Synergistic effects of zinc oxide and iron oxide photoinitiators for whole spectrum utilization of UV–Vis light in photo-curable coatings

In order to fully utilize the whole spectrum of UV–Vis light and eliminate the problems of organic photoinitiators in the photo-curable coatings, inorganic composited photoinitiators of ZnO and Fe₂O₃ nanoparticles (NPs) were prepared and added into the photo-curable waterborne polyurethane acrylates. The inorganic composited photoinitiators utilized both the ultraviolet and visible light, which easily extended the light absorption range of each photoinitiator of ZnO and Fe₂O₃ NPs. Fourier transform infrared spectroscopy, scanning electron microscopy, and ultraviolet–visible spectrophotometer were used to characterize the chemically composited particles, physically mixed particles, and their photo-curable coatings. Comparison with the pure waterborne polyurethane acrylates, better photoinitiation effect, light conversions, and mechanical properties of the photo-cured films were obtained when the chemically composited photoinitiators of ZnO and Fe₂O₃ NPs were added with a molar ratio of 1:1. The photo-curing kinetics characterized by the UV–Vis and FTIR spectroscopy also proved their improved synergistic photoinitiation effects. This study demonstrated that the chemically composited photoinitiators of ZnO and Fe₂O₃ NPs were a prospective solution to the complete utilization of illumination light during the conventional photo-curing processes.