Several thermoplasts have elastic properties similar to rubber. Further details can be found in section ⇒ TPE (Thermoplastic Elastomeres).
The historic differentation between plastics (=thermoplast) and elastomers (=cross linked polymers) therefore is no more valid.
The designation Rubber however still concerns the group of cross-linked cautchoucs. Still a very important cautchouc is natural cautchouc gained from cautchouc trees. A variety of synthetic cautchouc materials have been developped, where Nitril Rubber (NBR) and Styrol Butadien Rubber (SBR) have the biggest commercial relevance primarily because of low material costs. The performance of some synthetic rubbers is superior to natural rubber regarding thermal stability and chemical resistance, but regarding cold flex and abrasion no synthetic material is competitive against natural rubber.
All rubbers are usually characterized by a high coefficient of friction against almost all materials. In some cases (tires, shoe soles) this may be desired but in other applications, often in case of seals, this should be avoided. To avoid a high coefficient of friction, systems to coat rubbers with low friction coatings have been developped. Many of them take profit from plasma technologies. Plasma treatments to modify surface properties are plasma coating and functionalizing by fluoride atoms. Very important also is the application of low frictional lacquer. In order to achieve the high bonding strength needed to apply these lacquer plasma cleaning and plasma activation techniques are applied. More details are provided by section ⇒ lubricant coating