Epoxy/starch-modified nano-zinc oxide transparent nanocomposite coatings: A showcase of superior curing behavior

A new class of transparent epoxy-based nanocomposite coatings containing starch-modified nano-zinc oxide (ZnO-St) is presented. ZnO nanoparticles physically decorated with starch carbohydrate polymer increased compatibility with epoxy chains and sterically prevented flocculation of ZnO nanoparticles. Surface characteristics of pristine ZnO and ZnO-St are studied by FTIR spectroscopy corroborating self-assembled starch molecules on ZnO surface until reaching a complete coverage. Curing behaviors of epoxy and transparent nanocomposites containing ZnO and ZnO-St are studied by the aid of nonisothermal calorimetric analyses at four heating rates to compare the curing enthalpies, onset temperatures, peak temperatures, and curing intervals of transparent coatings. The ZnO-St, particularly at low heating rate of 5 degrees C/min, prolonged curing (corresponding to AT increase of ca. 166 for epoxy to 200 degrees C for Zn-St/epoxy), and increased the amount of heat release (in the same order from 328 to 380 J/g) due to epoxide ring opening by starch hydroxyl groups. Such novel class of epoxy/ZnO-St nanocomposite coatings can be applied as top-coats because of their transparency. Additionally, from an environmental/biological standpoint, one should consider that starch is a carbohydrate polymer and ZnO is antibacterial, which may put more stress on the use of transparent nanocomposite coatings developed in this work.