Nano-silica-containing acrylic polyurethane and acrylic-polyester hybrid polyurethane coatings for direct-to-metal (DTM) coating applications – a comparative study

In the era of sustainability, direct-to-metal coatings have proven to be a promising solution as it eliminates the need for underneath primer coating layers. In the present study, two coating systems, viz. acrylic polyurethane and acrylic-polyester hybrid polyurethane nano-composite coatings, were prepared by addition of nano-silica in various loadings for direct-to-metal coating applications. The addition of nano-silica along with selected resin systems enables to meet desired mechanical properties, chemical resistance along with weathering and corrosion resistance of DTM coating system. Incredible improvement in the overall mechanical properties of the coating including pencil hardness and scratch resistance has been observed by the addition of nano-silica. SEM technique was employed to evaluate the nano-silica dispersion into the coating system along with its morphology. SEM studies revealed thorough dispersion of the nanoparticles within the coating matrix for both the coating systems. Thermal properties were studied by thermogravimetric analysis along with structural characterization by Fourier transform infrared spectroscopy. Thermal stability of both the coating systems increased with the addition of nano-silica; however, acrylic-polyester hybrid polyurethane coatings revealed better thermal stability at 8% nano-silica loading. Color and gloss changes were studied before and after 500 h exposure to a QUV chamber. Anticorrosive properties were evaluated by salt spray exposure for 700 h. At 8% nano-silica loading, acrylic-polyester hybrid polyurethane coatings revealed better weathering performance along with anticorrosive properties and chemical resistance owing to the presence of hybrid polymer chains.