A P/N-containing hardener endowing bio-based epoxy thermosets with excellent thermal, mechanical and intrinsically flame-retardant performances

In view of the drawbacks of severe dependence on petroleum resources and flammability of commercial epoxy thermosets, a novel intrinsically flame-retardant bio-based epoxy resin was manufactured through the curing reaction between the synthesized cardanol-derived epoxy monomer (CFEP) and a DOPO-based curing agent (DPDM). In addition, CFEP and DGEBA thermosets cured by DDM were used as the contrast samples. The TGA results showed that CFEP-DPDM possessed significantly enhanced thermal stability with higher char residues of 10.3 % and 17.8 % at 700 °C for air and N₂ atmospheres, respectively, which were higher than those of both DGEBA-DDM (0.76 % and 12.4 %) and CFEP-DDM (3.4 % and 12.2 %). The T_g of CFEP-DPDM was 162.0 ℃ which was obviously higher than that of neat CFEP-DDM (95.2 ℃) and comparable to that of commercial DGEBA-DDM (154.1 ℃) under DMA test, and DSC test presented similar trend of T_g results. Moreover, CFEP-DPDM possessed the highest crosslinking density (ν_e), indicating excellent mechanical property, which was further verified by tensile analysis that the tensile strength (44.6 MPa) and tensile modulus (3.2 GPa) of CFEP-DPDM was comparable to commercial DGEBA-DDM. As for the fire-retardant performance, CFEP thermoset cured with DPDM exhibited a high LOI value of 33.5 % and passed UL-94 V0 rating. Furthermore, compared to those of CFEP-DDM, the PHRR, THR, CO₂P and FIGRA of CFEP-DPDM were declined by 41.0 %, 37.6 %, 60.0 % and 39.8 %, respectively. Ultimately, the flame-retardant mechanism of CFEP-DPDM was investigated by further condensed and gas phases analyses. In brief, the synthesized bio-based epoxy thermosets with excellent comprehensive performance displaying high promise for application.