Investigating the variations in properties of 2-pack polyurethane clear coat through separate incorporation of hydrophilic and hydrophobic nano-silica

In the present study, a 2-pack polyurethane clear coat curable at ambient conditions was selected. Two different types of nano-silica (i.e. hydrophilic and hydrophobic nano-silica) were employed as fillers in order to vary the properties of the resultant nano-composite polyurethane coatings. Various morphological, mechanical, theological and optical properties of such coatings were investigated. The results showed that coatings based on hydrophilic nano-silica gave a less transparent more UV absorbent coating. However, coatings based on hydrophobic nano-silica gave more miscible, transparent coating having improved mechanical properties especially scratch resistance. In the fluid state these coatings showed shear thinning behavior. The optimum range of adding 4-8% by weight of hydrophobic nano-silica to the chosen 2-pack acrylic polyol polyurethane clear coat gave optimal morphological, theological, mechanical and optical properties to the final nano-composite coatings. (c) 2007 Elsevier B.V. All rights reserved.