The effect of crosslinking and copolymer composition on the peel adhesion between chlorinated polyethylene and acrylonitrile-butadiene elastomers

The adhesion between chlorinated polyethylene (CM) and acrylonitrile-butadiene (NBR) elastomers was evaluated using a T-peel adhesion test. Peel measurements were conducted under a wide range of temperatures and peel rates. Joint strength between vulcanized elastomers was found to be highly temperature sensitive, varying over three orders of magnitude between 25 and 125°C. As peeling temperatures increased, joint strength generally decreased.; The purpose of this research was to determine why vulcanized CM and NBR joints are so weak at elevated temperatures. During the course of the investigation, the effect of crosslinking on both the adhesive and cohesive strength of each adherend was investigated as a function of peel rate and temperature. In addition, the dependence of peel strength on interphase thickness was investigated by altering the thermodynamic miscibility of the adherends.; Curative migration was found to be responsible for the weak bonding between conventionally crosslinked CM and NBR adherends. The dimercaptothiadiazole cure system used in the CM composition is inhibited by zinc, which was shown to diffuse from the ZnO-accelerated NBR adherend into the surface of the CM adherend. As a result, covulcanizates of CM and NBR are held together primarily by polymer entanglements, rather than covalent bonds. Crosslinking of the chains removed from the entangled interphase weakened the apparent joint strength by reducing inelastic energy dissipation in the bulk of each adherend.; Normal crosslinking of each polymer was found to take place in the interphase when a peroxide cure system was substituted into the NBR recipe. In this case, an optimum degree of crosslinking was identified where adhesion is maximized. This optimum took place very early in the crosslinking process, near the point of incipient gelation. At higher levels of crosslinking bond strength decreased, exhibiting a dependence of M_c0.66 ± 0.02 at elevated test temperatures.