Sub-Micro Organosolv Lignin as Bio-Based Epoxy Polymer Component: A Sustainable Curing Agent and Additive

Sub-micro organosolv lignin (OBs) isolated from beechwood biomass, comprising of sub-micro sized particles (570 nm) with low molecular weight and dispersity and relatively high total phenolic -OH content, is utilized for the production of bio-based epoxy polymer composites. OBs lignin is incorporated into the glassy epoxy system based on diglycidyl ether of bisphenol A (DGEBA) and aliphatic polyoxypropylene α,ω-diamine (Jeffamine D-230), being utilized both as a curing agent, partially replacing D-230, and as an additive, substituting part of both petroleum-derived components. Up to 12 wt % replacement of D-230 by OBs lignin is achieved, whereas approximately 17 wt % of OBs effectively replaces the conventional epoxy polymer. The incorporation of OBs lignin in the polymeric matrix is achieved without the use of any solvent or previous functionalization. Enhanced properties are obtained, with substantial increases in tensile strength, strain, stiffness, glass transition temperature, antioxidant activity, and resistance to solvents.