Investigation of crosslinking, mechanical properties and weathering stability of acrylic polyurethane coating reinforced by SiO2 nanoparticles issued from rice husk ash

In this study, rice husk ask (RHA)-SiO2 nanoparticles were successfully synthesized from rice husk ash by precipitation method. TEM images indicate that as-synthesized nanoparticles had amorphous structure with a relatively homogeneous size of about 20 nm. Crosslinking process, mechanical properties and weathering degradation of the nanocomposite coating based on acrylic polyols and polyisocyanate in the presence of nano RHA-SiO2 were investigated. The mechanical properties of the coating show the highest values with 2.5 wt%. of nano RHA-SiO2 as filler. FE-SEM analysis demonstrates that nano RHA-SiO2 nanoparticles were well dispersed in the coating. IR analysis, relative hardness, gel fraction and swelling degree measurements show that the nanoparticles improved conversion performance of isocyanate groups, gel fraction, swelling degree and relative hardness of the coating. Accelerated weathering test indicates that, after 36 cycles of test, the nanocomposite coating was degraded with the formation of several holes on the coating surface and the recorded weight loss was 9.1%. For the neat coating, the formation of various large holes of dimension ranging from 20 nm to several μm on the surface was observed and the weight loss is measured to be higher (12.7%) in the same conditions. Nano RHA-SiO2 possibly play a dual role: i) UV protector and ii) nanofiller helping to prevent the invasion of aging agents.