Abstract
An experimental study has been carried out of the self‐adhesion of thin layes of three crosslinked elastomers: cis‐polyisoprene (natural rubber) and two polybutadienes. For the polybutadiene materials, the strength of self‐adhesion was found to be strongly dependent upon the time of exposure of the two surfaces to air before they were brought into contact. The strength rose dramatically after the first hour or so of exposure so that in some instances the layers could not be forcibly separated later. When the surfaces were exposed to air for longer periods before joining them, the strength of self‐adhesion fell to low levels again. This remarkable enhancement in self‐adhesion, caused by prior exposure to air for short periods, did not take place on exposure to nitrogen or for samples of cis‐polyisoprene, and it was reduced or delayed in samples containing antioxidant. It is therefore attributed to surface oxidation reactions that can lead to the formation of interfacial covalent bonds with polybutadiene but not with polyisoprene. Some possible reaction schemes are discussed.