JP7650462B2 - Modified cellulose and resin composition - Google Patents

Description

The present invention relates to cellulose modified with 3-hydroxybutyric acid (hereinafter sometimes simply referred to as "3HB") or its oligomer, and a resin composition containing this modified cellulose.

In order to protect the environment and realize a sustainable society, the use of bio-based plastics (or biodegradable plastics) is increasing, with the partial or total conversion of plastic raw materials to biomass. From the viewpoint of durability and strength, such plastics are generally used in the form of resin compositions in combination with various additives and reinforcing materials. As reinforcing materials, fibrous reinforcing materials such as carbon fiber and glass fiber are used, but these fibrous reinforcing materials emit a lot of carbon dioxide during the manufacturing process and are poorly recyclable. On the other hand, cellulose, a fiber derived from plants, has a small environmental impact and is a sustainable resource, and has excellent properties such as a high elastic modulus, high strength, and a low linear expansion coefficient. Therefore, there is a demand for plant-derived fibers such as cellulose to replace cellulose as a reinforcing material. However, cellulose fibers and their nanofibers, cellulose nanofibers, generally have poor compatibility (affinity, miscibility) with plastics, and compatibilizers are used in combination.

JP 2017-171713 A (Patent Document 1) describes a master batch that contains acylated modified plant fibers, a thermoplastic resin, and a compatibilizer, and is diluted with a diluting resin, and describes an example in which acetylated modified plant fibers are used as the acylated modified plant fibers, polylactic acid is used as the thermoplastic resin, and polypropylene and polyethylene are used as the diluting resin.

JP 2016-79369 A (Patent Document 2) describes modified cellulose that is highly dispersible in resins and is modified with a compound having a 9,9-bisarylfluorene skeleton, and is useful as a material for compounding resins. Examples of resins include aliphatic polyester resins derived from biomass, such as polylactic acid.

Furthermore, if the resin composition contains components that are partially or completely non-biodegradable (plastics, additives, reinforcing materials, etc.), the non-biodegradable components that end up in the environment, including soil, lakes, and rivers, or in the ocean, are broken down and fragmented by ultraviolet rays and other factors, generating microplastics with diameters of 5 mm or less. There are concerns that these microplastics, when ingested into the living bodies of birds, fish, and other animals, could cause endocrine disruption.

Examples of biodegradable plastics include polylactic acid (PLA), polyhydroxyalkanoate (PHA), polybutylene succinate (PBS), and polycaprolactone (PCL). However, these biodegradable plastics have low biodegradability (or biogasification) under anaerobic conditions, and low biodegradability in the ocean. Since the biodegradable plastics are highly dense and sink in the ocean, solving the microplastic problem requires the development of plastics that have high biodegradability even in anaerobic conditions such as in the ocean.

H.Yagi et al., Polymer Degradation and Stability, 110, (2014), 278-283 (Non-Patent Document 1) evaluates the biodegradability of various biodegradable polyesters under anaerobic conditions, and discloses that poly-3-hydroxybutyrate (PHB) exhibits higher biodegradability under anaerobic conditions than PLA, PCL, and PBS. However, poly-3-hydroxyalkanoates such as PHB produced (biosynthesized) by microorganisms lack the mechanical properties required for general-purpose plastic molded bodies and are also less economical, so they have not been widely used.

On the other hand, as a biodegradable plastic into which 3HB has been introduced by chemical synthesis, JP 2017-025138 A (Patent Document 3) discloses a biodegradable copolymer in which the ratio of 3-hydroxybutyric acid (3HB) units to the total constituent units is 1 to 20 mol %. Patent Document 3 describes that a biodegradable copolymer into which 3HB units have been randomly introduced has high biodegradability under aerobic and anaerobic conditions.

JP 2017-171713 A JP 2016-79369 A JP 2017-025138 A

H.Yagi et al., Polymer Degradation and Stability, 110, (2014), 278-283

The masterbatch described in Patent Document 1 is suitable for preparing a fiber-reinforced resin composition. However, since the compatibilizer of the masterbatch does not exhibit biodegradability, it is not necessarily sufficient from the viewpoint of sustainable environmental conservation. In particular, if a dilution resin that does not exhibit biodegradability is used, the fiber-reinforced resin composition cannot be expected to be biodegradable. In addition, since each component has a predetermined solubility parameter relationship, there is a risk that the range of material selection will be narrowed. Furthermore, acylated modified plant fibers are not necessarily sufficiently biodegradable, particularly in terms of decomposition under anaerobic conditions.

The modified cellulose described in Patent Document 2 has high compatibility with resins, but is not sufficiently biodegradable. Therefore, even if the modified cellulose is added to a biodegradable plastic, the biodegradability of the entire resin composition cannot be improved.

The biodegradable copolymer described in Patent Document 3 has low reactivity with 3HB and is easily dehydrated intramolecularly by heat or acid, making it difficult to increase the molecular weight and sometimes resulting in insufficient mechanical properties.

The object of the present invention is therefore to provide modified cellulose fibers (or modified cellulose fibers) formed from biodegradable components and useful as reinforcing materials for resins, and to provide resin compositions containing the modified cellulose fibers.

Another object of the present invention is to provide modified cellulose fibers (or modified cellulose fibers) that can effectively reinforce biodegradable plastics without necessarily requiring a compatibilizer, and that are useful as a biodegradable reinforcing material, and a resin composition that contains the modified cellulose fibers.

