Optimization mechanical properties of polyurethane/Sio2 nanocomposite on Polypropylene substrate for automotive clear coating by Taguchi method

The effect of different parameters including: nano silica content, curing temperature, type of hardener, and flash-off time on mechanical and optical properties of polyurethane PU based clearcoat was investigated via standard Taguchi L9 method. Dispersion of nano silica in the resultant nanocomposites was explored by scanning electron microscopy SEM. SEM images showed a fine dispersion through the nanocomposites at different loadings. All PU nanocomposites showed gloss in the range of 91-94 which confirms the presence of nano silica did not have an adverse impact on optical properties. Moreover, the most significant factor contributed in the hardness of samples was the nano silica content. It was shown that using high amount of nano silica 5 wt reduced hardness of clearcoats due to interrupting curing process. The clearcoats performance after carwash test indeed showed that sample containing 2 nano silica cured at 85oC with a mixture of hardener 50 biuret, 50 trimer after flash-off time of 5 min had the optimum physical and optical properties.