Linseed-oil-based waterborne UV/air dual-cured wood coatings

Abstract

The synthesis of linseed oil (LO)-based waterborne polyurethane dispersion (PUD) wood coatings using different curing processes, as well as their coating and film properties, were examined. The waterborne prepolymer was synthesized first from modified linseed oil (MLO), dimethylol propionic acid (DMPA), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI) and hydroxyethyl methacrylate (HEMA) using an acetone process to prepare a solvent-borne prepolymer with CC bonds derived from methacrylic acid and fatty acids. The prepolymer was subsequently neutralized with triethylamine (TEA) and dispersed in water. After removing acetone, PUD was obtained. The results showed that the PUD could be readily synthesized and that it possessed reactive double bonds derived from HEMA and LO. Wood coatings were formulated by mixing PUD with photoinitiator for UV curing alone or by mixing PUD with metal dryers for air drying alone or by combining PUD with the two formulations as UV/air and air/UV dual-cured systems. The waterborne wood coatings were cured through different curing processes, as previously mentioned, and the properties of the cured films were characterized. The results showed that the durability and the lightfastness of films prepared using the UV/air dual-curing process (i.e., first UV-cured, followed by air drying) were better than those of the coatings cured using UV alone. Furthermore, the poor adhesion of the films cured using UV alone was significantly improved through the use of the UV/air dual-curing system. In conclusion, the linseed-oil-based waterborne UV/air dual-cured coatings possess the potential to provide high-efficiency, high-performance and environmentally friendly coatings for furniture finishing and it is a candidate for the application of coatings in the wood industry.