New insights into the curing of epoxidized linseed oil with dicarboxylic acids

The effect of systematically increasing chain length of a series of linear alpha,omega-dicarboxylic acids (DCAs) from C-6 to C-18 diacids and a cyclic diacid, Pripol 1009F, on thermal and mechanical properties of the resultant epoxy thermosets derived from epoxidized linseed oil (ELO) are reported. Different techniques including differential scanning calorimetry (DSC), solvent extraction, FT-IR, NMR, dynamic mechanical analysis (DMA), tensile tests and thermogravimetric analysis (TGA) are used in this study. The results indicated that the obtained epoxy resins were highly crosslinked polymers with only a small fraction of low molecular weight soluble materials. The glass transition temperature (T-g), tensile strength, Young's modulus, elongation at break and toughness decreased while the thermal stability increased with respect to increasing chain length of DCAs. Interestingly, strain hardening was only observed for adipic acid (C-6) sample for which the best mechanical properties observed.