JP7789341B2 - Method for producing thermoplastic resin composition, thermoplastic resin composition, and acylated plant fiber composition - Google Patents

Description

The present invention relates to a method for producing a thermoplastic resin containing acylated plant fibers that is light-colored and has excellent mechanical properties, a thermoplastic resin composition, and an acylated plant fiber composition.

Traditionally, carbon fiber and glass fiber have been widely used as reinforcing materials for molding resins. However, carbon fiber is flame-retardant, making it unsuitable for thermal recycling and expensive. Glass fiber is also relatively inexpensive, but disposal presents problems.

On the other hand, plant fibers are relatively inexpensive and have excellent thermal recycling properties, so the development of technology to use them as a reinforcing material for resins is being considered. However, because hydrophilic plant fibers have low dispersibility in hydrophobic resins, plant fibers added to resins tend to clump together, preventing the reinforcing effect from being achieved and instead causing a deterioration in mechanical properties such as strength.

In response to these issues, various studies have been conducted to improve the dispersibility of plant fibers in resins. Among these, acetylated cellulose has been actively studied because it has improved heat resistance compared to unmodified cellulose. Patent Document 1 discloses a composite of resin and chemically modified cellulose fine fibers, such as those obtained by acetylation, with a thermal decomposition onset temperature (TD) of 270°C or higher, a number-average fiber diameter of 10 nm to less than 1 μm, and a crystallinity of 60% or higher. Patent Document 2 also discloses a fiber-reinforced resin composition containing (A) microfibrillated cellulose fibers, (B) plant fibers, and (C) a thermoplastic resin, and states that both (A) and (B) may be chemically modified. The examples include acetylated microfibrillated plant fibers.

Patent Document 3 discloses a method for producing cellulose esters in which cellulose is acetylated using sulfuric acid as a catalyst, and then a base such as an alkali metal compound, alkaline earth metal compound, transition metal compound, or ammonia is added.

However, when using these methods, unreacted modifiers and catalysts used for modification coexist during melt-kneading with the thermoplastic resin (hereinafter sometimes simply referred to as "kneading"), which can cause the cellulose to become short fibers, making it impossible to achieve the desired mechanical properties, or can cause discoloration, impairing the appearance. Therefore, in either case, these must be removed by washing or other methods, which poses issues such as increased production time and costs associated with the removal process.

International Publication No. 2019/230970 Japanese Patent Application Laid-Open No. 2020-075950 Japanese Patent Application Laid-Open No. 2006-089574

The present invention aims to provide a thermoplastic resin composition that suppresses discoloration of the thermoplastic resin composition and has better mechanical properties than conventional compositions. Another object of the present invention is to provide an acylated plant fiber composition containing acylated plant fiber and alkaline earth metal salts of phosphoric acids in specific ratios as one embodiment of a raw material used in the production of the thermoplastic resin composition.

The inventors conducted extensive research in light of the above-mentioned problems and discovered that using phosphoric acids as a catalyst when modifying plant fibers with an acylating agent makes it possible to efficiently obtain acylated plant fibers with the desired degree of substitution without shortening the fibers; that neutralizing the phosphoric acids remaining in the acylated plant fibers obtained in this manner with a specific alkaline earth metal compound makes the fibers less likely to discolor even when kneaded directly with a thermoplastic resin without removing the catalyst; and that kneading acylated plant fibers with a thermoplastic resin in the presence of an alkaline earth metal salt of a phosphoric acid results in improved mechanical properties compared to a thermoplastic resin composition obtained in the absence of the salt, thereby completing the present invention.

