ZnO Nanoparticle-based Photoinitiators
In this chapter, especially recent developments with the use ZnO based photo-semiconductors to initiate photoinduced polymerisations with different light sources, such as LED, mid-pressure Hg and xenon light, are presented. This chapter mainly contains detailed results and mechanisms of ZnO nanoparticles as a model for the entire class of novel initiators based on photo-semiconductors. For ZnO, a capable process to photopolymerise acrylic esters in bulk even in the presence of a storage inhibitor and moderate amounts of oxygen is achieved. It was proven that optimized, modified or doped photo-semiconductors can be both “Norrish Type I” fragmenting and “Norrish Type II” non-fragmenting nano-photo initiators, NanoPIs, whereby the mechanism of radical formation is different to well-known molecular initiators. The possibilities for adaptation and variation for “Norrish Type II” particle-based initiators is especially interesting concerning the surface properties of the oxide, the initiating potential of the first radical, the matching with the resin properties, and so on. Finally, the hybrid material can lead to additional properties/applications, such as corrosion and irradiation protection.