JP7748255B2 - Fibrous cellulose composite resin - Google Patents

Description

The present invention relates to a fibrous cellulose composite resin.

In recent years, fine fibers such as cellulose nanofibers and microfiber cellulose (microfibrillated cellulose) have been attracting attention for their use as resin reinforcing materials. However, because fine fibers are hydrophilic while resins are hydrophobic, using fine fibers as resin reinforcing materials poses problems with the dispersibility of the fine fibers. To address this issue, a method has been proposed in which the hydroxy groups of the fine fibers are replaced with carbamate groups (carbamation) (see, for example, Patent Document 1). This proposal improves the dispersibility of the fine fibers, thereby increasing the rigidity of the resin and improving the flexural modulus and other properties of the resin. However, even if carbamate conversion increases the flexural modulus and other properties of the resin, it does not improve the impact resistance due to its flexibility. Therefore, adding an "α-olefin copolymer," which is believed to be effective in improving impact resistance, to the resin has been considered. However, the inventors have discovered that simply adding an α-olefin copolymer to the resin along with the fine fibers reduces the flexural modulus of the resin.

Japanese Patent Application Laid-Open No. 2019-1876

The problem that this invention aims to solve is to provide a fibrous cellulose composite resin that has excellent flexural modulus and impact resistance.

As mentioned above, the inventors initially assumed that adding an α-olefin copolymer to a resin along with fine fibers would improve the flexural modulus due to the fine fibers and the impact resistance due to the α-olefin copolymer. However, while adding the α-olefin copolymer improved impact resistance, it resulted in a decrease in the flexural modulus. Based on this background, the inventors came up with the following solution.

(Means described in claim 1)
A fibrous cellulose composite resin containing fibrous cellulose and a resin,
The composition contains an α-olefin copolymer in an amount of 1% by mass or more and 20% by mass or less,
the fibrous cellulose is a carbamate-modified fine fiber in which a hydroxy group is substituted with a carbamate group,
the degree of substitution of the carbamate group with the hydroxy group is 0.05 to 0.5;
A fibrous cellulose composite resin characterized by:

(Means described in claim 2)
The fine fibers have an average fiber width of 8 to 25 μm and an average fiber length of 0.1 to 1.00 mm.
The fibrous cellulose composite resin according to claim 1 .

(Means described in claim 3)
The fibrillation rate of the fine fibers is 2 to 7%.
The fibrous cellulose composite resin according to claim 1 or 2.

(Means described in claim 4)
Contains acid-modified resin,
a part or all of the carbamate groups are ionically bonded to the acid groups of the acid-modified resin;
The fibrous cellulose composite resin according to any one of claims 1 to 3.

(Means described in claim 5)
Contains a dispersant,
the molecular weight of the acid-modified resin is 2 to 2000 times the molecular weight of the dispersant;
The fibrous cellulose composite resin according to claim 4.

(Means described in claim 6)
The crystallinity of the fine fibers is 50 to 95%.
The fibrous cellulose composite resin according to any one of claims 1 to 5.

(Means described in claim 7)
The pulp viscosity of the fine fibers is 2 cps or more.
The fibrous cellulose composite resin according to any one of claims 1 to 6.

(Means described in claim 8)
The zeta potential of the fine fibers is −150 to 20 mV.
The fibrous cellulose composite resin according to any one of claims 1 to 7.

(Means according to claim 9)
The water retention of the fine fibers is 80 to 400%.
The fibrous cellulose composite resin according to any one of claims 1 to 8.

This invention results in a fibrous cellulose composite resin with excellent flexural modulus and impact resistance.

Next, we will explain the form for implementing the invention. Note that this embodiment is an example of the present invention. The scope of the present invention is not limited to the scope of this embodiment.

The fibrous cellulose composite resin of this embodiment is a fibrous cellulose composite resin containing fibrous cellulose (hereinafter also referred to as "cellulose fiber") and a resin. This fibrous cellulose composite resin further contains a predetermined proportion of α-olefin copolymer, and the fibrous cellulose is carbamate-modified fine fibers in which hydroxy groups (-OH groups) are substituted with carbamate groups to a predetermined degree of substitution. As mentioned above, the inclusion of α-olefin copolymer improves impact resistance, but increasing the α-olefin copolymer content decreases the flexural modulus. Therefore, it is necessary to limit the α-olefin copolymer content to a predetermined amount or less, but limiting the α-olefin copolymer content results in insufficient impact resistance. However, carbamate-modifying the fine fibers as in this embodiment improves impact resistance, thereby compensating for the disadvantages of limiting the α-olefin copolymer content. Therefore, this embodiment results in a fibrous cellulose composite resin with excellent flexural modulus and impact resistance. The addition of fine fibers not only contributes to improving the flexural modulus, but the significant significance of this embodiment is that the addition of fine fibers also contributes to improving impact resistance by means of carbamate formation. This is explained in detail below.

(Fine fibers)
In this embodiment, cellulose nanofibers or microfiber cellulose (microfibrillated cellulose), which are fine fibers, are used as part or all of the fibrous cellulose, preferably microfiber cellulose. The use of microfiber cellulose significantly improves the reinforcing effect of the resin. Furthermore, in the washing step performed to remove unreacted residual urea and the like after the carbamate reaction, if the fibers to be washed are cellulose nanofibers, the dehydration properties are very poor. In contrast, microfiber cellulose is easier to modify with carbamate groups (carbamation) than cellulose nanofibers, which are also fine fibers, from the standpoint of dehydration. However, it is more preferable to carbamate the cellulose raw material before pulverization, and in this case, the cellulose raw material is washed, so microfiber cellulose and cellulose nanofiber are equivalent.

In this embodiment, microfiber cellulose refers to fibers with a larger average fiber diameter (width) than cellulose nanofibers. Specifically, it is, for example, 0.1 to 28 μm, preferably 8 to 25 μm, more preferably 9 to 20 μm, and particularly preferably 10 to 19 μm. When the average fiber diameter of microfiber cellulose is less than 0.1 μm, it becomes no different from cellulose nanofibers, and the effect of improving the strength (particularly the flexural modulus) of the resin may not be fully achieved. Furthermore, the defibration time increases, requiring a large amount of energy. Furthermore, the dewaterability of the cellulose fiber slurry deteriorates. When dewaterability deteriorates, a large amount of energy is required for drying, and applying a large amount of energy to dry the microfiber cellulose may thermally deteriorate it, resulting in a decrease in strength. Furthermore, when the average fiber diameter of microfiber cellulose is less than 8 μm, in this embodiment using an α-olefin copolymer, the effect of improving the strength (particularly the flexural modulus) of the resin may not be fully achieved. This is thought to be because α-olefin copolymers and other resins are not completely compatible and may form two separate phases in an island-sea state. However, when the average fiber diameter of microfiber cellulose is less than 8 μm, it only interacts with either the α-olefin copolymer or the other resin, resulting in no improvement in the reinforcing strength of the composite resin as a whole.

On the other hand, if the average fiber diameter of the microfiber cellulose exceeds 28 μm, the number of fibers will be reduced, which may result in a lack of interaction between the fibers and insufficient reinforcing effect. Furthermore, if the average fiber width of the microfiber cellulose exceeds 25 μm, the fibers themselves may become the starting point of damage when an impact is applied, just like foreign matter, and breakage or damage may spread from this starting point, resulting in a decrease in impact resistance.

The average fiber diameter of the microfiber cellulose is measured as follows.
First, 100 ml of an aqueous dispersion of fine fibers (microfiber cellulose) with a solid content of 0.01 to 0.1% by mass is filtered through a Teflon (registered trademark) membrane filter, and the solvent is replaced once with 100 ml of ethanol and three times with 20 ml of t-butanol. The sample is then freeze-dried and osmium-coated to obtain a sample. This sample is then observed using an SEM electron microscope at a magnification of 3,000x to 30,000x depending on the width of the fibers constituting it. Specifically, two diagonal lines are drawn on the observed image, and three straight lines passing through the intersections of the diagonal lines are arbitrarily drawn. Furthermore, the widths of a total of 100 fibers intersecting with these three straight lines are visually measured. The median diameter of the measured values is then taken as the average fiber diameter.

Microfiber cellulose can be obtained by defibrating (refining) cellulose raw materials (hereinafter also referred to as "raw material pulp"). The raw material pulp can be one or more selected from the following: wood pulp made from hardwoods, softwoods, etc.; non-wood pulp made from straw, bagasse, cotton, hemp, bast fibers, etc.; and recycled paper pulp (DIP) made from recycled waste paper, broke, etc. The above-mentioned raw materials may also be in a pulverized (powdered) state, such as cellulose-based powder.