That is, the present invention provides:
<1> A method for producing a thermoplastic resin composition, comprising kneading (A) an acylated plant fiber and (B) a thermoplastic resin in the presence of (C) an alkaline earth metal salt of a phosphoric acid;
<2> A method for producing a thermoplastic resin composition, comprising (c-1) acylating plant fibers in the presence of phosphoric acids, (c-2) mixing the resulting mixture with an alkaline earth metal hydroxide and/or carbonate, and then kneading the resulting mixture with (B) a thermoplastic resin;
<3> (c-2) The method for producing a thermoplastic resin composition according to <2>, wherein the hydroxide and/or carbonate of an alkaline earth metal is magnesium hydroxide and/or calcium carbonate.
<4> The method for producing a thermoplastic resin composition according to <1> or <2>, wherein the phosphoric acid is phosphoric acid and/or polyphosphoric acid.
<5> The method for producing a thermoplastic resin composition according to <1> or <2>, wherein the alkaline earth metal is calcium and/or magnesium.
<6> The method for producing a thermoplastic resin composition according to <1> or <2>, wherein (B) the thermoplastic resin is a polyolefin and/or a polylactic acid.
<7> An acylated plant fiber composition comprising (A) an acylated plant fiber and (C) an alkaline earth metal salt of a phosphoric acid in a ratio of (A)/(C) = 100/1 to 50 (mass%);
<8> A thermoplastic resin composition comprising (A) an acylated plant fiber, (B) a thermoplastic resin, and (C) an alkaline earth metal salt of a phosphoric acid in a ratio of (A)/(B)/(C) = 1 to 60/10 to 98.99/0.01 to 30 (mass%).
<9> (C) The composition according to <7> or <8>, characterized in that in the alkaline earth metal salt of a phosphoric acid, the phosphoric acid is phosphoric acid and/or polyphosphoric acid, and the alkaline earth metal is calcium and/or magnesium.
is.

The manufacturing method of the present invention can provide a thermoplastic resin composition that suppresses coloration and has better mechanical properties than conventional compositions. It can also provide an acylated plant fiber composition that is useful as a raw material for the manufacture of thermoplastic resin compositions.

In the method for producing a thermoplastic resin composition of the present invention, (A) acylated plant fibers and (B) thermoplastic resin are kneaded in the presence of (C) an alkaline earth metal salt of a phosphoric acid.

<(A) Acylated Plant Fiber>
In the present invention, the acylated plant fiber (A) (hereinafter sometimes abbreviated as component (A)) is not particularly limited as long as it is a plant fiber modified by adding an acylating agent (a). However, the modification rate (degree of substitution, DS) of the acylated plant fiber is preferably 0.02 to 2.0, more preferably 0.05 to 1.5, and even more preferably 0.06 to 1.0. Compared to unmodified plant fibers, acylated plant fibers have higher heat resistance and hydrophobicity, making them more easily dispersed in thermoplastic resins. Furthermore, acylation inhibits intramolecular and intermolecular hydrogen bonding by the hydroxyl groups of the cellulose that constitutes the plant fiber, making it easier to micronize and defibrate when kneaded with the resin. The degree of substitution (DS) can be analyzed by various analytical methods, such as the weight gain method, elemental analysis, neutralization titration, FT-IR, and two-dimensional NMR ( ^1H and ^13C -NMR). In the present invention, the value measured by FT-IR using the following method is taken as the degree of substitution.

<Measurement of Degree of Substitution (DS) of Acylated Plant Fiber>
FT-IR measurements were performed on acylated plant fibers with multiple known degrees of substitution (DS), and a calibration curve was created from the peak of the ester bond at 1730 cm ^-1 and the degree of substitution. Next, FT-IR measurements were performed on the acylated plant fibers produced in the examples, and the degree of substitution was calculated from the relationship between the obtained peak of the ester bond and the calibration curve. Since acetic anhydride was used as the acylating agent in the examples, acetylated plant fiber was used as the acylated plant fiber to create the calibration curve. The degree of substitution of the acetylated plant fiber was calculated by adding an alkali to the acetylated plant fiber and titrating the amount of acetic acid generated by hydrolyzing the ester bond.

Plant fibers include wood, bamboo, hemp, jute, kenaf, cotton, and beet fiber. Preferred plant fibers include wood, such as pine, cedar, cypress, eucalyptus, and acacia. Pulp, paper, and recycled paper obtained from these materials can also be used. Plant fibers that do not contain lignin are preferred in order to prevent discoloration of the resin composition.

The plant fibers may be either microfibrillated or nanofibrillated by pre-defibration using a bead mill, high-pressure homogenizer, jet mill, ultrasonic agitator, or the like, or may be undefibrated. Undefibrated plant fibers may be acylated to produce (A) acylated plant fibers, which may then be defibrated when kneaded with (B) thermoplastic resin. Plant fibers that have been microfibrillated or nanofibrillated in advance have high water retention properties, which not only require a great deal of energy for dehydration but also tend to agglomerate during drying. Therefore, it is preferable that the (A) acylated plant fibers be undefibrated. When kneaded with component (B) in the presence of component (C), agglomeration is unlikely to occur, making it easier to obtain a thermoplastic resin composition with excellent physical properties. Furthermore, defibrating the plant fibers during kneading is more preferable because it improves mechanical properties.

