples and comparative examples based on JIS K6253 test.

(B-2) tensile test

For the samples of examples and comparative examples, tensile tests were carried out at 23 ± 2 ℃, a standard interline distance of 20mm, and a tensile speed of 500mm/min in accordance with JIS K6251 using a tensile tester, Autograph AG-X, manufactured by shimadzu corporation, for test pieces cut into dumbbell shapes of JIS 6, and tensile strength (ts (MPa)), elongation at break (Eb (%)), and 50% modulus (σ 50(MPa)) were measured. The measurement results are shown in tables 1 to 9.

(B-3) evaluation of processability

The samples of examples and comparative examples were evaluated for their workability in the kneading step described above in the production test with HNBR100g or EPDM100 g. The evaluation results (. smallcircle., within 30 minutes, good roll winding property,. DELTA.over 30 minutes to 1 hour, good roll winding property,. times.over 1 hour, poor roll winding property) are shown in tables 1 to 9.

(B-4) evaluation of defibrination and dispersibility

The fiber separation and dispersibility of the composite material were evaluated for the samples of examples and comparative examples. The tensile fracture surface of each sample was observed by a scanning electron microscope. The evaluation results (. smallcircle., no clumps having a maximum width of 50 μm or more,. DELTA.are clumps having a maximum width of 50 to 100 μm,. times.clumps having a width of 100 μm or more) are shown in tables 1 to 9. In addition, the electron micrographs of examples 2, 4 and 11 as the "o" sample are shown in fig. 6 to 8, the electron micrograph of comparative example 3 as the "x" sample is shown in fig. 9, and the electron micrographs of comparative examples 6 and 14 as the "Δ" sample are shown in fig. 10 and 11.

TABLE 1

TABLE 2

TABLE 3

TABLE 4

TABLE 5

TABLE 6

TABLE 7

TABLE 8

1 coupling agent 1: 3- (methacryloyloxy) propyltrimethoxysilane

Coupling agent 2: 3- (2, 3-glycidoxy) propyltrimethoxysilane

TABLE 9

3. coupling agent 3: n2 (aminoethyl) -3-aminopropyltrimethoxysilane

4. coupling agent 4: 3-isocyanatopropyltriethoxysilane

Coupling agent 5: 3-mercaptopropyl-methyldimethoxysilane

(C) Evaluation results

As shown in tables 1 to 5, the samples of examples 1 to 20 were "o" in the evaluation of "workability" and "defibrability and dispersibility" in the kneading step, and as shown in fig. 6 to 8, it was found that in the sample "o" in the evaluation of "defibrability and dispersibility", aggregates of the fiber material having a maximum width of 50 μm or more did not remain, and the cellulose nanofibers were defibrated.

It is understood that the samples of examples 1 to 14 using HNBR shown in tables 1 to 4 have larger values of "σ 50" and "TS" than the samples of pure rubber of comparative example 1 shown in table 6, and have a reinforcing effect by cellulose nanofibers. Further, it is understood that the samples of examples 1 to 5 and 8 to 14 using HNBR shown in tables 1 to 4 have a larger "σ 50" than comparative examples 2 and 3 having the same CNF amount shown in table 5, and the reinforcing effect by the cellulose nanofibers defibrated by the metal salt can be obtained. The sample of comparative example 4 shown in table 7 was too small in sodium methacrylate, and therefore, it was difficult to defibrate the cellulose nanofibers, and "workability" was "Δ" and "defibration and dispersibility" was "x". The samples of comparative examples 5 to 7 shown in Table 7 changed the amount of water in the swelling step, but had a problem particularly in "processability".

Although various silane coupling agents were used in place of the metal salts in the samples of comparative examples 8 to 14 shown in tables 8 and 9, the "processability" was improved by blending a predetermined amount of the silane coupling agent, but the "defibrination and dispersibility" was inferior to the samples of examples 1 to 16 using the metal salts.

It is understood that the samples of examples 17 to 20 using EPDM shown in table 5 have larger values of "σ 50" and "TS" than the sample of comparative example 15 shown in table 9, and have a reinforcing effect by cellulose nanofibers.

