Silk Fiber: Types, Properties, Manufacturing Process and Uses
Rahamat Ullah Joy
B.Sc. in Textile Engineering (Daffodil International University)
M.Sc. (University of Oulu, Finland)
Silk is a protein fiber made by silk worms and is the only natural fiber that is a filament fiber. Originally, it was believed that an ancient Chinese princess was the first to discover the process for manufacturing silk fabric from the filament fiber produced by silk worms. Even though this was considered to be a legend, the first country to manufacture silk fabric was China. According to Kadolph, Langford, Hollen, and Saddler (1993), China was the only country producing silk for approximately 3,000 years before spreading to other Asian countries. Japan is currently manufacturing more silk than any other country in the world.
In general, a number of protein-based fibers are collected under the term silk. The threads can be spun by caterpillars, spiders and mussels. Among the most relevant silk producers are the larvae of the silk moth. Conventional silk is produced as filaments, up to 0.5 km long, from secretions of the larvae of particular moths. Most silk is derived from the larvae of the moth, Bombyx mori, but some other silks come from the larvae of the Chinese Tussah moth (Antheraea pernyi) and the Indian Tussah moth.
Silk has set the standard in luxury fabrics for several millennia. The origins of silk date back to Ancient China. Legend has it that a Chinese princess was sipping tea in her garden when a cocoon fell into her cup, and the hot tea loosened the long strand of silk. Ancient literature, however, attributes the popularization of silk to the Chinese Empress Si-Ling, to around 2600 B.C. Called the Goddess of the Silkworm, Si-Ling apparently raised silkworms and designed a loom for making silk fabrics.
Silk is a filament spun by the caterpillars of various butter flies. Silk is a natural protein filament. It’s filament density is 1.34 g/cm³ which make it a medium weight fiber. Very light weight silk textile materials may be manufacturing from silk filaments.
Different types of silk:
Silk is usually referred to as the queen of the fibers. It is a product of the life cycle of the silk cocoon. There are two major varieties of silk, viz. (a)
cultivated silk and (b) wild silk. Without these, there are various types of silk. Major types are given below.
- Wild silk
- Thrown silk
- Organize silk
- Tram silk
- Chappell silk
1. Silk: It refers to cultivate silk.
2. Wild or tussah silk: Wild or Tussah silk is a tan-colored fiber from the cultivated silk worm which feeds on so rub oak. As the cocoon are always pierced the fibers are shorter than reeled silk. It is different both physically and chemically from ordinary silk. It is brown in colure, considerably stiffer and coarser. It is less reactive towards chemical. It is used in the shantung pongee.
3. Thrown or Greg silk: Thrown silk consists of two or more threads of raw silk reeled tighter and given a slight twist.
4. Organize silk: Organize silk is produced from best cocoons. It contains two or more stands each composed of number of greges twist together slightly. These threads are then doubled and retwisted in the opposite direction to the original twist in the strands (Strand mean a number of flexible strings twisted together into a rope. Organize silk is used for warp threads when high tensile strength is required.
5. Tram silk: Tram silk is usually made from cocoons of lower grade, like organize. It is composed of two or more strands of thrown silk lightly twisted together and then doubled.
6. Chappell silk: When silk is still in the green is spun the yarn is known as chappell.
Manufacturing Process of Silk:
Flow chart of spun silk yarn production is given below:
Spun silk yarn
The manufacturing steps of silk are,
- Sorting cocoons
- Softening the sericine
Sericulture the care & nurture of the silk caterpillar is a tedious pain streaking business. The worm cultivation is called sericulture. The process starts with silk mouth, which less eggs on specially prepared paper.
2) Softening Cocoons:
The cocoons are shorted according to colore, shape & texture.
3) Softening The sericine:
When the silk warm is grown it spins a double strand of silk fibers surrounded by water soluble substance is called sericine.
The process by which filament is taken up from the cocoons is called reeling. The diameter of the filament is so little that if it is reeled, its commercial value will be decrease. Moreover, double filament is too delicate to handle alone.
The production of yarn from reeled silk know as throwing consists adding twist or of doubling further twisting these strands into the desired size. When two or three of silk multifilament are twisted together to from heavier threads, this process is called throwing.
