Structure-property relationship in fully biobased epoxidized soybean oil thermosets cured by dicarboxyl terminated polyamide 1010 oligomer with different carboxyl/epoxy ratios

Dicarboxyl terminated polyamide 1010 oligomer was used to cure epoxidized soybean oil (ESO) to synthesize fully biobased epoxy thermosets with different chemical structures via changing carboxyl/epoxy equivalent ratio (R-value). The effect of chemical structures of the epoxy thermosets on their crosslink density, swelling property, crystallization behavior, dynamic and static mechanical properties, as well as thermal stability was studied systematically. The crosslink density of the epoxy thermosets increased obviously, the gel fraction almost kept unchanged, and the swelling ratio decreased gradually with increasing R-value. The crystallization capability and degree of crystallinity were enhanced meanwhile melting temperature shifted to higher temperature range with increasing R-value, due to the increased concentration of polyamide 1010 segments in the thermoset. Consequently, the stiffness and heat resistance of the epoxy thermosets were enhanced. The Young's modulus increased gradually and the break stress as well as the break strain first increased and then decreased with increasing R-value. This investigation provides a new strategy to regulate physical properties of soybean oil-based epoxy thermosets, which would be valuable for other plant oil-based polymers design.