Oxidation of model compound emulsions for alkyd paints under the influence of cobalt drier

A systematic investigation on the oxidation of different model compounds (including methyl oleate (MO), ethyl linoleate (EL), and methyl linolenate (MLn)) in emulsions under the influence of an emulsifiable cobalt drier was performed. Raman spectroscopy, attenuated total reflectance (ATR)-FTIR, and 1H NMR were used. Raman spectroscopy proved to be a powerful technique at following the oxidation of these model compounds in emulsions not only after but also during the water evaporation. Raman and ATR-FTIR (D2O was used instead of H2O) investigations clearly demonstrated that there was essentially no observable chemical change during the water evaporation. The oxidation of model compounds in emulsions, after the water evaporation, was found to be similar to the oxidation of bulk/solvent-borne model compounds. The presence of an emulsifier (sodium dodecyl sulfate) and water did not show any significant effects on the oxidation of the model compounds. An increase in the intensity of conjugated double bonds and isolated trans-double bonds was first observed, and followed by a decrease. More than 90% of double bonds disappeared for EL and MLn after 13 days of oxidation as examined by 1H NMR, which may be attributed to the addition of radicals to double bonds (propagation-like reaction) and the -scission of double-bond-containing radicals into by-products. The number of double allylic group in the model compounds also showed a significant influence on the rate of oxidation for emulsions after water evaporation.