Yet another object of the present invention is to provide a biodegradable resin composition in which all polymer components, including cellulose, are biodegradable even under anaerobic conditions in soil, water including the ocean, and the like.

As a result of intensive research into solving the above problems, the inventors discovered that 3-hydroxybutyric acid-modified cellulose (3HB-C), in which biodegradable cellulose fibers are modified with 3-hydroxybutyric acid or its oligomers, is made of biodegradable components and is useful as a reinforcing material for resins, thus completing the present invention.

That is, the modified cellulose of the present invention has 3-hydroxybutyric acid or an oligomer thereof bound to cellulose fibers. The modified cellulose may have the 3-hydroxybutyric acid or an oligomer thereof ester-bonded to the 6-position of an anhydroglucose unit of the cellulose fibers. The average degree of polymerization of the 3-hydroxybutyric acid or an oligomer thereof may be 1 to 10. The grafting rate of the 3-hydroxybutyric acid or an oligomer thereof may be 5 to 30 mol %. The 3-hydroxybutyric acid may be R-3-hydroxybutyric acid.

The present invention also includes a resin composition containing the modified cellulose and at least one resin selected from a thermoplastic resin and a curable resin. The resin may contain a biodegradable plastic. The resin may be a homopolymer or copolymer of at least one monomer selected from a hydroxyalkanoic acid and a lactone. The proportion of the modified cellulose may be 0.1 to 20 parts by mass relative to 100 parts by mass of the resin.

The present invention also includes a method of improving the mechanical properties of a resin by blending the modified cellulose with the resin. The resin may be a biodegradable plastic.

In the present invention, the biodegradable cellulose fibers are modified with 3-hydroxybutyric acid or its oligomers, and are therefore made of biodegradable components and are useful as reinforcing materials for resins.

In addition, cellulose-based fillers generally have low affinity with resins, but by modifying them with 3HB, their interfacial affinity with polyhydroxyalkanoates (PHAs) such as PHBH is improved. Therefore, the present invention does not necessarily require a compatibilizer, can effectively reinforce biodegradable plastics, and is useful as a biodegradable reinforcing material.

Furthermore, as shown in Non-Patent Document 1, PHA (and its monomer 3HA) and cellulose are all among the few polymers that are biodegradable even under anaerobic conditions, such as in soil and in water, including the ocean. Therefore, by combining 3HB-C and PHA, it is possible to form a biomass filler composed only of components that can be decomposed under anaerobic conditions, which can contribute to low carbon and decarbonization.

FIG. 1 is a chart showing FT-IR (Fourier transform infrared spectroscopy) of the raw materials used in the examples and the resulting modified cellulose. FIG. 2 is a chart of the solid-state ¹³ C-NMR spectrum of the modified cellulose obtained in the examples and comparative examples. FIG. 3 is a graph showing the results of the tensile tests on the films obtained in Comparative Examples 1 and 2 and Example 7. FIG. 4 is a graph showing the results of the tensile test on the films obtained in Comparative Examples 1 and 3 and Example 8. FIG. 5 is a graph showing the results of the tensile test on the films obtained in Comparative Examples 1 and 4 and Example 9. FIG. 6 is a scanning electron microscope (SEM) photograph of the tensile fracture surfaces of the films obtained in Example 8 and Comparative Example 4.

[Modified cellulose]
The modified cellulose of the present disclosure comprises cellulose fibers and 3-hydroxybutyric acid (3-hydroxybutanoic acid) or an oligomer thereof bonded thereto.

(Cellulose fiber)
Examples of cellulose constituting the cellulose fiber include pulps with low content of non-cellulose components such as lignin and hemicellulose, for example, pulps produced from plant-derived cellulose raw materials {for example, wood [e.g., coniferous trees (pine, fir, spruce, hemlock, cedar, etc.), broad-leaved trees (beech, birch, poplar, maple, etc.)], herbaceous plants [hemp (hemp, flax, Manila hemp, ramie, etc.), straw, bagasse, Mitsumata, etc.], seed hair fibers (cotton linters, bombax cotton, kapok, etc.), bamboo, sugar cane, etc.}, animal-derived cellulose raw materials (such as sea squirt cellulose), and bacterial-derived cellulose raw materials (such as cellulose contained in nata de coco). These celluloses can be used alone or in combination of two or more kinds. Among these celluloses, celluloses derived from wood pulp (e.g., coniferous pulp, broad-leaved pulp, etc.), and seed hair fiber pulp (e.g., cotton linter pulp) are preferred. The pulp may be mechanical pulp obtained by mechanically treating a pulp material, but chemical pulp obtained by chemically treating a pulp material is preferred because it has a low content of non-cellulose components.

The cellulose may be cellulose (or cellulose fiber) having high crystallinity, and the crystallinity of the cellulose may be, for example, 40 to 100% (e.g., 50 to 100%), preferably 60 to 100%, more preferably 70 to 100% (particularly 75 to 99%), and usually the crystallinity may be 60% or more (e.g., 60 to 98%). Examples of the crystal structure of the cellulose include type I, type II, type III, and type IV, and type I crystal structure, which has excellent linear expansion properties and elastic modulus, is preferred. The crystallinity can be measured using a powder X-ray diffraction device (Ultima IV, manufactured by Rigaku Corporation).

