JP5660333B2 - Method for producing composition containing cellulose and polylactic acid - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for producing a composition containing cellulose and polylactic acid, and more specifically, a composite resin in which cellulose fibers are dispersed in polylactic acid. Relates to a method for producing an improved composition.

From the viewpoint of protecting the natural environment, researches have been actively conducted to effectively use unused resources. Among them, cellulose is abundant in existing quantities, is a resource that is biodegradable and has a low environmental impact, has excellent properties as a material, such as high crystallinity, high tensile strength, and low coefficient of thermal expansion. It is a material expected from the future.
One method for effectively utilizing cellulose is to use it as a reinforcing material. Conventionally, in order to increase the mechanical strength of a resin molded body, a blend of inorganic fibers such as glass has been used. However, a resin molded body in which inorganic fibers are blended has a problem that a residue derived from the inorganic fibers is generated during incineration, and thus must be disposed of by landfill processing or the like. If plant fibers such as bamboo, hemp, kenaf, etc., which have relatively high strength, can be effectively used as reinforcing materials, these will eventually be decomposed into water and carbon dioxide, which will lead to the solution of the above problems. Yes.

  By the way, polylactic acid, which is a plant-derived biodegradable resin, is inferior in heat resistance if it is amorphous, and has the disadvantage that the elastic modulus does not improve even if it is crystallized, so reinforcement to supplement these physical properties The combination of materials is considered effective. Since polylactic acid itself is a plant-derived material, it is preferable to use plant natural fibers in the reinforcing material. From this viewpoint, several patents relating to composite resins of cellulose and polylactic acid have been proposed. .

For example, Patent Document 1 discloses a molded product in which a polylactic acid resin and powdered cellulose (average particle size: 1 to 60 μm) are melt-mixed and combined.
Patent Document 2 proposes a material that combines bacterial cellulose and polylactic acid in a powder form after disaggregating the produced bacterial cellulose (filtering with a 150 mesh filter) and then lyophilizing after substitution with acetone and cyclohexane. Has been.
Patent Document 3 discloses a material in which a commercially available microfibrillated cellulose (fiber diameter: 0.01 to 10 μm) is dipped in acetone and dehydrated to form a composite with polylactic acid using a dispersant. Has been proposed.

By the way, in the composite resin material composed of cellulose and polylactic acid, it is preferable to use a refined cellulose in consideration of the adhesiveness at the interface between the polylactic acid and the fiber and the appearance of the molded body. However, in the above-described techniques proposed so far, in the composite of powdered cellulose or microfibrillated cellulose and polylactic acid, a cellulose drying process is involved, and the process becomes complicated, and cellulose fiber-containing resin on an industrial scale. It was difficult to produce a molded product.
In addition, in a composite resin material in which cellulose and polylactic acid are simply melted and mixed, cellulose often appears in a granular form after molding, and there has been a demand for providing a resin composition that provides a molded article with an excellent appearance. .

  The present invention has been made in view of such circumstances, and more easily in the complexing of cellulose fiber and polylactic acid, a composite resin having high uniform dispersibility of cellulose fiber in polylactic acid and excellent moldability. The manufacturing method which obtains is provided.

  As a result of diligent investigations to solve the above problems, the present inventors have dissolved polylactic acid in an organic solvent dispersion of fine cellulose fibers and removed the solvent in a state where the resin is uniformly dissolved. As a result, it was found that a composite resin excellent in dispersibility of cellulose fibers in polylactic acid was obtained, and a molded article excellent in surface appearance could be easily produced from the composite resin, and the present invention was achieved.

  That is, the present invention provides a step of preparing a dispersion in which finely divided cellulose fibers are dispersed in an organic solvent in which polylactic acid can be dissolved, and the polylactic acid solution is prepared by dissolving polylactic acid in the dispersion in which the cellulose fibers are dispersed. This invention relates to a method for producing a cellulose fiber-containing resin composition, which comprises the steps of: preparing an organic solvent from the polylactic acid solution.

