Development of glossy and UV-resistant urushi coatings by thermal polymerization

Abstract

The use and development of natural biomass-based plastics are attracting attention with the aim of limiting environmental pollution and conserving energy resources. Urushi, a natural curing resin traditionally used in numerous applications such as decorative arts, furniture, and tableware, has great potential as an environment-friendly alternative to petroleum-based plastics. In this study, we produced urushi coatings in a short time using a thermal polymerization method, which is more convenient than the conventional oxidative polymerization method. The thermal polymerization method requires less time and energy than conventional oxidative polymerization and hence is more environmentally friendly. The urushi coatings were exposed to UV-A irradiation for 0–30 days, and the effects of irradiation on the surface were evaluated using Fourier-transform infrared spectroscopy, water contact angle measurements, scanning electron microscopy, gloss measurements, and pencil hardness tests. As a result, we developed functional high-gloss urushi-coated films with excellent hardness using thermal polymerization; these films retain these properties even after prolonged UV-A irradiation.