Cardanol as a versatile platform for fabrication of bio-based flame-retardant epoxy thermosets as DGEBA substitutes

The development of high-performance thermosetting polymers has spawn extensive research interest over the past decade because of increasing awareness of environmental protection and sustainable policy. In this work, three cardanol-derived epoxy monomers named after CFGE, ECF, and ECFGE were synthesized, and ECFGE was selected to be further treated by flame-retardant owing to its superior thermal stability and mechanical strength. ECFGE was subsequently combined with cardanol-derived phosphate (DPP-CFR) to obtain flame-retardant bio-based epoxy materials as diglycidyl ether bisphenol A (DGEBA)-type epoxy substitutes. The chemical structure of CFGE, ECF, ECFGE, and DPP-CFR was well characterized by nuclear magnetic resonance and elemental analysis. The influence of DPP-CFR on the curing kinetics of the ECFGE/DDM system was investigated by the non-isothermal DSC. The addition of DPP-CFR imparted excellent flame-retardancy to the cured ECFGE/DDM system. Specifically, the cured ECFGE/DDM system with 15 wt% of DPP-CFR exhibited UL-94V-0 classification and LOI value of 31.0%, and its peak heat release rate was declined by 48% and 72%, respectively, compared to the cured ECFGE/DDM and DGEBA/DDM. Additionally, the cured ECFGE/DDM system with 15 wt% of DPP-CFR also showed better tensile strength and toughness than the cured DGEBA/DDM counterpart. This study demonstrates that cardanol can be utilized as a versatile platform for the fabrication of high-performance bio-based thermosetting polymers with excellent comprehensive properties.