| Viscoelastic effects in the tear strength and adhesion of elastomers were investigated by: (1) using a viscoelastic data analysis tool, the Williams, Landel, and Ferry (WLF) equation, to understand the tear strength and adhesion of butyl rubber as a function of dwell time and contact temperature; (2) conducting a simple peel test to measure the adhesion of elastomers to filler particles; and (3) using an equation derived from the Johnson-Kendall-Roberts (JKR) theory to calculate the energy required to peel an elastomer strip from a layer of filler particles. The WLF equation was used to form mastercurves of fracture energy of butyl rubber versus effective rate of crack propagation. The peel strength was found to increase continuously over long periods of contact until failure became cohesive within the elastomer layer. At higher temperatures the peel strength increased more rapidly, consistent with the WLF relation governing molecular motion. It is postulated that slow molecular rearrangements occur at the interface, increasing bond strength. Secondly, a simple peel test was used to study the adhesion of three elastomers to filler particles. An interlayer of carbon black particles increased peel strength by up to 300% compared with self-adhesion. Silica particles also increased adhesion, but by a smaller factor. There were significant differences between the different elastomers. Also, the strength of adhesion depended on the degree of crosslinking of the elastomer layers; at higher levels of crosslinking, both self-adhesion and adhesion to particles were reduced. This simple experiment gives an indication of the relative strength of adhesion for different combinations of elastomer and reinforcing filler. Strengths calculated from the hypothesized equation agreed approximately with experimental values. |
