Optimization of the vegetable oil composition in alkyd resins: A kinetic approach based on FAMEs autoxidation

The autoxidation of FAMEs of colza, sunflower and linseed oils was studied at 40 degrees C under oxygen atmosphere at 150 kPa and was compared to that of mixtures of pure methyl oleate, linoleate and linolenate. Three steps corresponding to an induction time, an autocatalytic process and a pseudo steady-state could be distinguished and their kinetic constants were calculated for each oil. The influence of methyl linoleate on methyl oleate oxidation was determined at eight different ratios, highlighting that a 35/65 w/w composition corresponding to the sunflower one was a good compromise between oxidation time and minimization of methyl linoleate amount. Same approach was undertaken on this mixture to investigate the influence of methyl linolenate as a third constituent using pure ester and linseed oil FAMEs. A weight fraction of 15-20% was found to be optimal to favor the oxidation. Methyl linolenate has no influence on the relative disappearance of methyl linoleate versus methyl oleate. Hence, the most oxidizable composition with the lowest amount of the tri-unsaturated FAME is the ternary mixture methyl oleate/methyl linoleate/methyl linolenate = 29:53:18 ratio, which corresponds to a mixture of sunflower and linseed oils at a = 60:40 ratio. This would be the best vegetable oil composition for alkyd resins.