Influence of metal surface preparation on its surface profile, contact angle, surface energy and adhesion with glass fibre prepreg

Surface preparation of metal plays a vital role to enhance the adhesion of polymer coatings in ensuring the desired performance of metal infrastructure for the oil and gas industry. In this study, a range of techniques for the surface preparation of mild steel were evaluated which included garnet grit blasting, disk sanding, needle gun, flap wheel, strip wheel and wire brush. The surface profile and apparent surface energy parameters such as apparent surface energy, work of adhesion, Lifshitz-van der Waals acid–base components were measured from these trials correlation made with these properties to the metal to polymer coating bond strength and bond failure mode. The dolly pull-off strength was used to quantify the bond strength while the laminate failure area (%) was used to assess the bond failure mode. Based on the testing results, it was found that irrespective of the surface preparation technique used, the dolly pull-off strength and laminate failure area increased with increasing surface profile up to a value of approximately 21µm and both of these properties followed a plateau up to 24μm and then decreased above this surface profile value. The dolly pull-off strength was also seen to increase with the increase of surface energy and work of adhesion and decrease of contact angle. It was found that the maximum adhesion could be attained with three of the four grit sizes of the garnet grit blasting technique which appeared to have achieved the most favourable properties amongst all the surface properties studied here. Wenzel model was found to be in agreement with the values of the surface profile of different surface preparation techniques.