  The organic solvent removing step is preferably performed according to a reprecipitation method, or preferably according to a solvent concentration method.

  The refined cellulose fiber is preferably a cellulose fiber having a fiber diameter of 0.001 to 1 μm, and it is particularly preferable to use a cellulose fiber prepared by a wet pulverization method.

  The organic solvent is dimethyl sulfoxide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, toluene, 1,4-dioxane, N, N-dimethylformamide, tetrahydrofuran, 1,3-dioxolane or chloroform. Is preferred.

  Further, in the step of preparing the polylactic acid solution, the cellulose fiber is dispersed in dimethyl sulfoxide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, toluene, 1,4-dioxane or N, N-dimethylformamide. It is preferable to heat the dispersed liquid at a temperature of 60 to 150 ° C. to dissolve the polylactic acid.

According to the present invention, a resin composition having high uniform dispersibility of cellulose fibers in polylactic acid and excellent moldability can be produced regardless of the cellulose species used.
Further, according to the present invention, a resin composition having high uniform dispersibility of cellulose fibers and excellent moldability can be easily produced on an industrial scale.
Furthermore, according to the present invention, it is possible to produce a resin composition capable of producing a molded article having excellent surface appearance and excellent bending elastic modulus and impact strength.

FIG. 1 is a polarization micrograph observing the dispersion state of cellulose fibers in the resin composition prepared in Example 4. FIG. 2 is a polarization micrograph observing the dispersion state of cellulose fibers in the resin composition prepared in Example 5. FIG. 3 is a polarization micrograph observing the dispersion state of cellulose fibers in the resin composition prepared in Example 6. FIG. 4 is a polarization micrograph observing the dispersion state of cellulose fibers in the resin composition prepared in Example 7. FIG. 5 is a polarization micrograph observing the dispersion state of cellulose fibers in the resin composition prepared in Example 8. FIG. 6 is a polarization micrograph observing the dispersion state of cellulose fibers in the resin composition prepared in Example 9. FIG. 7 is a polarization micrograph observing the dispersion state of cellulose fibers in the resin composition prepared in Example 10. FIG. 8 is a polarization micrograph observing the dispersion state of cellulose fibers in the resin composition prepared in Comparative Example 1. FIG. 9 is a polarization micrograph observing the dispersion state of cellulose fibers in the resin composition prepared in Comparative Example 2. FIG. 10 is a polarization micrograph observing the dispersion state of cellulose fibers in the resin composition prepared in Comparative Example 3.

  The method for producing a cellulose fiber-containing resin composition of the present invention comprises (a) a step of preparing a dispersion in which finely divided cellulose fibers are dispersed in an organic solvent capable of dissolving polylactic acid, and (b) the cellulose fibers A step of dissolving polylactic acid in the dispersed dispersion to prepare a polylactic acid solution, and (c) a step of removing an organic solvent from the polylactic acid solution.

<(A) Process>
Examples of the cellulose used in the dispersion liquid in which the cellulose fibers used in the present invention are dispersed include cellulose made from pulp, bacterial cellulose, and squirt cellulose.

In the present invention, cellulose fibers pulverized and refined are used. The pulverization method of cellulose is not particularly limited, but it is preferable to use a wet pulverization method as disclosed in JP-A-2005-270891. That is, cellulose is pulverized by injecting and colliding a dispersion liquid in which cellulose is dispersed from a pair of nozzles at a high pressure. For example, by using a high-pressure pulverizer manufactured by Sugino Machine Co., Ltd. Can be implemented.
The fiber diameter of the cellulose fiber thus refined is 0.001 to 1 μm.

