Comparative study of surface preparation for paint adhesion on CF-PEKK composites: Plasma, Chemical, and Flame treatment

Abstract

Polyether ketone-ketone (PEKK) is a high-performance thermoplastic, and its fiber composites have various engineering applications. Fiber reinforced composites in long-term applications require a protective layer of coatings to avoid environmental degradation. In this work, the surface energy of carbon fiber-PEKK composites was modified by flame, chemical, and plasma treatments to improve paint adhesion. A detailed study was carried out to understand the physical, morphological, and chemical surface characteristics due to different surface treatments. We found through XPS that highly active surface functionalities (− C-Ȯ/−C = Ȯ) due to oxidation at the ketone/ether groups were for surface adhesion. In support of the enhanced surface functionality, we have also evaluated the wetting behavior of paint with respect to different treated surfaces using drop shape analyzer and found that the polar component of the surface free energy increased for all treatments compared to pristine. Surface crystallinity after surface treatment was assessed using XRD; flame and plasma showed reduced surface crystallinities (25.92 % and 38.18 %, respectively), compared to pristine (46.78 %), and yielded a good adherend for coatings. Surfaces with good wettability and functionalities show good adhesion between the paint and PEKK composites as found through adhesion tests following ASTM D3359. The findings demonstrate that plasma surface treatment outperformed flame and chemical treatments in terms of adhesion of the paint to the surface.