Evaluation of speciality elastomers for sealing applications

An evaluation of a range of selected elastomers has been carried out in an attempt to assess the potential usefulness of such materials as compression seals, valves, and diaphragms for use in gas distribution systems. Properties considered pertinent to the aforementioned applications were determined and compared with the schedule of requirements listed in the standards compiled by the British Gas authorities. The elastomers selected for evaluation were acrylonitrile/butadiene, chlorinated polyethylene, epichlorohydrin, ethylene acrylic elastomer, polyacrylic elastomer, ethylene/vinyt acetate, polychloroprene, polyurethane, and highly saturated nitrile. Formulations used for these rubbers were designed to give primarily low compression stressrelaxation and set at low temperatures: and minimum volume increase when in contact with hydrocarbon liquids and vapours. The diverse range of properties determined are discussed in terms of the innate molecular nature of these materials. On the basis of the evaluation it seems that epichlorohydrin and polyurethane elastomers possess the potential to satisfy the requirements stipulated by British Gas. However, an obvious drawback of polyurethane elastomers is their susceptibility to hydrolytic attack in moist environments. Indeed, water absorption tests were carried out on both epichlorohydrin and polyurethane elastomers lasting approximately 3 months. In the particular case of the polyurethane elastomer, a decrease in volume was observed; probably as a consequence of extraction following hydrolysis reactions occurring in the bulk of the polyurethane elastomer.