Butyl rubber was invented in 1937 as a copolymer derived from two distinct polymers: isoprene and isobutylene. It is modelled after natural rubber with very high molecular weight. In spite of a structure similar to that of natural rubber, it has different properties: for example, the raw form shows a lack of nerve and low tear resistance. In addition, compared to natural rubber, it needs higher doses of accelerators and activators, being devoid of the protein present in natural rubber.
Polyisoprene confers particular fluidity to compounds, a property that is particularly appreciated in moulding and specially calendering processes.
Unfortunately, due to its high cost, it has been replaced with natural rubber today. However, it is still used in friction compounds, specially when cut with polychloroprene, ensuring the prevention of overheating dangerous for burning.
An alternative version of butyl rubber called Halobutyl also exists, created by the addition of a small amount of chlorine or bromine to the main polymer chain. Halobutyl rubber can be vulcanized faster than normal butyl rubber and it is possible to use a smaller number of vulcanizing products in the process.
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