PROPERTIES OF SILK

a) Microscopic properties

Cultivated degummed silk viewed longitudinally under a microscope
resembles a smooth transparent rod. Wild silk tends to be quite uneven and
irregular in surface and is some what dark. It may exhibit longitudinal striations.

b) Physical properties

1. Length- Silk is the only natural filament fiber. Silk filaments are very fine and long.
They frequently measure about 900-1200 meters and can be as long as 2800 meters.

2.Luster- Silk has high luster, after the sericin has been removed, where as wild silk is some what dull.

3.Strength- Silk is the strongest of the animal fiber. It has a tenacity of 2.4 - 5.2
grams/denier when dry. It loses 15-25% of its strength when wet. Due to its low wet strength it demands special care while laundering.

4. Elastic recovery and elongation- Silk is very elastic fiber, but compared to wool its elasticity is slightly less. At 2% extension the fiber has 92% elastic recovery. When it is dry, the elongation varies from 10 to 25%. Wet silk has more elongation a s compared to dry silk.

5. Resiliency- Silk ranks next to wool in resiliency. Wrinkles hang out fairly readily but not as quickly as wool.

6. Moisture regain- Silk has high mosture regain. Silk absorbs 11% moisture at 65% relative humidity and 70 f temperature. Due to this property silk can be dyed and
printed in brilliant colors.

7. Density- Silk fiber is less dense than cotton, linen and wool. Density of silk is 1:25 -1:34 gm/cc. Low density of silk makes fabric light in weight.

c) Chemical properties

1. Effect of alkali- Silk is damaged by strong alkalies. Fibers dissolve in hot caustic soda; however silk reacts more slowly than wool. Weak alkalies such as soap, borax and ammonia cause little damage to silk unless they remain in contact with the fiber for a long time.

2. Effect of acids- Silk fibers are not damaged by organic acid. Mineral acids such as HCL, H2SO4, HNO3 will have harmful effect on fiber. Connectrated solutions of mineral acid will destroy silk, however they are not easily damged by dilute acids.

3. Effect of organic solvents- Dry cleaning solvents and spot removing agents don not damage silk.

d) Biological properties

1. Effect of mildew- Silk being a protein fiber is the least damaged of the natural fibers by mildew, but it is attacked if left in a damp condition for a period of time.

2. Effect of moth- Silk has good resistance to the cloths moth but carpet beetles will eat it.

e) Thermal properties

1. Effect of Heat- Silk will ignite and continues to burn with a smell of burning hair or feather it leaves crisp, brittle bead.

2. Heat conducitivty- It is not a good conductor of heat.