JPH0625260B2 - Novel biodegradable composite material and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel biodegradable composite material having excellent strength and capable of being decomposed by microorganisms in soil, for packaging, agriculture and horticulture. It is useful in the fields of film and materials for use, molding trays, etc.

[Conventional technology]

Conventionally, many molded products made of natural products such as cellulose, starch, chitosan, and protein are known. But,
All of them have problems that they are weak in strength as compared with general-purpose plastics, they are dissolved in water, and the strength in a wet state is extremely weak.

In order to improve these problems, for example, in the case of a molded body using starch, a crosslinking agent such as formaldehyde is reacted, or in the case of a molded body using a protein, a crosslinking agent such as isocyanate or dimethylolurea is reacted, Further, in the case of a molded body using chitosan, complicated operations such as fixing with alkali are carried out.

The present inventors have a new composite material having strength equal to or higher than that of general-purpose plastics and having sufficient strength even in water or in a wet state, by a simple method of combining natural material cellulose and chitosan. We applied for a patent because we found that (JP-A-2-6689) This composite material was also decomposed by microorganisms in soil, and in recent years, it has been found that it is useful as a pollution-free molding material amid plastic pollution.

[Problems to be solved by the invention]

The above, the novel composite material consisting of cellulose and chitosan has a fast microbial decomposition rate, and by changing the amount of chitosan and the temperature during the complexing, it is possible to adjust the strength and the microbial decomposition rate, Depending on the application, a higher microbial decomposition rate may be required.

[Means for solving problems]

The present inventors further increased the microbial decomposition rate of the novel composite material composed of the above-mentioned cellulose and chitosan, and as a result of diligent examination of a method capable of adjusting the rate arbitrarily, as a result, the protein was added to the fine cellulose fibers and chitosan. The inventors have found that the microbial decomposition rate can be increased without significantly lowering the strength by complexing with the above, and the microbial decomposition rate can be adjusted by changing the addition amount, and the present invention has been completed.

Cellulose fibers used in the present invention include wood, straw, cotton, hemp, bamboo, cellulose obtained from plants such as bagasse, hemicellulose, lignocellulose, pectocellulose and bacteria cellulose produced by bacteria. .

These cellulose fibers can be made fine by various known methods, but finely beaten cellulose fibers are particularly preferably used.

For the size of fine cellulose fiber, length 3000
The diameter is not more than μ and the diameter is not more than 50 μ, and particularly the length is not more than 1000 μ and the diameter is not more than 30 μ. If the size of the fine cellulose fibers exceeds the above range, the strength and transparency are deteriorated, which is not preferable.

The chitosan used in the present invention is deacetylated by subjecting chitin obtained from shells of crustaceans such as crab and shrimp, outer coat of insects, mycelium and the like to a chemical or biological treatment.

The molecular weight and degree of deacetylation of chitosan are not particularly limited, but those having a degree of deacetylation of 60% or more are preferable in terms of solubility.

Since chitosan does not dissolve in water as it is, it is used as a chitosan salt in water with an inorganic acid such as hydrochloric acid or an organic acid such as formic acid, acetic acid or lactic acid.

The protein used in the present invention includes casein,
Examples include albumin, gluten, soybean protein, gelatin, glue, and the like obtained by separating or concentrating from various animals and plants and microorganisms.

These are used by being dissolved in water adjusted to a pH suitable for dissolving each protein.

The production method of the composite material of the present invention is shown. A fine biodegradable composite material is obtained by mixing fine cellulose fibers, an aqueous solution of chitosan salt, and an aqueous protein solution, and drying the mixture to complete the composite. .

Although the mechanism of conjugation is not clear, the hydroxyl groups and carbonyl groups in cellulose, the amino groups in chitosan, and the amino groups and carboxyl groups in proteins form chemical bonds with each other during drying to form a complex. It is speculated that

As a blending ratio of raw materials used, fine cellulose fibers 10
2 to 100 parts by weight of chitosan, protein 2 to 0 parts by weight
To 100 parts by weight, particularly 5 to 80 parts by weight of chitosan, and 5 to 80 parts by weight of protein are preferable. Less than 2 parts by weight chitosan,
Or, if it exceeds 100 parts by weight, the wet strength becomes weak, which is not preferable. Further, if the amount of protein is less than 2 parts by weight, the microbial decomposition rate will not increase, and if it exceeds 100 parts by weight, the wet strength will be weak, which is not preferable.

The drying temperature is room temperature to 200 ° C, especially 50 ° C to
The range of 160 ° C is preferred. If the drying temperature exceeds 200 ° C., some decomposition starts and it is not preferable.

When producing the biodegradable composite material of the present invention, it is possible to add organic or inorganic fillers such as starch and silica, plasticizers, additives such as colorants, if necessary. is there.

