What are the properties of silk?

Microscopic Properties:
Longitudinal Section (L.S.): The silk that the larvae extrudes has a presence of water-soluble gum called sericin which gives the silk an irregular and rough surface however after the process of removal of gum (degumming) the L.S. of silk under the microscope appears to be smooth, transparent and rod-like.

Cross Section (C.S.): The C.S. of silk is triangular in which the strands are visible that are placed face to face with rounded corners.

Physical Properties:
• Length: Silk being in the natural fiber category is the only exception in which fibers are long in length of about 900-1200 metres.
•Diameter: Silk being a fine fiber has a diameter of 9-11 microns.
•Colour: The colour of mulberry silk is off-white to cream in colour while degumming lightens the colours to some extent. Muga silk is golden yellow in colour. Tussar silk is tan to light brown when the larvae feed on oak leaves due to the presence of tannin.
•Lustre: The triangular surface of silk reflects the incident light evenly which imparts the lustre to fiber however wild silk has dull lustre due to irregular surface.
•Tenacity: Silk is one of the strongest natural fibers but loses up to 20% of its strength when wet.
•Elongation and elastic recovery: Its elasticity is moderate to poor of about 10-25% and if elongated even a small amount it remains stretched.
•Resiliency: The resiliency of silk is better than cotton but less than wool due to the absence of crystalline linkages.
•Moisture regain: It has a good moisture regain of 11%.

Chemical Properties:
•Acids: Mineral acids since are strong in nature tend to destroy the fibroin protein present in silk however, they can bear the action of weak acids as well as organic acids and so weak acids such as acetic acids can be employed after washing.
•Alkalis: Alkalis have a harmful effect on fibroin and thus detergents that have basic composition should not be used in their washing.
•Organic Solvents: These do not harm or damage the silk fiber and so are used in dry cleaning.

It can be weakened if exposed to too much sunlight. It may also be attacked by insects, especially if left dirty.