Black liquor-based epoxy resin: Thermosets from untreated kraft lignin

The production of thermosetting resins from lignin is a promising route to upcycle this biomaterial, currently overwhelmingly used as fuel. Raw kraft black liquor with no prior purification or treatment was derivatised using epichlorohydrin and an aniline catalyst to yield a black liquor-based epoxy resin (BLER). BLER is a liquid resin, which can be processed using conventional moulding techniques prior to curing into black liquor-based thermosets using maleic anhydride as hardener. We report the production of liquid lignin-based thermosets containing a biocarbon content of ∼ 16%. These thermosets possess Young's moduli and tensile strengths exceeding 1 GPa and 40 MPa, respectively. The chemical composition of the starting material and BLER were characterised, and the mechanisms of cure as well as the mechanical properties of lignin-based thermosets were determined.