However, in order to minimize the inclusion of impurities, it is preferable to use wood pulp as the raw material pulp. As wood pulp, for example, one or more types can be selected from chemical pulps such as hardwood kraft pulp (LKP) and softwood kraft pulp (NKP), and mechanical pulp (TMP), etc.

Hardwood kraft pulp may be bleached hardwood kraft pulp, unbleached hardwood kraft pulp, or semi-bleached hardwood kraft pulp. Similarly, softwood kraft pulp may be bleached softwood kraft pulp, unbleached softwood kraft pulp, or semi-bleached softwood kraft pulp.

As mechanical pulp, one or more types can be selected and used from, for example, stone ground pulp (SGP), pressed stone ground pulp (PGW), refiner ground pulp (RGP), chemi-ground pulp (CGP), thermo-ground pulp (TGP), ground pulp (GP), thermo-mechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), refiner mechanical pulp (RMP), bleached thermo-mechanical pulp (BTMP), etc.

The raw pulp can be pretreated by a chemical method prior to defibration (this defibration is preferably carried out after the carbamate conversion). Examples of chemical pretreatments include hydrolysis of polysaccharides with acid (acid treatment), hydrolysis of polysaccharides with enzymes (enzyme treatment), swelling of polysaccharides with alkali (alkali treatment), oxidation of polysaccharides with an oxidizing agent (oxidation treatment), and reduction of polysaccharides with a reducing agent (reduction treatment). However, as a chemical pretreatment, enzyme treatment is preferred, and it is even more preferred to additionally carry out one or more treatments selected from acid treatment, alkali treatment, and oxidation treatment. Enzyme treatment is described in detail below.

The enzymes used in the enzymatic treatment are preferably cellulase enzymes or hemicellulase enzymes, and more preferably both. The use of these enzymes makes it easier to defibrate the cellulose raw material. Cellulose enzymes decompose cellulose in the presence of water. Hemicellulase enzymes decompose hemicellulose in the presence of water.

Cellulase enzymes that can be used include those produced by species of the Trichoderma (filamentous fungi), Acremonium (filamentous fungi), Aspergillus (filamentous fungi), Phanerochaete (basidiomycetes), Trametes (basidiomycetes), Humicola (filamentous fungi), Bacillus (bacteria), Schizophyllum (basidiomycetes), Streptomyces (bacteria), and Pseudomonas (bacteria). These cellulase enzymes are available commercially as reagents or reagent products. Examples of commercially available products include Celluleucin T2 (manufactured by HPI Corporation), Meicelase (manufactured by Meiji Seika Kaisha), Novozym 188 (manufactured by Novozym), Multifect CX10L (manufactured by Genencor), and cellulase enzyme GC220 (manufactured by Genencor).

Also, as the cellulase enzyme, either EG (endoglucanase) or CBH (cellobiohydrolase) can be used. EG and CBH can be used alone or in combination. They can also be used in combination with a hemicellulase enzyme.

Hemicellulase enzymes that can be used include, for example, xylanase, an enzyme that breaks down xylan, mannase, an enzyme that breaks down mannan, and arabanase, an enzyme that breaks down araban. Pectinase, an enzyme that breaks down pectin, can also be used.

Hemicellulose is a polysaccharide excluding pectins found between the cellulose microfibrils in plant cell walls. Hemicellulose is diverse and differs depending on the type of wood and the wall layers of the cell wall. Glucomannan is the main component in the secondary walls of softwoods, while 4-O-methylglucuronoxylan is the main component in the secondary walls of hardwoods. Therefore, when obtaining fine fibers from softwood bleached kraft pulp (NBKP), it is preferable to use mannase. Furthermore, when obtaining fine fibers from hardwood bleached kraft pulp (LBKP), it is preferable to use xylanase.

The amount of enzyme added to cellulose fibers is determined by, for example, the type of enzyme, the type of wood used as raw material (coniferous or broadleaf), the type of mechanical pulp, etc. However, the amount of enzyme added to cellulose fibers is preferably 0.1 to 3 mass%, more preferably 0.3 to 2.5 mass%, and particularly preferably 0.5 to 2 mass%. If the amount of enzyme added is less than 0.1 mass%, the effect of adding the enzyme may not be fully achieved. On the other hand, if the amount of enzyme added is more than 3 mass%, the cellulose may be saccharified, resulting in a decrease in the yield of fine fibers. There is also the problem that the improvement in effect may not be commensurate with the increase in the amount added.

When using a cellulase enzyme as the enzyme, the pH during enzymatic treatment is preferably in the weak acidic range (pH = 3.0 to 6.9) from the perspective of the reactivity of the enzymatic reaction. On the other hand, when using a hemicellulase enzyme as the enzyme, the pH during enzymatic treatment is preferably in the weak alkaline range (pH = 7.1 to 10.0).

Whether a cellulase enzyme or a hemicellulase enzyme is used, the temperature during enzyme treatment is preferably 30 to 70°C, more preferably 35 to 65°C, and particularly preferably 40 to 60°C. If the temperature during enzyme treatment is 30°C or higher, enzyme activity is less likely to decrease, and prolonged treatment time can be prevented. On the other hand, if the temperature during enzyme treatment is 70°C or lower, enzyme inactivation can be prevented.

The enzyme treatment time depends on factors such as the type of enzyme, the temperature of the enzyme treatment, and the pH during the enzyme treatment. However, the typical enzyme treatment time is 0.5 to 24 hours.

After enzymatic treatment, it is preferable to inactivate the enzyme. Methods for inactivating the enzyme include, for example, adding an alkaline aqueous solution (preferably pH 10 or higher, more preferably pH 11 or higher) or adding hot water at 80 to 100°C.

Next, the alkali treatment method will be described.
When cellulose fibers are treated with alkali prior to defibration, some of the hydroxyl groups in the hemicellulose and cellulose contained in the fibers are dissociated, and the molecules become anionic, weakening the intramolecular and intermolecular hydrogen bonds, which promotes the dispersion of the cellulose raw material during defibration.

The alkali used in the alkaline treatment can be, for example, sodium hydroxide, lithium hydroxide, potassium hydroxide, aqueous ammonia, or organic alkalis such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and benzyltrimethylammonium hydroxide. However, from the perspective of production costs, it is preferable to use sodium hydroxide.

By subjecting cellulose fibers to enzyme, acid, or oxidation treatment prior to defibration, it is possible to reduce the water retention of the fibers, increase their crystallinity, and improve their homogeneity. In this regard, cellulose fibers with low water retention are easier to dehydrate, improving the dewaterability of the cellulose fiber slurry.

When cellulose fibers are treated with enzymes, acids, or oxidation, the hemicellulose and amorphous regions of cellulose in the pulp are broken down. As a result, the energy required for defibration can be reduced, and the uniformity and dispersibility of the cellulose fibers can be improved. However, since pretreatment reduces the aspect ratio of microfiber cellulose, excessive pretreatment is preferably avoided.

Cellulose fibers can be defibrated by beating the raw pulp using, for example, a homogenizer such as a beater, high-pressure homogenizer, or high-pressure homogenizer, a grinder, a millstone-type friction machine such as a grinder, a single-shaft kneader, a multi-shaft kneader, a kneader refiner, or a jet mill. However, it is preferable to use a refiner or jet mill.

The average fiber length of microfiber cellulose (average length of single fibers) is, for example, 0.1 to 1.00 mm, preferably 0.15 to 0.9 mm, and more preferably 0.20 to 0.8 mm. If the average fiber length is less than 0.1 mm, the fiber reinforcing effect may be insufficient, and the flexibility-imparting effect of the α-olefin copolymer may be significantly enhanced, resulting in a reduced reinforcing effect of the resin. Furthermore, if the average fiber length is less than 0.15 mm, the same problems as those described above when the average fiber diameter is less than 8 μm may occur.

On the other hand, if the average fiber length exceeds 1.00 mm, the reinforcing effect may be insufficient because the length is the same as that of the raw material pulp. Furthermore, if the average fiber length exceeds 1.00 mm, the same problems as those described above when the average fiber diameter exceeds 25 μm may occur.

The average fiber length of microfiber cellulose can be adjusted as desired, for example, by selecting the raw pulp, pre-processing, defibrating, etc.

