JP2021021041A - Biodegradable composite material containing cellulose nanofiber and biodegradable resin - Google Patents

Abstract

To provide a biodegradable composite material that has enhanced strength and biodegradability.SOLUTION: The present invention relates to a biodegradable composite material containing cellulose nanofiber and biodegradable resin. In 100 wt.% of the total content of the cellulose nanofiber and biodegradable resin, the cellulose nanofiber content is 2 wt.% or more.SELECTED DRAWING: None

Description

The present invention relates to a biodegradable composite material in which strength and biodegradability are promoted by blending cellulose nanofibers with a biodegradable resin.

In order to prevent environmental pollution caused by plastic waste, the "3R movement" of reducing, reusing and recycling the amount of plastic used is being promoted all over the world. Separate collection of plastics is being carried out for reuse and recycling. The collected plastic waste was exported to China and Southeast Asia, but as these countries banned the import of plastic waste, plastic waste has accumulated in Japan. In recent years, there has been increasing interest in marine debris. When plastic waste flows into the ocean, it not only drifts as it is, but also becomes finer than 1 mm of microplastic over a long distance and for a long time, which creates a big problem of destroying the ecosystem. ing. Although the collected plastic waste was landfilled, it may flow into rivers due to floods and be washed away to the sea. According to 2010 estimates, the amount of plastic waste discharged from land to the ocean is 20,000 to 60,000. It was t / year (Non-Patent Document 1).
Reducing the amount of plastic used is a powerful solution, but in modern society it is not possible to reduce the amount used to zero, which is not ideal.

Therefore, various biodegradable plastics have been developed. Biodegradable plastics have the property of being decomposed by microorganisms and the like and eventually becoming carbon dioxide and water. Examples of biodegradable plastics include polylactic acid, polycaprolactone, polyhydroxyalkanoate, polybutylene succinate, copolymers of polybutylene adipate with terephthalate, polyglycolic acid, modified polyvinyl alcohol, casein, and starch-derived raw materials. Degradable plastics have also been developed.

Biodegradable plastics are expected to reduce environmental pollution, but have the disadvantage of low strength. Therefore, in order to increase the strength without impairing the biodegradability, research on composite materials mixed with plant-derived biomass is in progress (Patent Documents 1 and 2 and the like). Further, in order to improve the strength of the biomass / biodegradable resin composite material, an attempt has been made to improve the compatibility at the interface between different phases at the interface between the biomass and the biodegradable resin (Patent Document 3).

Japanese Unexamined Patent Publication No. 2000-160034 Japanese Patent Application Laid-Open No. 2002-069303 Japanese Unexamined Patent Publication No. 2018-100312

J. R. Jambeck et al., "Plastic waste inputs from land into the ocean; Science 13 Feb. 2015, p.768

Research on biodegradable composite materials as described above has focused on improving strength, but little is known about the effect of composites on biodegradability.
Therefore, the present inventor has studied a new biodegradable composite material with the aim of increasing the strength of the biodegradable resin and improving the biodegradability.

The present inventor increases the tensile strength of a biodegradable resin by 15% or more by blending a specific amount of cellulose nanofibers (CNF) in a biodegradable composite material containing cellulose nanofibers and a biodegradable resin. , We succeeded in promoting the decomposition rate by 7.5% or more.

More specifically, the present invention is a biodegradable composite material containing cellulose nanofibers and a biodegradable resin, wherein the cellulose nanofibers are contained in 100% by weight of the total amount of the cellulose nanofibers and the biodegradable resin. Provided are biodegradable composites having a content of 2% by weight or more, preferably 5% by weight, more specifically 5 to 30% by weight.

Cellulose nanofibers that can be suitably used in the present invention can be obtained by sorbothermally treating wood chips and chemically treating crushed crushed wood.

According to the present invention, since a biodegradable composite material is prepared by blending a specific CNF with a biodegradable resin, the tensile strength can be enhanced and the biodegradability can be improved.