When the dispersion of cellulose fibers refined by using the wet pulverization method is an aqueous dispersion, it can be easily made into a dispersion of cellulose fibers in an organic solvent using, for example, a solvent replacement method.
When the solvent substitution method is used, an organic solvent having a relatively high boiling point capable of easily replacing the aqueous dispersion with the organic solvent dispersion and dissolving polylactic acid is preferable. For example, dimethyl sulfoxide, N, N-dimethylacetamide, N-methyl -2-pyrrolidone, toluene, 1,4-dioxane, N, N-dimethylformamide and the like, and particularly solvents having high affinity with water and cellulose such as dimethylsulfoxide and N, N-dimethylacetamide Is preferred. In addition, you may use the low boiling-point organic solvent which can melt | dissolve polylactic acid, such as tetrahydrofuran, 1, 3- dioxolane, chloroform.

  The dispersion in which the cellulose fibers used in the present invention are dispersed is not limited to those obtained by solvent replacement from the aqueous dispersion, but is prepared directly as an organic solvent dispersion without solvent replacement. Can be used. In this case, it is preferable to use dimethyl sulfoxide because a desired dispersion liquid in which fine cellulose fibers are dispersed can be obtained.

<(B) Process>
The polylactic acid used in the present invention includes a homopolymer or copolymer of polylactic acid. When polylactic acid is a copolymer, the arrangement pattern of the copolymer may be any of random copolymer, alternating copolymer, block copolymer, and graft copolymer. Further, it may be a blend polymer with other resin mainly composed of polylactic acid homopolymer or copolymer. Examples of other resins include biodegradable resins other than polylactic acid, general-purpose thermoplastic resins, and general-purpose thermoplastic engineering plastics.
The polylactic acid is not particularly limited, and examples thereof include those obtained by ring-opening polymerization of lactide and those obtained by direct polycondensation of D-form, L-form and racemic form of lactic acid. Any of lactic acid, poly-L-lactic acid, a copolymer of D-lactic acid and L-lactic acid, and a mixture of poly-D-lactic acid and poly-L-lactic acid may be used. As a mixture of the poly-D-lactic acid and poly-L-lactic acid, stereocomplex polylactic acid exhibits higher heat resistance than poly-D-lactic acid or poly-L-lactic acid. The number average molecular weight of polylactic acid is generally about 10,000 to 500,000. In addition, polylactic acid obtained by crosslinking with a crosslinking agent using heat, light, radiation or the like can be used.

  When the polylactic acid is dissolved in the dispersion liquid in which the cellulose fibers prepared in the step (a) are dispersed, the aforementioned dimethyl sulfoxide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, toluene, 1 When 4,4-dioxane, N, N-dimethylformamide or the like is used, it is desirable to heat the dispersion to a temperature at which polylactic acid dissolves (depending on the organic solvent used). Since the decomposition of polylactic acid is promoted as it is heated to a higher temperature, the dispersion is heated at a temperature of 40 ° C. or higher, preferably 60 ° C. or higher and 150 ° C. or lower to dissolve the polylactic acid. It is preferable to prepare. On the other hand, when the above-mentioned tetrahydrofuran, 1,3-dioxolane or chloroform is used as the organic solvent, heating is unnecessary because polylactic acid dissolves at room temperature.

<(C) Process>
The step of removing the organic solvent from the polylactic acid solution thus obtained is carried out by (i) reprecipitation method or (ii) solvent concentration method.

(I) When using the reprecipitation method, the solvent used for reprecipitation is not particularly limited as long as it is a poor solvent for polylactic acid. For example, methanol, ethanol, and water can be used.
When performing reprecipitation, the polylactic acid solution is preferably added dropwise to a poor solvent in a state where the polylactic acid is completely dissolved.
The resin thus precipitated is preferably vacuum-dried at 40 to 80 ° C. to produce a cellulose fiber-containing resin composition.

  Moreover, (ii) When using the solvent concentration method, it is preferable to distill off a solvent in the state in which polylactic acid is completely dissolved. Specifically, a cellulose fiber-containing resin composition is produced by concentrating a polylactic acid solution as it is at 60 to 150 ° C. under reduced pressure.

