New 'green' synthetic fibres in the offing

Silkworms and spiders spin silk by pulling rather than pushing it out of their bodies, according to a study that could lead to new, greener ways of producing synthetic fibres.
Researchers from the University of Sheffield in the UK suggest that if this process can be copied in an industrial setting, it could improve how synthetic materials are processed and offer more environmentally-friendly alternatives.
Conventional synthetic textiles are made by extrusion - pushing a liquid feedstock through a dye and then using high changes in temperature and exposure to harsh chemicals to solidify.
However, silk can solidify into a fibre at room temperature and leave only water - therefore causing less environmental damage.

"Silk is one of the most promising green biomaterials, and could be the perfect replacement for nylon and polyester based clothing," said Jamie Sparkes, a PhD student at University of Sheffield.
"Traditional production process for silk is both arduous and time-consuming, but if we can bypass that by mimicking nature in an industrial setting, we could improve not only silk, but also how we process our synthetic materials," said Sparkes.

Researchers examined how animals, including silkworms and spiders, push materials like silk out of their bodies.
"While it is easy to assume that silk is propelled out of the body like we see in comic books, we wanted to put that to the test," said Chris Holland, Head of the Natural Materials Group at University of Sheffield.

"By combining computer models with experimental data and practical measurements, we determined the forces needed to squeeze unspun silk down the animals silk gland and spin a fibre," said Holland.
"We found that to spin silk by extrusion (pushing), means a silkworm would have to squeeze itself hard enough to generate more pressure than a firing diesel engine," said Sparkes, lead author of the study published in the journal Nature Communication.
This is not possible as the animals body would be unable to contain that pressure.
However, by measuring the forces required to pull silk from the animal's body, the researchers found that it was well within the capability of the silkworm to pull a fibre, a process they refer to as pultrusion.

The researchers achieved this by adapting a rheometer, a machine used normally to measure the viscosity of liquids, into a highly sensitive spinning wheel, capable of measuring the forces needed to spin.