(D) Preparation of sample Using thermosetting resin

The sample of example 21 was prepared as follows. A kneading step was carried out in the same manner as in example 15 except that a main component of an epoxy resin (bisphenol a, solid jER1001 manufactured by mitsubishi chemical corporation ("jER" is a registered trademark), epoxy equivalent of 450 to 500, softening point (ring and ball method) of 64 ℃, specific gravity of 1.19, molecular weight of 900) was charged into two rolls, and thereafter a swollen fiber material (CNF 1: Ca 0.1: water 4.0) prepared by changing the water of example 15 to 4.0 was slowly charged into the main component, the temperature of the first roll 10 was set to 60 ℃ to 70 ℃, and the temperature of the second roll 20 was set to 50 ℃ to 60 ℃. Thereafter, the mixture obtained in the kneading step was dried and pulverized, and then put into two rolls, added with a curing agent jER ST12 (polyamidoamine, "jER" is a registered trademark), kneaded again, press-molded under reduced pressure, cured at room temperature for one day, and then cured at 80 ℃ for 15 hours (post-baking) to obtain a sample of a composite material (epoxy resin 100 phr: CNF20 phr).

Further, as a sample of example 22, a composite material sample was obtained in the same manner as in example 21, except that the blending amount of calcium acrylate was 0.5.

The sample of example 23 was prepared as follows. A main component (novolak resin, softening point (ring and ball method) 80 ℃ (estimate)) of a phenol resin (AV LITE, product of asahi organic materials corporation) was charged into two rolls, and then a swollen fiber material (CNF 1: sodium acrylate 1: water 2.5) prepared in the same process as in example 4 was slowly charged into the main component, and the roll temperature was set to 60 ℃, and a kneading process was performed in the same manner as in example 4. Then, a curing agent was added to the mixture obtained in the kneading step, and the mixture was kneaded, and then the kneaded mixture was put into an extruder, kneaded, extruded and molded, and aged to obtain a sample of a composite material (phenolic resin 100 phr: CNF20 phr).

(E) Evaluation method

Tensile tests were carried out on samples of the composite materials of examples 21 and 22 in the same manner as in (B-2) above. The results of the tensile test are shown in fig. 12 as a stress-strain curve.

The coefficient of expansion of a sample of the composite material of example 23 was measured under a stress of 100kPa using a thermoanalytical rheometer manufactured by SII nanotechnology co, and the change in the coefficient of linear expansion in the temperature range of-10 ℃ to 190 ℃ is shown in the graph of fig. 13.

(F) Evaluation of

As shown in fig. 12, the samples of examples 21 and 22 showed 1.7 times increase in stress at 2% strain as compared with the sample of epoxy monomer. The composite material is reinforced by the cellulose nanofibers after fiber separation.

As shown in fig. 13, the average linear expansion coefficient of the sample of example 23 in the range of 30 ℃ to 120 ℃ was less than one fifth of the average linear expansion coefficient of the sample of phenol monomer. It is found that thermal expansion deformation of the composite material can be suppressed by the cellulose nanofibers after the fiber separation.

(G) Preparation of sample Using thermoplastic resin

A first temperature mixing step: the thermoplastic resin was charged into a bench-top two-axis kneading machine MC15 manufactured by Xplore Instruments and melted. Next, the swollen fiber material of example 5 was put into a bench type two-shaft kneading machine and kneaded at a first temperature to obtain a first mixture. The set temperature of the bench type two-shaft mixing and kneading machine was 165 ℃, the actual resin temperature was 155 ℃, and the mixing and kneading time was 3 minutes. The amounts (in terms of "wt%" and "phr") of the additives in the examples are shown in Table 10.

A low-temperature process: the set temperature of the table mixer was lowered to the set temperature (137 ℃) of the low-temperature mixing step.

A low-temperature mixing and kneading process: the first mixture was kneaded with a table type two-shaft kneading machine at a set temperature of 137 ℃ (measured resin temperature of 130 ℃). The kneading time was 8 minutes.

And an extrusion step of raising the set temperature of the table mixer to 165 ℃ (the measured resin temperature is 155 ℃), and then performing injection molding by using the table two-shaft mixer to obtain a JIS K71611BA dumbbell test piece molded by the composite material.

