Bio-based liquid crystal epoxy resins: Toughening and strengthening of conventional epoxy resins with strategically extended spacer layers

Abstract

Liquid crystal epoxy resin, as an ideal toughening agent, combines the features of liquid crystal ordering and network cross-linking, which can effectively optimize the comprehensive performance of blended epoxy resins and achieve an ideal balance of rigidity and toughness. Here we successfully synthesized rigid and flexible bio-based liquid crystal epoxy resin (THBR-EP) by finely tuning the length of alkyl side chains. Using aromatic diamine as curing agent, a homogeneous network without phase separation was constructed by taking advantage of the different activity but good compatibility with ordinary epoxy resins, which significantly improved the toughness of the blended system. Specifically, only a small amount of THBR-EP(2.5 wt%) was required to exhibit a maximum impact strength of 48.8 kJ/m². Moreover, the increase in system toughness was accompanied by a benign improvement in flexural strength, modulus and thermal stability. The ordered structure of the liquid crystals and their good compatibility with the resin matrix enhanced the ability to inhibit crack extension and energy dissipation. The feasibility to simultaneously achieve effective toughening and other property improvements of common resins broadens the application of resins under various demanding scenarios.