New method of unreeling cocoons could extend silk industry beyond Asia

The development and successful testing of a method for unreeling the strands of silk in wild silkworm cocoons could clear the way for establishment of new silk industries not only in Asia but also in vast areas of Africa and South America. The report appears in ACS' journal Biomacromolecules.

Fritz Vollrath, Tom Gheysens and colleagues explain that silk is made by unraveling— or unreeling — the fine, soft thread from cocoons of silkmoths. The practice began as far back as 3500 BC in ancient China, where silk was the fabric of royalty. Today, most silk comes from cocoons of the domesticated Mulberry silkworm (bred from a species native to Asia) because they are easy to unreel into long continuous strands. The cocoons formed by "wild" species are too tough for this process, so harsher methods are sometimes used. However, these methods damage the strands, producing a poor-quality silk. To overcome this challenge to the widespread commercial use of wild cocoons, the researchers developed a new way to loosen the strands without damaging them.

The group found that the surfaces of wild cocoons were coated with a mineral layer and that removing this layer ("demineralizing") made it easy to unreel the cocoons into long continuous strands with commercial reeling equipment. These strands were just as long and strong as those from Mulberry silkworm cocoons. The researchers say that the new method could expand the silk industry to new areas of the world where wild silkworms thrive.

More information: Demineralization enables reeling of Wild Silkmoth cocoons, Biomacromolecules, Just Accepted Manuscript, DOI: 10.1021/bm2003362

Abstract
Wild Silkmoth cocoons are difficult or impossible to reel under conditions that work well for cocoons of the Mulberry silkmoth, Bombyx mori. Here we report evidence that this is caused by mineral reinforcement of wild silkmoth cocoons and that washing these minerals out allows for the reeling of commercial lengths of good quality fibers with implications for the development of the ‘wild silk’ industry. We show that in the Lasiocampid silkmoth Gonometa postica, the mineral is whewellite (calcium oxalate monohydrate). Evidence is presented that its selective removal by ethylenediaminetetraacetic acid (EDTA) leaves the gum substantially intact preventing collapse and entanglement of the network of fibroin brins, enabling wet reeling. Therefore this method clearly differs from the standard “degumming” and should be referred to as “demineralizing”. Mechanical testing shows that such preparation results in reeled silks with markedly improved breaking load and extension to break by avoiding the damage produced by the rather harsh degumming, carding or dry reeling methods currently in use.

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