JP2686041B2 - Chitosan molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chitosan-based molded product which is excellent in water resistance and stability in physical properties over time.

[0002]

2. Description of the Related Art Chitosan, which is a natural polymer, and chitin, which is a raw material thereof, have high microbial degradability, biocompatibility, biodegradability and absorbability, and selective permeability which are not found in general synthetic polymers. Because of its properties, it has attracted attention as a functional polymer material, and application research on biodegradable films, medical materials, separation membranes, etc. is being actively conducted.

Chitosan is a straight-chain basic polysaccharide in which 2-amino-2-deoxy-D-glucose is bound to β-1,4-glucoside, and naturally exists in the cell wall of filamentous fungi and the like. Industrially, a large amount of natural chitin, 2-acetamido-2-deoxy-D-glucose, β-, contained in the outer shell of crabs and shrimp.
The 1,4-polymer can be obtained by treatment with concentrated alkali and complete or partial deacetylation.

When attempting to obtain a molded product such as a film or a fiber from these chitosan or chitin, none of them has to be molded from a solution because they have no thermoplasticity. Chitin is extremely difficult to dissolve in a general-purpose solvent, and when dissolved in a strong acid such as formic acid or sulfuric acid, which causes extremely low molecular weight, it is difficult to obtain a high-quality molded product. On the other hand, chitosan forms salts with many acids and becomes soluble in water,
Can be easily dissolved in an acid solution such as acetic acid or dilute hydrochloric acid,
It is more used as a polymer material for molding than chitin.

As a method for obtaining a molded product from a chitosan solution, there are a drying method in which a solvent is solidified by drying, a wet coagulation method in which the solution is solidified in a coagulating liquid such as an alkaline aqueous solution or a polyvalent metal salt aqueous solution. is there. Particularly in the case of a film, a drying method having a simple process is advantageous in terms of high productivity and economy.

However, in the molding method by the drying method, although the acid used for dissolving chitosan partially evaporates in the drying step, it cannot be completely removed, so that a large amount of acid remains in the molded body. Is inevitable.
As a result, the molded product has low water resistance, and the residual acid promotes the hydrolysis of chitosan over time, resulting in deterioration of the coloring and mechanical properties of the molded product during long-term storage and use. There is. When a volatile acid such as acetic acid is used to dissolve chitosan, the molded product has an acid odor, which reduces the commercial value of the product and induces alteration of substances that come into contact with the molded product when used. There is a risk of

In order to solve these problems, Japanese Patent Publication No. 52-41797 discloses that a molded product is immersed in an aqueous alkaline solution such as sodium hydroxide to neutralize the residual acid, and an excess amount of alkali and a salt produced. The post-treatment of washing away with water is described. However, such post-treatment remarkably increases the manufacturing cost of the molded product, and it becomes difficult to retain additives such as a plasticizer necessary for physical properties of the molded product.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation, and an object thereof is to form a chitosan-based molded article by a drying method in a step of drying an acid used for dissolving chitosan. A chitosan-based molded product that has high water resistance and stable physical properties over time without being subjected to post-treatment for acid removal by reducing the acid content remaining in the molded product by promoting evaporation To do.

[0009]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a stock solution of chitosan and 20% by weight or more of triethylene glycol with respect to chitosan is dissolved in a volatile organic acid aqueous solution. The chitosan-based product obtained by drying and solidifying
The present invention was completed by discovering that it contains coal, the acid content is extremely low, the water resistance is high, and the physical properties do not change over a long period of time.

The chitosan-based molded product of the present invention includes all those containing a small amount of chitosan, regardless of the amount of chitosan contained in the molded product component. That is, in addition to a film or fiber of chitosan alone, a composite of chitosan and a large amount of filler means a chitosan-based molded product. Examples of fillers that can be combined with chitosan include various starch particles such as corn starch, potato starch, rice starch, powdery or fine fibrous cellulose, calcium carbonate, talc and silica.
Furthermore, the chitosan-based molded product may be a mixture of chitosan and another polymer such as polyvinyl alcohol. Since a relatively large amount of triethylene glycol is added to chitosan, particularly in a chitosan-based molded product of a composite having a low chitosan content, the effect of triethylene glycol on the physical properties of the molded product is small and the effectiveness is high.

The degree of deacetylation and molecular weight of chitosan used are not particularly limited, and any one can be used depending on the purpose, but in general, considering the solubility in acid and the strength of the molded body, Deacetylation degree is 70 mol% or more, molecular weight is
It is preferably 50,000 or more.

Triethylene glycol contains a large amount of triethylene glycol in addition to a simple substance and has an average molecular weight of 2
You may add polyethylene glycol of about 00.
Even in that case, the content of triethylene glycol is 20% by weight or more, and more preferably 30% by weight, based on chitosan.
The above is added. If the amount of triethylene glycol added is less than 20% by weight, the effect of acid removal is insufficient and the molded product becomes water-soluble or has extremely low water resistance.
In addition, it is not possible to prevent changes in physical properties over time.

