Rubber (which also goes by the more general term elastomers), constitutes a large and very important group of polymer materials. What characterizes the rubber is that they have very low E-module (1 to 100 N / mm2) and high elongation at break (eB = 300-1000%), and that the glass transition temperature (Tg) is lower than about -20C. They regain its shape practically immediately, even after relatively large strains.
Rubber (cis-1,4 polyisoprene), which from time immemorial have been prepared from the juice of the rubber tree, was the first polymer got industrial importance. Already in 1839 found the American Charles Goodyear that natural rubber mechanical properties could be improved significantly by vulcanization with sulfur.
In our days it is synthetic rubber types covering a wide range of chemical and mechanical properties that are completely dominant. Development and production of synthetic rubbers accelerated. particularly during WW2 as a consequence of the Japanese occupation of Malaysia in 1942 stopped the supply of natural rubber.
Natural rubber has high molecular weight (about 350,000) and is in a “spaghetti” -like condition in which the long chains are heavily infiltrated into one another. The elastic properties due here a reversible stretching of the crumpled chains. It can be extracted from approximately 500 different trees and plants, the most important are the rubber tree (“Hevea Brasiliensis”) which gives a juice (latex) with 25-40% rubber particles in aqueous dispersion. Raw rubber processed and vulcanized possibly with sulfur.
Nitrile rubber is a copolymer of butadiene and acrylonitrile. It is highly resistant to solvents and gasoline, and heating and oxidation resistant. Rubber can by combustion lead to formation of toxic gases.
Butyl rubber is prepared by copolymerizing isobutylene with small amounts isoprenfor to make the product vulcanisable. Butyl rubber is resistant to the most common types of solvents.
EPDM rubber (ethylene propylene diene M-class rubber) is exceptionally in vibrators and seals; glass run channel; radiator, garden and appliance hose; tubing; washers; belts; electrical insulation, and speaker cone surrounds. It is also exceptionally as a medium for water resistance in high-voltage polymeric cable jointing installations, roofing membrane, geo-membranes, rubber mechanical goods, plastic impact modification, thermoplastic, vulcanisable, as a motor oil additive, pond liner, electrical cable-jointing, RV roofs, and chainmail applications.
Neoprene (polychloroprene) have low crystallization. It is very resistant to oxidation and is weather and oil resistant. Rubber can not compete in price as raw materials for tires, but has a number of special applications.