The proportion of microfiber cellulose fibers with a length of 0.2 mm or less (fine ratio) is preferably 20% or more, more preferably 40% or more, and particularly preferably 60% or more. If this ratio is below 20%, the reinforcing effect of the resin may not be fully achieved. On the other hand, there is no upper limit to the proportion of microfiber cellulose fibers with a length of 0.2 mm or less, and all fibers may be 0.2 mm or less.

The aspect ratio of the microfiber cellulose is preferably 2 to 15,000, more preferably 10 to 10,000. If the aspect ratio is below 2, a three-dimensional network cannot be formed, which may result in insufficient reinforcing effect. On the other hand, if the aspect ratio exceeds 15,000, the microfiber cellulose may become highly entangled, resulting in insufficient dispersion in the resin.

The fibrillation rate of microfiber cellulose is, for example, 1.0 to 30.0%, preferably 2 to 7%, more preferably 2 to 6%, and particularly preferably 3 to 5%. If the fibrillation rate exceeds 30.0%, the contact area with water becomes too large, which may make dehydration difficult even if the fibers are defibrated to an average fiber width of 0.1 μm or more. Furthermore, if the fibrillation rate exceeds 7%, the fibers may clump together during the kneading process, and when an external impact is applied, the clumped fibers may act like a foreign object and break from that point, which may result in reduced bending properties and impact resistance.

On the other hand, if the fibrillation rate is below 1.0%, there will be fewer hydrogen bonds between the fibrils, and it may not be possible to form a strong three-dimensional network. Furthermore, if the fibrillation rate is below 2%, the number of areas in contact with the resin will decrease, which may result in reduced interfacial adhesion and reduced impact resistance.

The fiber length and fibrillation rate of cellulose fibers are measured using a Valmet FS5 fiber analyzer.

The crystallinity of the microfiber cellulose is preferably 50% or more, more preferably 55% or more, and particularly preferably 60% or more. If the crystallinity is below 50%, although mixability with pulp and cellulose nanofibers will improve, the strength of the fiber itself will decrease, and there is a risk that the strength of the resin will not be improved. On the other hand, the crystallinity of the microfiber cellulose is preferably 95% or less, more preferably 90% or less, and particularly preferably 85% or less. If the crystallinity is above 95%, the proportion of strong hydrogen bonds within the molecule will increase, making the fiber itself rigid and resulting in poor impact resistance.

The crystallinity of microfiber cellulose can be adjusted as desired, for example, by selecting the raw pulp, pre-treating it, and refining it.

The crystallinity of microfiber cellulose is measured in accordance with JIS K 0131 (1996).

The pulp viscosity of the microfiber cellulose is preferably 2 cps or more, more preferably 4 cps or more. If the pulp viscosity of the microfiber cellulose is below 2 cps, it may be difficult to suppress the aggregation of the microfiber cellulose. As mentioned above, aggregation of cellulose fibers is undesirable for improving impact resistance.

The pulp viscosity of microfiber cellulose is measured in accordance with TAPPI T 230.

The freeness of the microfiber cellulose is preferably 500 ml or less, more preferably 300 ml or less, and particularly preferably 100 ml or less. If the freeness of the microfiber cellulose exceeds 500 ml, the average fiber diameter of the microfiber cellulose will exceed 10 μm, which may result in the resin not being able to fully improve its strength.

The freeness of microfiber cellulose is measured in accordance with JIS P8121-2 (2012).

The zeta potential of the microfibrous cellulose is preferably -150 to 20 mV, more preferably -100 to 0 mV, and particularly preferably -80 to -10 mV. If the zeta potential is below -150 mV, compatibility with the resin may be significantly reduced, resulting in insufficient reinforcing effect. On the other hand, if the zeta potential is above 20 mV, dispersion stability may be reduced.

The water retention of microfiber cellulose is preferably 80 to 400%, more preferably 90 to 350%, and especially preferably 100 to 300%. If the water retention is below 80%, it will be no different from the raw material pulp, and the reinforcing effect may be insufficient. On the other hand, if the water retention is above 400%, dewatering tends to be poor and the material is more susceptible to aggregation. In this regard, the water retention of microfiber cellulose can be further reduced by substituting the hydroxy groups of the fiber with carbamate groups, thereby improving dewatering and drying properties.

The water retention capacity of microfiber cellulose can be adjusted as desired, for example, by selecting the raw pulp, pre-processing, and defibrating it.

The water retention of microfiber cellulose was measured in accordance with JAPAN TAPPI No. 26 (2000).

The α-cellulose content of the microfiber cellulose is preferably 80 to 93%, more preferably 83 to 91%, and particularly preferably 85 to 90%. If the α-cellulose content is less than 80%, the microfiber cellulose will contain too many components other than the fibers, which can cause discoloration and odor when used in a composite resin, potentially limiting its applications even if the desired impact strength and flexural modulus are met. On the other hand, if the α-cellulose content exceeds 93%, compatibility with α-olefin copolymers and other resins will be insufficient, the flexibility of the α-olefin copolymer will not be fully exhibited, impact strength will decrease, and it may become impossible to achieve both flexural modulus and impact strength.

The α-cellulose content can be adjusted to the desired value, for example, by treating the cellulose raw material with carbamate and washing it to remove unnecessary components from the cellulose raw material.

The content of microfiber cellulose in the cellulose fibers is preferably 60 to 100% by mass, more preferably 70 to 99% by mass, and particularly preferably 80 to 98% by mass. If the microfiber cellulose content is less than 60% by mass, a sufficient reinforcing effect may not be obtained. Furthermore, if the microfiber cellulose content is less than 60% by mass, the pulp and cellulose nanofiber content will increase relatively, and the benefits of including microfiber cellulose may not be obtained.

The microfibrous cellulose is provided with a carbamate group, for example, by the method described below. That is, a carbamate (an ester of carbamic acid) is introduced into the microfibrous cellulose. The carbamate group is a group represented by -O-CO-NH-, such as -O-CO-NH ₂ , -O-CONHR, or -O-CO-NR _2. That is, the carbamate group can be represented by the following structural formula (1):

Here, n represents an integer of 1 or greater. Each R is independently at least one of a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an aromatic group, and derivatives thereof.

Examples of saturated linear hydrocarbon groups include linear alkyl groups having 1 to 10 carbon atoms, such as methyl, ethyl, and propyl groups.

Examples of saturated branched hydrocarbon groups include branched alkyl groups having 3 to 10 carbon atoms, such as isopropyl, sec-butyl, isobutyl, and tert-butyl groups.

Examples of saturated cyclic hydrocarbon groups include cycloalkyl groups such as cyclopentyl, cyclohexyl, and norbornyl.

Examples of unsaturated linear hydrocarbon groups include linear alkenyl groups having 2 to 10 carbon atoms, such as ethenyl, propen-1-yl, and propen-3-yl, and linear alkynyl groups having 2 to 10 carbon atoms, such as ethynyl, propyn-1-yl, and propyn-3-yl.

Examples of unsaturated branched hydrocarbon groups include branched alkenyl groups having 3 to 10 carbon atoms, such as propen-2-yl, buten-2-yl, and buten-3-yl, and branched alkynyl groups having 4 to 10 carbon atoms, such as butyn-3-yl.

Examples of aromatic groups include phenyl, tolyl, xylyl, and naphthyl groups.

Examples of derivative groups include groups in which one or more hydrogen atoms in the above-mentioned saturated linear hydrocarbon groups, saturated branched hydrocarbon groups, saturated cyclic hydrocarbon groups, unsaturated linear hydrocarbon groups, unsaturated branched hydrocarbon groups, and aromatic groups have been substituted with a substituent (e.g., a hydroxy group, a carboxy group, a halogen atom, etc.).

In microfiber cellulose containing carbamate groups (carbamate-introduced microfibers), some or all of the highly polar hydroxyl groups are substituted with relatively less polar carbamate groups. Therefore, this microfiber cellulose has low hydrophilicity and a high affinity for low-polarity resins. As a result, this microfiber cellulose exhibits excellent uniform dispersion in resins. Furthermore, the slurry of this microfiber cellulose has low viscosity and is easy to handle.

Cellulose is a polymer whose structural unit is anhydroglucose, and each structural unit has three hydroxyl groups. Therefore, if all hydroxyl groups are substituted with carbamate groups, the degree of substitution is 3. The degree of carbamate substitution is measured by nitrogen quantification using the Kjeldahl method.