Cellulose nanofibers (CNF) were blended with the biodegradable resin to prepare CNF-containing biodegradable composite materials, and the tensile strength and biodegradability of these biodegradable composite materials were improved.

Examples of biodegradable resins that can be used in biodegradable composite materials containing cellulose nanofibers and biodegradable resins according to the invention are polylactic acid (PLA); microbial polysaccharides such as pullulan and curdran; polycaprolactone ( PCL); starch-based biodegradable polymer; polyhydroxybutyrate (PHB), poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly (3-hydroxybutyrate-co-3-3) Biodegradable plastics from all microorganisms, including polyhydroxyalkanoates (PHA) such as hydroxyhexanoate (PHBH), polyhydroxybutyrate variate (PBAV); polyvinyl alcohol; polyamino acids; chitin and Chitosan; all cellulose-based biodegradable plastics including cellulose acetate, hydroxyethyl cellulose (HEC), hydroxypropylmethyl cellulose (HPMC); polyglycolic acid; polyethylene terephthalate succinate (PETS); polybutylene succinate (PBS) ) And all biodegradable resins such as polybutylene adipate-co-terephthalate (PBAT) and combinations thereof.

The CNF that can be used for the biodegradable composite material containing the cellulose nanofibers and the biodegradable resin according to the present invention is different from those produced by conventional production methods (for example, Patent Documents 4 and 5) in advance. It is obtained by sorbothermal treatment of wood of a size such as wood chips as it is without undergoing chemical treatment.
More specifically, the CNF used in the present invention is produced by a manufacturing method including a step of subjecting a wood chip to a sorbothermal treatment, a step of crushing the sorbothermally treated wood chip, and a step of subjecting the crushed wood chip to a chemical treatment. Manufactured.
The solvothermal treatment used in the present specification refers to a treatment in which a raw material such as wood chips is immersed in a solvent and subjected to a subcritical to supercritical state for a certain period of time under high temperature and high pressure conditions, and particularly when water is used as a solvent. May be called hydrothermal treatment.

The wood chips used as the raw material of the above-mentioned production method may be any raw material as long as it can extract natural cellulose, and for example, wood chips such as hardwood or softwood, or herbs may be used as a raw material. Further, the wood chip in the present invention has a size of preferably 0.5 × 0.5 cm to 2.0 × 2.0 cm, more preferably 0.7 × 0.7 cm to 1.5 × 1.5 cm, and most preferably 0.8 × 0.8 cm to 1.2 × 1.2 cm, such as a piece of wood. Includes those with a sword.

In the solvothermal treatment step of the above-mentioned production method, wood chips and herbs as raw materials are immersed in a solvent as they are, and are subjected to a subcritical to supercritical state under high temperature and high pressure conditions. Examples of the solvent used here include water, methanol, ethanol, propanol, pyrrolidone-based solvents such as N-methylpyrrolidone, acetate-based solvents such as butyl acetate, glycol ether-based solvents such as diethylene glycol monomethyl ether, and methyl ethyl ketone. Examples thereof include a ketone solvent, an aromatic solvent such as toluene and xylene, and a solvent such as a hydrocarbon solvent such as paraffin. Chips and the like immersed in a solvent are most preferably under 1 to 300 atm, ~ 400 ° C, preferably 2 to 250 atm, 5 to 200 ° C, more preferably 25 to 100 atm, 100 to 380 ° C. Is treated under 25 to 100 atm at 150 to 250 ° C. for 60 to 180 minutes within the range from subcritical to supercritical. By these solvothermal treatments, the chips and the like become soft and swollen crushed wood. The production method of the present invention is characterized in that wood chips and the like are directly subjected to a solvothermal treatment step. In the conventional CNF manufacturing method, wood chips and the like are first chemically treated, but in the above manufacturing method, a cellulose raw material having a certain size such as wood chips is first subjected to sorbothermal treatment without undergoing chemical treatment. However, there is a feature. The CNF produced by this production method enhances the physical characteristics of the composite material when mixed with a resin.

