What is rubber?

Rubbers are loosely described as materials which show “elastic” properties. Such materials are generally long chain molecules known as “polymers” and the combination of elastic and polymers has led to the alternative name of “elastomers”. Rubbers and elastomers will be considered to be synonymous in this work. Products made from rubber have a flexible and stable 3 – dimensional chemical structure and are able to withstand under force large deformations. For example the material can be stretched repeatedly to at least twice its original length and, upon immediate release of the stress, will return with force to approximately its original length. Under load the product should not show creep or relaxation. Besides these properties the modulus of rubber is from hundred to ten thousand times lower compared to other solid materials like steel, plastics and ceramics. This combination of unique properties gives rubber its specific applications like seals, shock absorbers and tyres.

Rubber is used as a name for 3 categories:

• Raw or base polymers.
  These determine the main characteristics of the final product.
• Semi-manufactured product
  The addition to raw rubber of various chemicals, to impart desirable properties, is termed compounding. The material is however stillmalleableand plastic.
• Final product
  Because of a vulcanisation process the rubber compound gets its elastic properties.

Modern rubber materials consists of approximately 60 percent of synthetic polymers and the other part consists of vulcanisation agents, softeners, accelerators, anti aging agents and other chemicals. These additions are necessary to achieve the desired properties of the final product.

Flexible chains Bonded

Polymers have a backbone of hydrocarbons. The hydrogen atom is often replaced by other atoms or molecules (like CH3, Cl or F) and thus create another type of elastomer. These chains are chemically bonded together by sulphur, peroxides or bisphenol. An exception is silicone. Silicone contain very flexible siloxane backbones (Si-O) and can only be cured with peroxide.