Effect of silane-based treatment on the adhesion strength of acrylic lacquers on the PP surfaces

The increasing use of polymeric materials in high technical fields, has forced the need to overcome some of their limitations by means of innovative processing. Good adhesion to the polypropylene (PP) surface is essential for coating applications. Due to its surface specifications such as low surface energy and absence of functional groups, the surface of PP is needed to be modified. In this study, the effect of two organofunctional silane-based treatments on the surface characteristics of flame-treated PP was investigated. Contact angle measurements, scanning electron microscopy (SEM), atomic force microscopy (AFM) and ATR-FTIR techniques were employed to study the changes in the surface of the samples after flame and silane treatments. The surface became relatively hydrophilic on exposure to the direct flame and a relative increase in the surface free energy was observed. The investigation onto the surfaces by SEM and AFM showed that the surface roughness increased after flame treatment. ATR-FTIR analysis showed formation of carbonyl groups on the flame-treated surfaces. Organofunctional silanes with different concentrations were then applied on the PP surfaces using wet method. Having applied the silanes, functional groups of the silanes were also appeared on the surface. Finally, two different acrylic lacquers with carboxyl and hydroxyl functionalities were applied on the surfaces. The adhesion strength of the lacquers to the treated substrates was evaluated using direct pull off method. The results showed that the silane compound with epoxy functional group significantly increased adhesion strength of acrylic lacquers with carboxyl functionality to the flame-treated PP surface.