JP7483461B2 - Method for producing resin composition - Google Patents

Description

The present invention relates to a method for producing a resin composition containing finely divided acetylated cellulose fibers.

Fine fibrous cellulose obtained by finely disintegrating plant fibers includes microfibril cellulose and cellulose nanofibers, and is a fine fiber with a fiber diameter of about 1 nm to several tens of μm. Fine fibrous cellulose is lightweight, has high strength and high elasticity, and has a low coefficient of linear thermal expansion, so it is ideally used as a reinforcing material for resin compositions.

Fine fibrous cellulose is usually obtained in a state dispersed in water, and it is difficult to mix it evenly with resins, etc. For this reason, attempts have been made to chemically modify the cellulose raw material in order to improve its affinity and miscibility with resins.

For example, in Patent Document 1, a cellulose raw material and urea are heat-treated to obtain a cellulose raw material in which some of the hydroxyl groups of the cellulose are replaced with carbamate groups, and this is then finely divided by mechanical treatment to obtain fine fibrous cellulose. The fine fibrous cellulose obtained by this method is less hydrophilic than conventional fine fibrous cellulose and has a high affinity with resins with low polarity, so that it disperses uniformly in the resin and gives a composite with high strength. Patent Document 1 further discloses that the mixture of the heat-treated cellulose raw material and urea is washed with water or the like to remove unreacted residual urea, etc.

However, there was a demand for an efficient method for producing a resin composition that could produce a resin molded product with even better tensile strength and elongation.

JP 2019-1876 A

The object of the present invention is to provide an efficient method for producing a resin composition that can produce a resin molded product having excellent tensile strength and elongation.

The present invention provides the following:
(1) A method for producing a resin composition, comprising: a first kneading step of feeding acetylated cellulose fibers having a weighted average fiber length of 0.20 mm to 1.50 mm, a compatibilizing resin, and urea into a kneader and kneading the fibers; and a hot water washing step of washing the kneaded product obtained in the first kneading step with hot water.
(2) The method for producing a resin composition according to (1), wherein in the hot water washing step, the temperature of the hot water is 50 to 100° C., and the washing time is 10 minutes to 24 hours.
(3) The method for producing a resin composition according to (1) or (2), further comprising a second kneading step of kneading the mixture obtained after the hot water washing step with a diluent resin.
(4) The method for producing a resin composition according to any one of (1) to (3), wherein the amount of urea added to the kneader in the first kneading step is 10 to 100% by weight relative to 100% by weight of the total amount of cellulose fibers, which is the total amount of cellulose and hemicellulose not containing an acetylated portion of the acetylated cellulose fibers.
(5) The method for producing a resin composition according to any one of (1) to (4), wherein the amount of cellulose fiber content, which is a combination of cellulose and hemicellulose that does not contain an acetylated portion among the acetylated cellulose fibers fed into the kneader in the first kneading step, is 35 to 85% by weight based on the total amount of the cellulose fiber content, the compatibilizing resin, and the urea.

The present invention provides an efficient method for producing a resin composition that can produce a resin molded product with excellent tensile strength and elongation.

The manufacturing method of the resin composition of the present invention will be described below. In the present invention, "~" includes the end values. In other words, "X~Y" includes the values X and Y at both ends.

The method for producing a resin composition of the present invention includes a first kneading step in which acetylated cellulose fibers having a weighted average fiber length (length-average fiber length) of 0.20 mm to 1.50 mm, a compatibilizing resin, and urea are fed into a kneader and kneaded together, and a hot water washing step in which the kneaded product obtained in the first kneading step is washed with hot water.

(acetylated cellulose fiber)
The acetylated cellulose fiber used in the present invention has hydrogen atoms of hydroxyl groups present on the surface of the cellulose of the cellulose raw material substituted with acetyl groups (CH ₃ -CO-). Substitution with acetyl groups increases hydrophobicity and reduces aggregation during drying, improving workability and facilitating dispersion and defibration in the resin after kneading. From the viewpoints of workability and maintaining the crystallinity of the cellulose fiber, the degree of acetyl group substitution (DS) of the acetylated cellulose fiber is adjusted to preferably 0.4 to 1.3, more preferably 0.6 to 1.1.

