TYPES OF YARN AND FIBER USED IN TEXTILE (SILK):-

Types of yarn and fiber used in textile:-

SILK:-

Silk is a natural fiber some form of which can be woven into textile . The protein fiber of silk is composed mainly of fibron and is produced by certain insects larvae to form cocoons. The best known silk is obtained from the cocoons of the the larvae of the Mulbury silk worm , Bombyx Mori reared in capitvity (sericulture). The shimmering appearance of silk is due to the triangular prism-like structure of the silk fiber , which allows silk cloth to refract in coming light at different angles , thus producing different colors. 

image of Four of the month important domesticated silk moth Top to bottom.

Silk is produced by several insects , but generally, only the silk of moth caterpillars has been used for textile manufacturing. There has been some research into other types of silk , which differ at the molecular level. Silk is mainly produced by larvae of insects undergoing complete metamorphosis, but some insects , such as webspinners are raspy crickets , produce silk throughout their lives. Silk production also occurs in hymenoptera (bees, wasps and ants) , silver fish , caddish flies, mayflies , thrips leafhopper, beetles , lacewings , fleas, flies and midges. Other types arthopods produce silk , most notably various arachnids such as spiders.

Production process:-

The process of silk production is known as sericulture. The entire production process of silk can be divided into several steps which are typically handled by different entities.

Extracting raw silk starts by cultivating the silk worm on mulbery leaves . Once the worm starts pupating in their cocoons these are dissolved in boiling water in order  for individual long fibers to extracted and fed into spinning reel. 

To produce 1 kg of silk, 104 kgs of mulbery leaves must be eaten by 3000 silk worms. It takes about 5000 silk worms to make a pure silk kimono . The major silk producers are China (54%) and India (14%).

The environmental impact of silk production is potentially large when compared with other natural fibres. Slige cycle assement of Indian silk production process has a large carbon and water foot-print, mainly due to the fact that it is an animal-derived fiber and more inputs such as fertilizer and water are needed per unit of fiber produced .

PROPERTIES OF SILK:-

Physical properties:- 

Silk fibers from Bombyx mori silk worm have a triangular cross section with round corners 5-10 um wide. The fibroin-heavy chain is compared mostly of beta-sheet , due to a 59-mer-amino acid repeat sequence with some variations. The flat surface of the fabrics reflects light at many angles , giving silk a natural Sheen.

The cross section from other silk worms can vary in shape and diameter crescent-like for Anaphe and elongation wedge to tussah. Silk worm fiber are naturally extrude from two silk worm gland as a pair of primary, filament (brin), which are stuck together, with sericin , proteins that act like glue to form a bave. Bave diameters for tussah silk can reach 65 um. See cited refence for cross-sectional SEM photographs. 

image of raw silk of domesticated silk worm showing its natural shine.

Silk has smooth , soft texture that is not slippery, unlike many synthetics fibers.

One example of the durable nature of silk over other fabrics is demonstrated by the recovery in 1840 of silk garments from a wreck of 1782. The most durable article found has been silk ,for besides pieces of cloaks and lace a pair of black satin breeches , and a large satin waist coat with flaps, were got up of which  the silk was perfect, but the lining entirely gone from the threads giving way. No articals of dress of woollen cloth have yet been found.

Silk is poor conductor of electricity and thus suspectible to static cling. Silk has a high emissivety for infrared light, making it feel cool to the touch. 

Unwashed silk chiffon may shrink upto 8% due to a relaxation of the fiber macrostructure , so silk should either be washed prior to garment construction or dry cleaned. Dry cleaning may still shrink the chiffon up to 4%. Occasionally, the shrinkage can be reversed by a gentle steaming with a press cloth. There is almost no gradual shrinkage nor shrinkage to molecular-level deformation.

Natural and synthetic silk is known to manifest piezoelectric properties in protein probably due to its molecular structure. 

Silkworm, silk was used as the standard for the denier, a mresurement of linear density in fibers . Silkworm silk therefote has a linear density of approximately 1 den or 1.1 d tex.

Chemical properties:- 

Silk emitted by the silk worm consist of two main protein sericin and fibroin being the structural center of the silk and sericin being the sticky material surrounding it. Fibroin is made up of the amino acid Gly-ser-Gly-Ala-Gly-Ala and form beta pleated sheets . Hydrogen bonds from between chains and side chains form above and below the plane of hydrogen band network.

The high proportion (50%) of Glycine allows tight packing . This is because Glycine's R group is only a hydrogen and so is not as sterically constrained. The addition of  alanine and serine makes the fiber strong and resistance to breakingb. This tensile strength is due to the many interceded hydrogen bands , and when stretched the force and applied to these numerous bonds and they not break.

Silk resist most mineral acids except for suphuric acid , which dissolve it. Chlorine bleach will also destroy silk fabrics.

Ref:-https://en.m.wikipedia.org