Comparative example 16 a dumbbell test piece similar to that of example 16 was injection-molded from a thermoplastic resin monomer (LLDPE), and comparative example 17 a dumbbell test piece was produced in the same manner as in example 24, using a powder obtained by drying a cellulose nanofiber dispersion of a raw material not blended with sodium acrylate, instead of the swollen fiber material.

In each of the tables, the table is shown,

"LLDPE": ULT-ZEX 15150J manufactured by Primepolymer, melting point 115 ℃;

"CNF": TEMPO oxidized cellulose nanofibers (average fiber diameter of cellulose nanofibers of 3.3nm, average aspect ratio of 225) manufactured by first industrial pharmaceutical co;

"sodium methacrylate": sodium methacrylate (metal component 19% to 21%, methacrylic acid component 75% to 80%) manufactured by shaltian chemical industries.

Since the second temperature in table 10 is required to be set within the range of the second temperature of each sample, the second temperature of the low-temperature kneading step is set to 130 ℃ (measured resin temperature), and the second temperature measurement samples for obtaining the composite material are performed as described above. DMA was measured with respect to the second temperature measurement sample blended in each example in the same manner as in the following (H). From the measurement results, a graph of storage modulus (E') and temperature was prepared, and by the above-described method, for example, in the case of the sample of example 24, temperature T4(132.5 ℃) was determined at 1.06 times (T3 ℃ C. times.1.06 times) inflection point temperature T1(121.5 ℃) and development temperature T2(108 ℃) of the processed region and development temperature T3(125 ℃) of the flat region. The method of determining the second temperature range of each sample was as described above, and the temperature dependence of the storage modulus in the DMA measurement of example 24 is shown in fig. 14.

The results of DMA measurement of the second temperature measurement samples of examples 24 to 26 include the second temperature used in the low-temperature kneading step in the range of the temperature T2 to T4 of all the samples.

(H) Evaluation method

(H-1) tensile test

Tensile tests were carried out on the dumb-bell test pieces of JIS K71611BA using a tensile tester Autograph AG-X manufactured by Shimadzu corporation at 23. + -. 2 ℃, a standard interline distance of 25mm, and a tensile speed of 25mm/min in accordance with JIS K7161, and tensile strength (TS (MPa), elongation at break (Eb (%)), and tensile stress at yield point (σ y (MPa)) were measured for the samples of examples 24 to 26 and comparative examples 16 and 17. The measurement results are shown in table 10.

Watch 10

(H-2) measurement of DMA

For the samples of examples 24 to 26 and comparative examples 16 and 17, a DMA test (dynamic viscoelasticity test) was carried out using a dynamic viscoelasticity tester DMS6100 manufactured by SII on test pieces cut into narrow strips (30 mm. times.5 mm. times.2 mm) at a measurement temperature of 20 ℃ to 200 ℃ at a distance between chucks of 10mm, a temperature rise rate of 1.5 ℃, a dynamic strain of. + -. 0.05% and a frequency of 1Hz in accordance with JIS K7244. The temperature dependence of the storage modulus of the sample of example 24 is shown in fig. 14.

(I) Evaluation of

The samples of examples 24 to 26 had higher tensile strength (ts (mpa)), higher elongation at break (Eb (%)), and higher tensile stress at yield point (σ y (mpa)) than those of comparative examples 16 and 17.

Claims (14)

1. A method of making a fibrous material, comprising:

a mixing step of mixing the cellulose nanofibers, the metal salt and the aqueous solvent to obtain a CNF dispersion, an

A drying step of removing an aqueous solvent from the CNF dispersion obtained in the mixing step to obtain a fiber material,

the mass ratio of the metal salt in the CNF dispersion to the cellulose nanofibers is 0.1 to 2 times,

the fiber material is used for direct swelling by water and is mixed with an elastomer or a synthetic resin to produce a composite material containing no cellulose nanofiber aggregates having a maximum width of 50 μm or more,

the metal salt is an unsaturated metal salt monomer containing at least one of a monovalent metal salt, a divalent metal salt and a trivalent metal salt,

the fiber material obtained in the drying step is a swollen fiber material containing a predetermined amount of water,

the mass ratio of the prescribed amount of water to the cellulose nanofibers is 0.5 to 4 times.