(Cellulose raw material)
In the present invention, the cellulose raw material may be any material that is mainly composed of cellulose, and includes lignocellulose (NUKP). Examples of the cellulose raw material include pulp (bleached or unbleached wood pulp, bleached or unbleached non-wood pulp, refined linters, pulp derived from herbs such as jute, Manila hemp, and kenaf, etc.), natural cellulose such as cellulose produced by microorganisms such as acetic acid bacteria, regenerated cellulose obtained by dissolving cellulose in a solvent such as a cuprammonium solution or a morpholine derivative and then reprecipitating it, fine cellulose obtained by depolymerizing the cellulose raw material by subjecting the above-mentioned cellulose raw material to mechanical treatment such as hydrolysis, alkaline hydrolysis, enzymatic decomposition, explosion treatment, and vibration ball milling, and various cellulose derivatives that do not affect acetylation and modification.

Lignocellulose is a complex carbohydrate polymer that constitutes the cell walls of plants, and is composed mainly of the polysaccharides cellulose and hemicellulose, and the aromatic polymer lignin. The lignin content can be adjusted by delignifying or bleaching the raw material pulp, etc.

In the present invention, when pulp is used as the cellulose raw material, either unbeaten or beaten pulp may be used, but it is preferable to use beaten pulp. This is expected to increase the specific surface area of the pulp and the amount of urea reaction. The degree of beating is preferably a freeness (C.S.F) of 400 mL or less, more preferably about 100 mL to 200 mL. If the freeness exceeds 400 mL, the effect cannot be exerted, and if it is less than 100 mL, the cellulose fibers are damaged and shortened, which hinders the strength improvement effect when made into a reinforced resin. In addition, if the weighted average fiber length (length average fiber length) is in the range of 0.2 to 1.5 mm, preferably 0.3 to 1.0 mm, when the acetylation reaction, washing treatment, and drying treatment described later are performed by performing this beating treatment, the crushing process described later may be omitted.

The beating method may be, for example, mechanical (mechanical) treatment of the pulp fibers using a known beating machine. As the beating machine, any beating machine that is normally used when beating pulp fibers may be used, such as a Niagara beater, a PFI mill, a disc refiner, a conical refiner, a ball mill, a stone mill, a sand grinder mill, an impact mill, a high-pressure homogenizer, a low-pressure homogenizer, a Dyno mill, an ultrasonic mill, a Kanda grinder, an attritor, a vibration mill, a cutter mill, a jet mill, a disintegrator, a household juicer mixer, or a mortar. Among these, a Niagara beater, a disc refiner, or a conical refiner is preferred, and a disc refiner or a conical refiner is even more preferred.

(Acetylation reaction)
The acetylation reaction can be carried out in a short time by suspending the raw material in an anhydrous aprotic polar solvent capable of swelling the cellulose raw material, such as N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF), and using acetic anhydride, acetyl halide such as acetyl chloride, or the like in the presence of a base. The base used in this acetylation reaction is preferably pyridine, N,N-dimethylaniline, sodium carbonate, sodium bicarbonate, potassium carbonate, or the like, and more preferably potassium carbonate. In addition, it is also possible to carry out the reaction under conditions without using an anhydrous aprotic polar solvent or a base by using an excess of an acetylation reagent such as acetic anhydride.

The acetylation reaction is preferably carried out, for example, at room temperature to 100°C while stirring. After the reaction process, drying under reduced pressure may be carried out to remove the acetylation reagent. If the target degree of acetyl group substitution has not been reached, the acetylation reaction and the subsequent drying under reduced pressure may be repeated any number of times.

(Washing)
The acetylated cellulose fibers obtained by the acetylation reaction are preferably subjected to a washing treatment such as water replacement after the acetylation treatment.

(dehydration)
In the washing treatment, dehydration may be performed as necessary. The dehydration method may be a pressurized dehydration method using a screw press or a reduced pressure dehydration method by evaporation, but from the viewpoint of efficiency, a centrifugal dehydration method is preferred. Dehydration is preferably performed until the solid content in the solvent is about 10 to 60%.

(Drying)
The acetylated cellulose fiber used in the present invention is dried after the above-mentioned dehydration step and before being used in the grinding step, which is carried out as necessary. The drying can be carried out using, for example, a microwave dryer, a blower dryer, or a vacuum dryer (reduced pressure dryer), but a dryer capable of drying while stirring, such as a drum dryer, a paddle dryer, a Nauta mixer, or a batch dryer equipped with a stirring blade, is preferred. Drying is preferably carried out as long as possible until the moisture content of the acetylated cellulose fiber reaches about 0.1 to 10%, preferably about 1 to 5%.