<Other additives>
The resin composition obtained by the production method of the present invention can contain a known inorganic filler. Examples of the inorganic filler include glass fiber, carbon fiber, talc, mica, silica, kaolin, clay, wollastonite, glass beads, glass flake, potassium titanate, calcium carbonate, calcium phosphate, magnesium sulfate, titanium oxide and the like. Can be mentioned. The shape of these inorganic fillers may be any of fibrous, granular, plate-like, needle-like, spherical, and powder. These inorganic fillers can be used within 300 parts by mass with respect to 100 parts by mass of polylactic acid.
Moreover, the resin composition obtained by the manufacturing method of this invention can contain a well-known flame retardant. Examples of the flame retardant include halogen flame retardants such as bromine compounds and chlorine compounds, melamine flame retardants, antimony flame retardants such as antimony trioxide and antimony pentoxide, aluminum hydroxide, magnesium hydroxide and silicone compounds. Examples thereof include inorganic flame retardants, red phosphorus, phosphoric acid esters, phosphorous flame retardants such as ammonium polyphosphate, phosphazene, and fluorine resins such as PTFE. These flame retardants can be used within 200 parts by mass with respect to 100 parts by mass of polylactic acid.
In addition to the above components, heat stabilizers, light stabilizers, UV absorbers, antioxidants, impact modifiers, antistatic agents, pigments, colorants, mold release agents, lubricants, plasticizers, compatibilizers, foaming Agents, fragrances, antibacterial and antifungal agents, other various fillers, and various additives usually used in the production of general synthetic resins can also be used in combination with the resin composition obtained by the production method of the present invention.

  When molding the resin composition obtained by the production method of the present invention, various molded products can be easily produced by using conventional molding methods such as general injection molding, blow molding, vacuum molding, compression molding, etc. Can do.

[Example 1: Preparation of aqueous dispersion of cellulose fiber]
In accordance with the procedure of “Polysaccharide wet pulverization method” disclosed in JP-A-2005-270891, cellulose fiber aqueous dispersions (1) to (3) were prepared as follows.
(1) After 740 g of water was added to 10 g of commercially available pulp-derived cellulose (Fibra-Cell BH-100 manufactured by Celite) and dispersed, pulverization was performed 100 times at 200 MPa using a high-pressure pulverizer manufactured by Sugino Machine Co., Ltd. A 0.7 mass% pulp-derived cellulose fiber aqueous dispersion was prepared.
(2) After adding 1,235 g of water to 15 g of commercially available pulp-derived microcrystalline cellulose (Funakoshi Co., Ltd., Funacell Powder II for column chromatography) and dispersing it, the pressure was increased to 200 MPa using a high-pressure pulverizer manufactured by Sugino Machine Co., Ltd. The powder was pulverized 100 times to prepare a 1.0 mass% pulp-derived microcrystalline cellulose fiber aqueous dispersion.
(3) Bacterial cellulose (manufactured by PT. NIRAMAS UTAMA) was added with water and pulverized with a home mixer, and then pulverized 30 times at 200 MPa using a high pressure pulverizer manufactured by Sugino Machine Co., Ltd. A mass% bacterial cellulose fiber aqueous dispersion was prepared.

[Example 2: Preparation of cellulose fiber / dimethyl sulfoxide dispersion]
(1) 150 g of dimethyl sulfoxide was added to 150 g of the 0.7 mass% pulp-derived cellulose fiber aqueous dispersion prepared in Example 1 (1) and stirred, and water was completely distilled off by concentration to obtain pulp-derived cellulose fiber / dimethyl. 81.5 g of a sulfoxide dispersion was prepared.
(2) 50 g of dimethyl sulfoxide was added to 50 g of the 1.0% by weight pulp-derived microcrystalline cellulose fiber aqueous dispersion prepared in Example 1 (2) and stirred, and water was completely distilled off by concentration. 28.5 g of a cellulose fiber / dimethyl sulfoxide dispersion was prepared.
(3) 200 g of dimethyl sulfoxide was added to 200 g of the 0.4% by weight bacterial cellulose fiber aqueous dispersion prepared in Example 1 (3) and stirred, and the water was completely distilled off by concentration to disperse the bacterial cellulose fiber and dimethyl sulfoxide. A liquid 170 g was prepared.

