Self-cleaning photocatalytic polyurethane coatings containing modified C 60 fullerene additives

Abstract

Surfaces are often coated with paint for improved aesthetics and protection; however, additional functionalities that impart continuous self-decontaminating and self-cleaning properties would be extremely advantageous. In this report, photochemical additives based on C 60 fullerene were incorporated into polyurethane coatings to investigate their coating compatibility and ability to impart chemical decontaminating capability to the coating surface. C 60 exhibits unique photophysical properties, including the capability to generate singlet oxygen upon exposure to visible light; however, C 60 fullerene exhibits poor solubility in solvents commonly employed in coating applications. A modified C 60 containing a hydrophilic moiety was synthesized to improve polyurethane compatibility and facilitate segregation to the polymer-air interface. Bulk properties of the polyurethane films were analyzed to investigate additive-coating compatibility. Coatings containing photoactive additives were subjected to self-decontamination challenges against representative chemical contaminants and the effects of additive loading concentration, light exposure, and time on chemical decontamination are reported. Covalent attachment of an ethylene glycol tail to C 60 improved its solubility and dispersion in a hydrophobic polyurethane matrix. Decomposition products resulting from oxidation were observed in addition to a direct correlation between additive loading concentration and decomposition of surface-residing contaminants. The degradation pathways deduced from contaminant challenge byproduct analyses are detailed.