In the present invention, urea is added simultaneously with the acetylated cellulose fiber and the compatibilizing resin to perform kneading. The mechanism of the phenomenon in which the strength of the acetylated cellulose fiber in the resin is improved by this operation has not yet been elucidated, but it is possible to explain part of it by considering it as follows. That is, urea is decomposed into ammonia and isocyanic acid when the temperature exceeds 135°C, but it is thought that by kneading urea simultaneously with the acetylated cellulose fiber, the unmodified hydroxyl groups newly appearing from inside the cellulose fiber by kneading react with the generated isocyanic acid to promote the formation of urethane bonds, and it is presumed that the hydrophobicity is increased compared to acetylated cellulose fiber not treated with urea. Furthermore, it is thought that by melt-kneading simultaneously with the compatibilizing resin containing an acid anhydride, the interaction between the amino groups newly introduced on the surface of the acetylated cellulose fiber by the urea treatment and the carboxylic acid of the compatibilizing resin is promoted, making it possible to form a stronger complex between the acetylated cellulose fiber and the compatibilizing resin.

The amount of urea required to achieve the above mechanism is preferably 10 to 100% by weight, more preferably 20 to 100% by weight, and even more preferably 30 to 70% by weight, relative to 100% by weight of the combined amount of cellulose and hemicellulose contained in the acetylated cellulose fiber (hereinafter sometimes referred to as the "cellulose amount").

(Compatibilizing resin)
In the present invention, the acetylated cellulose fiber and urea are kneaded by simultaneously adding a compatibilizing resin. The compatibilizing resin acts to uniformly mix and improve adhesion between the acetylated cellulose fiber and the dilution resin, which have different hydrophobicities. The compatibilizing resin used in the present invention (hereinafter, sometimes referred to as "master batch resin") is a polymer resin having a low molecular weight dicarboxylic acid capable of forming an acid anhydride such as maleic acid, succinic acid, or glutaric acid on a polyolefin chain such as polypropylene or polyethylene. Among them, it is preferable to use a resin mainly composed of maleic anhydride-modified polypropylene (MAPP) or maleic anhydride-modified polyethylene (MAPE) to which maleic acid is added, respectively, together with the dilution resin.

The factors that determine the characteristics of a compatibilizing resin are the amount of dicarboxylic acid added and the weight average molecular weight of the polyolefin resin that serves as the base material. A polyolefin resin with a large amount of dicarboxylic acid added increases compatibility with hydrophilic polymers such as cellulose, but the molecular weight of the resin decreases during the addition process, resulting in a decrease in the strength of the molded product. The optimal balance is an amount of dicarboxylic acid added of 20 to 100 mg KOH/g, and more preferably 45 to 65 mg KOH/g. If the amount added is small, there are fewer points in the resin that interact with the urea-derived amino groups. If the amount added is large, the strength of the reinforced resin will not be achieved due to self-aggregation caused by hydrogen bonds between carboxyl groups in the resin, or a decrease in the molecular weight of the olefin resin that serves as the base material due to excessive addition reactions. The molecular weight of the polyolefin resin is preferably 35,000 to 250,000, and more preferably 50,000 to 100,000. If the molecular weight is smaller than this range, the strength of the resin will decrease, and if it is larger than this range, the viscosity increases significantly when melted, reducing workability during kneading and causing molding defects.

The amount of the compatibilizing resin having the above characteristics added is preferably 10 to 70% by weight, more preferably 20 to 50% by weight, relative to the amount of cellulose. If the amount added exceeds 70% by weight, it is believed that the introduction of isocyanic acid derived from urea into the cellulose fiber is inhibited and the formation of a complex between the compatibilizing agent and urea is promoted, and the effects of the present invention are not achieved.

The compatibilizing resin may be used alone or as a mixture of two or more types. When used as a graft material of one or more types of polymers and polyolefin, the polyolefin resin that constitutes the graft material is not particularly limited, but polyethylene, polypropylene, polybutene, etc. can be used from the viewpoint of ease of manufacturing the graft material.

(First kneading step pretreatment-grinding step)
In the present invention, a crushing step may be provided prior to the first kneading step described below. By using acetylated cellulose fiber crushed in the crushing step, fiber agglomerates of the acetylated cellulose fiber are appropriately loosened when the acetylated cellulose fiber is fed into the kneader, and the occurrence of bridging (clogging) at the feed port (chute section) and poor engagement of the pulp with the screw can be suppressed.

