Comparative Analysis of Primers and Alternative Polypropylene Pre-Treatment Techniques

The test polypropylene substrates obtained from the original plastic car parts for Skoda Superb were subjected to 10 pre-treatment techniques: solvent cleaning (isopropanol, xylene), mechanical abrasion, immersion in a chromic acid mixture, flame activation, atmospheric and low-pressure plasma treatment, corona discharges and the application of two different primers (also called adhesion promoters). One of the primers, based on chlorinated polypropylene, was commercially available, while the other was prepared in our laboratory using polypropylene grafted with maleic anhydride. The test substrates were characterized using contact angle measurement for designation of surface free energy, Atomic Force Microscope (AFM) for roughness analysis, Scanning Electron Microscopy (SEM) for surface topography, and Energy Dispersive X-ray Spectrometry (EDX) for surface oxygen and contamination analysis. The suitability of the surface preparation methods in the industry was evaluated through peel strength tests (adhesive bonding process) and cross-cut tests (painting process). Not all tested methods were effective in increasing adhesion, especially in the adhesive bonding process, and even fewer in the painting process. However, some of them were suitable for both applications. The use of primers was found to be crucial.