JPH0686549B2 - Starch / chitosan-based biodegradable material and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial field of application The present invention is utilized for various applications such as packaging sheets and foamed molded articles that need to be rapidly decomposed after use. The present invention relates to a molding material that is transparent or translucent, has flexibility, and does not dissolve in water, and a method for producing the same. More specifically, the present invention relates to a natural polysaccharide obtained by combining chitosan and fine starch granules. The present invention relates to a molding material, which can be completely decomposed by microorganisms in soil after use, and a manufacturing method thereof.

Prior art and its problems Since chitosan is difficult to be an aqueous solution as it is, it is generally used by dissolving it in a dilute aqueous solution such as acetic acid and partially forming a salt form. However, molding and film formation from an aqueous salt solution of chitosan cannot be performed only by drying, and the complicated operation of fixing alkali and the expensiveness of chitosan hinder its use.

With respect to a molded product using starch, there is an example in which a cross-linking agent such as formaldehyde is used in order to prevent dissolution in water, but this cannot be said to be completely harmless to the human body. A sheet obtained by inducing gelled starch to dryness is known as an oblate, which easily absorbs and dissolves not only in water but also in humid air. on the other hand,
The present inventors have already applied for a patent that a composite of cellulose fiber and chitosan salt with starch maintains its shape in water and becomes a water-absorbing composite material having biodegradability after a certain period of time. Although this cellulose / chitosan / starch-based water-absorbing composite material is not soluble in water, this material has a drawback of poor transparency. We also applied for a patent for a composite material consisting of heat-dissolved starch, chitosan salt, and glycerin, but this starch-chitosan-glycerin-based material had the drawback that it was difficult to increase the concentration of the aqueous starch solution during the manufacturing process.

The present invention relates to a novel composite material which retains its shape in water without glycerin and can be used as a transparent and flexible molding material, and a method for producing the same. The present invention provides a material that can be easily prepared and molded to a high concentration, does not dissolve even in a wet state, and decomposes without pollution after use, and a method for producing the same by combining chitosan salt and finely divided starch granules. . There is no example of preparing such a composite material and no example of application.

Problems to be Solved by the Invention Of the molded articles used in human life,
The period of use is short, and many materials are desired to be decomposed immediately after disposal. The present invention provides a molding material which can be safely decomposed by microorganisms in water including the ocean or soil after a certain period of time and can be burned, in place of a conventional petroleum-based plastic, and a method for producing the same.

Means for Solving the Problems As a result of earnest research on a molding material having microbial degradability, the present inventors have found that a finely divided starch granule / chitosan-based novel composite material having appropriate microbial degradability and its The manufacturing method was found and the present invention was completed.

The main object of the present invention is to make a composite material of finely divided starch granules / chitosan series into a molded product capable of maintaining its shape in water. The complex is also biodegradable and decomposes without leaving contaminants after a period of time. It is intended to produce a new composite molded body having such properties.

When starch is heated with water, it gels and becomes α type. This composite material of gelled starch and chitosan has high transparency but low water resistance. In addition, since gelled starch is difficult to increase in concentration, molding operability is poor.

On the other hand, it is possible to use starch as it is. The starch granules are β-type spheres having a hard crystal structure and having a diameter of several μm or more, although they depend on the plant material. When starch granules were used as they were, the water resistance was high, but the complexation of starch and chitosan was not sufficient, and only a complex with low strength was obtained. Therefore, it was found that by mechanically pulverizing the starch granules to destroy some crystals without heating and then compounding this with chitosan, a complex utilizing the advantages of both of the above can be obtained. Is.

2% or more of the whole starch is 1μ
It is sufficient that the particle size is not more than m, and such miniaturization can be achieved by using various dry pulverizers or wet pulverizers such as a high-pressure homogenizer.

Among the materials used in the present invention, starch has various plant-derived starch granules, and any of them can be used as the raw material of the present invention. Further, chitin is a nitrogen-containing high molecular substance contained in shells of crustaceans, mycelium and the like. Among them, a substance having a high degree of deacetylation is called chitosan, and chitosan is used in the present invention. The use of chitosan is not particularly limited depending on its origin. Since chitosan is water-soluble in the present invention, it is used by dissolving it in a dilute aqueous solution of acetic acid, lactic acid or the like in the raw material.

