General Properties of Elastomers
"Elastomer" term is derived from elastic polymer. Mostly used interchangeably with "rubber" term. Elastomers are special class of linear polymers that display an exceptionally large amount of elastic deformation when a force is applied. Many can be streched to several times their original length. Upon release of the force, the deformation can be completely recovered, as the material quickly returns to its original shape.
Rubber
Natural rubber, the oldest commercial elastomer, is made from the processed sap of a tropical tree. In its crude form it is an excellent adhesive, and many cements can be made by dissolving it in suitable solvents. Its uses as an engineering material dates from 1839 when Charles Goodyear discovered that it could be vulcanized by the addition of about 30% sulfur followed by heating to a suitable temperature. Natural rubber compounds are outstanding for their flexibility, good electrical insulation, low internal friction, and resistance to most inorganic acids, salts and alkalies. However, they have poor resistance to petroleum products, such as oil, gasoline and naphtha. In addition, they lose their strength at elevated temperatures, so it is advisable that they not be used at temperatures above 80°C. Unless they are specially compounded, they also deteriorate fairly rapidly in direct sunlight.
Artificial Elastomers
Seeking to overcome some of the limitations mentioned above, as well as the uncertainty in the supply and price of natural rubber, a number of synthetic or artificial elastomers have been developed have come to assume a great commercial importance. The following table shows the properties and uses of common elastomers.
| Tensile St. (psi) | Elongation (%) | Resistance* | |||||||||
| Elastomer | Density | Hardness | Pure | Black | Pure | Black | Service Temp. (°C) | Oil | Water | Tear | Typical Application |
| Natural rubber | 0.93 | 20-100 | 2500 | 4000 | 750 | 650 | -54 - 82 | 1 | 3 | 3 | Tires, gaskets, hose |
| Polyacrylate | 1.10 | 40-100 | 350 | 2500 | 600 | 400 | -18 - 149 | 3 | 1 | 2 | Oil hose, O-rings |
| EPDM | 0.85 | 30-100 | 1 | 3 | 500 | -40 - 149 | 1 | 3 | 3 | Electric insulation, footwear, hose, belts | |
| CSM | 1.10 | 50-90 | 4 | 2 | 400 | -54 - 121 | 3 | 4 | 3 | Tank lining, chemical hose, shoes, soles and heels | |
| Polychloroprene | 1.23 | 20-90 | 3500 | 4000 | 800 | 550 | -46 - 107 | 3 | 3 | 3 | Wire insulation, belts, hose, gaskets, seals, linings |
| Polybutadiene | 1.93 | 30-100 | 1000 | 3000 | 800 | 550 | -62 - 100 | 1 | 1 | 3 | Tires, soles, heels, gaskets, seals |
| Polyisoprene | 0.94 | 20-100 | 3000 | 4000 | 600 | -54 - 82 | 1 | 3 | 3 | Tires, gaskets, hose | |
| Polysulfide | 1.34 | 20-80 | 350 | 1000 | 600 | 400 | -54 - 82 | 4 | 3 | 3 | Seals, diaphgrams, valve disks |
| Styrene butadiene | 0.94 | 40-100 | 2 | 1200 | -54 - 107 | 1 | 3 | 3 | Molded mechanical goods, disposable pharmaceutical items | ||
| Silicone | 1.10 | 25-90 | 1200 | 450 | -84 - 232 | 2 | 4 | 1 | Electric insulation, seals, gaskets, O-rings | ||
| Epichlorohydrin | 1.27 | 40-90 | 2 | 325 | -46 - 121 | 3 | 3 | 3 | Diaphgrams, seals, molded goods, low temp. parts | ||
| Urethane | 0.85 | 62-95 | 5000 | 700 | -65 - 100 | 4 | 2 | 4 | Caster wheels, heels, foam padding | ||
| Fluoroelastomers | 1.65 | 60-90 | 1 | 3 | 400 | -40 - 232 | 4 | 4 | 2 | O-rings, seals, gaskets, roll coverings | |
| * 1:Poor, 2:Fair, 3:Good, 4:Excellent | |||||||||||