(UV/Oxidative) dual curing polyurethane dispersion from cardanol based polyol: Synthesis and characterization

Abstract

This study reports the synthesis and property evaluation of UV/oxidative dual curing waterborne polyurethane dispersion prepared from cardanol-based polyol using different mode of curing. Cardanol-based polyol was prepared by reacting epoxidized cardanol with itaconic acid in presence of triphenyl phosphine catalyst. Structures of cardanol-based intermediates (both epoxidized cardanol and polyol) are confirmed by FTIR, 1H NMR and 13C NMR spectroscopy. The intermediates were characterized for various physicochemical properties such as hydroxyl value, acid value, epoxy equivalent weight (EEW), viscosity, color etc. Waterborne polyurethane oligomer was synthesized by reacting polyol, isophorone diisocyanate (IPDI), dimethylol propionic acid (DMPA) and 2-hydroxy methyl methacrylate (HEMA) in acetone as solvent. The prepolymer was neutralized with triethyl amine (TEA) and subsequently dispersed in deionized water and oligomer was obtained after removal of acetone. The coating films were formulated using suitable metal drier and/or photoinitiator blend based on different mode of curing, viz. oxidative curing, UV curing and (UV/oxidative) dual curing. The impact of curing process on properties of cured films was evaluated. Influence of curing process has been investigated by DMA, DSC and gel content analysis. The results showed that crosslink density plays an important role in deciding the final performance properties of cured films. The increase in crosslink density of UV/oxidative dual-cured system leads to an improvement in thermal, mechanical, chemical, water and solvent resistance properties along with other coating performance properties. In conclusion, the result of this study confirms that cardanol-based waterborne oligomer is suitable candidate for high performance environment-friendly coatings.