July 11, 2004


Putting the Special Properties of Silk to Work

* This article is under copyright protection.

Manabu Akaike
Universal Design Intelligence Inc.

The Search for New Functionality in Silk Proteins

Today many Asian nations are reaping success with low cost silk production, but a cottage industry sericulture as seen in the past has not materialized as a result. But as the importance of producing and using ecologically responsible materials is now meriting serious discussion, the potential of silk filament as an important raw material outside of the textile and apparel market is growing. But research at sericulture labs in the past has only been directed at ways to stabilize cocoon production and increase filament production. Virtually no research was carried out into silk characteristics and potential new applications. But in fact an outpouring of efforts into this new sector carries within it the potential for this age-old cottage industry to forge its way out of the current quagmire towards a new generation of silkworm farming.

As a high molecular protein in filament form, silk possesses an unusual string of amino acids. This protein can be hydrolyzed through chemical processing with alkali and acids into the form of amino acid, oligopeptide, and low molecular protein, and thus can be used in a wide variety of non-textile applications.

The research labs of Takayuki Nagashima, associate professor in the Department of Agriculture at Tokyo University of Agriculture are exploring the special characteristics and potential new uses for silk by transforming silk into the form of powder, gel, solution, membrane and sponge. Since silk is a high molecular form of protein, it has a strong affinity for bio-organisms, and also has the unusual characteristic of preventing the growth of microorganisms and bacteria.

In his pursuit of new functions for silk protein, Nagashima studies of silk in powder form revealed a previously unknown property of silk with groundbreaking potential, namely the UV (ultra-violet) ray inhibiting properties of silk protein taken from cultivated or farmed silkworms. Nagashima showed moreover that the cocoons of the yamamayuga type of silkworm or wild Japanese oakworm (antheraea yamamayuga) provide even stronger protection against a wider range of UV rays than farmed silkworms.

Depending on the length of the rays, UV light can have significant impact on not only tanning but on aging of the skin and hair, and can in fact be a cause of skin cancer. The volume of UV rays in our atmosphere has begun to increase due to the ongoing destruction of the ozone layer. Nagashima labs have already begun testing of silk based cosmetics that make good use of these UV inhibiting properties, and Nagashima has publicly declared the strong potential of this material as a next generation health enhancement. He says that UV inhibiting cosmetics that help protect the skin against UV rays which can be the predisposing cause of wrinkling and skin cancer promise to be particularly big business for the female and Caucasian markets.

Silk Sheeting That Can Be Easily Produced by Silkworm Farmers

While research into new functions for silk such as UV inhibitor continues, in the traditional realm of silkworm farming, an extended version of the technical expertise that Japan silkworm farmers have advanced over the year carries within the potential for a promising type of silk production for the future.

Before World War II, Yamagata Prefecture as one of the prefectures of the Tohoku Region known for its sericulture was home to 50,000 or more silk farmers, but that number has shrunk to barely 100. In order to change this situation, the local government initiated an experiment to help producers and users break free of the traditional perception of silk fiber as only for use in textile and apparel applications, and to transform it into a new high added value material. The experiment took the form of a project that aimed to change the form of silk fiber produced at the local farmer level into a new material with applications for household and interior goods, with the end result being the leveraging of the silk cocoon and fiber producers cumulative know-how.

The pillar of the project has been the Yamagata Prefecture Silk Fiber Research Center, which succeeded in 1997 in developing a new material out of silk. The genesis of this research was an accidental discovery. Silk fiber is made out of two proteins called fibroin and sericin. Sericin is a gummy substance that acts to cement the fibroin filaments together to form silk. Ordinary silk is produced by removing the sericin through chemical processing, but one day, a researcher happened upon a piece of raw filament that had dried out in the air and become stuck to the plate surface. He realized that instead of removing the sericin, its adhesive qualities could be utilized to make the filament take the form of a sheet with a broad flat surface. The new material that was born of this accident is known as silk sheeting.

The merits of silk sheeting are the beautiful glitter that is created by the diffused reflection of light off the surface, as well as ease of cutting and processing. Useful for making business cards and book bindings, interior decoration goods such as tablecloths, lampshades and tapestries, wallpaper, fusuma paper and craft materials, plus labels for glass bottles applications seem to extend without limit. Moreover, no special technology is needed for the manufacture of silk sheeting. The filament that is spun out by the cocoon is simply wound by hand continuously from side to side around a drum. Patient winding results in the buildup of a uniform layer in the shape of a wide flat sheet. Silk farm housewives can learn the process in just a few days. Sheets are priced at 5,000-6,000 yen per 90 x 180 centimeter sheet, with resulting revenue going not to a specialized maker but directly into the hands of the farming families, wherein lies the third and most important benefit of the new material.

JAPAN CLOSE-UP, September 2002, published by PHP

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