Cellulose fibers (particularly cellulose nanofibers) have a high cellulose component content (or cellulose purity). The cellulose component content can be selected from a range of, for example, about 60 to 100% by mass relative to the entire cellulose fiber, for example, 70 to 100% by mass (e.g., 70 to 98% by mass), preferably 80 to 100% by mass (e.g., 80 to 99% by mass), and more preferably 90 to 100% by mass.

Cellulose may contain non-cellulose components such as hemicellulose and lignin, and in the case of cellulose fibers (particularly, cellulose nanofibers), the proportion of non-cellulose components in the fibrous cellulose is 30% by mass or less, preferably 20% by mass or less, and more preferably 10% by mass or less. The cellulose fibers may be cellulose fibers that are substantially free of non-cellulose components (particularly, cellulose fibers that do not contain non-cellulose components).

The degree of polymerization of cellulose may be 500 or more, preferably 600 or more (e.g., about 600 to 100,000), and in the case of nanofibers, the viscosity average degree of polymerization may be, for example, 100 to 10,000, preferably 200 to 5,000, and more preferably 300 to 2,000.

The viscosity average degree of polymerization can be measured by the viscosity method described in TAPPI T230. That is, 0.04 g of modified cellulose fiber (or raw cellulose fiber) is weighed out, 10 mL of water and 10 mL of 1 M copper ethylenediamine aqueous solution are added, and the mixture is stirred for about 5 minutes to dissolve the modified cellulose. The resulting solution is placed in an Ubbelohde type viscosity tube, and the flow rate is measured at 25°C. A mixture of 10 mL of water and 10 mL of 1 M copper ethylenediamine aqueous solution is measured as a blank. Using the intrinsic viscosity [η] calculated based on these measured values, the viscosity average degree of polymerization can be calculated according to the following formula described in the Wood Science Experiment Manual (edited by the Japan Wood Research Society, Bun'ei-do Publishing).

Viscosity average degree of polymerization=175×[η].

The fiber diameter of the cellulose fibers may be on the order of microns or nanometers.

In detail, the average fiber diameter of the cellulose fibers can be selected from the range of about 3 nm to 100 μm, for example, 4 nm to 50 μm, preferably 5 nm to 30 μm, and more preferably 10 nm to 20 μm. In addition, when the cellulose fibers are on the order of microns, the average fiber diameter of the cellulose fibers may be, for example, 1 to 100 μm, preferably 3 to 50 μm, more preferably 5 to 30 μm, and more preferably 10 to 20 μm. In addition, when the cellulose fibers are nanometer-sized, the average fiber diameter of the cellulose fibers may be, for example, 1 to 1000 nm, preferably 3 to 500 nm, more preferably 5 to 300 nm, and more preferably 10 to 100 nm. If the fiber diameter is too small, when it is blended into a resin as a reinforcing material, it may be difficult to disperse the cellulose fibers uniformly in the resin, or it may be difficult to prepare the cellulose fibers themselves. Conversely, if the fiber diameter is too large, it may not be possible to improve the mechanical properties of the resin as a reinforcing material.

The average fiber length of the cellulose fibers can be selected, for example, from the range of about 0.01 to 500 μm (particularly 0.1 to 400 μm), and is usually 1 μm or more (e.g. 5 to 300 μm), preferably 10 μm or more (e.g. 20 to 200 μm), and more preferably 30 μm or more (particularly 50 to 150 μm). If the average fiber length is too short, there is a risk that the mechanical properties of the resin will decrease, and conversely, if it is too long, there is a risk that dispersibility in the resin will decrease.

The ratio of the average fiber length to the average fiber diameter of the cellulose fibers (aspect ratio) may be, for example, 1.5 or more (e.g., 1.5 to 10,000), preferably 2 or more (e.g., 2 to 1,000), more preferably 2.5 or more (e.g., 2.5 to 500), particularly 3 or more (e.g., 3 to 100), 4 or more (e.g., 4 to 50), or even 5 or more (e.g., 5 to 10). If the aspect ratio is too small, the reinforcing effect on the resin decreases, and conversely, if it is too large, uniform dispersion becomes difficult and the fibers may be easily decomposed (or damaged).

In this specification and claims, the average fiber diameter, average fiber length, and aspect ratio of cellulose fibers may be calculated by randomly selecting 50 fibers from a scanning electron microscope image and averaging them.

When the cellulose fibers are nanofibers, they can be prepared by defibrating the cellulose raw material to nanometer sizes using a conventional method, for example, a physical or mechanical method such as a high-pressure homogenizer method, an underwater collision method, a grinder method, a ball mill method, or a biaxial kneading method, or a chemical method using a TEMPO catalyst, phosphoric acid, a dibasic acid, sulfuric acid, hydrochloric acid, or the like.

(Modifier)
The modified cellulose contains 3HB as a modifying agent (esterifying agent), and 3HB or its oligomer (hereinafter sometimes referred to as "(poly)3HB") is chemically bonded to the cellulose. (Poly)3HB may be chemically bonded to any of the hydroxyl groups at the 2-, 3-, or 6-positions of the anhydroglucose unit (or glucose unit) which is a repeating unit of cellulose, but from the viewpoint of productivity, it is preferable that the (poly)3HB is ester-bonded to at least the 6-position.