[Example 3: Preparation of cellulose fiber / N, N-dimethylacetamide dispersion]
100 g of N, N-dimethylacetamide was added to 100 g of the 0.4 mass% bacterial cellulose fiber aqueous dispersion prepared in Example 1 (3), and the water was completely distilled off by concentration to give bacterial cellulose fiber N, N-. 34 g of dimethylacetamide dispersion was prepared.

[Example 4: Preparation of resin composition by solvent concentration method (1)]
6.8 g of polylactic acid (LACEA [registered trademark] H-100, manufactured by Mitsui Chemicals, Inc.) is added to 61.0 g of the pulp-derived cellulose fiber / dimethyl sulfoxide dispersion prepared in Example 2 (1) and heated to 110 ° C. Then, polylactic acid was dissolved by stirring. Dimethyl sulfoxide was distilled off by concentrating the solution under reduced pressure while heating at 110 ° C. to prepare 7.21 g of a resin composition of pulp-derived cellulose fiber and polylactic acid.

[Example 5: Preparation of resin composition by solvent concentration method (2)]
1.0 g of polylactic acid (LACEA [registered trademark] H-100, manufactured by Mitsui Chemicals, Inc.) is added to 4.0 g of the pulp-derived microcrystalline cellulose fiber / dimethyl sulfoxide dispersion prepared in Example 2 (2), and dimethyl is added. A small amount of sulfoxide was added, and the mixture was heated to 110 ° C. and stirred to dissolve polylactic acid. This solution was heated at 110 ° C. and concentrated under reduced pressure to distill off dimethyl sulfoxide, thereby producing 0.69 g of a resin composition of pulp-derived microcrystalline cellulose fibers and polylactic acid.

[Example 6: Preparation of resin composition by solvent concentration method (3)]
Add 17.8 g of polylactic acid (LACEA [registered trademark] H-100, manufactured by Mitsui Chemicals, Inc.) to 160 g of the bacterial cellulose fiber / dimethyl sulfoxide dispersion prepared in Example 2 (3), and heat to 110 ° C. and stir. As a result, polylactic acid was dissolved. This solution was heated at 110 ° C. and concentrated under reduced pressure to distill away dimethyl sulfoxide, thereby preparing 18.4 g of a resin composition of bacterial cellulose fiber and polylactic acid.

[Example 7: Preparation of resin composition by solvent concentration method (4)]
Add 0.50 g of polylactic acid (LACEA [registered trademark] H-100, manufactured by Mitsui Chemicals, Inc.) to 4.5 g of the bacterial cellulose fiber / N, N-dimethylacetamide dispersion prepared in Example 3, and heat to 80 ° C. Then, polylactic acid was dissolved by stirring. This solution was heated at 80 ° C. and concentrated under reduced pressure to distill away N, N-dimethylacetamide, thereby producing 0.30 g of a resin composition of bacterial cellulose fiber and polylactic acid.

[Example 8: Preparation of resin composition by reprecipitation method (1)]
50 g of N, N-dimethylacetamide and 4.5 g of polylactic acid (LACEA [registered trademark] H-100, manufactured by Mitsui Chemicals, Inc.) were added to 50 g of the pulp-derived cellulose fiber / dimethyl sulfoxide dispersion prepared in Example 2 (1). In addition, polylactic acid was dissolved by heating to 100 ° C. and stirring. 20 g of this solution was reprecipitated in 50 g of methanol, and the precipitated resin was filtered and vacuum dried at 40 ° C. to prepare 0.85 g of a resin composition of pulp-derived cellulose fibers and polylactic acid.
In this example, N, N-dimethylacetamide was used, but a resin composition of pulp-derived cellulose fiber and polylactic acid can be produced without using N, N-dimethylacetamide.