Chemical composition of silk:
- Silk Gum or Sericine → 22-25%
- Silk or Fibrin →62.5-67%
- Water →10-11%
- Salts →1-1.5%
Fibrin is composed of a number of α-amino acids in which the most important are.
- Glycine →38%.
- Alanine →22%
- Serine →15%
- Tyrocine →9%
- Other →16 %
Physical properties of silk:
- Specific gravity → 1.34% gm/cm³
- Moisture → MR %=11
- Tenacity → 3-6gm/tex
- Elongation → 13-20%
- Dry → 4.3 gm/d
- Wet → dry×0.92 gm/d
- Elasticity: Brea. ext: = 23.4%, Recovery = 52% at 5%
- Appearance and color: Slip fabric, Browny etc.
- Effect of light: Change color in sunshine.
- Resiliency: Moderate
- Absorption Resistance: Good
- Dimensional Stability: Good
- Fineness 1–3.5 dtex
- Diameter 10–13 μm
- Fiber length 700–1500 m
- Density 1.37 g / cm3
- Breaking strength → 25–50 cN / tex
- Color → Lustrous white
Chemical properties of silk:
The fibroin of silk is decomposed by concentrated acids into the constituent amino acids. Silk is more resistant to alkalis and organic solvents, except hydrogen bond-breaking solvents. Continuous exposure of silk fiber to sunlight results in strength loss. It begins to yellow at high temperatures and disintegrates above 165°C. The moisture absorption results in a temporary 10–25 % strength loss of silk fiber. It is easily attacked by moth and mildew.
- Effect of Bleaches
- Effect acid
- Effect alkalis
- Effect water
- Effect inorganic solvent
- Effect organic solvent
- Effect sunlight & Weather
Advantages of silk fabric:
- Luxurious hand (the feel of a fiber, yarn, or fabric to the wearer)
- Excellent drape (a fabric’s ability to fold while worn)
- Wonderful luster (reflection of light on fabric)
- Stain resistant
- Strong but lightweight
Disadvantages of silk fabric:
- Fair abrasion and resiliency
- Turns yellow if bleached
- Poor resistance to exposed sunlight
- Degrades over time with exposure to oxygen, making it difficult to preserve
End uses of silk fabric:
Dissolution of silk keratin and regeneration has been studied extensively for the production of composite materials for bioresorbable implants and scaffolds for medical applications. Also regeneration of fibers and membranes can be achieved from concentrated fibroin solutions.
This combination of properties, together with fineness, high degree of luster, softness and superb drape enables silk to be converted into many beautiful types of fabrics, from delicate chiffons to heavy brocades. The fineness, regularity, strength and elasticity of silk make it suitable for fine screens for printing and parachute fabrics.
Silk’s good absorbency makes it comfortable to wear in warm weather and while active. Its low conductivity keeps warm air close to the skin during cold weather. It is often used for clothing such as shirts, blouses, formal dresses, high fashion clothes, negligees, pyjamas, robes, skirt suits, sun dresses and underwear.
Silk’s elegant, soft luster and beautiful drape makes it perfect for many furnishing applications. It is used for upholstery, wall coverings, window treatments (if blended with another fiber), rugs, bedding and wall hangings.
Other end uses of silk are given below:
- Apparel: Luxury items, wedding dresses, evening gowns, blouses, scarves, neckties
- Interiors: Pillows, wall hangings, draperies, upholstery
- A fine lustrous fiber composed mainly of fibroin and produced by certain insect larvae to form cocoons, especially the strong, elastic, fibrous secretion of silkworms used to make thread and fabric.
- Thread or fabric made from this fiber.
- A garment made from this fabric.
- Silks The brightly colored identifying garments of a jockey or harness driver.
- A silky filamentous material, such as the webbing spun by certain spiders or the styles forming a tuft on an ear of corn.
- Introduction to Textile Fibres by Sreenivasa Murthy
- Textile Engineering – An Introduction Edited by Yasir Nawab
- Textile Chemistry by Thomas Bechtold, Tung Pham
- The Chemistry of Textile Fibres, 2nd Edition by Robert R. Mather, Roger H. Wardman
- Textile and Clothing Web
- Abrar Ahmed Apu, Asst. prof. Daffodil International University
- Samiha Sultana, Senior Lecturer, Daffodil International University
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.