3HB may be an optical isomer (R or S isomer) or may be a racemate, but from the viewpoint of biodegradability, it is preferable to contain at least the R isomer (R-3-hydroxybutyric acid). The ratio of the R isomer in 3HB, i.e., the optical purity (enantiomer or optical isomer excess), is, for example, 50% e.e. or more (e.g., 80% e.e. or more), preferably 90% e.e. or more (e.g., 95 to 100% e.e.), and more preferably 98 to 100% e.e. (e.g., 99 to 100% e.e., particularly substantially 100% e.e.). If the optical purity is too low, there is a risk of reduced biodegradability. 3HB may be a commercially available product, or 3HB produced by fermentation of a biomass raw material (a biological resource) by a microorganism may be used.

The average degree of polymerization of (poly)3HB may be 1 or more, for example, 1 to 100, preferably 1 to 10 (e.g., 2 to 5), more preferably 1.5 to 5, even more preferably 2 to 4.5, and most preferably 3 to 4. If the average degree of polymerization of (poly)3HB is too small, there is a risk that the effect of modification by (poly)3HB will not be manifested, and conversely, if it is too large, there is a risk that the function as a reinforcing material will be reduced.

In this specification and claims, the average degree of polymerization of (poly)3HB is the average degree of polymerization of the portion grafted to the hydroxyl groups of the cellulose fibers, and can be calculated using NMR, and more specifically, can be measured by the method described in the examples below.

The grafting rate with (poly)3HB should be 1 mol% or more, for example, 1 to 80 mol%, preferably 3 to 50 mol%, further preferably 5 to 30 mol%, even more preferably 7 to 20 mol%, and most preferably 10 to 15 mol%. If the grafting rate is too low, there is a risk that the effect of modification with (poly)3HB will not be manifested.

In this specification and claims, the grafting rate with (poly)3HB means the ratio of (poly)3HB (graft chain) per anhydroglucose unit of cellulose fiber [the grafting rate of (poly)3HB bonded to the hydroxyl group of the anhydroglucose unit via an ester bond]. The grafting rate with (poly)3HB can be calculated using NMR, and in detail, can be measured by the method described in the examples below.

The modified cellulose may be further modified with other modifiers [modifiers other than (poly)3HB] in addition to (poly)3HB.

Other modifiers (esterifying agents) include, for example, carboxylic acids, other hydroxyalkanoic acids (alkanoic acids other than 3HB) or their oligomers, and oligomers of 3HB and other hydroxyalkanoic acids.

Examples of carboxylic acids include monocarboxylic acids or their anhydrides [for example, aliphatic monocarboxylic acids such as acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, ethanoic propionic anhydride, (meth)acrylic anhydride, crotonic anhydride, and oleic anhydride; alicyclic carboxylic acids such as cyclohexane carboxylic acid and tetrahydrobenzoic acid; benzoic acid and 4-methylbenzoic acid; (Aromatic monocarboxylic acid anhydride, etc.), dicarboxylic acids (for example, aliphatic dicarboxylic acids such as succinic acid, adipic acid, maleic acid, itaconic acid, etc.; alicyclic dicarboxylic acids such as 1-cyclohexene-1,2-dicarboxylic acid, hexahydrophthalic acid, methyltetrahydrophthalic acid, etc.; aromatic dicarboxylic acids such as phthalic acid, naphthalic acid, etc.), polycarboxylic acids [for example, (anhydrous) polycarboxylic acids such as trimellitic acid, trimellitic anhydride, pyromellitic anhydride, etc.], etc.

Examples of other hydroxyalkanoic acids include hydroxy C 2-15 alkanoic acids which may have a C 1-6 alkyl group, such as glycolic acid, 2-hydroxypropanoic acid (lactic acid), 3-hydroxypropanoic acid, 2-hydroxybutanoic acid (2-hydroxybutyric acid), 4-hydroxybutanoic acid, 3-hydroxy-3-methyl-butanoic acid, 2-hydroxypentanoic acid (2-hydroxyvaleric acid), 3-hydroxypentanoic acid, 5-hydroxypentanoic acid, 2-hydroxy-2-methyl-pentanoic acid, 3-hydroxyhexanoic acid, 6-hydroxy-heptanoic acid, 3-hydroxyheptanoic acid, _7- hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 8-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 9-hydroxynonanoic acid, 3 _- hydroxydecanoic acid, and 10-hydroxydecanoic acid. The other hydroxyalkanoic acids may be the corresponding lactones.

The proportion of the other modifier may be 100 parts by mass or less (e.g., 0.01 to 100 parts by mass) relative to 100 parts by mass of (poly)3HB, and is, for example, 50 parts by mass or less, preferably 30 parts by mass or less, more preferably 10 parts by mass or less, and most preferably 0 parts by mass. If the proportion of the other modifier is too high, there is a risk of reduced biodegradability.

(Characteristics of modified cellulose)
The form of the modified cellulose of the present disclosure is not particularly limited, and may be in the form of a dispersion, but usually has a powder form, so that it is easy to handle.Furthermore, since the (poly)3HB bonded to the modified cellulose has high affinity or miscibility with various organic media (including resin), the modified cellulose shows high dispersibility in resin and has high reinforcing properties.Therefore, the modified cellulose of the present disclosure is useful as a reinforcing material for resin.

[Method of producing modified cellulose]
The modified cellulose of the present disclosure can be obtained by esterifying cellulose fibers (raw cellulose fibers) with 3HB (raw 3HB).

In the method for producing modified cellulose, the proportion of raw material 3HB can be selected from the range of about 50 to 10,000 parts by mass per 100 parts by mass of raw material cellulose fiber depending on the desired degree of modification, and is, for example, 100 to 5,000 parts by mass, preferably 150 to 4,000 parts by mass, and more preferably 200 to 3,000 parts by mass.