[Example 9: Preparation of resin composition by reprecipitation method (2)]
2.6 g of polylactic acid (LACEA [registered trademark] H-100, manufactured by Mitsui Chemicals, Inc.) is added to 50 g of the bacterial cellulose fiber / dimethyl sulfoxide dispersion prepared in Example 2 (3), and the mixture is heated to 110 ° C. and stirred. As a result, polylactic acid was dissolved. This solution was reprecipitated in 200 g of methanol, and the precipitated resin was filtered and vacuum dried at 40 ° C. to prepare 2.70 g of a resin composition of bacterial cellulose fiber and polylactic acid.

[Example 10: Preparation of resin composition by reprecipitation method (3)]
To 50 g of the bacterial cellulose fiber / N, N-dimethylacetamide dispersion prepared in Example 3, 2.6 g of polylactic acid (LACEA [registered trademark] H-100, manufactured by Mitsui Chemicals, Inc.) is added and heated to 110 ° C. and stirred. As a result, polylactic acid was dissolved. This solution was reprecipitated in 200 g of methanol, and the precipitated resin was filtered and vacuum dried at 40 ° C. to prepare 2.78 g of a resin composition of bacterial cellulose fibers and polylactic acid.

[Example 11: Preparation of resin composition by reprecipitation method (4)]
Polylactic acid (LACEA [registered trademark] H-100, manufactured by Mitsui Chemicals, Inc.) 4.5 kg is added to 50 kg of a pulp-derived cellulose fiber / dimethyl sulfoxide dispersion prepared in the same manner as in Example 2 (1). The polylactic acid was dissolved by heating to ° C and stirring. 54.5 kg of this solution was reprecipitated in 500 kg of methanol, and the precipitated resin was filtered and vacuum dried at 40 ° C. to produce 4.8 kg of a resin composition of pulp-derived cellulose fibers and polylactic acid.

[Comparative Example 1: Preparation of resin composition using aqueous dispersion of wet-pulverized cellulose fiber]
After 740 g of water was added to and dispersed in 10 g of commercially available pulp derived cellulose (Fibra-Cell BH-100 manufactured by Celite), pulverization was performed 100 times at 200 MPa using a high pressure pulverizer manufactured by Sugino Machine Co., Ltd. A 0 mass% pulp-derived cellulose fiber aqueous dispersion was prepared.
To 10 g of this aqueous dispersion, 910 mg of polylactic acid (Ingeo (registered trademark) 3001D manufactured by Nature Works) was added and stirred at room temperature. This dispersion was dropped into 50 g of methanol and filtered, followed by vacuum drying at 40 ° C. to produce 0.98 g of a pulp-derived cellulose fiber and polylactic acid mixture. 0.4 g of this mixture and 3.6 g of polylactic acid (Ingeo (registered trademark) 3001D, manufactured by Nature Works) were kneaded at 185 ° C., 50 rpm, 5 minutes in a lab plast mill (manufactured by Toyo Seiki Seisakusho), and derived from pulp 4.0 g of a resin composition of cellulose fiber and polylactic acid was produced.

[Comparative Example 2: Preparation of resin composition using unmilled cellulose]
By adding 102 mg of commercially available pulp-derived cellulose (Fibra-Cell BH-100 manufactured by Celite) and 896 mg of polylactic acid (Ingeo (registered trademark) 3001D manufactured by Nature Works) to 9.9 g of dimethyl sulfoxide, and heating and stirring at 100 ° C. Polylactic acid was dissolved. In this comparative example, the wet pulverization treatment was not performed. In addition, the average fiber diameter of the cellulose used by this comparative example is 20 micrometers, and average fiber length is 60 micrometers.
This solution was reprecipitated in 50 g of methanol, and the precipitated resin was filtered and vacuum dried at 40 ° C. to produce 888 mg of a resin composition of pulp-derived cellulose and polylactic acid.

