JPH03284337A - Separating membrane made of cross-linked thin film of sericin and production thereof - Google Patents

Abstract

PURPOSE:To obtain a polymer film useful as a separating membrane with sericin discarded until now by spreading an aq. sericin soln. contg. specified cross- linking agents on a glass plate and forming a crosslinked thin film. CONSTITUTION:An aq. hydrochloric acid soln., an aq. soln. of a crosslinking agent (A) such as formaldehyde and an aq. soln. of thermallyreactive water-soluble urethane resin as a cross-linking agent (B) are added to an ag. sericin soln. and they are mixed to obtain an aq. sericin soln. for spreading. This sericin soln. is spread on a smooth plate such as a glass plate at room temp. and allowed to stand at room temp. to carry out cross-linking with the cross-linking agent A. The resulting film is treated with hot air at about 100-150 deg.C to carry out cross-linking with the cross-linking agent B. A cross-linked thin film of sericin is formed and utilized as a separating membrane for an aq. soln. of water-soluble org. matter (water-alcohol). At this time, the film is well washed with water, held on a porous support and used.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for forming a crosslinked thin film of sericin for the purpose of crosslinking and forming sericin into a separation membrane, and a method for utilizing the same as a separation membrane.

The sericin-based separation membrane according to the present invention has a polyfunctional nature, so sericin easily takes an amorphous structure, and therefore forms a thin film with low crystallinity, exhibiting excellent separation performance, and water-alcohol separation. It can be widely used in industrial fields such as chemical industry and bioindustry.

Conventional technology Raw silk fibers are composed of two types of proteins: fibroin, which has high crystallinity and orientation, and sericin, which protects it. Silk is a fiber whose main component is fibroin, from which most of the sericin has been removed through refining, and a major technical challenge has been how to economically remove this sericin.

By the way, sericin can be dissolved in high temperature water.

In other words, it is well known in the field of silk science that it is relatively hydrophilic, has multifunctional properties and is highly reactive, for example, can be crosslinked with formaldehyde, and is highly amorphous. (Seizo Ishikawa, "Textiles," Tokyo Denki Oaza Publishing Bureau, p. 1 and 322, Kansai Clothing Lifestyle Research Group, 1981, etc.) In recent years, there has also been a movement to effectively utilize sericin as a natural resource. Enzyme-immobilized membrane cross-linked with glutaraldehyde (Miyato, Sugiura, Journal of Fermentat)
ion Technol.

gy56@No.4, page 303, 1978). However, no research has been reported on the use of sericin thin films as separation membranes.On the other hand, there are studies on selectively permeating and separating water from concentrated solutions of water-soluble organic substances such as water-ethanol, water-isobrobyl alcohol, and water-acetone. Research into selective water separation membranes has progressed steadily in recent years, and some of them have been put into practical use. However, the need for high-performance, stable, and inexpensive water-selective separation membranes is expected to continue in the future, and there are great expectations for the use of natural polymer compounds such as sericin as membrane materials as part of research and development. is the current situation.

Problems to be Solved by the Invention However, on the other hand, 2000 tons of removed sericin, which accounts for 20% of the weight of raw silk, is released into wastewater annually, contributing to environmental pollution. Prevention and effective use of sericin have long been a problem. There were high expectations.

The present invention was made for the purpose of obtaining a polymer membrane useful as a separation membrane by using sericin, which has not been used hitherto.

Means for Solving the Problems As a result of intensive research, the present inventors found that a sericin aqueous casting solution containing a certain type of crosslinking agent cast onto a glass plate formed a crosslinked thin film, and this formed a crosslinked thin film. - The present invention has been completed by discovering that it exhibits excellent performance in selectively separating water in alcohol systems. That is, the present invention relates to a method for forming a crosslinked thin film of sericin and a polymer separation membrane comprising the crosslinked thin film.

Since the present invention is hydrophilic, it is expected to have higher permeability than materials that selectively allow water to permeate, and because it is polyfunctional, a strong thin film can be formed with an appropriate crosslinking agent. A water-selective permeation type 11 membrane was manufactured by actively utilizing the properties of sericin. Crosslinking is progressed to form a crosslinked thin film, which is then washed to form a sericin separation membrane. The crosslinking agent-containing sericin aqueous solution to be cast, that is, the sericin aqueous solution for casting, is composed of a sericin aqueous solution, hydrochloric acid, a crosslinking agent A aqueous solution, and a crosslinking agent B aqueous solution. The concentration of the sericin aqueous solution is preferably 1 to 10%.
More desirably, it is 1 to 3%; if it exceeds 10%, the entire aqueous solution may gel and lose fluidity. There is no particular limit to the concentration of the hydrochloric acid aqueous solution, but it is usually desirable to have a concentration of about 1%.

