Natural rubber (NR) and polyisoprene rubber (IR) can be processed into soft rubber in addition to hard rubber. Typically, as with the hard rubber, they have good processability but inferior chemical resistance properties.
Soft rubber coatings are mainly used where a high degree of mechanical abrasion is expected without extensive chemical stress. Isobutylene - isoprene rubber (IIR) or standard pressed butyl rubber are similar to halogenated products (CIIR) rubber (isobutene-isoprene) only vulcanised to soft rubber. However, the vulcanisate has almost the same chemical resistance properties as natural hard rubber in additional to good resistance to water vapour diffusion; to the diffusion of sulphur dioxide and hydrofluoric acid, etc. Aging and weather resistance characteristics as well as resistance to mechanical abrasion are also significant. Polychloroprene (CR) can be vulcanised only to soft rubber which is also characterised by good chemical resistance as well as aging, weather and abrasion resistance. The resistance to halogenating and oxidizing media is weaker when compared with the butyl rubbers. However, polychloroprene is characterised by a higher stress resistance when exposed to oils. The relatively high chlorine content of about 25% also has self-extinguishing properties. The diffusion resistance when compared with the butyl rubbers is however, significantly reduced.
