Investigating the changes in properties when a hydrophobic nanosilica is added to a two-pack polyurethane clear coat

Abstract

Various concentrations of a hydrophobic nanosilica were employed to prepare a series of two-pack acrylic polyol polyurethane nanocoatings in order to study the changes in the properties of the resultant coatings. Furthermore, the morphological, mechanical, rheological, thermal and optical properties of such coatings were investigated. The morphological properties were carried out by the aid of a transmission electron microscope (TEM); whereas, the rheological properties were determined by a rotaviscometer. The optical properties were determined by UV-Visible spectrophotometric and turbidimetric techniques. The static mechanical properties were acquired by the aid of an Instron testing machine. The glass transition temperature (Tg) of the nanocoatings were obtained by DSC analyses. The results showed that coatings containing hydrophobic nanosilica exhibit excellent dispersion and compatibility of nanoSiO2 within the polyurethane matrix. Additionally, such coatings also exhibited improved mechanical properties, especially increases in the scratch resistance. In the fluid state, these coatings showed a shear thinning behaviour. In addition, the nanocomposites' Tg decreased compared to the pure polyurethane clear coat. The optimum range of adding hydrophobic nanosilica to the two-pack acrylic polyol polyurethane clear coat in order to achieve optimum mechanical, rheological and optical properties was determined to be within the range of 4-8%: by weight.