Improvement of adhesion properties of polypropylene substrates by methyl methacrylate UV photografting surface treatment

Polypropylene is a widely used commodity plastic from an industrial point of view. Typical applications include both low and high technological content, as it has a good balance between overall properties, processability and cost. However, it is important to remark its intrinsic low surface energy which leads to high chemical inertness. This has an important restriction on some technical applications that require joining and/or finishing processes such as painting. Therefore, the use of polypropylene in these applications requires previous surface modification in order to increase surface activity. Surface modification can be carried out by physical processes such as plasmas or by chemical ways. Surface chemical modification is characterized by relatively low cost and easy implementation at industrial scale. In this work, we have used a chemical process to improve adhesion properties on polypropylene substrates. The selected method has been ultraviolet photografting of methyl methacrylate (MMA) monomer. This process allows increasing surface activity and this has a positive effect on polypropylene–polypropylene adhesion joints. Surface changes have been followed by contact angle measurements and subsequent surface free energy calculation. The evolution of mechanical properties of adhesion joints (T-peel and shear conditions) in terms of the previous exposure time to UV radiation has been evaluated. Optical microscopy (OM) and scanning electron microscopy (SEM) have been used to characterize adhesion fracture type.