Microstructural studies of interfacial deformation in painted thermoplastic polyolefins (TPOs)

Abstract

The interfacial structure and deformation between chlorinated polyolefin (CPO) adhesion promoter and automotive TPO substrates have been characterized with optical, scanning electron, and transmission electron microscopy techniques. The diffusion of rubber phase into the CPO layer was observed and an interphase thickness around 200 nm was obtained from TEM imaging. In some cases, a coherent failure of the adhesion promoter during the paint delamination was observed, which could be explained by the strong interphase formed due to the interfacial diffusion. It was found that baking at 120°C could significantly enhance the swelling of the rubber phase underneath the polypropylene-rich skin layer and the diffusion of the rubber phase into this layer. With decreasing molecular weight of PP homopolymer, the apparent interfacial strength measured by tensile cracking test increased, which was ascribed to the enhanced interfacial diffusion at low molecular weight. The deformation of materials near the interface during the paint delamination process was found to be more extensive in samples with higher interfacial adhesion.