Silk is a natural textile fiber and it is collected from the insects named silkworm. The silk warm is the caterpillar of a small off white moth belonging to the species Bombyx mori. The fiber which is collected from the insects that is required to treat before fabric production. Different types of impurities are contained in the raw silk.
Chemical Composition of Silk Fiber: Various types of chemical components are composed in the chemical structure of the silk fiber. Here, I have presented a chemical composition of raw silk fiber.
Fibroin : 75%
Ash of Silk Fibroin : 0.5%
Sericin : 22.5%
Fat and Wax : 1.5%
Mineral Salt : 0.5%
This composition is calculated in 100 percent.
It is important to know that, the fibroin is composed of 16 various amino acids. Raw Silk is composed of two filaments which are produced by the fibroin. These two filaments are adjusted by the gum which is known as sericin and different types of mineral salt, fat and wax also involved with it.
This raw silk is treated for remove the gummy materials and various types of impurities from the silk by scouring process. Then the silk fiber is collected and supplied for producing silk fabric by weaving process.
Silk is an animal fiber and it is also called protein fiber. Silk is only natural fiber which is found in filament form. Silk is produced by insects. Fibroin is the main chemical components of silk.
Like all the textile fibers, silk has its own physical and chemical properties which are required to know for better processing in spinning, weaving, knitting, dyeing, printing as well as finishing. Here, I have written about physical and chemical properties of silk fiber.
Physical Properties of Silk: There have a lot of physical properties of silk. Followings are the physical properties of silk:
- Color: The color of silk fiber could be yellow, brown, green or grey.
- Tensile Strength: Cotton is a strong fiber. It has a tenacity of 3.5 – 5 gm/den. The strength is greatly affected by moisture; the wet strength of silk is 75 – 85%, which is higher than dry strength.
- Elongation at break: 20 -25% at break.
- Elastic Recovery: Not so good.
- Specific Gravity: Specific gravity is 1.25 to 1.34.
- Moisture Regain (MR %): Standard moisture regain is 11% but can absorb up to 35%.
- Effect of Heat: Silk will withstand at higher temperatures than wool. It will remain unaffected for prolonged periods at 1400C. Silk decomposes at 1750C.
- Effect of Sun Light: Sun light tends to encourage the decomposition of silk by atmospheric oxygen.
- Luster: Bright.
Chemical Properties of Silk: Chemical properties of the silk fiber are given below:
- Effect of Acids: The Fibroin of silk can be decomposed by strong acids into its constitute amino acids. In moderate concentration, acids cause a contraction in silk. Dilute acids do not attack silk under mild conditions.
- Effects of Alkalis: Silk is less readily damaged by alkalis than wool. Weak alkalis such as soap, borax and ammonia cause little appreciable damage. Silk dissolves in solutions of concentrated caustic alkalis.
- Effect of Organic Solvent: Silk is insoluble in the dry-cleaning solvents in common use.
- Effects of Insects: Insect does not affect silk.
- Effect of Mildew: Silk is affected by mildew slightly.
I think above physical and chemical properties will help us to be careful about the processing of silk in the different stages of processing from spinning to garments making. Day by day the use of silk products is increasing rapidly.