Natural silks beat plastics when it comes to generating fibres

Scientists have demonstrated for the first time that natural silks are 1,000 times more efficient than common plastics when it comes to forming fibres.

The team, made up of scientists from Oxford University and Sheffield University, compared silk from the Chinese silkworm with molten high-density polyethylene (HDPE) — a material from which the strongest synthetic fibres are made.

A new technique developed by Dr Oleksandr Mykhaylyk from Sheffield University was used to study and compare how the two materials form fibres.

Mykhaylyk’s technique involves shining polarised light through a disk rotating over a plate to study the how fibres are formed as the two materials are spun.

Dr Chris Holland of the Oxford Silk Group, part of Oxford University’s Department of Zoology, told The Engineer: ‘When you rotate the top disk, much like an LP player, the outer is going faster than the inside. Because the gap between the top and bottom disc is fixed, certain parts of the polymer melt are sheared faster than others.’

By looking at the speeds at which the polymers are sheared, he claimed that it is possible to determine how much energy has been used.

Holland said: ‘By comparing these figures, we found that silk generates fibres with 10 per cent less energy input than plastics.’

He added that, when you take into account the energy used to melt the polymers being used, the silkworm generates silk 1,000 times more efficiently than its synthetic counterpart.

Holland explained that the silkworm produces fibres at room temperature (25°C), whereas HDPE can only be used to produce fibres when it is melted into a liquid at 125°C.

To raise the temperature of HDPE is reported to require a 100-fold energy increase, thus making the overall energy requirement 1,000 times greater.

‘This project is taking the energy efficiency of silk into the quantitative age and assigning a number to it so it is no longer just an assumption that biological processes are more efficient,’ said Holland.

He believes the ‘bioinspired’ findings could have impacts on the way fibres are generated in the future and the extent to which we look to nature when devising polymer processing techniques.