Next, the obtained crushed wood is subjected to a crushing step to further refine the pulp such as the crushed wood. A ball mill, a disc mill, a wet cutter mill, a pressure homogenizer, or the like can be used in this crushing step. This crushing process turns the wood into smaller crushed wood of 0.05-0.5 mm.

Finally, the crushed wood crushed material is chemically treated. Examples of the chemical treatment include an oxidation treatment, a hydrolysis treatment, a base treatment, or a combination thereof. Oxidizing agents such as ozone, hypochlorous acid or a salt thereof, persulfate or a salt thereof, and a perorganic acid or a salt thereof can be used for the oxidation treatment. An oxidation catalyst such as an N-oxyl compound may be used in combination with this oxidation treatment. Further, a hydrolase such as a cellulase-based enzyme or a hemicellulase-based enzyme can be used for the hydrolysis treatment. Caustic soda, KOH, or the like can be used for the base treatment.

Lignin can also be added to wood chips and the like prior to solvothermal treatment. By adding lignin, the surface of the produced CNF is hydrophobized (hydrophobicized CNF). A composite material produced by mixing a hydrophobic CNF and a resin is more preferable because it has a higher tensile strength than a non-hydrophobic CNF composite material to which lignin is not added. The mixing ratio of the crushed wood and lignin is preferably crushed wood / lignin (weight ratio) = 0.5 to 2, preferably 0.7 to 1.5, and more preferably 0.8 to 1.2.

Various additives can be added to the biodegradable composite material containing the cellulose nanofibers and the biodegradable resin according to the present invention as long as the strength and biodegradability are not impaired. For example, in practice, organic pigments and inorganic pigments can be added for coloring.

Various resin molded products can be molded using the biodegradable composite material according to the present invention as a material.
Such resin molded products include cutlery products such as spoons, knives, and forks molded by the injection molding method, containers, tableware, home appliance parts, automobile parts, electronic parts, mobile phone parts, lenses, switches, and optical disks. , Medical devices such as syringes; Tray, container, tableware, etc. molded by vacuum molding method; Bottles, containers, etc. molded by blow molding method; Film, sheet, bag molded by film molding method or inflation molding method Etc .; Containers, tableware, home appliance parts, automobile parts, etc. molded by hot press molding; various foam molded products molded by the foam molding method, all resin molded products that can be molded by methods including other molding methods are listed. Be done.

[Example 1]
1 kg of wood chips (1.0x1.0 cm) and 10 L of N-methylpyrrolidone were mixed and solvothermally treated in an autoclave (200 ° C., 25 atm) for 2 hours. The obtained crushed wood is heat-treated in an aqueous solution of 10% hypochlorous acid at 90 ° C. for 1 hour, and the CNF of the present invention (Sorbothermal treatment / chemical treatment CNF: In the examples, the CNF of the present invention is simply used. It is referred to as "CNF").
30 g of the CNF produced above was mixed with 100 g of polylactic acid (PLA; manufactured by Natureworks) and mixed by a twin-screw extruder to prepare a biodegradable composite material containing about 23% by weight of CNF. ..
The tensile properties (tensile strength, elongation at break, elastic modulus) and bending properties (bending strength) of the biodegradable composite material obtained by mixing PLA and CNF are shown by the precision universal testing machine Autograph AG-X and Measurements were made using a small desktop tester EZ-X (manufactured by Shimadzu Corporation), and data processing was performed using the "TRAPEZIUM LITE X" equipped with a macro function attached to the tester. The measurement results are shown in Table 1.

