Adhesion of ethylene-octene copolymers to polypropylene: Interfacial structure and mechanical properties

Four separate ethylene-octene copolymers of differing molecular weight and co-monomer content have been moulded against polypropylene at various tempe ratures between 120 and 200 degreesC. The adhesion, measured by a 90 degree s peel test, varied with the particular copolymer, but for all of them it v aried with moulding temperature, showing a maximum at about 160 degreesC. I t is argued that the temperature variation depends on the extent to which i nterpenetration of chains occurs in the interfacial region. This, in turn, depends on the recrystallization temperature of the polypropylene. The rela tive magnitudes of peel energy for the different copolymers can be understo od in terms of the extent of plastic yielding necessary in order to transmi t a critical stress to the interfacial regions during peeling.