The reaction between the raw cellulose fiber and the raw 3HB may be carried out in the absence or presence of a catalyst. The modified cellulose of the present disclosure can sufficiently esterify 3HB even in the absence of a catalyst, but a catalyst may be used to adjust the polymerization degree and grafting rate of (poly)3HB. From the viewpoints of excellent operability and suppression of coloration, it is preferable to carry out the reaction in the absence of a catalyst.

As the catalyst, a conventional esterification catalyst can be used. The conventional esterification catalyst may be a base catalyst or an acid catalyst.

Examples of the base catalyst include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, etc.; alkali metal carbonates such as lithium carbonate, sodium carbonate, potassium carbonate, etc.; alkali metal hydrogen carbonates such as sodium hydrogen carbonate, potassium hydrogen carbonate, etc.; alkaline earth metal hydroxides such as magnesium hydroxide, calcium hydroxide, etc.; alkaline earth metal carbonates such as magnesium carbonate; alkaline earth metal hydrogen carbonates such as magnesium hydrogen carbonate; ammonia; tertiary amines such as tri-C _1-4 alkylamines such as trimethylamine, triethylamine, etc.;

Examples of acid catalysts include inorganic acids such as sulfuric acid, hydrogen chloride (or hydrochloric acid), nitric acid, and phosphoric acid; and organic acids such as sulfonic acids (alkanesulfonic acids such as methanesulfonic acid, ethanesulfonic acid, and trifluoromethanesulfonic acid, and arenesulfonic acids such as benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid).

The amount of catalyst used is, for example, 0.01 to 100 parts by mass, preferably 0.05 to 50 parts by mass, and more preferably 0.1 to 30 parts by mass, per 100 parts by mass of cellulose fiber.

The reaction may be carried out in the absence of an organic solvent or in the presence of an organic solvent. Examples of the organic solvent include alcohols (C _1-4 alkanols such as methanol, ethanol, propanol, and isopropanol), ethers (cyclic ethers such as dioxane and tetrahydrofuran), ketones (acetone, etc.), amides (dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, etc.), pyrrolidones (N-methyl-2-pyrrolidone, etc.), sulfoxides (dimethyl sulfoxide, etc.), alkanediols (C _2-4 alkanediols such as ethylene glycol and propylene glycol), cellosolves (methyl cellosolve, ethyl cellosolve), carbitols (ethyl carbitol, etc.), and carbonates (ethylene carbonate, propylene carbonate, dimethyl carbonate, etc.). These solvents may be used alone or in combination of two or more.

The modified cellulose of the present disclosure can be sufficiently esterified with 3HB even in the absence of an organic solvent, so it is preferable to carry out the reaction in the absence of an organic solvent from the standpoint of operability, etc.

The reaction may be carried out under normal pressure, elevated pressure, or reduced pressure, but is preferably carried out under reduced pressure in order to improve reactivity. The reduced pressure (gauge pressure) is, for example, 10 to 300 kPa, preferably 30 to 200 kPa, and more preferably 50 to 150 kPa.

The reaction temperature is, for example, 50 to 200°C, preferably 70 to 180°C, more preferably 80 to 150°C, and more preferably 100 to 130°C. The reaction time is, for example, 10 minutes to 48 hours, preferably 30 minutes to 24 hours, more preferably 1 to 12 hours, and more preferably 2 to 8 hours. The reaction can be carried out in air or in an inert gas atmosphere (such as nitrogen gas or a rare gas such as argon gas) with mixing or stirring.

As a method of mixing or stirring, the mixture may be kneaded by a conventional mixing or stirring means at a rotation speed of, for example, about 10 to 2000 rpm, preferably 20 to 1500 rpm, more preferably 30 to 1000 rpm, and particularly about 50 to 500 rpm. Examples of conventional mixing or stirring methods include methods using a ball mill, tumble mixer, ribbon blender, Henschel mixer, mixing roller, kneader, Banbury mixer, extruder (such as a single-screw or twin-screw extruder), etc.

The modified cellulose produced by the reaction may be separated and purified by a conventional method (e.g., centrifugation, filtration, concentration, extraction, etc.). For example, a solvent capable of dissolving at least 3HB may be added to the reaction mixture, and unreacted 3HB may be removed by a separation method (conventional method) such as centrifugation, filtration, extraction, etc., to separate and purify the cellulose. The separation operation may be carried out multiple times (e.g., about 2 to 5 times). Furthermore, modified cellulose in a powder form may be obtained by drying the separated and purified modified cellulose at room temperature or under heating, under reduced pressure or under normal pressure.

When the modified cellulose that has been purified by repeatedly removing unreacted 3HB using the above-mentioned separation method is analyzed using a method such as FT-IR analysis, a peak derived from the ester bond and a peak derived from 3HB are present, confirming that 3HB is bonded to the cellulose.

[Resin composition]
The resin composition of the present disclosure contains the modified cellulose and at least one resin selected from a thermoplastic resin and a curable resin.

Examples of thermoplastic resins include polyolefin resins, styrene resins, acrylic resins, vinyl chloride resins, polyvinyl alcohol resins, polyacetal resins, polyester resins, polycarbonate resins, polyamide resins, polyimide resins, polysulfone resins, polyphenylene ether resins, polyphenylene sulfide resins, fluororesins, and cellulose derivatives (excluding the modified cellulose of the present disclosure). These thermoplastic resins can be used alone or in combination of two or more.