[Tensile property test]
Tensile strength, elastic modulus and elongation at break of biodegradable composites were measured in accordance with JIS K 7161: 1994.
Test speed: 20 mm / min Dumbbell test piece size: 1B size [Bending property test]
The bending strength of the biodegradable composite material was measured in accordance with JIS K 7171: 1994.
Test speed: 2 mm / min Test piece dimensions: 80 x 10 x 4 mm
Indenter tip radius R1: 5 mm
Radius of fulcrum tip R2: 5 mm
Distance between fulcrums: 60 mm

[Examples 2 to 11]
In the same manner as in Example 1, instead of polylactic acid (PLA), polycaprolactone (PCL), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA), polybutylene adipate-co-terephthalate (PBAT) , Staple resin, mixed resin of starch resin and PLA (weight ratio 6: 4), mixed resin of starch resin and PBAT (weight ratio 6: 4), cellulose acetate, hydroxyethyl cellulose (HEC), hydroxypropyl Methyl cellulose (HPMC) was used to obtain biodegradable composites, each containing approximately 23-30% by weight of CNF.
The tensile strength, tensile stroke, elastic modulus, bending strength and bending stroke of each biodegradable resin and the biodegradable composite material obtained by mixing CNF with each were measured. The measurement results are shown in Table 1.

It was confirmed that the tensile strength of all biodegradable resins was enhanced by blending CNF.

[Comparative Examples 1 to 3]
Similar to Example 1, using polylactic acid (PLA), polybutylene succinate (PBS), polybutylene adipate-co-terephthalate (PBAT), each about 2% by weight untreated CNF (the present invention). A biodegradable composite material containing (raw material for CNF) was obtained.
The tensile strength of each biodegradable resin and the biodegradable composite material obtained by mixing untreated CNF with each was measured. The measurement results are shown in Table 2.

The untreated CNF had low dispersibility in the biodegradable resin and could not be blended in excess of about 2% by weight.
Moreover, the tensile strength was lowered by blending the untreated CNF.

[Example 12]
Using polylactic acid (PLA), the effect of CNF formulation on biodegradability was investigated.
5 g, 11 g or 30 g of CNF was blended with respect to 100 g of PLA to obtain a biodegradable composite material containing CNF having a CNF content of about 5% by weight, about 10% by weight or about 23% by weight, respectively. ..
Table 3 shows the results of the biodegradable properties of the biodegradable composite material obtained by mixing PLA and CNF with it.

[Biodegradability test]
After the sample material was freeze-milled into powder, an enzyme hydrolysis test with proteinase K was performed.
0.2M NaH ₂ PO ₄ 2.8mL was mixed with 0.2M Na ₂ HPO ₄ 22.8mL, and distilled water was added to make the total volume 50mL to prepare a phosphate buffer having a pH of 7.7. Separately, a predetermined amount of proteinase K (white crystalline powder; Fuji Film Wako Pure Chemical Industries, Ltd.) derived from Tritiracium album was weighed and dissolved in a phosphate buffer to prepare an enzyme solution.
A predetermined amount of the material was added to the enzyme solution, and the mixture was stirred well with a vortex to prepare a sample for measurement, which was set in a constant temperature shaker. After a predetermined time, the sample for measurement was taken out, cooled with ice, filtered through a 0.2 μ membrane filter, and the filtrate was diluted 5-fold with distilled water. The water-soluble total organic carbon concentration (TOC) of the diluted filtrate was measured with a TOC measuring device (Shimadzu Corporation, TOC-VCSH).
The net TOC value of the material was obtained by subtracting the TOC value derived from the enzyme and the TOC value derived from the trace water-soluble component in the material from the TOC value of the filtrate. The TOC value derived from the enzyme was measured using an enzyme solution, and the TOC value derived from the material was measured using a suspension obtained by putting each material into a phosphate buffer and stirring well with a vortex.
Since the carbon content in the repeating unit of polylactic acid (-O-CH (CH3) -CO-; M = 72) is C3 = 36, exactly half of the weight of polylactic acid is the carbon content (36/72 = 50). %). For example, when 10 mg polylactic acid in 5 mL phosphate buffer is 100% biodegraded (hydrolyzed) and solubilized, the amount of carbon in the 5 mL aqueous solution becomes 5 mg, so the TOC value is 5 mg / 5 mL = 1 mg / mL = 1000 ppm. Is calculated. At this time, if the TOC value after the enzymatic decomposition test is 500 ppm, the biodegradation rate is 50%. The calculation was performed on the assumption that only the polylactic acid portion is hydrolyzed and solubilized by the enzyme, but the cellulose nanofibers are not decomposed.

