Vanillin‐Based Recyclable Thermosets and their Glass Fiber Reinforced Composites

ABSTRACT The accumulation of end‐of‐life plastic materials and composite reinforcement waste materials has brought much attention to developing sustainable alternatives and their re‐processability. Incorporating covalent adaptable networks (CANs) into the crosslinked network bridges the concept of reversibility into the otherwise conventional non‐reversible networks. This study investigates the structure‐property relation in two reversible hardener systems derived from vanillin using Schiff base chemistry. The “ CAN ” systems were synthesized by condensation of vanillin with two amines, 4,4'‐oxydianiline and tris(2‐aminoethyl)amine, respectively, to form Va_ODA and Va_TAEA. The epoxy thermosets exhibited glass transition temperatures (T g ) of 125°C and 115°C, respectively, for Va_ODA and Va_TAEA, which is superior to most reversible vanillin‐based systems reported. The vitrimer‐thermosets exhibited promising mechanical and thermal properties, and reshaping abilities as a function of applied temperatures, indicating the dynamic nature of linkages. Chemical degradability was demonstrated by heating to 80°C for 12 h in aqueous acidic medium or excess amine. The fabricated glass fiber composites exhibited good mechanical properties with tensile strength of 361 MPa and degradability in acetic acid/water mixture with a fiber recovery of >98 %. The recovered glass fiber exhibited almost similar tensile strength as the virgin glass fiber, demonstrating its potential reusability. The epoxy vitrimers underwent mechanical reprocessing through hot‐pressing, as well as chemical reprocessing via 3D printing and by regeneration of imine bonds to form an epoxy resin.