Biobased Thermosets from Epoxidized Linseed Oil and its Methyl Esters

This work describes a model biobased epoxy thermoset resin incorporating epoxidized linseed oil fatty acid methyl esters (ELOMEs) with trimellitic anhydride (TMA) as a curing agent. Unlike epoxidized linseed oil (ELO), ELOME acts as a solvent at moderate temperatures and can dissolve the curing agent. Thermosets were prepared using a range of molar ratios of ELOME, or ELOME/ELO mixtures, to TMA. It was found that the storage moduli and glass-transition temperatures of the resulting thermosets increase with the increasing concentration of the curing agent due to enhanced cross-linking. On the other hand, the dynamic mechanical analysis demonstrated that an increase in the curing agent content, especially above the stoichiometric ratios of reactive moieties, hinders the formation of the cross-linked network when an excessive amount of TMA esters of ELOME are formed. These consume a large proportion of the available epoxy moieties and consequently limit further cross-linking and polymer network growth. The glass-transition temperature (T_g) of these resins was between 80 and 86 °C, depending on the stoichiometric ratio of the reactive moieties. In thermoset systems prepared with ELOME/ELO mixtures, an improvement in the thermomechanical properties (increase of T_g up to 102 °C) was observed, which was associated with the increase in cross-linking density resulting from the branched triacylglycerol structure of epoxidized linseed oil.