<Carbamate formation>
Regarding the introduction of carbamate (carbamation) into microfiber cellulose (or the cellulose raw material if carbamate conversion is performed before defibration), there are two methods: one is to carbamate the cellulose raw material and then pulverize it, and the other is to pulverize the cellulose raw material and then carbamate it. In this specification, defibration of the cellulose raw material is explained first, and then carbamate conversion (modification). However, either defibration or carbamate conversion can be performed first. However, it is preferable to perform carbamate conversion first, followed by defibration. This is because the cellulose raw material before defibration has high dehydration efficiency, and the heating associated with carbamate conversion puts the cellulose raw material in a state that is easy to defibrate.

The process of carbamate-converting cellulose fibers (microfiber cellulose, cellulose raw materials, etc.) can be divided into, for example, a mixing process, a removal process, and a heating process. The mixing process and removal process can also be collectively referred to as a preparation process for preparing a mixture to be subjected to the heating process.

In the mixing process, cellulose fibers and urea or a urea derivative (hereinafter simply referred to as "urea, etc.") are mixed in a dispersion medium.

Examples of urea and urea derivatives that can be used include urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, and compounds in which the hydrogen atoms of urea are substituted with alkyl groups. These ureas and urea derivatives can be used alone or in combination. However, urea is preferred because it is inexpensive, easily available industrially, highly soluble in water, and allows the chemical to come into contact with the raw pulp in an aqueous solution that places less strain on the environment.

The lower limit of the mixture mass ratio of urea etc. to cellulose fiber (cellulose fiber/urea etc.) is preferably 100/10, more preferably 100/20. On the other hand, the upper limit is preferably 100/100, more preferably 100/50. By setting the mixture mass ratio to 100/10 or more, the efficiency of carbamate formation is improved. On the other hand, if the mixture mass ratio exceeds 100/50, the carbamate formation reaction may proceed too quickly.

The dispersion medium is usually water. However, other dispersion media such as alcohol or ether, or a mixture of water and another dispersion medium, may also be used.

In the mixing process, for example, cellulose fibers and urea, etc. may be added to water, cellulose fibers may be added to an aqueous solution of urea, etc., or urea, etc. may be added to a slurry containing cellulose fibers. Furthermore, stirring may be performed after addition to ensure uniform mixing. Furthermore, the dispersion containing cellulose fibers and urea, etc. may contain other components.

In the removal process, the dispersion medium is removed from the dispersion liquid containing cellulose fibers, urea, etc. obtained in the mixing process. By removing the dispersion medium, the urea, etc. can be reacted efficiently in the subsequent heating process.

The dispersion medium is preferably removed by volatilizing it through heating. This method allows for efficient removal of only the dispersion medium while leaving behind components such as urea.

When the dispersion medium is water, the lower limit of the heating temperature in the removal step is preferably 50°C, more preferably 70°C, and particularly preferably 90°C. By setting the heating temperature to 50°C or higher, the dispersion medium can be efficiently volatilized (removed). On the other hand, the upper limit of the heating temperature is preferably 120°C, more preferably 100°C. If the heating temperature exceeds 120°C, the dispersion medium and urea may react, resulting in the urea decomposing independently.

The heating time in the removal process can be adjusted appropriately depending on the solids concentration of the dispersion, etc. Specifically, it is, for example, 6 to 24 hours.

In the heating process following the removal process, the mixture of cellulose fibers and urea, etc. is heat-treated. In this heating process, some or all of the hydroxyl groups of the cellulose fibers react with urea, etc., and are converted into carbamate groups. More specifically, when urea, etc. is heated, it decomposes into isocyanic acid and ammonia, as shown in the following reaction formula (1). Isocyanic acid is highly reactive, and forms carbamate with the hydroxyl groups of cellulose, for example, as shown in the following reaction formula (2).

NH ₂ -CO-NH ₂ → H-N=C=O + NH ₃ ...(1)

Cell-OH + H-N=C=O → Cell-O-CO-NH ₂ ...(2)

The lower limit of the heating temperature in the heating step is preferably 120°C, more preferably 130°C, particularly preferably above the melting point of urea (approximately 134°C), even more preferably 140°C, and most preferably 150°C. A heating temperature of 120°C or higher ensures efficient carbamate formation. The upper limit of the heating temperature is preferably 200°C, more preferably 180°C, and particularly preferably 170°C. If the heating temperature exceeds 200°C, the cellulose fibers may decompose, resulting in insufficient reinforcing effect.

The lower limit of the heating time in the heating step is preferably 1 minute, more preferably 5 minutes, particularly preferably 30 minutes, even more preferably 1 hour, and most preferably 2 hours. A heating time of 1 minute or more ensures that the carbamate reaction can be carried out reliably. On the other hand, the upper limit of the heating time is preferably 15 hours, more preferably 10 hours. A heating time of more than 15 hours is not economical, and 15 hours is sufficient for carbamate formation.

The above heat treatment is preferably carried out under acidic conditions. Carbamate formation proceeds more reliably by carrying out the treatment under acidic conditions. The upper limit of the pH of the mixture in the heating step is preferably 6, more preferably 5, and particularly preferably 4. On the other hand, the lower limit of the pH is preferably 1, more preferably 2, and particularly preferably 3. This pH adjustment can be carried out by adding an acidic compound (e.g., acetic acid, citric acid, etc.) or an alkaline compound (e.g., sodium hydroxide, calcium hydroxide, etc.) to the mixture.

The heating device used in the heating process may be, for example, a hot air dryer, paper machine, or dry pulp machine.

The mixture after the heat treatment may be washed. This washing can be done with water or the like. This washing can remove any unreacted urea or other substances that remain.

In this embodiment, cellulose nanofibers can be included in addition to microfiber cellulose as fibrous cellulose (cellulose fibers). Cellulose nanofibers are fine fibers like microfiber cellulose, and play a role in complementing microfiber cellulose in improving the strength of the resin. However, if possible, it is preferable to use only microfiber cellulose as fine fibers without including cellulose nanofibers, but if cellulose nanofibers are to be included, the following cellulose nanofibers are recommended.

First, cellulose nanofibers can be obtained by defibrating (refining) raw pulp (cellulose raw material). The raw pulp used can be the same as that used for microfiber cellulose, and it is preferable to use the same pulp as that used for microfiber cellulose.

The raw pulp for cellulose nanofibers can be pretreated and defibrated in the same way as for microfiber cellulose. However, the degree of defibration differs; for example, it must be defibrated so that the average fiber diameter is below 0.1 μm. Below, we will focus on the differences from microfiber cellulose.

The average fiber diameter (average fiber width; average diameter of a single fiber) of cellulose nanofibers is preferably 4 to 100 nm, more preferably 10 to 80 nm. If the average fiber diameter of cellulose nanofibers is below 4 nm, dewatering properties may deteriorate. Furthermore, when cellulose nanofibers are mixed with a dispersant, the dispersant may not sufficiently cover (stick to) the cellulose nanofibers, and dispersibility may not be sufficiently improved. On the other hand, if the average fiber diameter of cellulose nanofibers exceeds 100 nm, they can no longer be called cellulose nanofibers.

The average fiber diameter of cellulose nanofibers can be adjusted, for example, by selecting the raw pulp, pre-treating it, defibrating it, etc.

The methods for measuring the physical properties of cellulose nanofibers are the same as those for microfiber cellulose unless otherwise specified. The average fiber diameter of pulp is measured as follows.
First, 100 ml of an aqueous dispersion of pulp with a solid content concentration of 0.01 to 0.1% by mass is filtered through a Teflon (registered trademark) membrane filter and solvent-substituted once with 100 ml of ethanol and three times with 20 ml of t-butanol. The sample is then freeze-dried and osmium-coated to obtain a sample. This sample is then observed using an SEM electron microscope at a magnification of 100x to 1000x depending on the width of the fibers that make up the sample. Specifically, two diagonal lines are drawn on the observed image, and three straight lines are arbitrarily drawn passing through the intersections of the diagonal lines. Furthermore, the widths of a total of 100 fibers intersecting with these three straight lines are visually measured. The median diameter of the measured values is then taken as the average fiber diameter.

The average fiber length (length of a single fiber) of the cellulose nanofibers is preferably 0.1 to 1,000 μm, and more preferably 0.5 to 500 μm. If the average fiber length of the cellulose nanofibers is less than 0.1 μm, a three-dimensional network cannot be formed between the cellulose nanofibers, and the reinforcing effect may be insufficient. On the other hand, if the average fiber length of the cellulose nanofibers is more than 1,000 μm, the fibers may become easily entangled, and dispersibility may not be sufficiently improved.

The average fiber length of cellulose nanofibers can be adjusted, for example, by selecting the raw pulp, pre-treating it, defibrating it, etc.

The water retention of cellulose nanofibers can be adjusted, for example, by selecting the raw pulp, pre-treating it, defibrating it, etc.

