Abstract
Rigid polyurethane (PU) coatings were obtained from rapeseed oil (RO), triethanolamine (TEA), diethanolamine, and glycerol polyols. The dynamic mechanical analysis of PU coatings showed that the β-transition process occurs at −60°C for these PU networks. At 20°C, the tensile storage modulus (E′) is higher for those PU networks that are characterized with higher cohesive energy density (CED). There is a good correlation between the theoretical molecular weights between two crosslinking points (Mc) of the PU network and Mc that has been calculated from E′ based on the ideal rubber theory. PU coatings from a RO/TEA polyol and polymeric 4,4′-methylene diphenyldiisocyanate (MDI) were sprayed using a Graco Reactor E-10 industrial spraying machine with a volume ratio of the components A:B = 1.0:1.0. Eco-friendly volatile organic compounds-free, 100% solids, fast-curing two pack (2 K) PU coating compositions were formulated. The kinetics of gel formation was studied for PU coatings from RO/TEA, chain extenders, and polymeric MDI under adiabatic conditions; the temperature range was from 10 to 50°C. It was found that gel formation occurs with activation energy (Ea) 26.56–33.43 kJ/mol. When a PU coating is spray-applied on a substrate under nonadiabatic conditions, the gel formation time of the coating is not significantly influenced by the temperature of the components in the range 20–50°C.
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