2. A method of making a fibrous material, comprising:

a mixing step of mixing the cellulose nanofibers, the metal salt and the aqueous solvent to obtain a CNF dispersion, an

A drying step of removing an aqueous solvent from the CNF dispersion obtained in the mixing step to obtain a fiber material,

the mass ratio of the metal salt in the CNF dispersion to the cellulose nanofibers is 0.1 to 2 times,

the fiber material is used for direct swelling by water and is mixed with an elastomer or a synthetic resin to produce a composite material containing no cellulose nanofiber aggregates having a maximum width of 50 μm or more,

the metal salt is an unsaturated metal salt monomer containing at least one of a monovalent metal salt, a divalent metal salt and a trivalent metal salt,

the method for producing a fiber material further comprises a swelling step of swelling the fiber material obtained in the drying step with water to obtain a swollen fiber material containing a predetermined amount of water,

the mass ratio of the prescribed amount of water to the cellulose nanofibers is 0.5 to 4 times.

3. The method of manufacturing a fibrous material according to claim 1 or 2,

the metal salt includes at least one of a monovalent metal salt and a divalent metal salt.

4. The method of manufacturing a fibrous material according to claim 1 or 2,

the metal salt is a monovalent metal salt of a metal,

the mass ratio of the monovalent metal salt in the CNF dispersion to the cellulose nanofibers is 0.2 to 2 times.

5. The method of manufacturing a fibrous material according to claim 1 or 2,

the metal salt is a divalent metal salt that is,

the mass ratio of the divalent metal salt to the cellulose nanofibers in the CNF dispersion is 0.1 to 2 times.

6. A method for manufacturing a composite material, characterized in that,

a method for producing a composite material, comprising a kneading step of mixing the swollen fiber material according to any one of claims 1 to 5 with an elastomer to obtain a composite material,

the kneading step includes a step of thin passing using an open roll having a roll interval of 0.1mm to 0.5mm and a roll temperature of 0 ℃ to 50 ℃.

7. A method for manufacturing a composite material, characterized in that,

a method for producing a composite material, comprising a kneading step of mixing the swollen fiber material according to any one of claims 1 to 5 with a synthetic resin to obtain a composite material.

8. The method for manufacturing a composite material according to claim 7,

the synthetic resin is a thermoplastic resin and the synthetic resin is,

the kneading step includes a step of kneading at a kneading temperature within a range from a working region development temperature of the storage modulus of the thermoplastic resin composition in the vicinity of the melting point Tm ℃ of the thermoplastic resin to a temperature T3 ℃ C.. times.1.06 of a flat region development temperature T3 ℃ of the storage modulus.

9. The method for manufacturing a composite material according to claim 7,

the synthetic resin is a thermosetting resin,

the kneading step further includes a step of kneading the swollen fiber material with a main agent of the thermosetting resin at a kneading temperature ranging from a temperature lower than the softening point of the main agent by 20 ℃ to a temperature higher than the softening point by 10 ℃, and then mixing a curing agent.

10. The method for manufacturing a composite material according to any one of claims 6 to 9,

the method for producing a composite material further includes a dehydration step of dehydrating the composite material obtained in the kneading step.

11. A fibrous material, characterized in that,

comprising cellulose nanofibers incorporating a metal from a metal salt,

the mass ratio of the metal salt to the cellulose nanofibers is 0.1 to 2 times,

the fiber material is used for directly swelling by water in a mass ratio of 0.5 to 4 times with respect to the cellulose nanofibers and mixing with an elastomer or a synthetic resin, thereby manufacturing a composite material containing no cellulose nanofiber aggregates having a maximum width of 50 μm or more,

the metal salt is an unsaturated metal salt monomer containing at least one of a monovalent metal salt, a divalent metal salt, and a trivalent metal salt.

12. Fibrous material according to claim 11,

the metal salt includes at least one of a monovalent metal salt and a divalent metal salt.

13. A composite material, characterized in that,

comprising cellulose nanofibers defibrated from the fiber material of claim 11 or 12 and an elastomer or a synthetic resin.

14. The composite material according to claim 13,

the composite material does not contain cellulose nanofiber aggregates having a maximum width of 50 μm or more.

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