The crystallinity of the cellulose nanofiber is preferably 95-50%, and more preferably 90-60%. If the crystallinity of the cellulose nanofiber is within this range, the strength of the resin can be reliably improved.

The degree of crystallinity can be adjusted as desired, for example, by selecting the raw pulp, pre-treating it, defibrating it, etc.

The pulp viscosity of the cellulose nanofiber is preferably 1.0 cps or more, and more preferably 2.0 cps or more. Pulp viscosity is the viscosity of the solution obtained after dissolving cellulose in a copper ethylenediamine solution, and a higher pulp viscosity indicates a higher degree of polymerization of the cellulose. A pulp viscosity of 1.0 cps or more imparts dewaterability to the slurry while suppressing decomposition of the cellulose nanofiber when kneaded with the resin, thereby achieving a sufficient reinforcing effect.

If necessary, the cellulose nanofibers obtained by defibration can be dispersed in an aqueous medium to form a dispersion before mixing with other cellulose fibers. It is particularly preferable that the aqueous medium is entirely water (aqueous solution). However, the aqueous medium may also contain other liquids, some of which are compatible with water. Examples of other liquids that can be used include lower alcohols with 3 or fewer carbon atoms.

The Brookfield viscosity of a cellulose nanofiber dispersion (1% concentration) is preferably 10 to 2,000 cp, and more preferably 30 to 1,500 cp. Keeping the Brookfield viscosity of the dispersion within this range facilitates mixing with other cellulose fibers and improves the dewatering properties of the cellulose fiber slurry.

The B-type viscosity of the dispersion (solids concentration 1%) was measured in accordance with JIS-Z8803 (2011), "Method for measuring viscosity of liquids." B-type viscosity is the resistance torque when stirring the dispersion; the higher the viscosity, the more energy is required for stirring.

The cellulose nanofiber content in the cellulose fiber is preferably 40% by mass or less, and more preferably 20% by mass or less. If the cellulose nanofiber content exceeds 40% by mass, the cellulose nanofibers will aggregate strongly and may not be able to disperse in the resin, resulting in insufficient reinforcing effect and impact resistance. As mentioned above, it is most preferable to not include cellulose nanofibers, i.e., to have a content of 0% by mass.

If necessary, cellulose nanofibers can be carbamate-converted using methods similar to those used for microfiber cellulose. However, carbamate-converting cellulose nanofibers is generally difficult.

In addition to fine fibers, fibrous cellulose can also contain pulp. Pulp plays a role in significantly improving the dewatering properties of the cellulose fiber slurry. However, it is preferable to keep the pulp content within a specified range (see below).

The pulp content in the cellulose fiber is preferably 40% by mass or less, and more preferably 20% by mass or less. If the pulp content exceeds 40% by mass, the fine fiber content will decrease, which may result in the resin strength not being guaranteed. As with cellulose nanofibers, it is most preferable to not include any pulp, i.e., to have a content of 0% by mass.

The pulp used can be the same as the raw pulp used for microfiber cellulose, etc., and it is preferable to use the same raw pulp as the raw pulp used for microfiber cellulose. Using the same pulp as the raw pulp used for microfiber cellulose improves the affinity of the cellulose fibers, resulting in improved homogeneity of the cellulose fiber slurry.

If necessary, the fibrous cellulose containing fine fibers is dispersed in an aqueous medium to form a dispersion (slurry). It is particularly preferable for the aqueous medium to be entirely water, but aqueous media containing a portion of another liquid that is compatible with water can also be used. Examples of other liquids that can be used include lower alcohols with 3 or fewer carbon atoms.

The solids concentration of the slurry is preferably 0.1 to 10.0% by mass, more preferably 0.5 to 5.0% by mass. If the solids concentration is below 0.1% by mass, excessive energy may be required for dehydration and drying. On the other hand, if the solids concentration exceeds 10.0% by mass, the fluidity of the slurry itself may decrease, making it impossible to uniformly mix the dispersant.

(α-olefin copolymer)
The fibrous cellulose composite resin of this embodiment contains an α-olefin copolymer. An α-olefin copolymer is a polymer obtained by copolymerizing an α-olefin (an olefin having a terminal carbon-carbon double bond) with a monomer such as ethylene or propylene, and contains an α-olefin with a long side chain. Therefore, the polymer chains are less likely to align, crystallize, or become rigid. Unlike polyethylene or polypropylene, this polymer can impart flexibility to the composite resin and improve impact resistance. Since α-olefin copolymers impair the rigidity of composite resins, fiber reinforcement is used to maintain rigidity. However, if the compatibility between the fibers and the α-olefin copolymer is insufficient, fracture will occur starting from the fibers when an external force is applied, and even if rigidity is maintained, the impact resistance improvement effect of adding the α-olefin copolymer will not be fully realized. Therefore, in this embodiment, the cellulose raw material is modified with a carbamate group to improve the compatibility between the cellulose raw material and the α-olefin copolymer, thereby achieving both impact resistance and rigidity.

From the above perspectives, the degree of substitution of the carbamate group is preferably 0.05 to 0.5, more preferably 0.1 to 0.4, and particularly preferably 0.2 to 0.3. By setting the degree of substitution of the carbamate group to 0.05 or more, the compatibility between the α-olefin copolymer and the cellulose raw material is sufficiently improved, ensuring the benefits of introducing the carbamate group. On the other hand, if the degree of substitution exceeds 0.5, although compatibility with the α-olefin copolymer is sufficient, the reinforcing properties of the fiber itself may be impaired, and the flexibility imparted by the α-olefin copolymer may not be achieved.

Examples of α-olefins include linear units such as propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene, as well as cyclic units such as cyclopentene, cycloheptene, norbornene, 5-methyl-2-norbornene, tetracyclododecene, and 2-methyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene.

The blending ratio of the α-olefin copolymer is preferably 20 parts by mass or less, more preferably 1 to 18 parts by mass, and particularly preferably 3 to 15 parts by mass, based on the total amount of composite resin. If the blending ratio of the α-olefin copolymer exceeds 1% by mass, sufficient flexibility is imparted to the composite resin, reducing the possibility of the composite resin lacking in impact resistance. On the other hand, if the blending ratio exceeds 20% by mass, excessive flexibility is imparted, and even if compatibility with the fiber is high, the reinforcing properties of the fiber cannot be fully exerted, resulting in insufficient rigidity.

(acid-modified resin)
The fibrous cellulose composite resin of this embodiment preferably contains an acid-modified resin, and some or all of the carbamate groups are ionic-bonded to the acid groups of the acid-modified resin, which improves the reinforcing effect of the resin.

Examples of acid-modified resins that can be used include acid-modified polyolefin resins, acid-modified epoxy resins, and acid-modified styrene-based elastomer resins. However, acid-modified polyolefin resins are preferred. Acid-modified polyolefin resins are copolymers of unsaturated carboxylic acid components and polyolefin components.

The polyolefin component can be one or more selected from polymers of alkenes such as ethylene, propylene, butadiene, and isoprene. However, polypropylene resin, which is a polymer of propylene, is preferred.

As the unsaturated carboxylic acid component, one or more selected from maleic anhydrides, phthalic anhydrides, itaconic anhydrides, citraconic anhydrides, citric anhydrides, etc. can be used. However, it is preferable to use maleic anhydrides. In other words, it is preferable to use maleic anhydride-modified polypropylene resin.

The amount of acid-modified resin mixed is preferably 0.1 to 1,000 parts by mass, more preferably 1 to 500 parts by mass, and particularly preferably 10 to 200 parts by mass, per 100 parts by mass of fine fibers. In particular, when the acid-modified resin is maleic anhydride-modified polypropylene resin, the amount is preferably 1 to 200 parts by mass, more preferably 10 to 100 parts by mass. If the amount of acid-modified resin mixed is less than 0.1 part by mass, the improvement in strength will be insufficient. On the other hand, if the amount mixed is more than 1,000 parts by mass, it will be excessive and strength will tend to decrease.

The weight-average molecular weight of the maleic anhydride-modified polypropylene is, for example, 1,000 to 100,000, preferably 3,000 to 50,000.

The acid value of the maleic anhydride-modified polypropylene is preferably 0.5 mgKOH/g or more and 100 mgKOH/g or less, and more preferably 1 mgKOH/g or more and 50 mgKOH/g or less.

