Hindering the decrease in wear resistance of UV-exposed epoxy powder coatings by adding nano-SiO2 through ball milling

Abstract

The wear resistance of organic coatings has an important role in order to extend their in-service life. Epoxy powder coatings were mixed with nanosilica through ball milling to study their effect on the wear performance after ultraviolet (UV) exposure. Two types of SiO2 nanoparticles were added: hydrophilic (HL) and hydrophobic (HB) at different percentages (0.25–1% by wt.). Modified powders were applied by electrostatic spraying gun on carbon steel sheets. After curing, coatings were exposed to a xenon lamp for 500 h. The surface of coatings was analyzed by scanning electron microscope (SEM). Reciprocating sliding wear tests were performed at room temperature and dry conditions, under 5 N load and 10 Hz frequency. The countermaterial was a 6 mm-stainless steel ball. Wear tracks were analyzed by an optoelectronic microscope and SEM. In order to analyze possible chemical changes, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was performed. Finally, universal hardness was evaluated to study mechanical properties. Results reveal that small amounts of both types of nanosilica, make the epoxy-matrix coatings chemically degrade less than non-reinforced ones under irradiation, increasing their mechanical behavior and thus wear resistance. The 0.75-1HL and the 0.75HB coatings exhibit the best wear performance after UV exposure.