Polymerizable ZnO photoinitiators of surface modification with hydroxyl acrylates and photopolymerization with UV-curable waterborne polyurethane acrylates

Abstract

In order to find an alternative method to effectively distribute ZnO, an inorganic photoinitiator, in the UV-cured films of waterborne polyurethane acrylates (WPUAs), toluene diisocyanate and hydroxyl acrylate were reacted onto the ZnO surface to prepare novel polymerizable ZnO photoinitiators, which were characterized by the Fourier transform infrared spectroscopy, X-ray diffraction analysis, particle size analysis, Zeta potential analysis, energy dispersive spectroscopy, and thermogravimetric analysis etc. The thermogravimetric analysis data showed that the reacted content of hydroxyl acrylates on the ZnO surface was about 4.2%. Then, the polymerizable ZnO photoinitiators were added into UV-curable WPUAs to formulate UV-curable coatings. Effects of polymerizable ZnO contents and the types of hydroxyl acrylates on the properties of the UV-cured films were studied. Figures of scanning electron microscope showed that the modified ZnO was uniformly dispersed in UV-cured WPUAs films. The real-time UV-curing kinetics showed that the photopolymerization process of the UV-curable WPUAs was zero-order reaction. The UV-cured films’ properties proved the double bonds on ZnO could participate in the UV-curing reaction, which made better combination of ZnO as both inorganic photoinitiators and additives. Therefore, this investigation demonstrated a novel method for ZnO photoinitiators to have a good compatibility within organic coatings matrix.