The cellulose fibers crushed in the crushing process are preferably passed through a screen having a diameter of 1 mm or more and 5 mm or less, preferably 3 mm or more and 5 mm or less. The weighted average fiber length (length-average fiber length) of the acetylated cellulose fibers thus obtained is preferably about 0.20 to 1.5 mm, more preferably 0.30 to 1.0 mm.

It is preferable to use dried acetylated cellulose fibers to be ground in the grinding process in order to reduce the drying load during kneading.

(First kneading step)
In the first kneading step of the present invention, acetylated cellulose fibers having a weighted average fiber length of 0.20 to 1.50 mm, preferably 0.30 to 1.00 mm, compatibilizing resin, and urea are simultaneously charged into a kneader as essential components, and melt kneading is performed. If necessary, optional components such as antioxidants may be charged into the kneader simultaneously with the essential components. The weighted average fiber length (length average fiber length) of the acetylated cellulose fibers can be measured using a fiber tester (manufactured by L&W Co., Ltd.) or the like. When charging into the kneader, various commercially available feeders and side feeders can be used. When the compatibilizing resin, urea, and additives such as antioxidants used as necessary are powdered in advance, the acetylated cellulose fibers, compatibilizing resin, urea, and additives such as antioxidants can be mixed and charged using a commercially available mixer or the like before charging. Even if the compatibilizing resin is not powdered, it can be charged by preparing multiple feeders, such as a feeder for pellets and a feeder for acetylated cellulose fibers. In the first kneading step, the amount of the cellulose fiber content of the acetylated cellulose fiber fed into the kneader is preferably 35 to 85% by weight, and more preferably 40 to 65% by weight, based on the total amount of the cellulose fiber content, compatibilizing resin, and urea.

(Kneading machine)
The kneader used in the first kneading step of the present invention is preferably one that can melt-knead the compatibilizing resin and urea and has a strong kneading force that promotes nanoization of the acetylated cellulose fiber, and it is preferable to use a multi-axis kneader such as a twin-axis kneader or a four-axis kneader, and the parts that make up the screw should preferably include multiple kneaders or rotors. As long as the same kneading force as the above can be secured, kneaders such as bench rolls, Banbury mixers, kneaders, and planetary mixers may be used. In addition, in order to remove moisture and volatilized urea associated with the cellulose fiber, it is preferable to knead part or all of the inside of the kneader barrel under reduced pressure.

The melt-kneading temperature can be adjusted according to the melting temperature of the compatibilizing resin used. When using maleic anhydride-modified polypropylene suitable for the present invention as the compatibilizing resin, the temperature is preferably 135°C or higher to promote the decomposition of urea, and more preferably 160°C or higher at which the compatibilizing resin having dicarboxylic acid residues capable of forming acid anhydrides melts and some ends are ring-closed by dehydration. The above temperature setting generates isocyanic acid from urea and forms urethane bonds with unmodified hydroxyl groups on the cellulose fibers. This achieves the introduction of amino groups on the cellulose fibers, making it possible to promote interaction with the compatibilizing resin. In addition, the above temperature causes the dicarboxylic acid residues in the compatibilizing resin to ring-close to form acid anhydrides, which causes an esterification reaction with the acetylated cellulose fibers, making it possible to form a stronger resin composite. On the other hand, if the kneading temperature exceeds 200°C, the polypropylene resin, which is the base material, begins to deteriorate and its strength decreases.

In the present invention, the acetylated cellulose fibers, compatibilizing resin, and urea fed into the kneader in the first kneading step are melt-kneaded, and at least a portion of the acetylated cellulose fibers are defibrated by the shear force generated during this melt-kneading, thereby preparing a resin composition containing acetylated cellulose nanofibers.
The cellulose nanofibers are preferably fine fibers having a fiber diameter of about 1 to 1000 nm and an aspect ratio of at least 100. The resin composition according to the present invention may contain the cellulose nanofibers in a majority, and may also contain undefibrated fibers.

(Antioxidant)
In the present invention, when the melting point of the diluent resin described later is high, it is preferable to melt-knead an antioxidant in addition to the essential components by simultaneously feeding the antioxidant into the kneader in the first kneading step in order to suppress a decrease in strength due to decomposition of the pulp. For example, when polyamide 6 (PA6) (melting point: about 230°C) is used as the diluent resin, it is preferable to add an antioxidant. The antioxidant is not particularly limited, but examples include hindered phenol-based, hindered amine-based, phosphorus-based, and sulfur-based antioxidants, and it is preferable to use a hindered phenol-based antioxidant.