(A) When acylated plant fibers are pre-defibrated, the defibrated state can be confirmed as follows.
Acylated plant fibers before and after defibration were added to a mixture of water and alcohol to a concentration of 0.02-0.1%, and then thoroughly dispersed by ultrasonic treatment to prepare dispersions. Next, one drop of each dispersion was placed in a glass Petri dish, and after removing excess liquid with a cover glass, the dish was observed at 100-500x magnification using an optical microscope to measure the fiber length and fiber diameter of the acylated plant fibers before and after defibration. Differences in fiber length and fiber diameter before and after defibration were confirmed. Because nano-defibration cannot be seen with a polarizing microscope, the resin was washed out of the thermoplastic resin composition using hot xylene, etc., and the fiber diameter of the defibrated fibers was measured by observation with an electron microscope.

The defibrated state of the (A) acylated plant fiber in the thermoplastic resin composition can be confirmed by taking 0.2 g of the thermoplastic resin composition, applying a pressure of 10 MPa at 170°C in a heat press (manufactured by Toyo Seiki Seisakusho), and visually counting the number of coarse particles of 0.5 mm or larger on the pressed film. A practical level is one with fewer than three particles.

<(B) Thermoplastic resin>
The thermoplastic resin (B) (hereinafter sometimes abbreviated as component (B)) is not particularly limited as long as it is one commonly used in molding material applications. Examples of thermoplastic resins include polyamide resins such as nylon; polyolefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, and ethylene-vinyl acetate copolymer; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polylactic acid; acrylic resins such as polymethyl methacrylate and polyethyl methacrylate; styrene resins such as polystyrene and (meth)acrylate-styrene resin; ionomer resins, cellulose resins, and other thermoplastic resins, as well as thermoplastic elastomers such as olefin elastomers, vinyl chloride elastomers, styrene elastomers, urethane elastomers, polyester elastomers, and polyamide elastomers, and mixtures of two or more of these. Preferred are polyolefin resins and polylactic acid.

<(C) Alkaline Earth Metal Salt of Phosphates>
When components (A) and (B) are kneaded together in the presence of (C) an alkaline earth metal salt of a phosphoric acid (hereinafter sometimes abbreviated as component (C)), the mechanical properties of the resulting thermoplastic resin composition are improved compared to kneading in the absence of component (C). Examples of component (C) include beryllium phosphate, magnesium phosphate, magnesium hydrogen phosphate, magnesium dihydrogen phosphate, calcium phosphate, calcium hydrogen phosphate, calcium dihydrogen phosphate, calcium pyrophosphate, strontium phosphate, barium phosphate, magnesium polyphosphate, and calcium polyphosphate. Preferably, the alkaline earth metal is a salt of at least one selected from the group consisting of calcium and magnesium with a phosphoric acid, more preferably magnesium phosphate, calcium phosphate, calcium polyphosphate, or magnesium polyphosphate, and even more preferably magnesium phosphate or calcium phosphate.

<Kneading method>
The method for kneading components (A) and (B) in the presence of component (C) can be any of the various methods used for kneading thermoplastic resins, such as melt kneading in which the components are heated while being mechanically ground using a single- or multi-screw kneader, a Labo Plasto Mill, a pressure kneader, a Banbury mixer, a ball mill, or any of a variety of mills.

When using a multi-screw kneader, a twin-screw kneader is preferred due to its versatility and availability. Either a co-rotating or counter-rotating twin-screw extruder can be used as the twin-screw kneader. The screw length/screw diameter of the twin-screw kneader used in the present invention is usually about 15 to 60, preferably about 30 to 60. The screw may also have a dam structure in one or more locations.

The kneading temperature is not particularly limited as long as it is a temperature at which component (B) can be melted. When component (A) is defibrated using a kneader during kneading, the number of passes (number of passes) varies depending on the fiber diameter and length of the desired plant fibers, the desired physical properties of the thermoplastic resin composition, etc., but is usually about 1 to 8 times, preferably about 1 to 4 times, and more preferably about 1 to 2 times. If the number of passes is too high, not only will productivity decrease, but the plant fibers themselves may also thermally deteriorate, leading to a deterioration in the color of the thermoplastic resin composition.

