Silk Protein fiber Silk It is also called

Silk Protein fiber

Silk It is also called Queen of fibers. It is natural protein fiber of animal origin. Instead of being grown in the form of hair, it is produced by insects in the form of continuous fine strand of fibers called as filament, to build cocoons. There about 300~400 varieties of moth but only a few are profitable to collect.

Silk producing Countries: Most historians agree that silk and sericulture (the production of silkworms) had their origin in china nearly 2500 BC. Now there are over 40 countries on the world map producing silk. China is the largest producer and supplier of silk followed by India and then Brazil. * Production of silkworm is called as Sericulture

Silk Types of silk ( w. r. t) silkworms: The silk is obtained from the cocoons of certain caterpillars (larvae), they build cocoons to protect themselves. Most common types are : a. Cultivated silk spun by Bombyx mori silkworm. b. Wild silk spun by certain wild species of silk worm.

Silk Life cycle in sericulture Hatching of egg: The first stage in sericulture process is the production of silk worm eggs in a controlled environment. Female moth deposits about 400 eggs at a time. Hatching of eggs is normally done by spreading eggs over shallow trays in the

Silk Eggs are kept in hatching shed, which is closely regulated at 80 ⁰F for about 8 to 10 days. Finally tiny eggs are hatched into Larvae (caterpillars). At this point, the Larva is about quarter of an inch.

Silk Feeding period: Once hatched, the larvae are placed in huge trays and fed huge amount of chopped mulberry tree leaves.

Silk During this stage silkworm do nothing but eat After about 30 to 35 days since it was hatched, it stops eating and changes color to greenish white and filled with liquid silk. It is about 10, 000 times heavier than when it hatched. The silkworm is now ready to spin a silk cocoon.

Silk Spinning the cocoon: The silk worm now starts spinning of cocoon and liquid silk secretions extrude from two glands.

This viscous, clear liquid is forced through the openings, on the mouthpart of larva, harden on exposure to air and form twin filaments. A second pair of glands nearby secretes a gummy binding fluid called sericin which binds two filaments (fibrions) together steadily over the next 3 to 4 days, the silkworm rotate its body into a figure- 8 movement over some 300, 000 times constructing a cocoon and producing about a mile of silk filament.

Silk The caterpillar then changes from larva to pupa and in this condition it sleeps for about 18 to 20 days. Then if left undisturbed it transforms into moth. If pupa is not killed it will transform into moth and becomes fully awake and strives to emerge from cocoons. It will push itself against the wall of cocoon by breaking some of the obstructing fibers. The continuous silk filament is thus broken up into thousands of short pieces. Within the few days of making its cocoons, the silk producers kill the pupa in the cocoon.

Silk The usual method of killing are; 1. Immersing the cocoons in the steam for few minutes. 2. By baking cocoons in hot oven. 3. By placing the cocoons in the boiling water. 4. By freezing the cocoons to death.

Processes: Reeling Throwing Degumming

Silk Reeling of silk: The process of unwinding the filament from the cocoon is called reeling. This process is carried out in a building called filature or reeling plant. The cocoons are soaked in boiling water to soften the sericin gum that is holding the filaments in place.

Silk The cocoons are taken out and loose fluffy silk on outside is cleaned off which is then used in production of spun silk yarn. The cocoons are again placed in hot water basin and labor use a brush or broom to push cocoons up and down in the water until some loose end of filament becomes attached to broom. The filament is drawn out gently; the cocoons tumbles around in water and gradually unreel itself. * A single filament of silk is very fine (12~30μm)

Silk Throwing: It is a process in which two or more multifilament strands are combined and twisted together to form heavier threads.

Silk Degumming: The process of removing the sericin from raw silk or thrown silk is called Degumming. The natural sericin gum is normally left on silk during reeling, throwing and weaving. It acts as a size which protects the filaments and fibers from mechanical injury. The gum is removed from finished yarn by boiling with soap and water.

Cross section of raw silk is roughly elliptical. Figure shows that triangular twin fibroin filaments, covered by sericin, face each other. The beauty, softness and luster of silk are due to the triangular cross section of the silk filament. After degumming process, twin fibroin filaments separates into individual filaments giving finer and more lustrous fiber. It lacks longitudinal features along the longitudinal-section

Silk fabrics woven with sericin have a characteristic stiffness of handle and dull in appearance. After degumming silk acquire beautiful luster. One third of weight of fabric is lost when sericin gum is removed in this way. Raw silk with gum still on filament is called hard silk.

Silk Spun silk: Short length of silk fibers obtained from the various silk waste are not used in reeled silk and in making thrown silk yarns but these are spun into yarns just like cotton, linen or wool yarns. Spun silk yarn are strong but they are less lustrous than reeled silk yarn and not as strong and elastic as reeled silk filament yarn.

Sources of staple silk : Pierced cocoons Floss Double cocoons

Silk worm diseases: The silk worm is subject to number of severe diseases the most common of which is “Pebrine” Black spots appear on the body of silk worm. The infected silkworm kill off by the disease before they can spin

Longitudinal view Cross Sectional view (Triangular)

Properties of silk fiber: Tensile strength: Silk is strong fibre. Its strength is due to linear structure and very crystalline polymer. Usually 30. 9 – 44. 1 c. N/tex * Which one is more stronger Silk or Steel? ? ? Elongation: Silk filament has elongation at break 20 -25 %. Specific gravity: Its specific gravity is 1. 25

Elastic properties: Silk is considered to be more plastic than elastic. Because it’s a crystalline polymer it does not allow polymer movement which could only occur in amorphous region. Its handle is regarded as soft because of the smooth, even, and regular surface of silk filament. Effect of moisture: It absorbs moisture. Its moisture regain is 11%. Degummed silk will swell as it takes up moisture.

Effect of heat: Silk will withstand higher temperature of 140 degree centigrade and decompose at 165 degree centigrade. Effect of age: Silk may suffer a gradual loss of strength if stored not carefully. Effect of sunlight: Silk starts decomposition by exposure to strong radiation of sunlight. Effect of acids: Dilute acids should be used.

Effect of alkalis: Light alkali like ammonia cause little damage. Effect of insects: It can be readily attacked by clothes moth or carpet beetles. Effect of microorganism: Silk is resistant to mildew and bacteria unless it is left for some period of time under extreme conditions.

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) Hydrophilic Stain resistant Strong but lightweight

DISADVANTAGES OF SILK FABRIC: Fair abrasion and resiliency Turns yellow if bleached Poor resistance to exposed sunlight Expensive Degrades over time with exposure to oxygen, making it difficult to preserve

Applications of silk fiber: Ø Dietary Ø Pharmaceutical Ø Biomedical Ø Cosmetic Ø Automobile Ø House Building Ø Anti-bacterial * Consult the article given for detailed study of silk fiber applications (will be included in exam)