Triethylene glycol has not only an acid-removing effect but also a weak plasticizing effect on chitosan. However, if necessary, other plasticizers such as glycerin and various additives such as colorants may be added to the stock solution. You can also Since no washing treatment for acid removal is required after molding, these additives can exhibit their effects without being lost to the end.

The volatile organic acid that dissolves chitosan must have sufficient volatility under normal pressure, and examples of such volatile organic acid include formic acid, acetic acid, propionic acid, trichloroacetic acid and the like. Of these, acetic acid is most preferable in terms of economy and handleability. In addition to such organic acids, chitosan is soluble in inorganic acids such as hydrochloric acid, but inorganic acids have a strong interaction with chitosan, and even if triethylene glycol is added, the chitosan molded product can be heated by heating. Cannot be used because it is not detached. Although the amount of the volatile organic acid used is not particularly limited, it is suitable to be about 0.7 to 1.5 gram equivalent per amino group of chitosan.
Below 0.7 gram equivalent, the solubility of chitosan is poor,
If it is more than 1.5 grams equivalent, the amount remaining after drying increases,
Either case is not preferred.

In order to obtain a chitosan-based molded product from the undiluted solution, various methods are adopted depending on the shape of the molded product. For example, in the case of a film or sheet, the stock solution is cast onto a corrosion-resistant surface such as a stainless steel belt or a chrome-plated rotating drum. Good. It is preferable that the drying temperature is as high as possible because the evaporation of the acid is further promoted. However, when the drying temperature is 100 ° C. or higher, a boiling phenomenon occurs due to boiling of water, and therefore 70 to 95 ° C. is preferable. A molded product having a shape like a hard pharmaceutical capsule can be obtained by applying the undiluted solution to the surface of a mold having a three-dimensional surface and drying by the same method. In addition, fibers can be molded by a method such as spinning the stock solution from a fine nozzle into hot air.

By further heat-treating the thus-obtained chitosan-based molded product, the acid content in the molded product can be further reduced. In this case, the heat treatment temperature may be 100 ° C. or higher.

[0017]

The reason why the presence of triethylene glycol accelerates the evaporation of the acid in the molded article is not always theoretically clear, but the following phenomenon was experimentally observed. When triethylene glycol is not added, after the evaporation of a part of the acid, even if it is reheated, no further reduction occurs. In comparison with this, in the case of adding triethylene glycol, the evaporation of the acid proceeds depending on the degree of heating even after the drying and solidification. By adding triethylene glycol, it is possible to obtain a chitosan-based molded product having a low acid content and good water resistance and good physical stability over time.

[0018]

As described above, according to the present invention, since the acid as well as the water as the solvent is removed only by the heating and drying step, the obtained chitosan-based molded article has a low acid content and a high water resistance. Also, the stability of physical properties over time is good. Since it has water resistance, triethylene glycol and slightly residual acid can be removed by washing with water, so it can be used in applications where the inclusion of water-soluble substances in the molded product is a problem, such as dialysis membranes. it can.

Further, since most of the acid is evaporated in the heating and drying step, the acid can be recovered by a method such as washing hot air after drying with water and can be reused for dissolving chitosan.
Therefore, it is possible to mass-produce the chitosan-based compact at low cost.

[0020]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1 Chitosan (Flownac C, manufactured by Kyowa Technos Co., Ltd.) having a deacetylation degree of 89.4 mol% was dissolved in a 3 wt% acetic acid aqueous solution at a concentration of 9 wt%. Triethylene glycol was added to chitosan in an amount of 20 to 100 as shown in Table 1.
% By weight to give a stock solution for film preparation. This stock solution was cast on a glass plate to a uniform thickness, dried for 30 minutes in a hot air dryer at 80 ° C., and then peeled from the glass plate to form a film having a thickness of about 30 μm. This film was cut into small pieces to prepare a sample for measuring the residual amount of acetic acid. This sample was immersed in an aqueous sodium hydroxide solution for 3 hours or more to neutralize the acetic acid in the film, and then the excess alkali was neutralized and titrated with hydrochloric acid to quantify the amount of acetic acid in the film, and this value was cast. The value obtained by dividing the amount of acetic acid in the stock solution was calculated as the acetic acid residual rate. Further, the film was immersed in water and its water resistance was evaluated. Next, the film produced under the same conditions as above was further hung in a hot air dryer at 120 ° C. and re-dried for 15 minutes. Similarly, the acetic acid residual rate was determined and the water resistance was evaluated.

Comparative Example 1 The amount of triethylene glycol relative to chitosan is shown in Table 1.
0 to 10% by weight was added to prepare a stock solution for film preparation. A film was prepared in the same manner as in Example 1 except for the above. The performance of this film was evaluated under the same conditions as in Example 1.

