Bio-based epoxy resin from gallic acid and its thermosets toughened with renewable tannic acid derivatives

The designing of low-cost, high-performance, bio-based epoxy thermosets that can cope with the global oil crisis and climate change is a challenge. A bio-based epoxy resin was synthesized from gallic acid using epichlorohydrin, and a carboxylic acid-modified tannic acid (CATA) was obtained using simple esterification in which the gallic acid-based epoxy resin (GA-EP)/methyl nadic anhydride (MNA)/2-ethyl-4-methylimidazole (2,4-EMI) curing system was used as a toughener. Moreover, the structural characterization, mechanical performance, curing behavior, and thermal properties of epoxy thermosets were investigated. Consequently, the addition of only 1.0 wt% CATA increased the toughness from 9.9 to 17.3 kJ/m(2) by similar to 74.7% relative to the GA-EP/MNA/2,4-EMI system. Furthermore, the 1.0 wt% CATA-toughened GA-EP/MNA/2,4-EMI showed considerable tensile strength of 52.1 MPa. Such toughness and tensile property of the epoxy thermoset was primarily attributed to CATA participating in the cross-linking network and forming a homogenous system after curing. Our study provides a novel strategy for developing cost-effective high-performance bio-based epoxy thermosets. [GRAPHICS] .