Furthermore, the MFR (melt flow rate) of the acid-modified resin is preferably 2000 g/10 min (190°C/2.16 kg) or less, more preferably 1500 g/10 min or less, and particularly preferably 500 g/10 min or less. If the MFR exceeds 2000 g/10 min, the dispersibility of the cellulose fibers may decrease.

Acid value is measured in accordance with JIS-K2501 by titration with potassium hydroxide. MFR is measured in accordance with JIS-K7210 by placing a load of 2.16 kg on the sample at 190°C and determining the weight of the sample that flows out in 10 minutes.

(Dispersant)
Fibrous cellulose, including microfibrous cellulose, is more preferably mixed with a dispersant, which is preferably an aromatic compound having an amine group and/or a hydroxyl group, or an aliphatic compound having an amine group and/or a hydroxyl group.

Examples of compounds having an amine group and/or a hydroxyl group in an aromatic group include anilines, toluidines, trimethylanilines, anisidines, tyramines, histamines, tryptamines, phenols, dibutylhydroxytoluenes, bisphenol A, cresols, eugenols, gallic acids, guaiacols, picric acids, phenolphthalein, serotonins, dopamines, adrenalines, noradrenalines, thymols, tyrosines, salicylic acids, methyl salicylates, and These include varnish alcohols, salicylic alcohols, sinapyl alcohols, diphenidol, diphenylmethanols, cinnamyl alcohols, scopolamines, tryptophols, vanillyl alcohols, 3-phenyl-1-propanols, phenethyl alcohols, phenoxyethanols, veratryl alcohols, benzyl alcohols, benzoins, mandelic acids, mandelonitriles, benzoic acids, phthalic acids, isophthalic acids, terephthalic acids, mellitic acids, and cinnamic acids.

Furthermore, examples of compounds having an amine group and/or a hydroxyl group in an aliphatic group include capryl alcohols, 2-ethylhexanols, pelargonic alcohols, capric alcohols, undecyl alcohols, lauryl alcohols, tridecyl alcohols, myristyl alcohols, pentadecyl alcohols, cetyl alcohols, stearyl alcohols, elaidyl alcohols, oleyl alcohols, linoleyl alcohols, methylamines, dimethylamines, trimethylamines, ethylamines, diethylamines, and ethylenediamines. , triethanolamines, N,N-diisopropylethylamines, tetramethylethylenediamines, hexamethylenediamines, spermidines, spermines, amantadine, formic acids, acetic acids, propionic acids, butyric acids, valeric acids, caproic acids, enanthic acids, caprylic acids, pelargonic acids, capric acids, lauric acids, myristic acids, palmitic acids, margaric acids, stearic acids, oleic acids, linoleic acids, linolenic acids, arachidonic acids, eicosapentaenoic acids, docosahexaenoic acids, and sorbic acids.

These dispersants inhibit hydrogen bonding between the fine fibers. This ensures that the fine fibers are dispersed (re-dispersed) in the resin when they are mixed with the resin. These dispersants also improve the compatibility between the fine fibers and the resin. This improves the dispersibility of the fine fibers in the resin.

It is possible to add a separate compatibilizer (chemical) when kneading the fine fibers and resin, but rather than adding the chemical at this stage, mixing the fine fibers with a dispersant (chemical) before kneading with the resin will ensure that the chemical adheres more evenly to the fine fibers, resulting in a greater effect of improving compatibility with the resin.

For example, polypropylene has a melting point of 160°C, so the fine fibers and resin are mixed at around 180°C. However, if a dispersant (liquid) is added in this state, it will dry out instantly. Therefore, one method is to create a masterbatch (a composite resin with a high concentration of fine fibers) using a resin with a low melting point, and then reduce the concentration with a regular resin. However, resins with low melting points generally have low strength. Therefore, this method may reduce the strength of the composite resin.

The amount of dispersant mixed is preferably 0.1 to 1,000 parts by mass, more preferably 1 to 500 parts by mass, and particularly preferably 10 to 200 parts by mass, per 100 parts by mass of fine fibers. If the amount of dispersant mixed is less than 0.1 part by mass, the improvement in strength may not be sufficient. On the other hand, if the amount mixed is more than 1,000 parts by mass, the amount becomes excessive and strength tends to decrease.

In this regard, the acid-modified resin described above improves compatibility and enhances reinforcing effects by forming ionic bonds between the acid groups and the carbamate groups of the fine fibers. Its large molecular weight also makes it compatible with the resin, which is thought to contribute to improved strength. Meanwhile, the dispersant described above intervenes between the hydroxyl groups of the fine fibers to prevent aggregation, thereby improving dispersibility in the resin. Furthermore, because its molecular weight is smaller than that of the acid-modified resin, it can enter the narrow spaces between the fine fibers that the acid-modified resin cannot, improving dispersibility and improving strength. From these perspectives, the molecular weight of the acid-modified resin described above is preferably 2 to 2,000 times, and preferably 5 to 1,000 times, the molecular weight of the dispersant.

Explaining this point in more detail, resin powder physically intervenes between the fine fibers, inhibiting hydrogen bonding and thereby improving the dispersibility of the fine fibers. In contrast, acid-modified resins improve compatibility by forming ionic bonds between the acid groups and the carbamate groups of the fine fibers, thereby enhancing the reinforcing effect. While dispersants also inhibit hydrogen bonding between the fine fibers, resin powder, being on the micron order, physically intervenes and inhibits hydrogen bonding. Therefore, although dispersibility is lower than that of dispersants, the resin powder itself melts and becomes a matrix, so it does not contribute to a decrease in physical properties. On the other hand, dispersants are at the molecular level and are extremely small, so they coat the fine fibers, inhibiting hydrogen bonding and are highly effective in improving the dispersibility of the fine fibers. However, they may remain in the resin and contribute to a decrease in physical properties.

(Manufacturing method)
The mixture of fine fibers, acid-modified resin, dispersant, etc. can be dried and pulverized to form a powder prior to kneading with the resin. This form eliminates the need to dry the fine fibers before kneading with the resin, resulting in good thermal efficiency. Furthermore, particularly when a dispersant is mixed into the mixture, there is little risk that the fine fibers, such as microfiber cellulose, will not redisperse even if the mixture is dried.

If necessary, the mixture may be dehydrated prior to drying to produce a dehydrated product. This dehydration can be carried out using one or more dehydration devices selected from the following: belt press, screw press, filter press, twin roll, twin wire former, valveless filter, center disc filter, membrane treatment, centrifuge, etc.

The mixture can be dried using one or more of the following methods: rotary kiln drying, disc drying, airflow drying, media flow drying, spray drying, drum drying, screw conveyor drying, paddle drying, single-axis kneading drying, multi-axis kneading drying, vacuum drying, and agitator drying.

The dried mixture (dried material) is pulverized to form a powder. The dried material can be pulverized using one or more mills selected from the group consisting of a bead mill, kneader, disperser, twist mill, cut mill, and hammer mill.

The average particle size of the powder is preferably 1 to 10,000 μm, more preferably 10 to 5,000 μm, and particularly preferably 100 to 1,000 μm. If the average particle size of the powder exceeds 10,000 μm, it may be difficult to knead with resin. On the other hand, reducing the average particle size of the powder to less than 1 μm requires a large amount of energy, which is not economical.

The average particle size of powdered materials can be controlled by controlling the degree of pulverization, as well as by classification using classification devices such as filters and cyclones.

The bulk density of the mixture (powder) is preferably 0.03 to 1.0, more preferably 0.04 to 0.9, and particularly preferably 0.05 to 0.8. A bulk density of more than 1.0 means that the hydrogen bonds between the fibrous cellulose are stronger, making it difficult to disperse in the resin. On the other hand, a bulk density of less than 0.03 is disadvantageous in terms of transportation costs.

Bulk specific gravity is a value measured in accordance with JIS K7365.

The moisture content of the mixture (powder) is preferably 50% or less, more preferably 30% or less, and particularly preferably 10% or less. If the moisture content exceeds 50%, the energy required to knead it with the resin becomes enormous, making it uneconomical.

The moisture content was calculated using the following formula, in which a sample was kept at 105°C for 6 hours or more using a constant temperature dryer, and the mass at which no change in mass was observed was taken as the mass after drying.
Moisture percentage (%) = [(mass before drying - mass after drying) ÷ mass before drying] x 100

The dehydrated and dried product may contain resin. If resin is present, it will inhibit hydrogen bonding between the dehydrated and dried fine fibers, improving their dispersibility in the resin when kneaded.

The resin contained in the dehydrated and dried product may be in the form of, for example, powder, pellets, or sheets. However, powder (powdered resin) is preferred.

