3 2 Physical and Chemical Properties of Silk

3. 2 Physical and Chemical Properties of Silk. Uses of Silk. By: Dr. Jyoty Angotra(Lecturer) Govt. Degree College, Poonch.

Silk �Silk has been the queen of fibers for centuries. �Silk is the natural protein fibre secreted by silk worm in making their cocoons and collected to make thread and fabric. �It is used for luxury fabrics and high fashion cloths. �Silk principally consists of two proteins, Fibroin and Sericin in a ratio of 80: 20 in case of mulberry silk or pure silk.

Discovery of Silk �Silk was first discovered by Chinese princess Leizu, while she was having tea in the imperial garden. �A cocoon fell into her tea and unraveled, she noticed that it was made of long and strong thread. �She then discovered to combine the silk fibers into a thread.

Physical properties of silk: �Tenacity: Tenacity of silk fibre ranges between 3 to 6 grams/ denier. Silk fibers has very good strength due to presence of many hydrogen bonds to be formed in a more regular pattern. When it comes into contact of water( wetting conditions), it gets weakened due to hydrolization of a large numbers of hydrogen bonds present in it by water molecules.

Physical properties of silk: �Elongation: Silk fibre shows very good elongation properties. Silk fibre has an elongation at break of 20 -25% under standard conditions. It's elongation at break gets increased up to 33% at 100% R. H.

Physical properties of silk: �Elasticity: Silk is considered to be more plastic than elastic fibre. If the silk material is stretched excessively, the silk polymers will slide past each other. This happens due to Beta configuration present in the silk polymers. A large number of hydrogen bonds get ruptured due to application of stretching force. Thus silk behaves like a more plastic nature than elastic.

Physical properties of silk: �Hydroscopic nature: Since silk has a very crystalline polymer system, it is less absorbent than wool, however it is satisfactorily absorbent. It has more absorbency than cotton. The moisture regain of silk is 11%. It absorbs moisture more quickly than cotton but it gets dried fairly quickly too.

Physical properties of silk: �Thermal: Silk is very sensitive to heat. This is because of dearth of any covalent cross-links in the polymer system of silk. The existing peptide bonds, salt linkage and hydrogen bonds of silk polymer system tend to break down once the temperature goes beyond 100 C. The silk fibre starts to burn at 175°c (begins to fuse).

Physical properties of silk: �Exposure to Sunlight: The silk fibre is more sensitive to light than any other natural fibre. When this comes for long time exposure to sunlight, it's color gets spotted partially. Fabric also gets yellowish due to degradation occurred by sunlight.

Chemical properties of silk: �Effect of Water: When silk fibre is kept in boiled water for a short period of time, it does not show any type of effect of boiled water. Silk fibre tends to loss its strength to some extent when it is kept in boiling water for long time. This strength loss occurs due to hydrolysis action of water. Silk fibre withstands, however, the effect of boiling better than wool.

Chemical properties of silk: �Effect of Acids: Silk fibre reacts with acids more quickly. Silk fibre is soluble in hot and concentrated sulphuric acid and hydrochloric acid. It gets yellowish when it comes into contact of Nitric acid. It is slightly affected by diluted organic acids at room temperature. The concentrated organic acids dissolve the silk fibers.

Chemical properties of silk: �Effect of Alkalis: When silk fibre comes into contact of Alkaline solutions, it begins to swell. It dissolves completely after some time. It is treated with 16%-18% solution of sodium hydroxide at low temperature to creat crepe effect blended fabric having cotton.

Chemical properties of silk: �Effect of Oxidizing Agents: The fibroin present in the silk doesn't get affected badly by hydrogen peroxide solution. The weight loss occurs when it is treated in hydrogen peroxide solution. Chlorine solution affects more badly than Hypochlorite. Low concentration of chlorine solution does damage to fibroin present in the silk.

Uses of Silk has many other industrial and commercial uses: � Raw silk is used for clothing such as shirts, suits, ties, blouses, pajamas, jackets etc. � Hand spun mulberry silk is used for making comforters and sleeping bags. � Other variety fabric material like plain silk, deluxe , satin, chiffon, crepe, brocades are made from mulberry silk.

Uses of Silk �Knitted materials from silk fibers i. e. socks, stockings are very costly. �Reeling waste, bad cocoons are used to make spun silk fabrics. �Waste silks are hand spun into matka, katan, fesuna and noil yarns. �Tasar silk fabrics use for making Gichanoil, tasar plain, cotton-tasar blend, tasarmulberry blend, peduncle fabric.

Uses of Silk �Muga silk cloth is very largely used by the Assamese women as mekhela, riha-sador sarees. �Eri spun silk is used for dress materials and the coarse variety for making scarves, chadders, shawls and quilts. �Trimoulters silk yarns is used as package material in pencil industry and for making talcum powder puff.

Uses of Silk �In France 22 -24 denier silk is used in tyre manufacturing to have longer life span than rubber tyres. �Parachutes are made from 13 -15 denier silk fiber. �Silk is used raw materials for preparing sound free gears for making precision machinery.

THANK YOU