Degradable, intrinsically flame-retardant, low-water-absorbing vanillin-derived epoxy thermoset with a Schiff base structure

Given the issues of non-renewability, poor degradability, and high flammability associated with petroleum-derived bisphenol A-type epoxy (DGEBA) resins, developing degradable and flame-retardant epoxy resins from renewable biomass is of great importance. However, it is still a challenge at present. Herein, a novel Schiff base diepoxy compound (BV-EP) was successfully synthesized from lignin-derived vanillin and commercial amine 9,9-Bis(4-aminophenyl)fluorene (BAPF) through a simple, two-step procedure. After cross-linking with 4,4ʹ-diaminodiphenylmethane (DDM), the vanillin-derived Schiff base epoxy thermoset (BV-EP/DDM) displayed better thermal properties (glass transition temperature Tg: 197°C) and flame retardancy than the control sample (DGEBA/DDM). The peak heat release rate (PHRR) and the total heat release (THR) of BV-EP/DDM were reduced by 60.1% and 19.8%, respectively, compared with those of DGEBA/DDM. Furthermore, the degradable Schiff base and the hydrophobic fluorenyl Cardo structure provide the BV-EP/DDM with good acid-catalytic degradation and low water absorption properties. In this work, the fluorenyl Cardo structure plays the role of “killing three birds with one stone” in enhancing the performance of BV-EP/DDM. This synergistic strategy paves the way for fabricating more practical degradable and intrinsically flame-retardant epoxy resins from renewable biomass resources.