JPH0459830A - New biodegradative composite material and its production - Google Patents

Abstract

PURPOSE:To obtain the title material having excellent strength, capable of being degraded by microorganisms in soil and useful as a film for packaging, agriculture, horticulture, material therefor, molded tray, etc., by blending a fine cellulose fiber with an aqueous solution of chitosan salt and an aqueous solution of protein, and drying the blend. CONSTITUTION:A fine cellulose fiber (preferably having <=1000mu length and <=30 MU diameter) is blended with an aqueous solution of chitosan salt (preferably having >=60% deacetylation degree) and an aqueous solution of protein (e.g. casein, albumin, gluten or soybean protein) and the blend is dried to provide the objective material. Furthermore, the above-mentioned blend is carried out at amounts of chitosan of 5-80 pts.wt. and protein of 5-80 pts.wt. based on 100 pts.wt. cellulose fiber.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a novel biodegradable composite material that has excellent strength and can be decomposed by microorganisms in soil, and is suitable for packaging, agriculture, and horticulture. It is useful in fields such as films and materials for use in plastics, molded trays, etc.

[Conventional technology]

Many molded products made from natural materials such as cellulose, starch, chitosan, and protein have been known for a long time, but they have problems such as being weaker in strength than Tsuku, dissolving in water, and having extremely low strength in wet conditions. It has points.

In order to improve these problems, for example, in the case of a molded object using starch, a crosslinking agent such as formaldehyde is reacted, and in the case of a molded object using protein, a crosslinking agent such as isocyanate or dimethylol urea is reacted. Furthermore, in the case of molded articles using chitosan, complicated operations such as alkali fixation are performed.

The present inventors have developed a new composite material that has strength equal to or greater than general-purpose plastics and that maintains sufficient strength even in water and in wet conditions by combining the natural materials cellulose and chitosan. We discovered that this could be obtained and applied for a patent. (Jikai Hei 2-6689) This composite material is also decomposed by microorganisms in the soil, and as plastic pollution has become a problem in recent years, it has also been found to be useful as a non-polluting molding material.

(Problems to be solved by the invention) The above-mentioned novel composite material made of cellulose and chitosan has a fast microbial decomposition rate, and by changing the amount of chitosan and the temperature during compounding, the strength and microbial decomposition rate can be improved. However, depending on the intended use, a faster microbial decomposition rate may be required.

[Means for solving problems]

The inventors of the present invention further accelerated the microbial decomposition rate of the above-mentioned novel composite material consisting of cellulose and chitosan, and as a result of intensive study on a method to arbitrarily adjust the rate, the inventors added protein to the fine cellulose fibers and chitosan. The present inventors have discovered that by compounding, the microbial decomposition rate can be increased without significantly reducing the strength, and that the microbial decomposition rate can be adjusted by changing the amount added.

Examples of cellulose fibers used in the present invention include cellulose, hemicellulose, lignocellulose, and pectocellulose obtained from plants such as wood, straw, cotton, hemp, bamboo, and bagasse, and fibers made from grouper cellulose produced by bacteria. It will be done.

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

Regarding the size of fine cellulose fibers, the length is 3000
μ or less, the diameter is 50 μ or less, and particularly preferably the length is 1000 μ or less and the diameter is 30 μ or less.

When the size of fine cellulose fibers exceeds the above range,
This is undesirable because strength and transparency decrease.

The chitosan used in the present invention is obtained by deacetylating chitin obtained from the shells of crustaceans such as crabs and shrimps, the rinds of insects, mycelium, etc. by chemically or biologically treating it.

There are no particular restrictions on the molecular weight or degree of deacetylation of chitosan, but from the viewpoint of solubility, the degree of deacetylation is preferably 60% or more.

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

Proteins used in the present invention include those obtained by concentrating mosquitoes.

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

The method for manufacturing the composite material of the present invention is shown in that by mixing fine cellulose fibers, an aqueous solution of chitosan salt, and an aqueous protein solution and drying, the composite is completed and a novel biodegradable composite material is obtained. .

Although the mechanism of conjugation is not clear, hydroxyl groups and carbonyl groups in cellulose, amino groups in chitosan, and amino groups and carboxyl groups in proteins form chemical bonds with each other during drying, resulting in conjugation. It is presumed that it has changed.