When powdered, the average particle size of the resin powder contained in the dehydrated and dried product is preferably 1 to 10,000 μm, more preferably 10 to 5,000 μm, and particularly preferably 100 to 1,000 μm. If the average particle size exceeds 10,000 μm, the particles may be too large to enter the kneading device. On the other hand, if the average particle size is less than 1 μm, the particles may be too small to inhibit the hydrogen bonding between the fine fibers. The resin used here, such as the resin powder, may be the same or different from the resin (main raw material resin) to be kneaded with the fine fibers, but it is preferable that they are the same type.

Resin powder with an average particle size of 1 to 10,000 μm is preferably mixed in an aqueous dispersion state before dehydration and drying. Mixing in an aqueous dispersion state allows the resin powder to be uniformly dispersed among the fine fibers, which in turn allows the fine fibers to be uniformly dispersed in the composite resin after kneading, further improving strength properties.

The powdery material (resin reinforcing material) obtained in this manner is kneaded with resin to obtain a fibrous cellulose composite resin. This kneading can be performed, for example, by mixing the powdery material with pelletized resin, or by first melting the resin and then adding the powdery material to the melt. Acid-modified resins, dispersants, etc. can also be added at this stage.

For the kneading process, one or more of the following may be selected and used: a single-screw or multi-screw kneader with two or more screws, a mixing roll, a kneader, a roll mill, a Banbury mixer, a screw press, a disperser, etc. Among these, it is preferable to use a multi-screw kneader with two or more screws. Two or more multi-screw kneaders with two or more screws may also be used in parallel or in series.

The peripheral speed of the screws of a twin or more screw multi-screw kneader is preferably 0.2 to 200 m/min, more preferably 0.5 to 150 m/min, and particularly preferably 1 to 100 m/min. If the peripheral speed is less than 0.2 m/min, it may not be possible to disperse the fine fibers in the resin. On the other hand, if the peripheral speed exceeds 200 m/min, the shear force on the fine fibers may be excessive, and the reinforcing effect may not be achieved.

The ratio of the screw diameter to the length of the kneading section of the kneader used in this embodiment is preferably 15 to 60. If the ratio is less than 15, the kneading section will be too short and the fine fibers and resin may not be able to be mixed. On the other hand, if the ratio exceeds 60, the kneading section will be too long, which may increase the shear load on the fine fibers and prevent the reinforcing effect from being achieved.

The kneading temperature is above the glass transition point of the resin, and varies depending on the type of resin, but is preferably 80 to 280°C, more preferably 90 to 260°C, and especially preferably 100 to 240°C.

The resin can be either a thermoplastic resin or a thermosetting resin.

Thermoplastic resins can be selected from one or more of the following: polyolefins such as polypropylene (PP) and polyethylene (PE); polyester resins such as aliphatic polyester resins and aromatic polyester resins; polyacrylic resins such as polystyrene, methacrylate, and acrylate; polyamide resins; polycarbonate resins; and polyacetal resins.

However, it is preferable to use at least one of polyolefin and polyester resin. Furthermore, it is preferable to use polypropylene as the polyolefin. Furthermore, examples of polyester resins include aliphatic polyester resins such as polylactic acid and polycaprolactone, and aromatic polyester resins such as polyethylene terephthalate, but it is preferable to use biodegradable polyester resins (also simply referred to as "biodegradable resins").

As biodegradable resins, for example, one or more selected from hydroxycarboxylic acid-based aliphatic polyesters, caprolactone-based aliphatic polyesters, dibasic acid polyesters, etc. can be used.

Hydroxycarboxylic acid-based aliphatic polyesters can be selected from one or more of the following: homopolymers of hydroxycarboxylic acids such as lactic acid, malic acid, glucose acid, and 3-hydroxybutyric acid; and copolymers using at least one of these hydroxycarboxylic acids. However, polylactic acid, copolymers of lactic acid and the above hydroxycarboxylic acids excluding lactic acid, polycaprolactone, and copolymers of caprolactone and at least one of the above hydroxycarboxylic acids are preferred, with polylactic acid being particularly preferred.

For example, L-lactic acid or D-lactic acid can be used as this lactic acid, and these lactic acids may be used alone or in combination of two or more.

As caprolactone-based aliphatic polyesters, one or more types can be selected and used from, for example, homopolymers of polycaprolactone, copolymers of polycaprolactone or the like with the above-mentioned hydroxycarboxylic acids, etc.

As the dibasic acid polyester, for example, one or more selected from polybutylene succinate, polyethylene succinate, polybutylene adipate, etc. can be used.

Biodegradable resins may be used alone or in combination of two or more types.

Examples of thermosetting resins that can be used include phenolic resins, urea resins, melamine resins, furan resins, unsaturated polyesters, diallyl phthalate resins, vinyl ester resins, epoxy resins, urethane resins, silicone resins, and thermosetting polyimide resins. These resins can be used alone or in combination.

The resin may contain inorganic fillers, preferably in a proportion that does not interfere with thermal recycling.

Examples of inorganic fillers include simple metal elements from Groups I to VIII of the periodic table, such as Fe, Na, K, Cu, Mg, Ca, Zn, Ba, Al, Ti, and silicon, as well as oxides, hydroxides, carbonates, sulfates, silicates, and sulfites, and various clay minerals composed of these compounds.

Specific examples include barium sulfate, calcium sulfate, magnesium sulfate, sodium sulfate, calcium sulfite, zinc oxide, silica, heavy calcium carbonate, light calcium carbonate, aluminum borate, alumina, iron oxide, calcium titanate, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, sodium hydroxide, magnesium carbonate, calcium silicate, clay wollastonite, glass beads, glass powder, silica sand, silica stone, quartz powder, diatomaceous earth, white carbon, and glass fiber. A combination of these inorganic fillers may be used. They may also be those contained in recycled paper pulp.

The blending ratio of fine fibers and resin is preferably 1 part by mass or more of fine fibers and 99 parts by mass or less of resin, more preferably 2 parts by mass or more of fine fibers and 98 parts by mass or less of resin, and particularly preferably 3 parts by mass or more of fine fibers and 97 parts by mass or less of resin. Also, preferably 50 parts by mass or less of fine fibers and 50 parts by mass or more of resin, more preferably 40 parts by mass or less of fine fibers and 60 parts by mass or more of resin, and particularly preferably 30 parts by mass or less of fine fibers and 70 parts by mass or more of resin. In particular, when the fine fibers are 10 to 50 parts by mass, the strength of the resin composition, particularly the bending strength and tensile modulus, can be significantly improved.

The content ratio of fine fibers and resin in the final resin composition is usually the same as the above-mentioned blend ratio of fine fibers and resin.

The difference in solubility parameters (cal/cm ³ ) ^1/2 (SP value) between the fine fibers and the resin, that is, the SP _MFC value of the fine fibers and the SP _POL value of the resin, can be expressed as SP value difference = SP _MFC value - SP _POL value. The SP value difference is preferably 10 to 0.1, more preferably 8 to 0.5, and particularly preferably 5 to 1. If the SP value difference exceeds 10, the fine fibers may not disperse in the resin, and the reinforcing effect may not be obtained. On the other hand, if the SP value difference is less than 0.1, the fine fibers may dissolve in the resin, not function as a filler, and the reinforcing effect may not be obtained. In this regard, the smaller the difference between the SP _POL value of the resin (solvent) and the SP _MFC value of the fine fibers (solute), the greater the reinforcing effect. The solubility parameter (cal/cm ³ ) ^1/2 (SP value) is a measure of the intermolecular force acting between a solvent and a solute, and the closer the SP values of a solvent and a solute are, the greater the solubility.

(Other Compositions)
In addition to the above-mentioned fine fibers and pulp, the resin composition (composite resin) can also contain or may contain fibers derived from plant materials obtained from various plants such as kenaf, jute, Manila hemp, sisal, gampi, mitsumata, kozo, banana, pineapple, coconut, corn, sugarcane, bagasse, palm, papyrus, reed, esparto, sabaigrass, wheat, rice, bamboo, various conifers (such as cedar and cypress), broad-leaved trees, and cotton.

One or more of the following may be added to the resin composition, as long as they do not impair the effects of the present invention: antistatic agents, flame retardants, antibacterial agents, colorants, radical scavengers, foaming agents, etc. These raw materials may be added to the dispersion of fine fibers, when kneading the fine fibers and resin, to the kneaded product, or by other methods. However, from the standpoint of production efficiency, it is preferable to add them when kneading the fine fibers and resin.