Crosslinking agent A rt Aldehydes such as formaldehyde and glutaraldehyde that easily cause crosslinking reactions with amino groups, carboxyl groups, etc. in sericin molecules, and the concentration of the aqueous solution is preferably 5 to 40% in the case of formaldehyde, more preferably 30%, In the case of glutaraldehyde, it is preferably 5 to 25%, more preferably 10%. Crosslinking agent B strongly crosslinks sericin molecules through urethane bonds and is useful for improving the strength of the thin film, and is called a heat-reactive water-soluble urethane resin.

As the aqueous solution, commercially available products can be used as they are. The aqueous sericin solution for casting is prepared by mixing the aqueous solutions of each of the above constituent components. In this case, the sericin aqueous solution is 80
90 parts of crosslinking agent A aqueous solution, 0 to 10 parts of crosslinking agent A aqueous solution, and 2 to 20 parts of crosslinking agent B aqueous solution, preferably 100 parts in total. An aqueous hydrochloric acid solution is added as necessary so that the overall pH is about 4 to 6. The amount of sericin aqueous solution is related to the thickness of the thin film. The amount of crosslinking agent A is mainly related to the degree of crosslinking within the thin film, and the larger the amount, the denser the crosslinked structure. Crosslinking agent B forms a strong crosslinked structure, and therefore its amount is related to the strength of the thin film.

The sericin aqueous solution for casting prepared as described above is preferably cast onto a smooth imide film at room temperature under as clean an environment as possible. After casting, the temperature should be kept at room temperature or preferably at a relative humidity of about 50% and 20% to avoid dust.
The crosslinking agent A is allowed to stand for 40 to 50 hours in a dryer adjusted to around 100 to 150 °C.
A sericin crosslinked film is formed by the above steps of treating with hot air at 0°C, preferably around 120°C, for 5 to 20 minutes, preferably about 10 minutes, to advance crosslinking with crosslinking agent B. In forming such a sericin crosslinked film, hydrochloric acid may be added to maintain the aqueous sericin solution for casting on the acidic side of about 4 to 6 pH.

This promotes crosslinking by crosslinking agents A and B, but the sericin crosslinked film may become brittle due to hot air treatment at 100 to 150°C in the presence of acid components, so keep this in mind when adjusting the treatment time. It is necessary to take measures such as shortening the time.

When the formed sericin crosslinked membrane is used as a separation membrane, the membrane is thoroughly washed with water and then held on a porous carrier. A membrane separation method for an aqueous solution of a water-soluble organic substance such as a water-alcohol system involves placing an aqueous solution of a water-soluble organic substance on one side of the membrane, applying reduced pressure on the other side, and separating the aqueous solution while passing through the membrane and evaporating. The present invention will be explained in further detail using a zero-order example in which the vaporization method is preferred.

Examples 90 parts by weight of a 2.4% aqueous solution of sericin, 5 parts by weight of a 35% formaldehyde aqueous solution, heat-reactive water-soluble polyurethane resin (manufactured by Dai-Kogyo Taiyaku Co., Ltd., Elastron E-37)
) A sericin aqueous solution for casting consisting of 5 parts by weight was prepared.

The sericin water droplet solution for casting was placed in a mold with a polyimide film placed on a glass plate, and placed in a dryer at approximately 50% RH for 40 minutes.
It was left to dry for ~50 hours. The thin film thus produced was further treated with hot air at 120° C. for 10 minutes to obtain a sericin thin film. By drying twice, the liquid height of the sericin aqueous solution for casting in the mold was reduced from 6 mm to 0.13 mm, resulting in a thin film. A part of the membrane was cut out, and a small piece weighing 514 mg was heated at 40°C.
When left in warm water, the amount was 9 mg. Water-soluble substances such as uncrosslinked sericin in the membrane are thought to have been removed after being left for 26 hours.A membrane of the size required for the primary separation performance measurement was cut and left in warm water at 40°C for 26 hours, then pervaporation. The membrane was installed in a separator, and the weight was 83.9 at 40°C.

A pervaporation experiment was conducted using a % ethanol aqueous solution.

The permeate concentration at that time was 34.2% by weight, and the ethanol aqueous solution was diluted and permeated. - In other words, it can be seen that the membrane is effective as a water selectively permeable separation membrane. The amount of permeation was 0.201 g/hour.

Noting that this is a protein with relatively high reactivity, the aim is to actively utilize this protein, and the membrane thus formed is not only suitable for use as a water-alcohol separation membrane for guests; This will inhibit the release of sericin into wastewater. Furthermore, the crosslinking film forming method of the present invention is effective in widely utilizing sericin as a natural resource, and can be used, for example, as a filamentous carrier for enzyme immobilization or a spherical carrier for aromatic agents.

Claims (2)

[Claims] (1) Sericin characterized by casting a mixed aqueous solution containing sericin, formaldehyde, and a heat-reactive water-soluble urethane resin onto a smooth surface to form a thin film, and then crosslinking the sericin in the film to solidify it. cross-linked thin film method. (2) A sericin-based crosslinked polymer separation membrane formed by the method according to claim 1.