Thermosetting resin based on epoxidised linseed oil and bio-derived crosslinker

Abstract

Thermosetting resins were synthesised from epoxidised linseed oil (ELO) in combination with a bio-derived diacid cross linker (Pripol 1009) in the presence of amine catalysts (triethylamine (TEA), 1-methylimidazole (1-MeIm), 2-methylimidazole (2-MeIm), 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP), yielding a 99.5% bio-derived, highly flexible transparent film, with significant water resistance. It was demonstrated that the mechanical and thermal properties of the resulting films were significantly influenced by the type of amine catalyst selected. The use of catalysts significantly enhanced the mechanical properties of the films; tensile strength improved by up to 545% (DMAP), Young's modulus improved by up to 422% (2-MeIm) and elongation at break improved by 14–84%. An infrared spectroscopic study coupled with simultaneous thermal analysis and modulated differential scanning calorimetry (MDSC) was undertaken in an attempt to elucidate the curing mechanism. Epoxide ring opening is clearly evidenced by infrared spectroscopy and the studies suggest that DMAP probably aids crosslinking between ELO and Pripol 1009 via epoxide ring opening, followed by etherification, due to its good nucleophilicity. The optimum DMAP catalyst loading giving the highest value of Young's modulus was determined at 1% with respect to the total resin weight. Higher concentrations of DMAP (5% wt) decreased the Young's modulus.