Examples of the curable resin include phenolic resin, melamine resin, urea resin, benzoguanamine resin, silicone resin, epoxy resin, unsaturated polyester resin, vinyl ester resin, polyurethane resin, etc. These curable resins can be used alone or in combination of two or more kinds.

Among these, thermoplastic resins are preferred from the viewpoint of moldability, and thermoplastic resins having ester bonds and/or carbonate bonds (for example, polyalkylene arylate resins such as polyethylene terephthalate; polycarbonate resins such as bisphenol A polycarbonate, etc.) are more preferred from the viewpoint of excellent affinity with modified cellulose, with polyester resins being the most preferred.

Examples of polyester resins include polyester resins and polyester carbonate resins. Of these, polyester resins are preferred because of their excellent affinity with modified cellulose, and homopolymers or copolymers of at least one monomer selected from hydroxyalkanoic acids and lactones are particularly preferred. Examples of hydroxyalkanoic acids include the hydroxyalkanoic acids exemplified in the section on modifiers for modified cellulose.

Since the modified cellulose of the present disclosure has excellent biodegradability, it is preferable that the resin is also a biodegradable plastic. Examples of biodegradable plastics include polyvinyl alcohol-based resins, polyether-based resins, aliphatic polyester-based resins, aliphatic polyamide-based resins, and cellulose derivatives (excluding the modified cellulose of the present disclosure). Of these, aliphatic polyester-based resins are preferable because of their excellent affinity with the modified cellulose.

Examples of aliphatic polyester resins include polyhydroxyalkanoates (PHAs) such as polylactic acid (PLA), poly3-hydroxybutyrate (PHB), 3-hydroxybutyrate-3-hydroxyhexanoate copolymer (PHBH), and polyhydroxyvaleric acid; polymers of aliphatic dicarboxylic acids and aliphatic diols such as polyethylene adipate and polybutylene succinate (PBS); and lactone ring-opening polymers such as polycaprolactone (PCL). These aliphatic polyester resins can be used alone or in combination of two or more.

Of these aliphatic polyester resins, PHA is preferred because of its high affinity with modified cellulose, biodegradable resins (e.g., PHB, PHBH, etc.) containing homopolymers or copolymers of 3HB (particularly R-3HB) are more preferred because they have high biodegradability even under anaerobic conditions, and 3HB copolymers such as PHBH are most preferred because they have an excellent balance of various properties such as mechanical properties.

The molecular weight of the thermoplastic resin (particularly, PHA such as PHBH) is not particularly limited, and the weight average molecular weight (unit: ×10 ⁴ ) may be, for example, 0.1 to 100, preferably 1 to 80, and more preferably about 2 to 70; the number average molecular weight (unit: ×10 ⁴ ) may be, for example, 0.1 to 100, preferably 1 to 80, and more preferably 2 to 70; and the dispersity (M _w /M _n ) may be, for example, 1 to 5, preferably 1 to 3, more preferably 1 to 2, and particularly 1 to 1.5. The weight average molecular weight (M _w ) and number average molecular weight (M _n ) of the resin can be measured in polystyrene equivalent by GPC (Gel Permeation Chromatography).

The proportion of modified cellulose can be selected from the range of about 0.01 to 100 parts by mass per 100 parts by mass of the resin (particularly PHA such as PHBH), and is, for example, 0.05 to 30 parts by mass, preferably 0.1 to 20 parts by mass, further preferably 0.2 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and most preferably 0.5 to 3 parts by mass. If the proportion of modified cellulose is too low, there is a risk that the effect as a reinforcing material will not be expressed, and conversely, if it is too high, there is a risk that the mechanical properties will decrease.

The resin composition may further contain various additives [e.g., plasticizers, flame retardants, stabilizers (thermal stabilizers, antioxidants, UV absorbers, etc.), colorants (pigments, etc.), fillers, antistatic agents, lubricants, release agents, antibacterial agents, antifungal agents, etc.] as necessary. These additives may be used alone or in combination of two or more. The total proportion of these additives can be selected according to the type of additive, and the total amount of additives can be selected from the range of 0.001 to 100 parts by mass relative to 100 parts by mass of the resin, and is, for example, 100 parts by mass or less (e.g., 0.01 to 80 parts by mass), preferably 70 parts by mass or less (e.g., 0.1 to 60 parts by mass), and more preferably 50 parts by mass or less (e.g., 0.1 to 40 parts by mass).

Molded articles made from the resin composition have excellent mechanical properties. For example, in a resin composition containing 2% by mass of modified cellulose, the Young's modulus in a tensile test may be 1200 MPa or more, for example, 1200 to 2000 MPa, preferably 1230 to 1500 MPa, and more preferably 1250 to 1300 MPa. In addition, in a resin composition containing 2% by mass of modified cellulose, the elongation at break in a tensile test may be 10% or more, for example, 10 to 50%, preferably 12 to 40%, and more preferably 13 to 30%.

In this specification and claims, the maximum stress and elongation at break in the tensile test can be measured by the method described in the examples below.

The resin composition can be molded into a desired shape, such as a line, film or sheet, cylinder or pipe, or three-dimensional shape such as a casing or housing, by conventional molding methods (such as hot press molding, extrusion molding, injection molding, and melt molding methods such as calendar molding, and casting). The molding temperature is, for example, 130 to 230°C, preferably 140 to 200°C, further 150 to 190°C, and more preferably 160 to 180°C. Pressurization may be applied during molding, and the pressure is, for example, 1 to 100 MPa, preferably 5 to 50 MPa, and further preferably 10 to 30 MPa.

