Efficient bonding of ethylene-propylene-diene M-class rubber to stainless steel using polymer brushes as a nanoscale adhesive

Abstract

A novel approach to bond rubber to metal using nanometers thick polymer brushes in the interface is investigated. An atom transfer radical polymerization (ATRP) initiator is grafted to the surface of stainless steel (SS) and poly(glycidyl methacrylate) (PGMA) brushes are grown from the surface. Benzoyl peroxide (BPO) is drop casted on the polymer films before the samples are overmolded with ethylene-propylene-diene M-class (EPDM) rubber. For surface concentrations below 0.2 µmol cm-2 regions with adhesive failure were observed. Thermal infrared reflectance absorption spectroscopy (T-IRRAS) and X-ray photoelectron spectroscopy (XPS) show a conversion of oxirane groups after heating samples to 170 °C.A compression molding system designed to mold uncured rubber on modified SS samples and subsequently to perform peel tests of the rubber-steel specimens are presented. Four stages of crack propagation are identified in the peel data: 1) elastic loading, 2) stable crack propagation, 3) unstable crack propagation, and 4) loss of load carrying capacity. The novel nanometer thick bonding system was benchmarked against a commercial bonding system. Calculated peel energies are in good agreement with previously reported values and show no significant difference compared to a commercial bonding agent. Therefore, it is concluded that the novel bonding system applying only a nanometer thick surface immobilized polymer brush layer offers similar adhesion as existing micrometer thick primer adhesives.