Calcination of UV shielding nanopowder and its effect on weather resistance property of polyurethane nanocomposite films

In this study, the synergistic effect of ZnO nanoparticles in combination with two different crystal phases of TiO₂ nanoparticles on improving weather resistance property of polyurethane (PU) film has been studied. The UV shielding nanopowder containing TiO₂ and ZnO nanoparticles was calcinated at varying conditions, and the process was optimized to obtain the desired crystal structure. After calcination, the change in crystal phase, crystal size, inter-planer distance in crystal and particle size was characterized using XRD, TEM and particle size analyzer, while chemical changes were analyzed by FTIR and EDX. The as-received as well as calcinated UV shielding nanopowders (1–5 wt%) were incorporated in PU matrix by melt mixing in a twin-screw extruder, and the extrudate nanocomposites were used to make films. The neat PU and nanocomposite films were exposed in accelerated artificial weathering for 300 h, while the films were analyzed at a 100-h interval. The physical and chemical changes of exposed film surface were analyzed by SEM, AFM and FTIR. The UV protection factor (UPF) of both types of PU nanocomposite films increased with increased loading of nanoparticles, although the UPF values were slightly lower for calcinated UV shielding nanopowder-based PU nanocomposite films. The calcinated UV shielding nanopowder showed good potential in improving weather resistance of PU nanocomposite films in term of—(1) lower change in surface morphology and surface chemistry and (2) better retention in tensile properties after exposure in accelerated artificial weathering. The synergistic effect of ZnO nanoparticle and rutile phase enriched TiO₂ nanoparticles in calcinated UV shielding nanopowder enhanced the weather resistance of PU films significantly.