Formation of a boundary layer of polyolefins adhesively bonded to steel

The change in peel strength A of adhesive joints of PE or ethylene copolymer with vinylacetate with steel, the thickness of a residual adhesive layer h on a metal substrate after a cohesive fracture of the adhesive joints, and some structural characteristics of this layer (content of cross-linked and low-molecular parts of the polymer and molecular weight) are studied as functions of a contact time t under conditions of catalytic contact oxidation. The A(t) curves of both the studied polymers are similar. Fracture of adhesive joints is of cohesive character, and h grows with contact time. The structure of the boundary layer significantly differs from the bulk adhesive. Competing contact oxidation processes—cross-linking and destruction—proceed simultaneously in the adhesive boundary layer. The contact time function of an empirical quantity K, which estimates the ratio of contribution of two competing contact oxidation processes, coincides with the t function of the ratio AV=A/h, which is a peel energy per unit volume of a polymer layer involved in deformation followed by fracture and is determined by its strength-deformation characteristics.