8

Chitinous Membranes and Analogous Material

117

filament consisting of fibrils, microfibrils and polymer molecules is rather notable

[17, 18].

About Sericulture

Sericulture is the term, which denotes the production of silk through silkworm rearing

commercially. Sericulture is a labour-intensive agro-industry ideally suited for rural

areas. Sericulture provides an excellent and unique opportunity for socioeconomic

development and employment in developing countries like India. Historical evidence

shows that silk was discovered in China and that the industry spread from there to

other parts of the world. Geographically, Asia is the main producer of silk in the

world and produces over 95% of the total global output. Though there are over 40

countries on the world map of silk, the bulk of it is produced in China and India.

Chemical Composition and Properties

The percentages of fibroin and sericin have been shown in Table 8.1. Glycine, alanine,

serine and tyrosine contribute to 90% of fibroin molecules. Sericin binds the fibroin

filaments and has a protein structure having similar to rubber elastic properties.

Mulberry silk has good elastic properties and it is also hydroscopic. It also exhibits

anisotropy and has high electrical resistance. It is unaffected by temperature up to

140 °C. Silk can be dyed with all kinds of dyes as used in the case of wool. Silk

has a wide range of applications in textiles, protein chemistry, genetics and also

in genetic engineering. Minimum numbers of allergies have been reported in the

medical literature. It is a natural fibre which can be compared with any synthetic

fibre and the product has its uses in industry, medicine and parachuting.

Physico-Chemical and Mechanical Properties of Silk

The solubility of spider silk is based on its hydrophilic nature. The density of spider

silk is about 1.4 gm/cm³ and on the other hand that of steel is 7.8 gm/cm³. Spider silk

has very good tensile strength and exhibits torsional resistance. The silk is highly

elastic, i.e. to the extent of 300%. It can withstand the impact of the weight of a honey

bee weighing 200 mg flying with a velocity of 3 m/s. This character as a predator

helps in catching and eating the insects.

Genetic Engineering

There is a lot of variation in the mechanical and physiological properties of silk as

produced by various spiders. Most of these fibres share a common primary structural