Silkworm silk is a protein-based fibre with mechanical properties rivalling synthetic fibres and spun using a fraction of the energy. Yet despite decades of research, many aspects of natural silkworm spinning remain a mystery.
Selected as front cover in the prestigious Advanced Materials journal, IFM and Sheffield researchers have taken one step closer to solving this mystery by wet spinning a new class of silk that produces fibres that outperform natural silk.
A materials breakthrough
This research, led by Dr Allardyce and Mr Zaki of IFM, with expert input from Sheffield University's Professor Chris Holland, involves sidestepping degumming - a commonplace industrial process. Prof. Holland comments, “silk has evolved over millions of years to be a careful balance of materials, with each one playing a role. Whilst we may not know what each one does, yet, it’s clear that removing one has made it harder to spin silk in a natural way”
Experimenting with dissolving entire silk cocoons the team were able to produce a spinnable solution that contains more of the proteins found in naturally spun silk. This solution was wet spun using IFM’s state-of-the art pilot fibre and textile facility to produce fibres that more closely matched natural silk.
Undegummed versus degummed silk
Traditionally, industry has used degumming to unravel the silkworms cocoon to produce their fibres. "It is also commonly used by researchers to facilitate 'unspinning' silk back into a solution that can then be solidified into new forms," Professor Holland said. "However removing a key component to the natural material, the sericin gum coating, often causes some collateral damage to the silk proteins. Hence degumming is often considered a necessary evil."
Mr Zaki explains that the team wanted to produce better materials while simultaneously understanding how. "We took a step back and asked why has no one attempted this? Is it because it is too hard, or because everyone degums silk and no one has considered doing something different? In industry, the largest portion of water waste, labour, and energy consumption usually comes from the degumming process. By-passing this step, we increase the potential of a more sustainable technology."
Dr Allardyce adds "Undegummed cocoons are normally insoluble. Our innovative process combines a milling step followed by a supersaturated solvent that enables dissolution.
"No-one has attempted to artificially spin undegummed silk before. And no-one has ever successfully dissolved undegummed cocoons and re-spun them in this way."
A materials breakthrough
According to IFM’s Deputy Director Joe Razal, the team’s discovery is a world first and demonstrates how IFM researchers are creating new sustainable materials that have real-world application and impact.
Professor Razal said: "Ben and Martin challenged the norm by creating silk fibres in a laboratory setting. They wet spun a cocktail of solubilised, non-separated silk components that mimic the properties produced in nature.
“The team identified a way to recreate the fibre produced by the silkworm and unlock the potential for it to be just as biodegradable, tough and energy efficient. In fact, when spun under identical conditions, undegummed solutions produce fibres 8 times stronger and 218 times tougher than degummed silk feedstocks.”
Future applications
Degummed silk is used in nerve repair, coating foods to improve shelf-life and biodegradable batteries.
This ground-breaking research forges a new pathway to recreate a fibre with structures akin to native silk.
Prof. Holland believes that the solution to many of today’s problems can be found by looking to nature.
“Silk represents the pinnacle of fibre processing, an energy efficient and materially inspiring solution that we can learn a lot from, provided we take the time to ask the right questions”.
Dr Allardyce maintains that it’s also an innovation that could apply to other next generation fibres.
"If the knowledge could be applied to other biopolymers - other proteins, cellulosic fibres - we could potentially produce new fibres that have a fraction of the energy input to synthetics but perform just as well while retaining the advantage of biodegradability."
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