Unit 2 - Lecture 9 Topic 2

Question 1

What is the strength of silk?

Answer 1

Silk has moderate strength and the highest tenacity of protein fibres. Its strength derives from its high orientation, crystallinity, and hydrogen bonding capability. Because of its hydrogen bonds, silk is weaker when wet.

Question 2

What is the elongation of silk?

Answer 2

Silk has medium elongation: around 10-25% at 65% R.H. and 33% at 100% R.H.

Question 3

What is the elastic recovery and resiliency of silk like?

Answer 3

Silk is lower than wool but higher than cotton. Unlike wool, it does not have disulphide bonds to help return polymers.

Question 4

How is silk often damaged?

Answer 4

Alkalis in strong detergents damage silk. As a precaution, many silk items are labelled as dry clean only. Silk also deteriorates in sunlight. White fabrics become yellow, and the fabric’s strength is compromised.

Question 5

How does silk react to water?

Answer 5

Silk is hydrophilic and hygroscopic with a moisture regain of 11%.

Question 6

How does temperature affect silk?

Answer 6

Silk heat absorption is slightly lower than wool. The smooth yarns create a ‘cool’ feeling against the skin but static cling can develop at low humidity levels.

Question 7

What is the lustre of silk?

Answer 7

Silk lustre is higher in degummed silk than in raw. Because silk is not perfectly triangular, lustre may not be as “shiny” as manufactured fibres. Silk lustre is greater in filament fibres than spun staple fibres.

Question 8

How resilient is silk?

Answer 8

Silk is moderately resilient, but its wrinkle recovery is not as good as wool. It is better
than cotton or linen. H-bonds can slip past each other and reform in new positions.

Question 9

What is the dimensional stability of silk?

Answer 9

Silk does not tend to stretch, but relaxation shrinkage can still occur.