Rubber is a polyterpene consisting of a long chain of thousands of isoprene units. Isoprene is a five carbon compound and a basic unit of rubber. The isoprenes are joined together end to end to form a giant molecule called polymer.
The word rubber was first used by Priestly in 1770.
- Rubber is obtained from latex, found in tropical and subtropical region.
- Without Euphorbiaceae, about 20 families are involved.
- Such as: Moraceae (Ficus elastica), Apocynaceae.
- 95-98% rubber is obtained from Hevea brsiliensis – Hevea rubber or, para rubber – Euphorbiaceae.
Latex is a gummy fluid, full of monute globules and is a mixture of water, hydrocarbon, resin, oil, acid and salt.
Physical characteristics :
1. Rubber is soft and translucent at 20°C when it chilled from 0-10 Cit becomes hard and at temperature over 20°C it losses elasticity and becomes sticky.
2. Rubber is insoluble in water but soluble in benzene, carbon-di-sulfide, ether, chloroform and chlorinated hydrocarbon.
3. Rubber is amorphous in the unstretched state but shows crystalline behaviour when kept at 0°C for a long time.
Chemical characteristics :
1. Consists of long chain of isoprene unit connected with end to end to form polymer.
2. Rubber form compounds with halogen, halogen acids, metal halides, ozone and oxide of nitrogen.
3. Rubber is oxidized by nitric acids, potassium permanganate, H2O2.
4. Michel Faraday in 1826 established that the chief constituent of rubber is hydrocarbon which has the formula C5H8.
- Greville Williams in 1860 named the hydrocarbon as isoprene.