Processing and properties of spray-applied, 100% solids polyurethane coatings from rapeseed oil polyols
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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 (M c) of the PU network and M c 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 (E a) 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.
KeywordsRapeseed oil Polyurethane VOC-free spray-applied coating Curing process Mechanical properties 100% solids
The work was financed by the European Regional Development Fund Contract No. 2010/0214/2DP/184.108.40.206.0/10/APIA/VIAA/054.
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