JPH0673098A - Method for coagulation and coagulant - Google Patents

Abstract

PURPOSE:To coagulate and regenerate a silk fibroin solution. CONSTITUTION:The objective method for coagulation is characterized by using a 2-20% aqueous solution of an alkali metallic halide in a lower aliphatic alcohol as a coagulant in coagulating a dope containing silk fibroin dissolved therein with a solution prepared by dissolving the alkali metallic halide at >=30% concentration in a mixed solvent of a lower aliphatic alcohol with water at >1 mixing ratio of alcohol/water. Furthermore, the objective coagulant is such that the lower aliphatic alcohol is one of methyl alcohol, ethyl alcohol and isopropyl alcohol or a mixture thereof; the alkali metallic halide is lithium bromide or lithium chloride at its concentration of 5-15% and the moisture content in the coagulant is <=5%.

Description

Detailed Description of the Invention

[0001]

[Industrial field of application] Although the recycling of a large amount of waste generated during the silk production process has been studied for a long time, its recycling as fiber has not been successful. The reason is,
This is because no suitable solvent or non-solvent has been found. The present invention relates to a coagulation method and a coagulant for regenerating and coagulating silk fibroin dissolved in a specific solvent from a solution, whereby a regenerated fiber of silk fibroin,
Production of film etc. becomes possible.

[0002]

2. Description of the Related Art Studies on coagulation and regeneration of silk fibroin can be broadly divided into those relating to a solvent and those relating to a regeneration method. As for the former, the present inventors have already found a good one. For the latter, it has been proposed to use water or a weakly acidic aqueous solution, but in this case it is necessary to remove inorganic salts by dialysis before solidifying. This operation is difficult and is not industrially good. In addition, gelation may occur during dialysis.

[0003]

DISCLOSURE OF THE INVENTION The present invention is intended to develop a method for immediately obtaining coagulation regeneration without dialysis which is carried out as a pretreatment for regeneration of a fibroin solution to obtain a good molded product. It is a thing. In this pretreatment method, it is necessary to lower the solution viscosity because it is necessary to make the dialysis specific surface area as large as possible. Therefore, it is necessary to keep the solution concentration low, and a step of concentrating after dialysis is added. The solution from which the inorganic salt has been removed is unstable and often gels in this step, which may make the subsequent coagulation regeneration step difficult.
In order to solve this, it is necessary to newly develop a solvent or non-solvent that does not require dialysis. For this purpose, the present invention has examined a coagulation method and a coagulant for coagulating and regenerating a good molded product from a fibroin solution dissolved in a good solvent of silk fibroin.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have surprisingly utilized a lower aliphatic alcohol solution of an alkali metal halide as a coagulant. Therefore, it was found that the silk fibroin dissolved in this good solvent can be easily coagulated and regenerated without dialysis of the inorganic salt contained in the solvent. The reason for this is not clear, but when a fibroin solution dissolved in a good solvent is added to a solution prepared by dissolving 2 to 20% of an alkali metal halide in a lower aliphatic alcohol which is a non-solvent, the alkali metal in the solution is The halide moves into the non-solvent due to the concentration difference, and the amount becomes less than the limit. It can be considered that this is because fibroin aggregates and solidifies. In this case, the method of moving the metal salt and the alcohol is controlled by the difference in the alkali metal halide concentration in the solvent and the non-solvent, and the scope of the present invention is effective. The present invention will be described in detail below. The present invention relates to a novel solvent for silk fibroin already developed by the present inventors. It is an effective coagulant for obtaining a better regenerated product when fibroin is coagulated and regenerated from a fibroin solution dissolved in these novel solvents. A feature of the present invention is, unlike the existing methods, a method in which an inorganic salt in a solution can be directly coagulated and regenerated without dialysis. An effective coagulant composition for this is a solution of an alkali metal halide in a lower aliphatic alcohol. Among the alkali metals referred to herein, lithium and sodium are particularly preferable, but the alkali metal is not limited thereto. Among the halogens mentioned here, chlorine and bromine are particularly preferable, but the halogen is not limited thereto.
Among these alkali metal halides, lithium bromide and lithium chloride are particularly preferable, but are not limited thereto. The lower aliphatic alcohol referred to here is methyl alcohol, ethyl alcohol, and isopropyl alcohol, but is not limited thereto. Concentration of alkali metal halide is 2-20%
However, it is particularly preferably 5 to 20%, but not limited to this. The amount of water contained in these solutions is preferably as small as possible and should not exceed 5%. The temperature of the coagulation bath is not particularly limited, but a lower temperature is preferable from the viewpoint of explosion protection. The coagulation method may be carried out by spinning the prepared dope directly into a coagulation bath from nozzles of various forms, or by contacting with a coagulant what has been cast on a flat plate such as glass in advance. However, the present invention is not limited to these. The form of the nozzle used in this case is also not limited. Further, the dope spun in the coagulation bath is in a spinning form, and the cast dope is coagulated and regenerated in the form of a thin film, and the obtained regenerated product can be continuously taken out of the bath.