The blending ratio of the raw materials used is: 10 fine cellulose fibers
0 parts by weight, 2 to 100 parts by weight of chitosan, 2 parts by weight of protein
~100 parts by weight, particularly preferably 5 to 80 parts by weight of chitosan and 5 to 80 parts by weight of protein.

If the amount of chitosan is less than 2 parts by weight or more than 100 parts by weight, the wet strength will become weak, which is not preferable. Furthermore, if the protein content is less than 2 parts by weight, the rate of microbial decomposition will not be increased, and if it exceeds 100 parts by weight, the wet strength will be weakened, which is undesirable.

In addition, the drying temperature is room temperature to 200°C, especially 50°C.
A range of 160°C to 160°C is preferred. If the drying temperature exceeds 200°C, partial decomposition begins, which is not preferable.

In addition, when producing the biodegradable composite material of the present invention, it is also possible to add additives such as starch, organic fillers such as silica, inorganic fillers, plasticizers, colorants, etc. be.

[Effect]

The novel biodegradable composite material of the present invention is composed of fine cellulose fibers, chitosan, and protein during the drying process, and exhibits excellent dry strength and sufficient wet strength. Furthermore, by incorporating protein, the microbial decomposition rate can be increased compared to a composite material consisting of fine cellulose fibers and chitosan, and the microbial decomposition rate can be adjusted by changing the blending ratio.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. In these examples, all parts are by weight.

Tensile strength was measured according to ASTM D882-81, and wet strength was measured immediately after the sample was immersed in water at 23°C for 24 hours and then taken out.

The microbial decomposition test was performed by culturing the film with chitosan-degrading bacteria and measuring the number of days until the film fragmented into pieces.

Examples 1 to 7, Comparative Example 1.2 Table 1 shows the tensile strength of the obtained films and the number of days for microbial decomposition.

Examples 8 to 11, Comparative Example 3 An aqueous dispersion of fine cellulose fibers (concentration 1'7%) obtained by beating softwood bleached pulp and an aqueous solution of chitosan acetate (
Concentration 1''T%), and soybean protein aqueous solution (concentration 3'T%,
pH 8) were mixed to give the composition shown in Table 2. This was cast onto a glass plate and dried with air at 70°C for 6 hours to obtain a translucent film.

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

(concentration 31'Ii%, pH 6) were mixed to give the composition shown in Table 1. This was cast onto a glass plate and heated to 10°C.
The film was air-dried for 6 hours to obtain a translucent film.

Example 12 An aqueous dispersion of fine cellulose fibers obtained by beating softwood bleached pulp (concentration 1″1%) and an aqueous chitosan acetate solution (
(concentration 1'7%), and formal dress casein aqueous solution (concentration 307%)
%, pH 8) are mixed in such a manner that 50 parts of chitosan and 20 parts of formal casein will be added to 100 parts of fine cellulose fiber. This was cast onto a glass plate and dried with air at 70°C for 6 hours to obtain a translucent film.

The obtained film had a dry tensile strength of 1135 kg, a wet temperature tensile strength of 219 kg/i, and a microbial decomposition period of 2.5 days.

Comparative Example 4 An aqueous dispersion of fine cellulose fibers (concentration IM?%) obtained by beating softwood bleached pulp and an aqueous solution of chitosan acetate (
Mix 50 parts of chitosan to 100 parts of fine cellulose fibers. This was cast onto a glass plate and dried with air at 70°C for 6 hours to form a translucent film. Obtained.

The resulting film has a dry tensile strength of 1218 kg/c1
! Wet tensile strength 200 kg/d, microbial decomposition days 4
It was day.

[Effects of the Invention] 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 from natural materials, it does not contain harmful substances even after being decomposed. It has the characteristic that it does not produce any pollution, and exhibits excellent effects as a non-polluting molding material in the fields of packaging films, agricultural films, molding trays, seedling pots, etc.

Agent: Patent Attorney: Mi Ogawa

Claims (2)

[Claims] (1) A novel biodegradable composite material consisting of fine cellulose fibers, chitosan, and protein. (2) A method for producing a novel biodegradable composite material, which comprises mixing fine cellulose fibers, an aqueous chitosan salt solution, and an aqueous protein solution, and drying the mixture.