Effect of cold plasma treatment on surface roughness and bonding strength of polymeric substrates

For an effective application of polymers, it is essential to have good adhesion behaviour to ensure good mechanical properties and durable components. Unfortunately, in general terms, polymers are characterized by high chemical inertness, which leads to very low surface energy values and, consequently, poor adhesive properties; this is particularly true for polyolefins. In this study, the effects of low pressure plasma treatment on surface roughness of polyethylene and polypropylene samples and on shear properties of adhesive bonded joints based on these substrates have been investigated. In particular, the optimization of three plasma process parameters, exposure time, voltage and working gas, were studied performing roughness measurement, contact angle evaluation and lap-shear tests. The experimental results show that the optimized plasma process may remarkably change the surface morphology, increasing wettability properties of the surfaces and shear strength of the bonded joints. These good properties remain almost unchanged even after some days of storage in the laboratory.