Performance of alternative biowax powders replacing PTFE fillers in bio-based epoxy coatings

In view of sustainable-by-design issues, there is an urgent need to replace harmful coating ingredients with more ecological, non-toxic alternatives derived from bio-based resources. In particular, fluorine derivatives such as polytetrafluoroethylene (PTFE) are frequently applied in coatings because of their versatile role in rendering hydrophobicity and lubrication. In this research, a screening study is presented on the performance of alternative biowaxes derived from different natural sources, when used in protective coating applications. Micronized powders from carnauba wax, rapeseed wax, rice bran wax, palm oil wax, or sunflower wax are added into epoxy clear-coat formulations. When dispersed into a bio-based epoxy from epoxidized flaxseed oil and a proprietary acid hardener, the thermal curing process significantly affects the efficiency of the biowax additives. In concentration ranges of 1 to 10 wt. %, it was observed that the biowaxes consequently present higher hardness and hydrophobicity as coatings as compared to the PTFE additives, while similar abrasive resistance and scratch resistance could be obtained. Moreover, the proprietary mixture ratios of biowax to PTFE powders provide synergistic effects. The granulometry of the biowax powders is a crucial parameter as smaller micrometer grain sizes improve dispersibility in the coating. The mechanistic effects of micronized biowax powder in the epoxy coating are further evaluated through spectroscopic analysis, indicating their interference with the curing process of the epoxy coating.