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Science, Maths & Technology

Silk

Updated Monday 26th September 2005

Find out how silk can be so smooth, yet weight for weight it's stronger that steel

Silk is thought to have been discovered by the Chinese and woven into cloth over 4000 years ago.

Silk flowers [Image: racineur under CC-BY-NC-ND licence Creative commons image Icon racineur via Flickr under Creative-Commons license
Silk flowers [Image: racineur under CC-BY-NC-ND licence]

It’s of animal origin and is made from the cocoon of the silk moth.

The silkworm (the larval stage of the silk moth) spins a thread of silk around itself from its spinneret (its mouth appendage) when it’s ready to pupate.

The thread is continuous and can be up to two kilometres long. The worm uses mainly alanine and glycine, amino acid monomers (the chemical building blocks which make up polymers) to build the protein called ’fibroin’ that makes up the raw silk filament.

The chains of fibroin are not coiled, as they are in wool, but held together in a zig-zag arrangement by hydrogen bonds, creating rigid sheets, which are known as ’beta pleated sheets’.

In the sheets the chains are nearly fully extended. The structural differences between wool and silk are the reason why silk is less elastic than wool and smoother to the touch.

The sheets of protein are loosely stacked in silk and can slide over each other with ease, giving a smooth and flexible fabric.

Silk is very strong - in fact, weight for weight, silk is stronger than steel or Kevlar.

 

 

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