When an antioxidant is added, the amount to be added is not particularly limited as long as it is within a range that does not impair the effects of the present invention. However, since excessive addition can cause a decrease in strength, an amount of approximately 0.1 to 3% by weight, and more preferably 0.5 to 2% by weight, based on the cellulose fiber content is preferred.

(Hot water washing process)
The method for producing a resin composition of the present invention includes a hot water washing step in which the kneaded product obtained in the first kneading step is washed with hot water. By washing the kneaded product with hot water, it is possible to remove residual urea in the kneaded product and by-products derived from urea (biuret, cyanuric acid, melamine, etc.) that may be generated in small amounts in the kneading step, and it is believed that aggregation of fibers and the like caused by the residual urea and its by-products is eliminated. Therefore, the resin molded product obtained using the washed kneaded product has excellent tensile strength and elongation.

The method for washing the kneaded material obtained in the first kneading step using hot water may be any method that can stir or disperse the material, such as stirring using a three-one motor or using known stirrers or dispersers including an agitator, homomixer, homogenizer, mixer, etc.

The temperature of the hot water used for washing is 50 to 100°C, preferably 60 to 90°C, and more preferably 60 to 80°C, from the viewpoint of improving the solubility of the residual urea and its by-products. The total washing time is preferably 10 minutes to 24 hours, and considering the efficiency, 0.5 to 5 hours is more preferable, and 1 to 3 hours is even more preferable. From the viewpoint of chemical equilibrium, the hot water is exchanged 0 to 10 times, preferably 1 to 5 times, during the washing time. The weight percentage of the kneaded product obtained in the first kneading step in hot water during washing is preferably 0.1 to 50% by weight, and more preferably 0.1 to 15% by weight, from the viewpoint of chemical equilibrium. Furthermore, washing is preferably performed until the amount of residual urea is less than 1%, particularly less than 0.1%. The amount of residual urea can be determined from the weight loss when heated at 140°C for 270 minutes, for example, since the thermal decomposition starting temperature of urea is 135°C.

In the method for producing a resin composition of the present invention, it is preferable to dry the kneaded material washed in the hot water washing step described above from the viewpoints of preventing ring closure and ring opening of the modifying group in the compatibilizer in the second kneading step, preventing decomposition of the acetylated cellulose fiber and diluent resin due to remaining water, and reducing the drying load during kneading. The drying process can be carried out using, for example, a microwave dryer, a blower dryer, or a vacuum dryer, but a dryer that can dry while stirring, such as a drum dryer, a paddle dryer, a Nauta mixer, or a batch dryer with a stirring blade, is preferable. Drying is preferably carried out until the moisture content of the kneaded material reaches about 0.1 to 5%.

(Second kneading step)
The method for producing a resin composition of the present invention may further include a second kneading step in which the kneaded product obtained in the first kneading step and further washed in a hot water washing step is kneaded with a diluent resin. When the second kneading step is included, the kneaded product obtained in the first kneading step and further washed in a hot water washing step can be used as a master batch.

(Resin for dilution)
As the diluent resin used in the present invention, the following general thermoplastic resins having a melting temperature of 250° C. or less can be used.

That is, polyolefin resins, polyamide resins, polyvinyl chloride, polystyrene, polyvinylidene chloride, fluororesins, (meth)acrylic resins, polyesters, polylactic acid, copolymer resins of lactic acid and esters, polyglycolic acid, acrylonitrile-butadiene-styrene copolymers (ABS resins), polyphenylene oxide, polyurethanes, polyacetals, vinyl ether resins, polysulfone resins, cellulose resins (triacetylated cellulose, diacetylated cellulose, etc.), etc. can be used.

Polyolefin resins that can be used include polyethylene, polypropylene (hereinafter also referred to as "PP"), ethylene-propylene copolymer, polyisobutylene, polyisoprene, polybutadiene, etc., and from the viewpoint of interaction with the compatibilizing resin, it is preferable to use polypropylene when using MAPP, and it is preferable to use polyethylene when using MAPE.