In the production of the thermoplastic resin composition of the present invention, specifically, any one of the following embodiments (i) to (iii) can be adopted.
Aspect (i): (c-1) Plant fibers are acylated by adding (a) an acylating agent to the plant fibers in the presence of phosphoric acids, and then (c-2) an alkaline earth metal hydroxide and/or carbonate is mixed therewith to obtain a mixture containing (A) acylated plant fibers and (C) an alkaline earth metal salt of phosphoric acids, which is then kneaded with (B) a thermoplastic resin.
Mode (ii): (A) Acylated plant fibers and (C) an alkaline earth metal salt of phosphoric acid are mixed, and then kneaded with (B) a thermoplastic resin.
Mode (iii): (A) acylated plant fibers, (B) a thermoplastic resin, and (C) an alkaline earth metal salt of a phosphoric acid are mixed and then kneaded.

<When mode (i) is adopted>
(c-1) Plant fibers are acylated with an acylating agent (a) in the presence of phosphoric acids, followed by the addition of an alkaline earth metal hydroxide and/or carbonate (c-2) to obtain a mixture containing components (A) and (C), which is then kneaded with component (B) using the kneading method described above. Using phosphoric acids as catalysts in the acylation reaction not only enables acylated plant fibers with the desired degree of substitution to be obtained without fiber shortening compared to when sulfuric acid is used as a catalyst, but also suppresses discoloration of the resulting acylated plant fibers. Furthermore, compared to when no catalyst is used or when a catalyst other than phosphoric acids is used, the efficiency of modification is improved, allowing for a reduction in the amount of acylating agent used and a shortened reaction time. Furthermore, since the phosphoric acids are neutralized during kneading with component (B), washing is not necessary, and since the resulting mixture contains component (C), which is essential for kneading, it can be used directly in the kneading step.

<(c-1) Phosphoric acids>
Examples of (c-1) phosphoric acids used as catalysts in the acylation reaction include phosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid, monoalkyl phosphate esters, dialkyl phosphate esters, sodium phosphite, and sodium hypophosphite. Phosphoric acid and polyphosphoric acid are preferred. From the viewpoints of reaction efficiency and the amount of salts with (c-2) alkaline earth metal hydroxides and/or carbonates produced, which will be described later, it is preferable to use 0.4 to 6% by mass of phosphoric acids based on the plant fiber.

<(a) Acylating Agent>
Examples of the (a) acylating agent include acid anhydrides such as acetic anhydride, propionic anhydride, butyric anhydride, valeric anhydride, hexanoic anhydride, decanoic anhydride, benzoic anhydride, and stearic anhydride; and polycarboxylic acid anhydrides such as maleic anhydride, succinic anhydride, phthalic anhydride, alkyl or alkenyl succinic anhydride, maleic anhydride-modified polyolefin, and maleic anhydride-modified polybutadiene. Among these, from the viewpoint of compatibility with the resin, acetic anhydride, propionic anhydride, and alkyl or alkenyl succinic anhydride are preferred, and acetic anhydride is particularly preferred from the viewpoint of ease of availability and ease of introduction. From the viewpoint of the degree of substitution (DS) of the plant fiber, it is preferable to use the (a) acylating agent in an amount of 50 to 120% by mass relative to the plant fiber.

The reaction temperature when acylating plant fibers with (a) the acylating agent is preferably about 20 to 160°C, more preferably about 40 to 120°C, and even more preferably about 60 to 100°C. Higher temperatures increase the reaction efficiency between the plant fibers and (a) the acylating agent, but if the temperature is too high, some of the plant fibers may deteriorate, so it is preferable to keep the temperature within the above range.

(a) When acylating plant fibers with an acylating agent, a solvent may be used as long as it does not interfere with the acylation reaction. The solvent is not particularly limited, but examples include amide solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone (NMP), and hexamethylphosphoric acid triamide; sulfur-based solvents such as dimethyl sulfoxide (DMSO); ether solvents such as dimethyl and diethyl derivatives of alcohols such as ethylene glycol, propylene glycol, and polyethylene glycol; halogen-based solvents such as methylene chloride, chloroform, and carbon tetrachloride; ketone solvents such as acetone and methyl ethyl ketone (MEK); cyclic ether solvents such as tetrahydrofuran (THF) and dioxane; hydrocarbons such as hexane and heptane; and aromatic solvents such as benzene and toluene. It is preferable to remove the solvent used in the acylation reaction after the reaction or simultaneously with the kneading with component (B).

