Weatherability of Bio-Based versus Fossil-Based Polyurethane Coatings

The use of bio-based feedstock for the formulation of protective coatings has been implemented in the increased industrial supply of building blocks synthesized from biomass. The alternation of traditional polyurethane coatings by bio-based polyurethanes has focused on the replacement of the polyisocyanate component in combination with polyester or polyacrylate polyols. In this research, the performance of an aliphatic isocyanate synthesized from crude oil (i.e., HDI, or hexamethylenediisocyanate) has been compared to an alternative hardener synthesized through fermentation of biomass (i.e., PDI, or pentamethylenediisocyante). As the chemical structure of the bio-based PDI is slightly different, with an aliphatic chain of five compared to six carbon atoms, an almost similar or better performance as a protective coating is demonstrated. The application of bio-based PU coatings resulted in lower drying times and higher hardness with similar gloss, chemical resistance and mechanical resistance. In particular, the resistance of bio-based coatings after QUV accelerated weathering testing was improved owing to the better hydrophobicity of the bio-based PDI hardener. There was a gradual trend in evolution of the performance with stepwise replacement of fossil-based with bio-based content.