In addition, polyamide resin (PA) is expected to interact with the hydroxyl groups and acetyl groups of cellulose that are not affected by the action of urea, and can be used preferably. Examples of PA include aliphatic PA such as polyamide 6 (nylon 6, PA6), polyamide 11 (nylon 11, PA11), polyamide 12 (nylon 12, PA12), polyamide 66 (nylon 66, PA66), polyamide 46 (nylon 46, PA46), polyamide 610 (nylon 610, PA610), and polyamide 612 (nylon 612, PA612), and aromatic PA consisting of aromatic diamine such as phenylenediamine and aromatic dicarboxylic acid such as terephthaloyl chloride or isophthaloyl chloride or its derivative. From the viewpoint of high affinity with acetylated cellulose fiber and acetylated cellulose nanofiber, it is preferable to use aliphatic PA, and it is more preferable to use PA6, PA11, and PA12, and it is particularly preferable to use PA6. In addition, one type of polyamide resin may be used alone, or two or more types of polyamide resins may be mixed and used.

When the kneaded product washed in the hot water washing step is used as a master batch, a resin composition further containing a diluent resin can be obtained by adding a diluent resin to the master batch and melt-kneading. When adding a diluent resin and melt-kneading, both components may be mixed at room temperature without heating and then melt-kneaded, or they may be mixed while heating and then melt-kneaded.

When adding the diluent resin and melt-kneading, the same kneader as used in the first kneading step can be used as the kneader for melt-kneading. The melt-kneading temperature can be adjusted to match the compatibilizing resin used in the first kneading step. The heating temperature during melt-kneading is preferably set to about ±20°C of the minimum processing temperature recommended by the thermoplastic resin supplier, but if the kneading is for a short period of time, it is possible to retain the shape of the acetylated cellulose fiber even with kneading at an upper limit of 300°C. However, from the viewpoint of making it easier to maintain the molecular weight of the resin, it is preferable to knead at a temperature near the melting point of the resin. Therefore, when polypropylene is used as the diluent resin, the melt-kneading temperature is preferably 140 to 230°C, and more preferably 160 to 200°C. When polyamide 6 is used as the diluent resin, the melt-kneading temperature is preferably 140 to 240°C, and more preferably 160 to 220°C. By setting the mixing temperature within this temperature range, the acetylated cellulose fiber and the resin can be mixed uniformly.

The resin composition produced by the production method of the present invention may further contain additives such as surfactants; polysaccharides such as starches and alginic acid; natural proteins such as gelatin, glue and casein; inorganic compounds such as tannins, zeolites, ceramics and metal powders; colorants; plasticizers; fragrances; pigments; flow regulators; leveling agents; conductive agents; antistatic agents; UV absorbers; UV dispersants; deodorants and antioxidants. The content ratio of any additive may be appropriately adjusted within a range that does not impair the effects of the present invention.

(Resin composition)
The resin composition obtained by the production method of the present invention may be a kneaded product (master batch) kneaded in a first kneading step and washed in a hot water washing step, or may be a resin composition obtained in a second kneading step in which the kneaded product (master batch) kneaded in the first kneading step and washed in a hot water washing step is kneaded with a diluent resin.

The present invention provides a method for producing a resin composition that can produce a resin molded product with excellent tensile strength and elongation.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

(Method for measuring degree of acetyl substitution (DS))
(Measurement of DS by back titration method)
A sample of acetylated cellulose fiber was dried, and 0.5 g (A) was accurately weighed. 75 mL of ethanol and 50 mL (0.025 mol) of 0.5N NaOH (B) were added thereto, and the mixture was stirred for 3 to 4 hours. The mixture was filtered, washed with water, and dried. FT-IR measurement of the sample on the filter paper was performed, and it was confirmed that the absorption peak due to the carbonyl of the ester bond had disappeared, that is, the ester bond had been hydrolyzed.
The filtrate was used for the back titration described below.
The filtrate contained sodium acetate salt resulting from hydrolysis and excess NaOH, which was titrated with 1N HCl (phenolphthalein was used as an indicator).

0.025 mol (B) - (number of moles of HCl used for neutralization)
= the number of moles of acetyl groups ester-bonded to hydroxyl groups of cellulose, etc. (C)
(Cellulose repeat unit molecular weight 162
× moles of cellulose repeat units (unknown (D))
+ (Molecular weight of acetyl group 43 × (C))
= 0.5 g of weighed sample (A)
The number of moles of the repeating unit of cellulose (D) was calculated from the above formula.