The resin composition may contain an ethylene-α-olefin copolymer elastomer or a styrene-butadiene block copolymer as a rubber component. Examples of α-olefins include butene, isobutene, pentene, hexene, methylpentene, octene, decene, and dodecene.

(Second additive: ethylene glycol, etc.)
When kneading the fine fibers and resin, in addition to additives such as polybasic acids, at least one additive (second additive) selected from ethylene glycol, ethylene glycol derivatives, ethylene glycol polymers, and ethylene glycol polymer derivatives can be added. Addition of this second additive significantly improves the dispersibility of the microfibrous cellulose. In this regard, the present inventors have found that when the cellulose fibers are cellulose nanofibers, the dispersibility of the cellulose fibers is poor. On the other hand, it is presumed that the second additive enters between the microfibrous cellulose particles, suppressing aggregation in the resin and improving dispersibility. Furthermore, because cellulose nanofibers have a significantly higher specific surface area than microfibrous cellulose, it is presumed that even if an excessive amount of the second additive is added, it will not enter between the cellulose nanofibers.

The amount of the second additive added is preferably 0.1 to 1,000 parts by mass, more preferably 1 to 500 parts by mass, and particularly preferably 10 to 200 parts by mass, per 100 parts by mass of microfiber cellulose. If the amount of the second additive added is less than 0.1 parts by mass, it may not contribute to improving the dispersibility of the microfiber cellulose. On the other hand, if the amount of the second additive added exceeds 1,000 parts by mass, it will be excessive and may actually reduce the strength of the resin.

The molecular weight of the second additive is preferably 1 to 20,000, more preferably 10 to 4,000, and particularly preferably 100 to 2,000. It is physically impossible for the molecular weight of the second additive to be less than 1. On the other hand, if the molecular weight of the second additive exceeds 20,000, it becomes too bulky and may not fit between the microfiber cellulose.

(Molding process)
The kneaded mixture of fine fibers and resin can be molded into a desired shape after further kneading, if necessary. The size, thickness, shape, etc. of the molded product are not particularly limited, and may be, for example, a sheet, pellet, powder, fiber, etc.

The temperature during the molding process is above the glass transition point of the resin, and varies depending on the type of resin, but is, for example, 90 to 260°C, preferably 100 to 240°C.

The kneaded material can be molded by, for example, mold molding, injection molding, extrusion molding, blow molding, foam molding, etc. The kneaded material can also be spun into fibers and mixed with the plant materials mentioned above to form a mat or board. Mixing can be achieved, for example, by simultaneous deposition using air laying.

As an apparatus for molding the kneaded material, one or more types can be selected from, for example, an injection molding machine, a blow molding machine, a hollow molding machine, a blow molding machine, a compression molding machine, an extrusion molding machine, a vacuum molding machine, a pressure molding machine, etc.

The above molding can be carried out following kneading, or the kneaded material can be cooled and then chipped using a crusher or similar device, and the chips can then be fed into a molding machine such as an extruder or injection molding machine. Of course, molding is not an essential requirement of the present invention.

Next, an embodiment of the present invention will be described.
Softwood bleached kraft pulp with a moisture content of 50% or less was mixed with an aqueous urea solution with a solids concentration of 30% so that the mass ratio of pulp to urea was 100:50 in terms of solids, and the mixture was dried at 105° C. Thereafter, the mixture was allowed to stand at 160° C. for 1 hour to allow the mixture to react, thereby obtaining a carbamate-modified pulp.

The resulting carbamate-modified pulp was diluted with distilled water, stirred, and dehydrated and washed twice to a solids concentration of 3.0% by mass, yielding washed carbamate-modified pulp.

The washed carbamate-modified pulp was beaten using a beater until the fine ratio (the proportion of fibers 0.2 mm or less as measured by FS5 fiber length distribution) reached 40% or more, yielding carbamate-modified microfibrous cellulose.

27.5 g of maleic anhydride-modified polypropylene was added to 1,833 g of carbamate-modified microfibrous cellulose with a solids concentration of 3.0% by mass, followed by 17.5 g of polypropylene powder. After stirring, the mixture was heated and dried in a contact dryer heated to 140°C to obtain a carbamate-modified microfibrous cellulose-containing material. The moisture content of the carbamate-modified microfibrous cellulose-containing material was 5-22%.

The carbamate-modified microfiber cellulose material was kneaded in a twin-screw kneader at 180°C and 200 rpm, and then cut into cylindrical shapes with a belleter, measuring 2 mm in diameter and 2 mm in length, to obtain a carbamate-modified microfiber cellulose composite resin with a fiber loading ratio of 55%.

A composite resin with a fiber loading ratio of 55%, polypropylene (PP) pellets, and an α-olefin copolymer (Tafmer DF640 manufactured by Mitsui Chemicals, Inc.) were dry-blended in the ratios shown in Table 1, kneaded in a twin-screw kneader at 180°C and 200 rpm, and cut into cylindrical shapes with a diameter of 2 mm and a length of 2 mm using a beletter, to obtain a carbamate-modified microfiber cellulose composite resin with a fiber loading ratio of 10%.

Carbamate-modified microfiber cellulose composite resins containing 10% of each fiber were injection molded at 180°C into rectangular specimens (length 59 mm, width 9.6 mm, thickness 3.8 mm).

In addition, in Test Examples 1 to 4, softwood bleached kraft pulp was used instead of carbamate-modified pulp, adjusted to a solids concentration of 3.0% by mass, and the beating process was carried out as described above, resulting in an unmodified microfiber cellulose composite resin.

The flexural modulus, flexural strength, and impact resistance of various fibrous cellulose composite resins were examined. The results are shown in Table 1. The measurement methods for each test were as follows. The impact resistance ratio is shown as the ratio to the case where the α-olefin copolymer blending ratio was set to 0.

(Flexural modulus)
Various fibrous cellulose composite resins were molded into bending test pieces, and the bending modulus of the molded pieces was measured. The bending modulus was roughly determined in accordance with JIS K 7171:2008.

(Bending strength)
The resultant was molded into a bending test piece, and the bending strength of the molded product was measured in accordance with JIS K 7171:2008.

(Impact resistance test)
Various fibrous cellulose composite resins were molded into multipurpose test pieces in accordance with JIS K 7139, and the impact resistance of these molded pieces was examined. The impact resistance was measured by measuring the Charpy impact strength in accordance with JIS K 7111-1:2008.

The present invention can be used as a fibrous cellulose composite resin. For example, the fibrous cellulose composite resin can be used for interior, exterior, and structural materials for transportation vehicles such as automobiles, trains, ships, and airplanes; housings, structural materials, and internal parts for electrical appliances such as personal computers, televisions, telephones, and watches; housings, structural materials, and internal parts for mobile communication devices such as mobile phones; housings, structural materials, and internal parts for portable music players, video players, printing machines, copying machines, sporting goods, office equipment, toys, and sporting goods; interior, exterior, and structural materials for buildings and furniture; office equipment such as stationery; and other applications such as packaging, trays, and other containers, protective materials, and partition materials.

Claims (9)

A fibrous cellulose composite resin containing fibrous cellulose and a resin,
The composition contains an α-olefin copolymer in an amount of 1% by mass or more and 20% by mass or less,
the fibrous cellulose is a carbamate-modified fine fiber in which a hydroxy group is substituted with a carbamate group,
the degree of substitution of the carbamate group with the hydroxy group is 0.05 to 0.5;
A fibrous cellulose composite resin characterized by: The fine fibers have an average fiber width of 8 to 25 μm and an average fiber length of 0.1 to 1.00 mm.
The fibrous cellulose composite resin according to claim 1 . The fibrillation rate of the fine fibers is 2 to 7%.
The fibrous cellulose composite resin according to claim 1 or 2. Contains acid-modified resin,
a part or all of the carbamate groups are ionically bonded to the acid groups of the acid-modified resin;
The fibrous cellulose composite resin according to any one of claims 1 to 3. Contains a dispersant,
the molecular weight of the acid-modified resin is 2 to 2000 times the molecular weight of the dispersant;
The fibrous cellulose composite resin according to claim 4. The crystallinity of the fine fibers is 50 to 95%.
The fibrous cellulose composite resin according to any one of claims 1 to 5. The pulp viscosity of the fine fibers is 2 cps or more.
The fibrous cellulose composite resin according to any one of claims 1 to 6. The zeta potential of the fine fibers is −150 to 20 mV.
The fibrous cellulose composite resin according to any one of claims 1 to 7. The water retention of the fine fibers is 80 to 400%.
The fibrous cellulose composite resin according to any one of claims 1 to 8.