Polymer such as rubber, suberin, melanin and lignin. Naturally occurring polymers such as cotton, starch and rubber were familiar materials for years before synthetic polymers such as polyethene and perspex appeared on the market. Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and cellulose to form nitrocellulose and the formation of vulcanized rubber by heating natural rubber in the presence of sulfur. Ways in which polymers can be modified include oxidation, cross-linking and endcapping. Especially in the production of polymers the gas separation by membranes has acquired increasing
Rubber technology 1844, but is a process restricted to polymer chains having a Double bond in the backbone. Such materials include natural rubber and polybutadiene. The range of materials available is much wider however, since all polymers become elastomeric above their Glass transition temperature. However, the elastomeric state is unstable because chains can slip past one another resulting in creep or stress relaxation under static or dynamic load conditions. Chemical cross links add the stability to the network that is needed for most practical applications. WORKER PROCESSING RUBBER Methods for processing rubber include mastication and various operations like mixing, calendering, extrusion, all