The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. The raw materials and evaluation methods used are as follows.

(Raw materials)
Cellulose: Cellulose powder manufactured by Nacalai Tesque, Inc., product number 07748-75, average fiber diameter 12.6 μm, average fiber length 77.3 μm (average fiber diameter and average fiber length are the average values of 20 measurements taken using a scanning electron microscope)

3HB: R-3-hydroxybutyric acid synthesized by the following method (method of synthesis of 3HB)
An aqueous solution of R-3-hydroxybutyric acid produced according to the method described in Example 1 of JP 2019-176839 A was concentrated until no water was released using an evaporator set at 70° C. 30% by mass of ethyl acetate and about 0.1% by mass of seed crystals of R-3-hydroxybutyric acid were added to the concentrated solution, which was then left overnight at 4° C., filtered, and dried.

PHBH: Made by Kaneka Corporation, product name "AONILEX X131A".

(FT-IR analysis)
The molecular structures and functional group introduction of the raw material 3HB, raw material cellulose, and modified cellulose were measured before and after the reaction using an FT-IR analyzer to confirm the introduction of 3HB. The FT-IR analyzer used was a Nicoleti S5 spectrometer (manufactured by Thermo Fisher SCIENTIFIC Co., Ltd.) equipped with an iD5ATR attachment. The measurement range was 4000 to 400 cm ^-1 .

(Grafting rate of modified cellulose)
The modified cellulose was quantitatively analyzed by solid-state ¹³ C-NMR using a Bruker AVANCE III WB (manufactured by BRUKER) with the nuclide ¹³ C. FIG. 2 shows a chart of the solid-state ¹³ C-NMR spectrum of the modified cellulose, and the grafting ratio was calculated based on a comparison between the carbon amount of C7,11 (value based on integral intensity) and the carbon amount of C1. That is, since 3HB bonded to cellulose is an oligomer, the number of graft chains was calculated by the carbon amount of C7,11/(n+1) (n+1 indicates the average degree of polymerization of 3HB) and compared with the carbon amount of C1, which corresponds to the number of glucose units in the cellulose main chain. In detail, the grafting ratio was calculated by the carbon amount of C7,11/(n+1)/carbon amount of C1×100%.

(Average degree of polymerization of 3HB n+1)
The modified cellulose was quantitatively analyzed by solid-state ¹³ C-NMR using a Bruker AVANCE III WB (manufactured by BRUKER) with ¹³ C as the nuclide to measure the average degree of polymerization (n+1) of 3HB.

(Tensile test)
The resin composition was subjected to measurement of Young's modulus, maximum stress, and breaking elongation using a small tabletop testing machine ("EZ-Graph" manufactured by Shimadzu Corporation) in accordance with JIS K 7161. The test conditions were a crosshead speed of 10 mm/min, a test piece length of 20 mm, a width of 2 mm, and a thickness of approximately 0.1 mm. A load cell of 100 N was used.

Example 1
1 g of cellulose and 5 g of 3HB were mixed and reacted for 4 hours under conditions of 110°C and -97 kPa (G). An excess amount of methanol was added to the reaction product, which was then stirred and filtered. An excess amount of chloroform was then added, which was then stirred and filtered, followed by drying under reduced pressure at room temperature to obtain powdered 3HB-modified cellulose (3HB-C).

Example 2
3HB-C was obtained by reaction and washing under the same conditions as in Example 1, except that the amount of 3HB was changed to 10 g.

Example 3
3HB-C was obtained by reaction and washing under the same conditions as in Example 1, except that the amount of 3HB was changed to 15 g.

Example 4
3HB-C was obtained by reaction and washing under the same conditions as in Example 1, except that the amount of 3HB was changed to 30 g.

Example 5
The reaction and washing were carried out under the same conditions as in Example 2, except that the reaction time was changed to 2 hours, to obtain 3HB-C.

Example 6
The reaction and washing were carried out under the same conditions as in Example 2, except that the reaction time was changed to 8 hours, to obtain 3HB-C.

The results of FT-IR analysis of 3HB-C obtained in Examples 1 to 6 are shown in Figure 1 together with the results for the raw material 3HB and raw material cellulose. As is clear from Figure 1, in the 3HB-C obtained in Examples 1 to 6, the peak at around 1700 cm ^-1 derived from the carboxylic acid of 3HB disappeared, and a peak derived from an ester was observed at around 1730 cm ^-1 , confirming that 3HB and cellulose formed an ester.

Furthermore, for the 3HB-C obtained in Examples 1 to 6, the grafting ratio and average polymerization degree were calculated from solid ¹³ C-NMR, and the results are shown in Table 1.

It was confirmed from the results of solid-state ^13C -NMR that the modified celluloses obtained in Examples 1 to 6 had 3HB bonded to the 6th carbon position (C6) of the anhydroglucose unit at a grafting rate of about 7 to 15% and an average degree of polymerization of about 3 to 4.

Comparative Example 1
The PHBH was hot pressed at 170° C. and 20 MPa to obtain a film for tensile testing.