[Comparative Example 3: Preparation of resin composition using wet pulverized / lyophilized cellulose fiber]
After 740 g of water was added to and dispersed in 10 g of commercially available pulp derived cellulose (Fibra-Cell BH-100 manufactured by Celite), pulverization was performed 100 times at 200 MPa using a high pressure pulverizer manufactured by Sugino Machine Co., Ltd. A 0 mass% pulp-derived cellulose fiber aqueous dispersion was prepared.
The aqueous dispersion was subjected to solvent replacement with acetone by dialysis to prepare a cellulose fiber / acetone dispersion. Thereafter, the solvent was replaced from acetone to cyclohexane to prepare a cellulose fiber / cyclohexane dispersion. This cellulose fiber / cyclohexane dispersion was freeze-dried at 0 ° C. or lower to obtain powdery cellulose fibers.
Next, 0.2 g of this powdery cellulose fiber and 3.8 g of polylactic acid (Ingeo (registered trademark) 3001D, manufactured by Nature Works) were used at 185 ° C., 50 rpm using Labo Plast Mill (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Kneading for 5 minutes produced 4.0 g of a resin composition of pulp-derived cellulose fiber and polylactic acid.

[Observation with a polarizing microscope]
About each resin composition prepared in Example 4 thru | or Example 10 and Comparative Example 1 thru | or Comparative Example 3, the dispersion state of the cellulose fiber was observed using the polarization microscope. The results are shown in FIGS. 1 to 7 and FIGS.
In addition, the imaging conditions of the polarization micrograph are as follows.
<Measuring device> Polarized microscope ECLIPSE LV100POL manufactured by Nikon Corporation
<Measurement conditions> Heat the resin composition to 185 ° C., observe the molten state, 200 times magnification

In FIG. 1 to FIG. 10, white and high-brightness portions indicate the presence of cellulose.
As shown in FIGS. 1 to 7, it was observed that the resin compositions prepared in Examples 4 to 10 had high dispersibility of cellulose fibers in polylactic acid. On the other hand, the resin compositions prepared in Comparative Examples 1 to 3 (FIGS. 8 to 10) resulted in aggregation of cellulose and inferior uniform dispersibility as compared with the Examples.

[Appearance evaluation]
Sample preparation method:
Polylactic acid (Ingeo (registered trademark) 3001D manufactured by Nature Works) was added to each of the resin compositions prepared in Examples 4 to 6, Example 8, Example 10, and Comparative Examples 2 and 3. Using a Laboplast mill (manufactured by Toyo Seiki Seisakusho Co., Ltd.), melt kneading (185 ° C., 50 rpm, 5 minutes) was performed to prepare a resin composition containing 1% by mass of cellulose fiber in polylactic acid. This resin composition was molded by hot pressing (185 ° C.) to produce a film having a thickness of about 200 μm. In addition, since the resin composition produced in Comparative Example 1 contained 1% by mass of cellulose fiber in polylactic acid, the resin composition was directly molded by hot pressing without newly adding polylactic acid.
Evaluation method: Visual appearance evaluation Evaluation criteria: ○: No agglomerates in molded product
Δ: Confirmation of agglomerates in micro units in the molded product
×: Confirmed agglomerates in millimeters in the molded product

As shown in Tables 1 and 2, the films produced using the resin compositions of Examples 4 to 6, Example 8, and Example 10 were not found to have agglomerates in the molded product visually. A molded product having an excellent appearance could be formed.
On the other hand, the films produced using the resin compositions of Comparative Examples 1 to 3 were found to have inferior surface appearance because microscopic or millimeter agglomerates were observed in the molded product by visual observation. It was.

