Multifunctional tannin extract-based epoxy derived from waste bark as a highly toughening and strengthening agent for epoxy resin

Abstract To reduce crude oil consumption and the corresponding environmental impact, the use of sustainable resources has recently attracted much attention. Herein, a low-viscosity and efficient tannin-based epoxy resin (MTEBPE) was prepared using liquefaction of renewable tannin (MTEBP) and epichlorohydrin feedstocks, and then used as modifier to enhance the toughness and strength of fossil fuel-based bisphenol A diglycidyl ether (DGEBA). The results show that the mechanical properties of the thermosets could be significantly improved after blending with MTEBPE; in particular, the tensile, flexural, and impact strengths, as well as the elongation at break of 5 wt% MTEBPE/DGEBA increased by 35.8%, 45.4%, 243.8%, and 81.6%, respectively, compared with those of neat DGEBA. The enhanced toughness and strength of the epoxy thermosets can be attributed to the combined effect of the crosslinking density, intramolecular cavities, and branched structure of MTEBPE. More importantly, the temperatures corresponding to 5% and 50% weight loss (T5% and T50%, respectively) and the char yield at 600 °C of the 5 wt% MTEBPE/DGEBA thermosets were basically the same as those of neat DGEBA. In addition, the thermosets exhibited excellent chemical resistance, also to alkali and organic solvents. In brief, MTEBPE, a multifunctional bio-based epoxy derived from waste bark, shows great application advantages in coatings, adhesives, and functional materials.