<(c-2) Hydroxide and/or Carbonate of Alkaline Earth Metal>
Examples of alkaline earth metal hydroxides and/or carbonates used to neutralize the (c-1) phosphoric acid used as a catalyst for the acylation reaction include beryllium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, strontium hydroxide, beryllium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate, and barium carbonate. Magnesium hydroxide and calcium carbonate are preferred. The alkaline earth metal hydroxides and/or carbonates also contribute to neutralization of any remaining unreacted acylating agent acid. Therefore, they are preferably used in excess of the equivalent amount of the phosphoric acid, more preferably 1 to 5 equivalents relative to the acid equivalent of the phosphoric acid. Neutralizing the phosphoric acid and unreacted acylating agent with an alkaline earth metal hydroxide and/or carbonate not only makes it possible to knead them with the subsequent component (B) without removing them, but also allows them to be utilized as the component (C), which is a neutralized salt with the (c-1) phosphoric acid, thereby enabling an acylated plant fiber composition to be obtained by pre-mixing the component (A) with the component (C) used in the production method for the thermoplastic resin composition of the present invention.

When mode (ii) is employed, components (A) and (C) are mixed in advance, and then kneaded with component (B) using the kneading method described above. When components (A) and (C) are mixed, component (C) may be added as a powder or as an aqueous dispersion. The mixing temperature may be room temperature or heated, and is typically 10 to 100°C, preferably 20 to 80°C. There are no particular restrictions on the mixing vessel, but to prevent localization of component (C), a reaction vessel equipped with a stirring device is preferred, such as a planetary mixer, Banbury mixer, or Henschel mixer.

When embodiment (iii) is adopted, components (A), (B), and (C) are mixed and then kneaded using the kneading method described above.

In aspects (i) and (ii), when the acylated plant fiber composition in which component (A) is premixed with component (C) is stored or provided to a customer, it is preferable to include (A) acylated plant fiber and (C) alkaline earth metal salt of phosphates in any ratio within the range of (A)/(C) = 100/1 to 50 (mass%) depending on the intended use, since the amounts of the components can be easily adjusted when kneading with component (B).

The ratio of (A) acylated plant fiber, (B) thermoplastic resin, and (C) alkaline earth metal salt of phosphates varies depending on the application, but is typically (A)/(B)/(C) = 1-60/10-98.99/0.01-30 (mass%), preferably (A)/(B)/(C) = 2-50/25-97.9/0.1-25 (mass%), and more preferably (A)/(B)/(C) = 5-40/40-94.8/0.2-20 (mass%).

<(D) Compatibilizer>
In producing the thermoplastic resin composition of the present invention, a compatibilizer may be further used during kneading of components (A) to (C), provided that the effects of the present invention are not impaired. Examples of the (D) compatibilizer include maleic anhydride-modified polyethylene resin, acrylic acid-modified polyethylene resin, maleic anhydride-modified polypropylene resin, maleic anhydride-modified ethylene vinyl acetate resin, and epoxy group-containing resins (e.g., copolymers of glycidyl methacrylate and ethylene). Commercially available compatibilizers may also be used. It is also preferable to premix the compatibilizer with component (A) or (B) and then knead with the other components, as this facilitates more uniform mixing. The amount of (D) compatibilizer used is preferably in the range of 10 to 50 mass% relative to component (B), from the viewpoints of uniform mixing of components (A) and (B) and the mechanical properties of the resulting thermoplastic resin composition.

The thermoplastic resin composition of the present invention may contain various additives such as dispersants, surfactants, antioxidants, flame retardants, pigments, dyes, inorganic fillers, plasticizers, UV absorbers, light stabilizers, nucleating agents, and foaming aids, as long as the effects of the present invention are not impaired.

The thermoplastic resin composition of the present invention can be molded into a molded article using various molding methods, such as injection molding, extrusion molding, pressing molding, blow molding, pressure molding, compression molding, and 3D printing. Examples of uses for the molded article include interior and exterior materials and housings for transportation machinery such as automobiles, motorcycles, bicycles, trains, drones, rockets, aircraft, and ships; energy machinery such as wind turbines and hydroelectric generators; housings for home appliances such as air conditioners, refrigerators, vacuum cleaners, microwave ovens, AV equipment, digital cameras, and personal computers; electronic circuit boards; housings for communication devices such as mobile phones and smartphones; medical equipment such as crutches and wheelchairs; shoes such as sneakers and business shoes; tires; balls for ball games; ski boots; snowboards; golf clubs; and protectors. , sporting goods such as fishing line and artificial bait, outdoor goods such as tents and hammocks, civil engineering and construction materials such as electrical wire coverings, water pipes and gas pipes, building materials such as pillars, flooring, decorative panels, window frames and insulation, furniture such as bookshelves, desks and chairs, industrial robots, household robots, hot melt adhesives, filaments and support agents for laminated 3D printers, binder resins for recording materials such as paints, inks and toners, packaging materials such as film and tape, resin containers such as PET bottles, and household goods such as eyeglass frames, trash cans and mechanical pencil cases.