DS was calculated according to the following formula.
DS = (C) / (D)

(Measurement of tensile strength and tensile strain)
The resin compositions obtained in the examples and comparative examples were put into a pelletizer to obtain pellet-shaped resin molded bodies. 150 g of the pellet-shaped resin molded body was put into a small molding machine ("MC15" manufactured by Xplore Instruments), and the temperature of the heating cylinder (cylinder) was set to 200°C when the dilution resin was PP, and 250°C when the dilution resin was PA6, and the mold temperature was set to 40°C. A dumbbell-shaped test piece (Type A12, JIS K 7139) was molded under these conditions. The tensile strength (yield strength) and tensile strain (strain and elongation until breakage) of the obtained test piece were measured using a precision universal testing machine ("Autograph AG-Xplus" manufactured by Shimadzu Corporation) at a test speed of 1 mm/min and an initial gauge distance of 30 mm. The ratio of the measured values of each sample when the tensile strength values of the dilution resins PP and PA6 were each set to 100 among the measured values was taken as the reinforcement ratio, and the results are shown in Table 1. When acetylated cellulose fibers are used and PP is used as the diluent resin, a tensile strength of 125 or more indicates excellent strength. When acetylated cellulose fibers are used and PA6 is used as the diluent resin, a tensile strength of 175 or more indicates excellent strength. The larger the tensile strain value, the more excellent the elongation.

(Crusher used to crush acetylated cellulose fiber)
"UGO3-280XKFT" manufactured by Horai Co., Ltd.
Rotary blade type: Open straight cutter

(Mixers and operating conditions used in producing masterbatches and resin compositions)
A twin-screw kneader "MFU15TW-45HG-NH" manufactured by Technovel Co., Ltd. Screw diameter: 15 mm, L/D: 45, processing speed: 300 g/hour. The screw rotation speed was operated at 200 rpm.

(Materials used in the production of master batches and resin compositions)
(a) Acetylated cellulose fiber (b) Compatibilizing resin (masterbatch resin)
Maleic anhydride modified polypropylene (MAPP): (TOYOTAC PMA-H1000P, manufactured by Toyobo Co., Ltd.: dicarboxylic acid addition amount 57 mg KOH/g)
(c) Urea: (manufactured by Wako Pure Chemical Industries, Ltd.)
(d) Dilution Resin Polypropylene (PP): (PP MA04A manufactured by Japan Polypropylene Corporation)
Polyamide 6 (PA6): (PA6 1013FB manufactured by Ube Industries, Ltd., melting point: about 230°C)
(e) Antioxidant: (Irganox 1010 manufactured by BASF)

Example 1
(Preparation of acetylated cellulose fibers)
20 kg (solid content 10 kg) of water-containing softwood unbleached kraft pulp (NUKP) that had been beaten until the CSF was 150 mL was added to a mixer ("FM150L" manufactured by Nippon Coke & Engineering Co., Ltd.), and then stirring was started and dehydration was performed under reduced pressure at 80°C. Then, 4.0 kg of acetic anhydride was added and reacted at 80°C for 2 hours. After the reaction, the mixture was washed with water to obtain acetylated cellulose fiber (acetylated modified NUKP). The acetylated cellulose fiber was then placed in a dryer and dried under reduced pressure at 60 to 70°C. The moisture content of the obtained acetylated cellulose fiber was measured with an infrared moisture meter. The moisture content was 2.3% by weight. The acetyl group substitution degree (DS) of the acetylated cellulose fiber was 0.7. The weighted average fiber length of the acetylated cellulose fiber measured with a fiber tester (manufactured by L&W) was 0.664 mm.

(Masterbatch manufacturing)
The acetylated cellulose fiber subjected to the beating treatment (483.7 g as absolute dry matter, of which the cellulose amount including the cellulose not containing the acetylated portion and the hemicellulose: 360 g), a powdered compatibilizing resin (MAPP: 108 g), and a powdered urea (252 g: a blending amount of 70% based on the cellulose amount) were placed in a polyethylene bag and mixed by shaking. The obtained mixture (843.7 g) was fed into the kneader using a feeder (manufactured by Technovel Co., Ltd.) attached to the above-mentioned twin-screw kneader, and kneaded at 180° C. to produce a master batch.

