Dispersion of γ-methacryloxypropyltrimethoxysilane-functionalized zirconia nanoparticles in UV-curable formulations and properties of their cured coatings

Highly dispersible zirconia (ZrO2) nanocrystals were functionalized with γ-methacryloxypropyltrimethoxysilane (MPS) and dispersed in trimethylolpropane triacrylate (TMPTA), 1,6-hexandiol diacrylate (HDDA), tripropyleneglycol diacrylate (TPGDA) and aliphatic polyurethane oligomer (PU)/TPGDA mixtures, respectively. The dispersion behavior of MPS-functionalized ZrO2 (MPS-ZrO2) as well as its mechanical reinforcement for the PU/TPGDA matrixes was investigated. It was found that the dispersion of MPS-ZrO2 nanoparticles in UV-curable formulation strongly depends on the ZrO2 load, the grafting density of MPS, the composition of organic matrix and the type of monomer. A critical ZrO2 load beyond which phase separation of MPS-ZrO2 nanoparticles takes place exists for all cases. MPS-ZrO2 nanoparticles are more efficient to improve the pendulum hardness and scratch resistance of PU/TPGDA-based coatings that contains higher amount of TPGDA, being presumably due to quicker increase of the cross-linking density of the coatings. Additionally, a completely transparent TPGDA-based nanocomposite coating with ZrO2 load of as high as 60 wt.% can be obtained, and has absolutely high refractive index of 1.78.