The following describes examples of the present invention. However, the present invention is not limited to these examples. Unless otherwise specified, "parts" refers to "parts by mass."

<Physical property measurement method>
The methods for measuring physical properties used in some of these examples are as follows.

<Measurement of Degree of Substitution (DS) of Acylated Plant Fiber>
FT-IR measurements were performed on acylated plant fibers with multiple known degrees of substitution (DS), and a calibration curve was created from the peak of the ester bond at 1730 cm ^-1 and the degree of substitution. Next, FT-IR measurements were performed on the acylated plant fibers produced in the examples, and the degree of substitution was calculated from the relationship between the obtained peak of the ester bond and the calibration curve. Since acetic anhydride was used as the acylating agent in the examples, acetylated plant fiber was used as the acylated plant fiber to create the calibration curve. The degree of substitution of the acetylated plant fiber was calculated by adding an alkali to the acetylated plant fiber and titrating the amount of acetic acid generated by hydrolyzing the ester bond.

<Color measurement of acylated plant fibers>
Ten grams of the acylated plant fiber obtained in the production example was taken, and the lightness (L*) was measured using a colorimeter (Konica Minolta CM-600d). The higher the lightness, the better. However, since the color of the acylated plant fiber itself affects the color of the resin composition after melt-kneading, it is preferable that L* be 94 or higher.

<Color Measurement of Thermoplastic Resin Composition>
The color of the injection-molded articles of the acylated plant fiber-blended thermoplastic resin compositions obtained in the Examples and Comparative Examples was measured using a colorimeter to measure the L* of the injection-molded articles. An L* of 60 or more was considered to be at a practical level.

<Measurement of tensile strength of thermoplastic resin composition>
The thermoplastic resin composition obtained by employing the above-mentioned embodiment (i) was charged into an injection molding machine (manufactured by Imoto Manufacturing Co., Ltd.) to obtain a 1BA type dumbbell-shaped small test piece. The tensile strength (tensile modulus) of the obtained test piece was measured in accordance with JIS K 7161-1 using a tensile tester "Tensilon RTM-50 (manufactured by Orientec Co., Ltd.)."

<Confirmation of defibrated state of acylated plant fibers in thermoplastic resin composition>
0.2 g of the thermoplastic resin composition was sampled and pressed using a heat press (manufactured by Toyo Seiki Seisakusho) at 170°C and a pressure of 10 MPa to produce a pressed film. When three or more coarse particles of 0.5 mm or more were visually observed, the film was rated as x, and when 0 to 2 particles were visible, the film was rated as ◯. ◯ indicates a practical level.

<Production and Evaluation of Acylated Plant Fiber Compositions>
(Production Example 1)
166 parts by mass of 30% concentration bleached wood kraft pulp (NBKP) (solids content 50.0 parts by mass) into a clean container equipped with a stirrer, and 50.0 parts by mass of diethylene glycol diethyl ether (Hisorb EDE, manufactured by Toho Chemical Industry Co., Ltd.) were added and dehydrated under reduced pressure at 60 ° C. with stirring. Next, (a) 31.0 parts by mass of acetic anhydride (manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd., special grade) as an acylating agent, (c-1) 0.30 parts by mass of phosphoric acid (manufactured by Kanto Chemical Co., Ltd., first grade), diethylene glycol diethyl ether 30.0 parts by mass was added, and the mixture was stirred at normal pressure until a predetermined reaction rate was reached at 70 ° C., and then desolvation was carried out at 80 ° C. under reduced pressure. Furthermore, 20 parts by mass of an aqueous suspension containing 2.16 parts by mass of calcium carbonate (special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as (c-2) an alkaline earth metal hydroxide and/or carbonate was added, and after stirring for 30 minutes, the solvent was distilled off under reduced pressure at 130°C to obtain an acylated plant fiber composition (X-1) containing acetylated plant fiber and calcium phosphate.

(Production Example 2)
An acylated plant fiber composition (X-2) was obtained in the same manner as in Production Example 1, except that 2.14 parts by mass of polyoxyethylene lauryl ether phosphate (Phosphanol ML-220, manufactured by Toho Chemical Industry Co., Ltd.) was added instead of phosphoric acid.

(Production Example 3)
An acylated plant fiber composition (X-3) was obtained in the same manner as in Production Example 1, except that 0.91 parts by mass of calcium hydroxide (special grade reagent, manufactured by Junsei Chemical Co., Ltd.) was added instead of calcium carbonate.