(Hot water cleaning)
800 g of the master batch obtained above was washed with 10 L of hot water at 65 to 80°C for 2 hours. Hot water was exchanged once during the washing. Stirring was performed using a Primix Automixer 40. The temperature was maintained using a water bath. After washing, the master batch was placed in a dryer and dried at 105°C overnight (or until a constant weight was reached).

(Production of resin composition)
The master batch obtained after hot water washing and drying was mixed with a diluent resin (PP) in a ratio such that the amount of cellulose fiber derived from the acetylated cellulose fiber was 10% of the total amount of the resin (compatibilizing resin and diluent resin), the acetylated cellulose fiber, and urea, and the mixture was kneaded at 180°C in the twin-screw kneader to obtain a resin composition.

Example 2
A resin composition was produced in the same manner as in Example 1, except that the amount of urea added during the production of the masterbatch was changed to a compounding amount of 50% (180 g) relative to the amount of cellulose, and that the masterbatch was changed to 750 g and the amount of hot water to 9.38 L in order to standardize the ratio of the masterbatch weight to hot water during washing.

(Comparative Example 1)
A master batch was produced in the same manner as in Example 1, and a resin composition was produced in the same manner as in Example 1, except that the master batch obtained was used as it was without being washed with hot water and dried thereafter.

(Comparative Example 2)
A resin composition was produced in the same manner as in Example 1, except that unbeaten NUKP was used, and after acetylation, it was pulverized in the above-mentioned pulverizer and then passed through a screen with a diameter of 3 mm, and the master batch was washed with hot water and then dried at the time when the production of a resin composition with a fiber content of 10% was completed. The weighted average fiber length of the acetylated cellulose fiber was 0.761 mm.

Example 3
Except for the fact that an antioxidant was further added in an amount of 10% (36 g) based on the amount of cellulose during the production of the master batch, the master batch was produced by kneading in the same manner as in Example 2. The obtained master batch was washed with hot water and then dried in the same manner as in Example 2.

(Production of resin composition)
The master batch obtained after hot water washing and drying was mixed with a diluent resin (PA6) in a ratio such that the amount of cellulose fiber derived from the acetylated cellulose fiber was 10% of the total amount of the resin (compatibilizing resin and diluent resin), acetylated cellulose fiber, urea, and antioxidant, and the mixture was kneaded at 210°C in the twin-screw kneader to obtain a resin composition.

(Comparative Example 3)
A master batch was produced in the same manner as in Example 3, and a resin composition was produced in the same manner as in Example 3, except that the master batch obtained was used as it was without being washed with hot water and dried thereafter.

As shown in Table 1, the method for producing a resin composition of the present invention includes a first kneading step in which the acetylated cellulose fiber of the present invention, a compatibilizing resin, and urea are fed into a kneader and kneaded, and a hot water washing step in which the kneaded product obtained in the first kneading step is washed with hot water. This method can obtain a resin composition that has high tensile strength and gives an excellent molded product with improved elongation even when using the same resin, compared to Comparative Example 1 and Comparative Example 3, which do not include a hot water washing step.

Claims (5)

a first kneading step in which acetylated cellulose fibers having a weighted average fiber length of 0.20 mm to 1.50 mm, a compatibilizing resin, and urea are charged into a kneader and kneaded at a kneading temperature of 135 to 200° C .;
A hot water washing step of washing the kneaded product obtained in the first kneading step with hot water ,
A method for producing a resin composition , wherein the compatibilizing resin is a polymer resin having a dicarboxylic acid capable of forming an acid anhydride on a polyolefin chain . The method for producing a resin composition according to claim 1, wherein in the hot water washing step, the temperature of the hot water is 50 to 100°C, and the washing time is 10 minutes to 24 hours. The method for producing a resin composition according to claim 1 or 2 further comprises a second kneading step in which the kneaded product obtained after the hot water washing step is kneaded with a diluent resin. The method for producing a resin composition according to any one of claims 1 to 3, wherein the amount of urea added to the kneader in the first kneading step is 10 to 100% by weight relative to 100% by weight of the total amount of cellulose fiber, which is the total amount of cellulose and hemicellulose that does not contain acetylated portions of the acetylated cellulose fibers. The method for producing a resin composition according to any one of claims 1 to 4, wherein the amount of the cellulose fiber content, which is a combination of cellulose and hemicellulose that does not contain an acetylated portion of the acetylated cellulose fiber fed into the kneader in the first kneading step, is 35 to 85% by weight based on the total amount of the cellulose fiber content, the compatibilizing resin, and the urea.