Wetting behavior of polymer melts on coated and uncoated tool steel surfaces

The wettability of steel and coatings used for tools and screws in polymer processing is often determined at room temperature. However, it has to be taken into account that polymeric materials are processed at higher temperatures. Contact angle measurements of melted PP, HDPE, PMMA, and PA 6.6 on steel and on TiN, TiAlN, CrN, DLC, and PTFE were performed in this work to investigate the wetting behavior under closer-to-processing conditions. The contact angle is dependent on time and the ambient atmosphere. Oxidation and degradation of the polymer melts influence wetting significantly. TiN, TiAlN, CrN, and DLC exhibit a rather good wettability, whereas the highest contact angle of the polymer melts was observed with PTFE. Higher roughnesses of the surfaces lead to an increase in the contact angle. It was also shown that a higher temperature causes a better wetting of the solid surfaces.