(Production Example 4)
An acylated plant fiber composition (X-4) was obtained in the same manner as in Production Example 1, except that 1.26 parts by mass of magnesium hydroxide (manufactured by Junsei Chemical Co., Ltd., for chemical use) was added instead of calcium carbonate.

(Production Example 5)
An acylated plant fiber composition (X-5) was obtained in the same manner as in Production Example 1, except that highly beaten NBKP (hereinafter, sometimes referred to as "rNBKP") was used instead of NBKP.

(Comparative Production Example 1)
166 parts by mass of 30% concentration softwood bleached kraft pulp (NBKP) (solids content: 50.0 parts by mass) and 50.0 parts by mass of diethylene glycol diethyl ether were added to a clean container equipped with a stirrer, and the mixture was dehydrated under reduced pressure at 60° C. with stirring. Next, 31 parts by mass of acetic anhydride and 30 parts by mass of diethylene glycol diethyl ether were added, and the mixture was stirred at 70° C. under normal pressure for the same period as in the examples. The mixture was then heated to 130° C. under reduced pressure to remove the solvent, and a comparative acylated plant fiber composition (RX-1) was obtained.

(Comparative Production Example 2)
An acylated plant fiber composition for comparison (RX-2) was obtained in the same manner as in Production Example 1, except that 0.15 parts by mass of sulfuric acid (special grade reagent, manufactured by Kanto Chemical Co., Ltd.) was used instead of phosphoric acid.

(Comparative Production Example 3)
An acylated plant fiber composition (RX-3) was obtained in the same manner as in Production Example 1, except that calcium carbonate was not added.

ML-220: Polyoxyethylene lauryl ether phosphate (Phosphanol ML-220, manufactured by Toho Chemical Industry Co., Ltd.)
CaCO3: Calcium carbonate (special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
Ca(OH)2: Calcium hydroxide (special grade reagent, manufactured by Junsei Chemical Co., Ltd.)
Mg(OH)2: Magnesium hydroxide (Junsei Chemical Co., Ltd., chemical grade)

Table 2 shows the compositions of the acylated plant fiber compositions (X-1) to (X-5) and (RX-1) to (RX-3) obtained in Production Examples 1 to 5 and Comparative Examples 1 to 3, as well as the evaluation results of the degree of substitution (DS) of the acylated plant fiber (A) and the color of the acylated plant fiber compositions. Visual observation of the acylated plant fiber composition (RX-2) in Comparative Example 2 revealed that the acylated plant fibers had become shorter, and DS measurement by FT-IR revealed the presence of acylated plant fibers with a high degree of substitution in some areas.

The acylated plant fiber compositions of Examples 1 to 5, in which phosphoric acids were used as catalysts for the acylation reaction and then neutralized with alkaline earth metal hydroxides and/or carbonates without washing, had a higher degree of substitution (DS) for the same reaction time than Comparative Example 1, in which no phosphoric acids were used, and also had better color tone than Comparative Example 2, in which sulfuric acid was used as the acylation catalyst.

<Production of Thermoplastic Resin Composition (1)>
Example 6
As components (A) and (C), 40 parts by weight of acylated plant fiber composition (X-1), as component (B), 52 parts by weight of low-density polyethylene resin (SBC818, manufactured by Braskem, MFR 8.3 (190 ° C. 2.16 kg)), as component (D), 8 parts by weight of maleic anhydride-modified polyethylene (Hiwax (registered trademark) HW4052E, manufactured by Mitsui Chemicals, Inc.) were added to a batch mixer Labo Plastomill (manufactured by Toyo Seiki Seisaku-sho, Ltd.) and melt-kneaded at 150 ° C. and 100 rpm, and then removed. 50 parts by weight of the resulting kneaded mixture was added to 50 parts by weight of low-density polyethylene resin and further melt-kneaded at 150 ° C. and 100 rpm to prepare a thermoplastic resin composition containing 20% by weight of the acylated plant fiber composition.
The obtained thermoplastic resin composition was charged into an injection molding machine (manufactured by Imoto Manufacturing Co., Ltd.) to obtain a dumbbell-shaped test piece. Molding was performed at a cylinder temperature of 190° C. The evaluation results are shown in Table 3.

(Examples 7 and 8)
Dumbbell-shaped test pieces were obtained in the same manner as in Example 6, except that the acylated plant fiber composition (X-1) in Example 6 was replaced with the acylated plant fiber compositions (X-2) and (X-4), which were kneaded to prepare thermoplastic resin compositions. The evaluation results are shown in Table 3.