All of these materials are biodegradable, and there is no concern about soil contamination even after decomposition. Even if I eat again,
There is no problem with safety for the human body. A material based on this composite is a solid that can be molded and has a film-forming ability, and further has biodegradability. The molded product does not dissolve in water, and the microbial degradability can be controlled by the molding conditions.
It is also easy to dispose of without pollution by combustion.

Specifically, chitosan is added to the fine starch granules in the range of 1 to 150
%, Preferably 5-80%, in the form of an aqueous chitosan salt solution, and dried by heating to mold. It does not prevent the addition of fillers, plasticizers, reinforcing agents, foaming agents, etc. to the raw material of this mixture.

By heating and drying this mixture raw material, starch
Although the composite of chitosan type is completed and the molded body is manufactured, 25
Molding at 250 ° C. or lower is preferable because coloring is remarkable at 0 ° C. or higher. In the case of a high-concentration raw material mixture, it does not prevent the molding by heating and pressurization, and the foaming by steam at that time can be utilized for the molding.

EFFECTS OF THE INVENTION The molded article prepared by the method of the present invention is easily microbially decomposed in a marine river or soil, and does not generate a harmful substance after being decomposed. Further, this molded body has various strengths. For this reason, the molded body can be used for various purposes, and it becomes unnecessary to dispose of it after use. Therefore, by using the material of the present invention as a molded body, it is possible to solve the problem of pollution of plastic waste, which is now becoming serious.

EXAMPLES Next, the composite material of the present invention and the method for producing the same will be described in more detail with reference to examples, but the invention is not limited thereto.

Example 1 About 15% of the whole corn starch finely divided by a ball mill to 1 μm or less, chitosan as an aqueous acetate solution was added to corn starch.
20% was mixed, and a slab piece was composite-molded by heat drying. The starch concentration of the raw material aqueous solution was 50%. The drying temperature was 30 to 300 ° C., and heat-drying was performed in a metal container for the time until drying to form a plate piece having a thickness of about 1 mm. Table 1 shows the strength of the molded product (unit: kg / cm ² ). All the molded products had sufficient strength, but the ones molded at a compounding temperature of 300 ° C or higher showed remarkable coloring. Therefore, the temperature is 250 ° C.
The following are preferred.

In addition, these molded products (15 mm × 15 mm × 1 mm) should have a water content of 25 ° C.
When buried in 2% of soil, all decomposed and disappeared within 3 months.

Example 2 A potato starch grain refined to about 15% 1 μm or less by a high-pressure homogenizer was mixed with an aqueous acetic acid solution of shrimp shell-derived chitosan (deacetylation degree 99%) so that chitosan was 1 to 150%. A polyol-based plasticizer was added to this mixed solution (60% based on starch) to give the film flexibility. Aqueous solution has a starch concentration of 10%
And This is cast on a stainless petri dish, and it is 3 at 70 ℃.
A film having a thickness of about 60 μm was produced by air blowing and drying. Drying, wet strength (unit: kg / cm ² ) and 25 ° C. of the obtained film,
Table 2 shows the decomposition time in soil with a water content of 12%.

From this result, it can be seen that when the chitosan addition amount is 1% or less, it has no strength in water, but when it is 5% or more, it has some strength. Also, it can be seen that the strength of chitosan continues to increase up to 80%.

It was found that all of these films decomposed in the soil within 3 months without leaving any trace.

Example 3 An aqueous lactate solution of chitosan was used as chitosan for corn starch granules finely ground to various degrees by a ball mill.
Example 1 was mixed with 20% and 60% of glycerin as a plasticizer.
The strength of the obtained film (unit:
kg / cm ² ) and water resistance were investigated. The results are shown in Table 3, and it can be seen that the dry and wet strengths of the film are high when starch containing 2% or more of fine particles of 1 μm or less is used. However, the wet strength decreased when starch containing 80% fine particles was used.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takamasa Kubo 2-3-3 Hananomiya-cho, Takamatsu-shi, Kagawa Inside Shikoku Industrial Technology Laboratory, Institute of Industrial Technology (56) Reference JP-A 64-81837 (JP, A) ) JP-A-61-159430 (JP, A)

Claims (2)

[Claims] 1. A biodegradable material obtained by compounding chitosan with starch granules which have been miniaturized by mechanical impact. 2. A mixture of finely divided starch granules with an aqueous salt solution of chitosan and heating and drying at 300 ° C. or lower.
A method for producing the microbial degradable material according to the item.