Butyl Rubber Nanocomposites with Reduced Air Permeability: Theory and Practice

Polyisobutylene (PIB) and other isobutylene-based polymers such as Butyl rubber (isobutylene-isoprene copolymers), Halobutyl rubber (brominated or chlorinated Butyl rubber), and Exxpro (brominated isobutylene-paramethyl styrene copolymers) have air permeabilities about 10x lower than other elastomers, and this has led to their being the material of choice for the inner tubes and innerliners that act to retain the air pressure in nearly all modern pneumatic tires. However, there is a continuing need to improve the air retention characteristics of such components even further, in order to improve their performance in terms of both energy efficiency and vehicle safety. One route to such improvements has been the production of nanocomposites of these isobutylene-based elastomers with clay, wherein nanometer-scale clay sheets are dispersed within the rubber to lower the permeability even further, by a factor of 2 or 3 or even more. Of course, in developing such materials for tires it is key that they maintain the good mechanical properties that are required in modern vehicles. I will describe the principles involved in this technology and discuss several possible routes to such nanocomposites that could find use in tires..