[Action]

The novel biodegradable composite material of the present invention exhibits excellent dry strength and sufficient wet strength by being combined with fine cellulose fibers, chitosan and protein during the drying process. In addition, by adding a protein, the microbial decomposition rate can be increased as compared with a composite material composed of fine cellulose fibers and chitosan, and the microbial decomposition rate can be adjusted by changing the mixing ratio.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. All parts in these examples refer to parts by weight.

Tensile strength is measured according to ASTM D882-82,
The wet strength was measured immediately after the sample was immersed in water at 23 ° C. for 24 hours and then taken out.

The biodegradability test was measured by an accelerated test in which the film was incubated with a chitosan-degrading bacterium and the number of days until the film was fragmented was observed.

Examples 1 to 7 and Comparative Examples 1 and 2 An aqueous dispersion of fine cellulose fibers obtained by beating softwood bleached pulp (concentration 1 ^WT %), an aqueous solution of chitosan acetate (concentration 1 ^WT %), and an aqueous gelatin solution ( Concentration 3 ^WT %, pH
6) are mixed so as to have the composition shown in Table 1. This was cast on a glass plate and blow-dried at 70 ° C. for 6 hours to obtain a translucent film.

Table 1 shows the tensile strength and the number of days of microbial decomposition of the obtained film.

Examples 8 to 11, Comparative Example 3 An aqueous dispersion of fine cellulose fibers (concentration 1 ^WT %) obtained by beating softwood bleached pulp, an aqueous solution of chitosan acetate (concentration 1 ^WT %), and an aqueous soybean protein solution (concentration). 3 ^WT %, pH
8) are mixed so as to have the composition shown in Table 2. This was cast on a glass plate and blow-dried at 70 ° C. for 6 hours to obtain a translucent film.

Table 2 shows the tensile strength and the number of days of microbial decomposition of the obtained film.

Example 12 An aqueous dispersion of fine cellulose fibers obtained by beating softwood bleached pulp (concentration 1 ^WT %), an aqueous solution of chitosan acetate (concentration 1 ^WT %), and an aqueous dairy casein solution (concentration 3 ^WT %, p
H8) is mixed so that 50 parts of chitosan and 20 parts of dairy casein are mixed with 100 parts of fine cellulose fibers.
This was cast on a glass plate and blow-dried at 70 ° C. for 6 hours to obtain a translucent film.

The obtained film had a dry tensile strength of 1135 kg / cm ^{2 and a} wet tensile strength of 219 kg / cm ² , and the number of days of microbial decomposition was 2.5 days.

Comparative Example 4 An aqueous dispersion of fine cellulose fibers obtained by beating softwood bleached pulp (concentration 1 ^WT %) and an aqueous solution of chitosan acetate (concentration 1 ^WT %) were added to 50 parts of chitosan per 100 parts of fine cellulose fibers. Mix so that This was cast on a glass plate and blow-dried at 70 ° C. for 6 hours to obtain a translucent film.

The resulting film was dry tensile strength 1218kg / cm ² wet tensile strength 200 kg / cm ^2, was biodegraded days 4 days.

〔The invention's effect〕

The composite material obtained by the present invention, which can be rapidly decomposed by microorganisms, has excellent dry strength and sufficient wet strength, and since it is made of a natural product, it does not produce harmful substances even after being decomposed. It has an excellent effect as a pollution-free molding material in the fields of packaging films, agricultural films, molding trays, seedling raising pots and the like.

Front page continuation (72) Inventor Yoshihara, 1st year, 2-3-3 Hananomiyacho, Takamatsu City, Kagawa Prefectural Institute of Industrial Technology, Shikoku Institute of Industrial Technology (72) Inventor, Takamasa Kuno, Hananomiyacho, Takamatsu City, Kagawa Prefecture 2-3 chome, Shikoku Institute of Industrial Technology, Institute of Industrial Technology (72) Inventor Kunio Kanaoka, 1515 Nakatsu-cho, Marugame City, Kagawa Prefecture, Research Institute, Okura Industrial Co., Ltd. (72) Kazuo Kondo, Nakatsu-cho, Marugame City, Kagawa Prefecture 1515 Okura Industrial Co., Ltd.Inside the Research Institute (72) Inventor Satoshi Maruyama 1515 Nakatsu-cho, Marugame-shi, Kagawa Inside Okura Industrial Co., Ltd. Research Institute (72) Kenji Tateishi 1515, Nakatsu-cho, Marugame-shi, Kagawa Okura Industrial Ceremony Company in-house (72) Inventor Akihiko Ueda 1515 Nakatsu-cho, Marugame-shi, Kagawa Okura Industrial Co., Ltd. In-house inspector Masami Kobayashi

Claims (2)

[Claims] 1. A novel biodegradable composite material comprising fine cellulose fibers, chitosan, and protein. 2. A fine cellulose fiber and an aqueous chitosan salt solution,
And a novel method for producing a biodegradable composite material, which comprises mixing an aqueous protein solution and drying.