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
Polymer blend more than one kind of polymer. A new polymers modification process, based on a simple mechanical mixture of two polymers first appeared when Thomas Hancock got one mixture of natural rubber with gutta-percha. This process generated a new polymer class called "polymer blends". Polymer blends can be broadly divided into three categories: The use of the term polymer alloy for a polymer blend is discouraged, as the former term includes multiphase copolymers but excludes incompatible polymer blends. Examples of miscible polymer blends: Polymer blends can be used as thermoplastic elastomer Polymer blend A polymer blend, or polymer mixture, is a