Example 9
25 parts by mass of acylated plant fiber composition (X-1) was washed with water and ethanol to wash off the phosphoric acid used as a catalyst, and then 1.65 parts by mass of calcium phosphate was added to prepare acylated plant fiber composition (X-6). This acylated plant fiber (X-6) was kneaded and molded in the same manner as in Example 6 to obtain dumbbell-shaped test pieces. The evaluation results are shown in Table 3.

(Comparative Example 4)
Dumbbell-shaped test pieces were obtained by kneading and molding in the same manner as in Example 6, except that the acylated plant fiber composition (X-1) in Example 6 was replaced with a comparative acylated plant fiber composition (RX-2). The evaluation results are shown in Table 3.

(Comparative Example 5)
Dumbbell-shaped test pieces were obtained by kneading and molding in the same manner as in Example 6, except that the acylated plant fiber composition (X-1) in Example 6 was replaced with a comparative acylated plant fiber composition (RX-3). The evaluation results are shown in Table 3.

Examples 6 to 9, in which components (A) and (B) were kneaded in the presence of component (C), were found to be superior in both tensile strength (tensile modulus) and color compared to Comparative Examples 4 and 5, which did not contain component (C). Furthermore, in Comparative Example 5, in which component (A) was kneaded directly with component (B) without removing the phosphoric acid, the defibration state of component (A) was inferior.

<Production of Thermoplastic Resin Composition (2)>
Example 10
40 parts by weight of acylated plant fiber composition (X-5) as components (A) and (C) and 60 parts by weight of polylactic acid resin (Ingeo 4032D, manufactured by Nature Works) as component (B) were placed in a batch kneader, Labo Plastomill (manufactured by Toyo Seiki Seisakusho, Ltd.), and melt-kneaded at 150°C and 50 rpm for 2 minutes, then at 100 rpm for 10 minutes, and then removed. 50 parts by weight of polylactic acid resin was added to 50 parts by weight of the resulting kneaded mixture, and further melt-kneaded at 150°C and 50 rpm for 1 minute, then at 100 rpm for 5 minutes to prepare a thermoplastic resin composition containing 20% by weight of the acylated plant fiber composition. The resulting thermoplastic resin composition was placed in an injection molding machine (manufactured by Imoto Seisakusho, Ltd.) to obtain dumbbell-shaped test pieces. Molding was performed at a cylinder temperature of 200°C. The tensile strength (tensile modulus) of the obtained test piece was measured using a tensile tester "Tensilon RTM-50 (manufactured by Orientec Co., Ltd.)." The evaluation results are shown in Table 4.

(Comparative Examples 6 and 7)
Dumbbell-shaped test pieces were obtained in the same manner as in Example 10, except that the acylated plant fiber composition (X-5) in Example 10 was replaced with the comparative acylated plant fibers (RX-2) and (RX-3), respectively, and the resulting mixture was kneaded to prepare a thermoplastic resin composition. The evaluation results are shown in Table 4.

It can be seen that Example 10, in which components (A) and (B) were kneaded in the presence of component (C), was superior in both tensile strength (tensile modulus) and color tone compared to Comparative Examples 6 and 7, which did not contain component (C).

Claims (6)

A method for producing a thermoplastic resin composition, comprising kneading (A) acylated plant fibers and (B) a thermoplastic resin in the presence of (C) an alkaline earth metal salt of phosphoric acid and/or polyphosphoric acid . A method for producing a thermoplastic resin composition, comprising: (c-1) acylating plant fibers in the presence of phosphoric acids; (c-2) mixing alkaline earth metal hydroxides and/or carbonates; neutralizing the (c-1) phosphoric acids; and then kneading the resulting mixture with a thermoplastic resin (B). The method for producing a thermoplastic resin composition according to claim 2, characterized in that (c-2) the hydroxide and/or carbonate of an alkaline earth metal is magnesium hydroxide and/or calcium carbonate. 3. The method for producing a thermoplastic resin composition according to claim 2 , wherein the phosphoric acid is phosphoric acid and/or polyphosphoric acid. The method for producing a thermoplastic resin composition according to claim 1 or 2, characterized in that the alkaline earth metal is calcium and/or magnesium. The method for producing a thermoplastic resin composition according to claim 1 or 2, characterized in that (B) the thermoplastic resin is a polyolefin and/or polylactic acid.