Comparative Example 2
0.01 g of raw cellulose and 1.99 g of PHBH were added to chloroform, stirred, and reprecipitated by adding an excess amount of methanol. The precipitate was filtered and dried under reduced pressure at room temperature (about 20°C) to obtain a cellulose/PHBH composite powder. This powder was then hot pressed at 170°C and 20 MPa to obtain a film for tensile testing.

Comparative Example 3
A film for tensile testing was obtained in the same manner as in Comparative Example 2, except that the amount of raw cellulose was 0.02 g and the amount of PHBH was 1.98 g.

Comparative Example 4
A film for tensile testing was obtained in the same manner as in Comparative Example 2, except that the amount of raw cellulose was 0.04 g and the amount of PHBH was 1.96 g.

Example 7
0.01 g of 3HB-C and 1.99 g of PHBH obtained in Example 2 were put into chloroform, stirred, and reprecipitated by adding an excess amount of methanol. The precipitate was filtered and dried under reduced pressure at room temperature to obtain a 3HB-C/PHBH composite powder. Next, this powder was hot pressed under conditions of 170°C and 20 MPa to obtain a film for tensile testing.

Example 8
A film for tensile testing was obtained in the same manner as in Example 7, except that the amount of 3HB-C was 0.02 g and the amount of PHBH was 1.98 g.

Example 9
A film for tensile testing was obtained in the same manner as in Example 7, except that the amount of 3HB-C was 0.04 g and the amount of PHBH was 1.96 g.

The films obtained in Examples 7 to 9 and Comparative Examples 1 to 4 were subjected to tensile tests, and the results are shown in Table 2.

As is clear from the results in Table 2, the composite films of the examples had improved Young's modulus and maximum stress compared to Comparative Example 1, which did not contain cellulose. In addition, a comparison of Comparative Examples 2 to 4 with Examples 7 to 9 shows that the Young's modulus, maximum stress, and elongation at break were all improved by modifying cellulose. In other words, the results of the tensile test clearly show that the 3HB-C/PHBH composite film has improved elastic modulus, strength, and elongation at break compared to the raw cellulose/PHBH composite material. Figure 3 shows the results of the tensile test on the composite films obtained in Comparative Examples 1 and 2 and Example 7, Figure 4 shows the results of the tensile test on the composite films obtained in Comparative Examples 1, 3, and Example 8, and Figure 5 shows the results of the tensile test on the composite films obtained in Comparative Examples 1, 4, and Example 9. In all of these figures, it is easy to see that the tensile properties are improved by modifying cellulose.

Figure 6 shows SEM photographs of the tensile fracture surfaces of the composite films obtained in Example 8 (PHBH/3HB-C) and Comparative Example 4 (PHBH/raw cellulose). Enlarged views are also provided for both the examples and comparative examples so that the interface can be clearly seen. As is clear from Figure 6, in Comparative Example 4, peeling occurred at the interface between the raw cellulose and PHBH, but in Example 8, no such peeling was observed at the interface between 3HB-C and PHBH. For example, in the enlarged view of the photograph of Example 8, in which 3HB-C was blended, the interface between 3HB-C and PHBH can be clearly observed to be compatible, whereas in the enlarged view of the photograph of Comparative Example 4, a large hollow gap has occurred at the interface. In other words, it was found that by modifying cellulose with 3HB, 3HB (oligomer) on the cellulose surface functions as a compatibilizer.

The modified cellulose of the present disclosure can be used as an additive for resins, particularly as a reinforcing material. The resin composition of the present disclosure can be used to form various molded articles, such as daily necessities, electrical and electronic devices, and building materials, depending on the type of resin. In particular, when used as a reinforcing material for biodegradable plastics, the modified cellulose exhibits biodegradability under aerobic and anaerobic conditions (particularly under anaerobic conditions), and therefore the resin composition containing the modified cellulose fiber is useful for disposable products such as tableware (straws, cups, plates, chopsticks, spoons, forks, etc.) and packaging materials (e.g., containers for food, daily necessities, electrical and electronic devices and parts; bags such as plastic shopping bags, Eco Bags (registered trademark), and garbage bags).

Claims (11)

A modified cellulose in which 3-hydroxybutyric acid or its oligomer having an average degree of polymerization of 1.5 or more is bonded to cellulose fibers. The modified cellulose according to claim 1, in which the 3-hydroxybutyric acid or its oligomer is ester-bonded to the 6-position of the anhydroglucose unit of the cellulose fiber. 3. The modified cellulose according to claim 1, wherein the average degree of polymerization of said 3-hydroxybutyric acid or its oligomer is from 1.5 to 10. The modified cellulose according to any one of claims 1 to 3, wherein the grafting rate of the 3-hydroxybutyric acid or its oligomer is 5 to 30 mol %. The modified cellulose according to any one of claims 1 to 4, wherein the 3-hydroxybutyric acid is R-3-hydroxybutyric acid. A resin composition comprising the modified cellulose according to any one of claims 1 to 5 and at least one resin selected from thermoplastic resins and curable resins. The resin composition according to claim 6, wherein the resin includes a biodegradable plastic. The resin composition according to claim 6 or 7, wherein the resin is a homopolymer or copolymer of at least one monomer selected from hydroxyalkanoic acid and lactone. The resin composition according to any one of claims 6 to 8, wherein the proportion of the modified cellulose is 0.1 to 20 parts by mass per 100 parts by mass of the resin. A method for improving the mechanical properties of a resin by blending the modified cellulose described in any one of claims 1 to 5 with the resin. The method according to claim 10, wherein the resin is a biodegradable plastic.

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