Researchers develop novel method for silk thread unravelling
Scientists led by Oxford University in the United Kingdom have discovered that a layer of mineral calcium oxalate covers the surfaces of wild cocoons, making unravelling a complex process. Removal of this layer facilitates the unreeling of cocoons into long strands of silk comparable to those derived from the domesticated mulberry silkworm (Bombyx mori, B. mori). The research was funded in part by the SABIP ('Silks as biomimetic ideals for polymers) project, which has clinched a European Research Council (ERC) grant worth almost EUR 2.3 million under the EU's Seventh Framework Programme (FP7). Presented in the journal Biomacromolecules, the findings could lead to the development of new silk industries in Asia, Africa and South America, areas where wild silkworm numbers are in abundance.
People have long recognised how crucial a role silkmoths play in the silk industry. Silk fabric first materialised in ancient China, as far back as 3500 BC. Made by the unravelling of fine, soft thread from the silkmoth's cocoons, the majority of silk found in today's markets comes from cocoons of B. mori. Unravelling (unreeling) the threads from this silkworm is easy, allowing long continuous strands to emerge.
For those working in the silk industry, unravelling the cocoon threads of 'wild' species is not as easy. In order to get the product they want, workers use harsher methods on the cocoons. The drawback, however, is that the strands are usually damaged, resulting in poorer quality silk. Enter the Oxford team, which successfully developed and tested a method to unravel the strands of silk of wild cocoons without damaging them.
They tested their new method on the wild silkworm Gonometa postica. Using a warm solution of ethylenediaminetetraacetic acid (EDTA), the team softened the cocoons enough that unravelling the farmed silk without damaging the threads went without a hitch.
By 'demineralising' the surfaces of wild cocoons – i.e. removing the mineral calcium oxalate layer – the researchers were able to unreel the cocoons into long continuous strands with commercial reeling equipment. These strands could easily compete against those of the Mulberry silkworm cocoons.
'Unlike traditional ways of treating wild silk cocoons – such as degumming using pineapple juice, carding and hand—spinning – our new method softens the cocoon so that it can be reeled but does not damage the strands which give silk its sought—after properties,' explains Tom Gheysens from the Department of Zoology at Oxford University, who led the work with Oxford supervisor Professor Fritz Vollrath. 'The demineralising process makes it possible, for the first time, to create long continuous strands of silk from wild cocoons producing a high quality wild silk which is, potentially, a match for the 'farmed' variety.'
Writing in the paper, the researchers conclude: 'The fibres of G. postica, which previously had not been examined in any great detail, when obtained this way showed competitive properties to fibres produced by the commercial mulberry silkworm B. mori. This suggests that our degumming method should increase the range of wild silkmoth species that can be wet reeled and may be important for the development of the silk industries not only in Asia but also in Africa and South America.'
Scientists from the University of Bristol and the Commercial Insects Program, International Center of Insect Physiology and Ecology in Kenya contributed to this study.