An Overview of Silk Fiber

An Overview of Silk Fiber

Ramandeep Singh
B.Tech, Dept. of Textile Engineering
Giani Zail Singh Punjab Technical University Campus,
Bathinda, Punjab, India

Silk is a natural protein fiber excreted by the moth larva Bombyx mori, better known as the common silkworm. It's amino acid composition is close to that of the human skin. Silk is a fine continuous monofilament fiber of high luster and strength and is highly valued as a prestige fiber. Because of its high cost, it finds very 1imited use in textiles. A minor amount of wild tussah silk is produced for specialty items. Attempts have been made to commercialize silk from spiders over the years, but all ventures have met with failure. Domestic and wild silks are essentially uncross linked and relatively simple in amino acid composition compared to the keratin fibers. The properties for silk 1isted here are for silk formed by Bombyx mori moth larvae.
Silk fiber
This fiber is the result of caterpillar secretions of certain wild or domestic butterflies which constitutes cocoons in which they lock themselves inside during the metamorphosis.

Physical Properties of Silk Fiber:

Silk fibers are strong with moderate degrees of recovery from deformation. Silk has a dry tenacity of 3-6 g/d (27-54 g/tex) and a wet tenacity of 2.5-5 g/d (23-45 g/tex). Silk exhibits a recovery of 90% from 2% elongation and of 30%-35% from 20% elongation. Silk fibers are moderately stiff and exhibit good to excellent resiliency and recovery from deformation, depending on temperature and humidity conditions. Silk has a specific gravity of 1.25-1.30 and a moisture regain of 11% under standard conditions. Silk is soluble in hydrogen bond breaking solvents such as aqueous lithium bromide, phosphoric acid, and cuprammonium solutions. It exhibits good heat insulating properties and is little affected by heat up to 150°C. Silk has moderate electrical resistivity and tends to build up static charges. Physical properties of silk fiber are pointed out below:

Physical Properties:
  • Thickness : 12 to 25 micrometers
  • Color : whitish, yellowish or greenish
  • Length : 10 to 250 mm
  • Density : 1.25 g/cc
  • Tenacity : 25 to 40 cN/tex
  • Moisture regain : 11% (at 65% R.H and 20°C)
  • Elongation : 15 to 20% (dry) , 25 to 30% (wet)
  • Flame reaction : partial burning , odor of burnt horn
Chemical Properties:
Silk is slowly attacked by acids but is damaged readily by basic solutions. Strong oxidizing agents such as hypochlorite rapidly discolor and dissolve silk, whereas reducing agents have little effect except under extreme conditions. Silk is resistant to attack by biological agents but yellows and loses strength rapidly in sunlight. Silk is often weighted with tin and other metal salts. These salts make silk even more sensitive to 1ight-induced oxidative attack. Silk undergoes charring and oxidative decomposition when heated above 175°C in air over a prolonged period of time.

Characteristics of Silk:
  • High wet strength
  • Good moisture regain
  • Soft feel
  • Good lustier
  • Expensive cleaning
  • Sensitive to cleaning & washing
  • Sensitive to the sun and heat
  • Poor wrinkle and abrasion resistance
End Uses:
Silk possesses a combined set of aesthetic properties that make it useful for high-fashion luxury textile goods. Silk has a high luster and is translucent. Silk fabrics have pleasing appearance and drapability, and a characteristically pleasing crisp hand. Silk is highly moisture absorbent and has good to excellent resistance to wrinkling. It is a moderately strong fiber with moderate recovery properties. It exhibits fair abrasion resistance and good resistance to pilling. Silk is sensitive to chlorine bleaches and to alkalies and is easily damaged by sunlight. The fiber may be dyed with a wide variety of dyes to give dyed fibers with high colorfastness.

Silk may be laundered under mild, nonalkaline conditions and dry cleans readily. Because of its high affinity for water, it dries slowly but may be dried or ironed safely up to 150°C. Silk burns slowly and self-extinguishes when removed from a flame. Silk is used extensively in luxury fabrics and apparel and home furnishings, and in accessories such as scarfs.

End uses of silk fiber are highlighted below:
  • Clothing : Luxury clothes , neck ties , scarves , gloves, shirts, underwear, skirts , costumes, dresses, night gowns. 
  • Home furnishings : Bed covers , curtains, draperies, upholstery . 
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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