As a result, as shown in Table 1, at 80 ° C., 30
In the case of drying for 1 minute, 80% or more of acetic acid used for dissolving chitosan remains in the film containing 10% by weight or less of triethylene glycol even if triethylene glycol is not added (comparative example 1), and the film is easily dissolved in water. Dissolved in. On the other hand, in the film in which 30% by weight or more of triethylene glycol was added (Example 1), the residual rate of acetic acid was significantly decreased and the water resistance was improved as the amount of addition was increased. When 70% by weight or more was maintained, a film having good water resistance with little swelling and high strength was obtained. Further, when the film thus primary dried was re-dried at 120 ° C. for 15 minutes, the effect of adding triethylene glycol became more remarkable. That is, in the film to which triethylene glycol was not added at all, the acetic acid residual rate was hardly reduced even by re-drying, but the acetic acid residual rate of the film to which 30% by weight or more of triethylene glycol was added was remarkably reduced, and in the primary drying, It was revealed that a film having extremely high water resistance can be obtained even in the case of 50% by weight, which had a problem in strength.

[0024]

[Table 1]

Evaluation of Water Resistance A: Little swelling and high film strength.

B: The shape of the film is maintained, but swelling is large and strength is low.

C: Not dissolved, but remarkably swells and decomposes into small pieces.

D: It dissolves.

Example 2 Chitosan (Flownac N, manufactured by Kyowa Technos Co., Ltd.) having a deacetylation degree of 83.2 mol% or more was dissolved in a 0.5 wt% aqueous acetic acid solution at a concentration of 1.5 wt%, Rice starch particles (manufactured by Shimada Chemical Industry Co., Ltd., Micropearl) were added thereto in an amount of 200% by weight with respect to chitosan, and 150% by weight of triethylene glycol, and uniformly mixed to prepare a stock solution for forming a biodegradable film. did. This stock solution was cast on a glass plate to a uniform thickness and dried at 80 ° C. for 40 to 120 minutes to obtain a film having a thickness of 60 μm.

Comparative Example 2 A film was prepared under the same conditions as in Example 2 except that triethylene glycol was not added.

For the films of Example 2 and Comparative Example 2, the amount of acetic acid in the film was measured in the same manner as in Example 1,
The water resistance was evaluated. Further, the tensile strength and the elongation in an atmosphere of 23 ° C. and 50% RH were measured, and the color of the film was measured by a color difference meter in the L ^* a ^* b ^* color system.
Further, these films were hermetically packaged with a polyethylene film laminated with aluminum foil, and the changes in tensile strength, elongation and color of the film after storage at room temperature for 5 months were examined.

As a result, as shown in Table 2, when triethylene glycol was not added, the amount of acetic acid was large and the amount did not decrease at all even if the drying time was prolonged, and in water, it significantly swelled. It was not strong enough to be handled as a film. On the other hand, when 150% by weight of triethylene glycol was added, the content of acetic acid was less than half that of no addition even after drying for 40 minutes, which was close to the limit of drying, and the value increased due to the extension of the drying time. Fell sharply and became a film having good strength even in water.

[0033]

[Table 2]

Further, the color change of the film with the passage of time is highly correlated with the acetic acid content, and a triethylene glycol-free film having a high acetic acid content is markedly colored yellow during storage for 5 months, The change in the chromaticness index, especially the increase in b ^* , which indicates yellow color quality, was also remarkable when the values measured by the color difference meter were examined. On the other hand, in the film to which triethylene glycol is added, there is almost no color change after 5 months, and the tensile strength and elongation are largely reduced when the drying time is insufficient at 40 minutes, but 60 minutes or more. The change was extremely small in the dried film containing a small amount of acetic acid, and it was revealed that a film having stable physical properties with time can be obtained by adding triethylene glycol and heating sufficiently.

The film prepared in this example was buried in the soil of an orchard and examined for biodegradability. As a result, it was partially decomposed after one month regardless of the addition of triethylene glycol. Started and the film disappeared completely after 2 months.

Comparative Example 3 By the same method as in Example 1, a polyhydric alcohol other than triethylene glycol was added to chitosan at 30 or 70.
The effect of removing acetic acid when added by weight% was investigated, and the results are shown in Table 3.

As the polyhydric alcohol, glycerin, ethylene glycol, propylene glycol and diethylene glycol were used. 8 at 30% by weight addition
Even after primary drying at 0 ° C. for 30 minutes and re-drying at 120 ° C. for 15 minutes, more than half of the amount of acetic acid used to dissolve chitosan remained in the film, and the film dissolved in water or decomposed into small pieces. . Also, when 70% by weight of polyhydric alcohol was added, the residual rate of acetic acid was high compared to the result of addition of triethylene glycol in Example 1, and water resistance sufficient to maintain the shape of the film in water was obtained by primary drying. I couldn't get it. When these films were dried at 120 ° C. for 15 minutes, the acetic acid residual ratios of the glycerin and diethylene glycol-added films were 34.5 and 33.1, respectively.
%, The water resistance was improved as compared with the case of only primary drying, but the swelling in water was still large and sufficient water resistance was not exhibited, and ethylene glycol and propylene glycol were added. The film decomposed into pieces in water even after re-drying.

[0038]

[Table 3]

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Claims (1)

(57) [Claims] 1. A Ri name by drying and solidifying the stock solution obtained by dissolving at least 20 wt% of triethylene glycol in a volatile organic acid aqueous solution to chitosan and chitosan, triethyl
A chitosan-based molded product containing ren glycol .