[0005]

The present invention will be described in more detail with reference to the following examples. Examples 1 to 21 and Comparative Examples 1 to 4 Silk fibroin was prepared by using silkworm cocoons in a 5% Marcel soap aqueous solution.
After boiling for a long time to sufficiently remove sericin, it was neutralized with acetic acid, washed with hot water, and dried. 20% of silk fibroin was added to a mixed solvent composed of water, lithium bromide, and any one of methyl alcohol, ethyl alcohol, and isopropyl alcohol, and having various concentrations and mixing ratios of various dope solvent compositions.
The dissolved fibroin dope was cast to a thickness of 1 mm on the surface of a glass preparation, and one of lithium bromide or lithium chloride was dissolved in methyl alcohol, ethyl alcohol, or isopropyl alcohol in a coagulant solution. It was immersed at room temperature and the solidified state was observed. As a comparative example, the coagulation state of various fibroin dopes was examined for water, methanol, ethanol, and a 10% lithium bromide aqueous solution as coagulants. Table 2 shows the coagulant composition of Examples 1 to 21 and Comparative Examples 1 to 4 and the evaluation results of the coagulation state at room temperature by the coagulant. The evaluation of the coagulation state by the coagulant was carried out by the 5-point method shown below. 5: Stretchable film formation 4: Stretchable, but sometimes bubbles are present 3: Even if a film is formed, there are many bubbles 2: Almost no film formation 1: No film formation

[0006]

[Table 1]

[0007]

[Table 2]

Examples 22 to 32, Comparative Examples 5 to 27 Silk fibroin, dope solvent composition, fibroin dope concentration and film preparation were carried out in the same manner as in the above examples, and the coagulation state by the coagulant was evaluated. Table 3 shows the coagulant composition of Examples 22 to 32 and Comparative Examples 5 to 27 and the results of the 5-point method evaluation of the coagulated state by the coagulant.

[0009]

[Table 3]

[0010]

INDUSTRIAL APPLICABILITY The present invention solves the problems relating to the regeneration of silk fibroin that have been heretofore known, and its effects are immeasurable. By utilizing the method according to the present invention, it is possible to easily manufacture the silk fibroin regenerated fiber, which has been difficult until now. Furthermore, it becomes possible to newly manufacture various molded products including a film. This makes it possible to recycle the silk fibroin waste, which has been discarded for no purpose until now, as a fiber or a film, which also helps reduce waste.

Claims (5)

[Claims] 1. A mixed solvent of a lower aliphatic alcohol and water, the mixing ratio of which is alcohol / water> 1,
Regarding coagulation of a solution in which silk fibroin is dissolved in a dope solvent of a solution in which a concentration of alkali metal halide is 30% or more, 2 to 20% of alkali metal halide is used.
% Lower aliphatic alcohol aqueous solution is used as a coagulant, and a coagulant and a coagulant. 2. The coagulation method and coagulant according to claim 1, wherein the lower aliphatic alcohol is one of methyl alcohol, ethyl alcohol and isopropyl alcohol, or a mixture thereof. 3. The coagulation method and coagulant according to claim 1, wherein the alkali metal halide is lithium bromide or lithium chloride. 4. The water content of the coagulant is 5% or less.
Coagulation method and coagulant. 5. The coagulation method and coagulant according to claim 1, wherein the concentration of lithium bromide is 5 to 15%.