[Examples 13 to 17]
In the same manner as in Example 12, instead of polylactic acid (PLA), polycaprolactone (PCL), polybutylene succinate (PBS), polybutylene adipate-co-terephthalate (PBAT), polyhydroxybutyrate variate ( Obtained a biodegradable composite material containing PBAV), a mixed resin of starch-based resin and PBAT, cellulose acetate, hydroxyethyl cellulose (HEC), hydroxypropylmethyl cellulose (HPMC), and each containing about 5 to 25% by weight of CNF. It was.
Table 3 shows the results of the biodegradable properties of each biodegradable resin and the biodegradable composite material obtained by mixing CNF with each resin.

As can be seen from Table 3, it was confirmed that when CNF was added in an amount of 5% by weight or more, not only the strength of the biodegradable resin was enhanced, but also the decomposition rate was improved at the same time.

[Comparison example]
Table 3 shows the results of the biodegradation properties of the biodegradable composite material containing about 2% by weight of untreated CNF in polylactic acid (PLA) in the same manner as in Example 12.
Table 4 shows the results of the biodegradable properties of the biodegradable composite material obtained by mixing PLA with untreated CNF.

The untreated CNF had low dispersibility in the biodegradable resin and could not be mixed in excess of about 2% by weight.
The biodegradability was reduced by blending untreated CNF.

The untreated cellulose nanofibers had low dispersibility in the resin and could not be mixed in excess of about 2% by weight. Then, when the upper limit of 2% by weight is added to the resin, both the strength and the biodegradability are lowered. On the other hand, the cellulose nanofibers of the present invention have high dispersibility in biodegradable resins and can be blended with resins according to desired strength. Furthermore, surprisingly, the effect of improving the biodegradation rate of the biodegradable resin was demonstrated.

By blending the cellulose nanofibers of the present invention with a biodegradable resin, a biodegradable resin composition having improved strength and biodegradability can be obtained at the same time.

Claims (7)

A biodegradable composite material containing cellulose nanofibers and a biodegradable resin, wherein the content of the cellulose nanofibers is 2% by weight or more in 100% by weight of the total amount of the cellulose nanofibers and the biodegradable resin. The biodegradable resins include polylactic acid; purulan and curdran; polycaprolactone; starch-based biodegradable polymer; polyhydroxybutyrate, poly (3-hydroxybutyrate-co-3-hydroxyvalerate), poly (3). -Hydroxybutyrate-co-3-hydroxyhexanoate), polyhydroxybutyrate variate, polyhydroxyalkanoate; polyvinyl alcohol; polyamino acids; chitin and chitosan; cellulose acetate, hydroxyethyl cellulose, hydroxypropylmethyl cellulose; polyglycol A biodegradable composite material selected from acids; polyethylene terephthalate succinates; polybutylene succinates; and polybutylene adipate-co-terephthalate copolymers or combinations thereof. The cellulose nanofibers are subjected to a step of subjecting a piece of wood or wood chips to a sorbothermal treatment, a step of crushing a sorbothermally treated wood chip, and a step of subjecting the crushed wood chips to a chemical treatment to obtain cellulose nanofibers (CNF). The biodegradable composite material according to claim 1, which is produced by a production method including the steps of obtaining the material in this order. The biodegradable composite material according to claim 2, wherein the solvothermal treatment is performed under critical or subcritical conditions. The biodegradable composite material according to claim 2 or 3, wherein the piece of wood or wood chip is a piece of wood or wood chip of softwood or hardwood. The biodegradable composite material according to any one of claims 2 to 4, wherein the chemical treatment is an oxidation treatment. The biodegradable composite material according to any one of claims 2 to 5, further comprising a step of adding lignin before the solvothermal treatment step. A molded product formed by using the biodegradable composite material according to any one of claims 1 to 6.