[Preparation of mechanical property evaluation specimen (1)]
Polylactic acid (Ingeo (registered trademark) 3001D manufactured by Nature Works) was added to the resin composition prepared in Example 11 above, and a barrel temperature of 185 was used using a twin screw extruder (KZW15-30TGN manufactured by Technobell). Melt kneading was performed at 0 ° C. to obtain a resin composition containing 1% by mass of cellulose fiber in polylactic acid.
Next, the obtained resin composition was melted at a cylinder temperature of 185 ° C. using an injection molding machine (SE18S manufactured by Sumitomo Heavy Industries, Ltd.) and injected into a 30 ° C. mold. After holding the resin for 15 seconds to cure the resin, a molded product (length 80 mm × width 10 mm × thickness 4 mm) was taken out from the mold to prepare a test piece (1).

[Preparation of mechanical property evaluation specimen (2)]
Polylactic acid (Ingeo (registered trademark) 3001D, manufactured by Nature Works) was injection-molded in the same manner as in [Preparation of test piece for mechanical property evaluation (1)] except that the cellulose fiber-containing resin composition was not used. Thus, a test piece (2) was produced.

[Preparation of mechanical property evaluation specimen (3)]
A commercial pulp-derived cellulose (Fibra-Cell BH-100 manufactured by Celite) was used in place of the cellulose fiber-containing resin composition without wet pulverization, and the same method as in “Preparation of test piece (1)” was used. , The pulp-derived cellulose and polylactic acid (Ingeo [registered trademark] 3001D, manufactured by Nature Works) were melt-kneaded, and the obtained resin composition (containing 1% by mass of cellulose in polylactic acid) was injection-molded and tested. A piece (3) was produced.

[Mechanical property evaluation]
Evaluation method: Using a universal material testing machine (model 5582 manufactured by Instron), a bending test was performed at a bending speed of 2 mm / min according to JIS K7171. Further, using an impact tester (CEAST 6546, 2J hammer), an Izod impact test (edgewise, no notch) was performed according to JIS K 7110. The tightening torque of each test piece was 6 Nm.

  As shown in Table 3, the test piece (1) using the resin composition prepared in Example 11 has a flexural modulus as compared with the test piece (2) using only polylactic acid not containing the resin composition. Improved impact strength. In addition, the test piece (3) using the unpulverized pulp-derived cellulose-containing resin composition is improved in both the flexural modulus and impact strength compared to the test piece (2), but the cellulose fiber refined by wet grinding. The test piece (1) using the resin composition containing a greater degree of improvement in physical properties was obtained. It can be said that the above results show that the use of refined cellulose fibers provides the effect of improving the flexural modulus and impact strength, which are mechanical properties.

JP 2005-145028 A Japanese Patent Laid-Open No. 11-241027 JP 2007-238812 A

Claims (5)

Preparing an organic solvent dispersion in which finely divided cellulose fibers are dispersed in an organic solvent capable of dissolving polylactic acid,
A method for producing a cellulose fiber-containing resin composition, comprising: dissolving polylactic acid in an organic solvent dispersion in which the cellulose fibers are dispersed to prepare a polylactic acid solution; and removing the organic solvent from the polylactic acid solution. Because
In the step of preparing the polylactic acid solution, an organic solvent dispersion liquid in which the cellulose fibers are dispersed in dimethyl sulfoxide or N, N-dimethylacetamide is heated at a temperature of 60 to 150 ° C., and polylactic acid is dissolved therein. Manufacturing method. The method according to claim 1, wherein the organic solvent removing step is performed according to a reprecipitation method. The method according to claim 1, wherein the organic solvent removing step is performed according to a solvent concentration method. The manufacturing method according to claim 1, wherein the refined cellulose fiber is a cellulose fiber having a fiber diameter of 0.001 to 1 μm. The manufacturing method according to claim 4, wherein the refined cellulose fiber is a cellulose fiber prepared by a wet pulverization method.