A P/N-Containing Hardener for High-Efficiency Intrinsically Flame-Retardant Bio-Based Epoxy Thermoset

Abstract

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 at high temperature under both air and N2 atmospheres with the char residues of 10.3% and 17.8% at 700 °C, respectively, which were higher than those of both DGEBA-DDM (0.76% and 12.4%) and CFEP-DDM (3.4% and 12.2%). The CFEP-DPDM possessed a Tg value of 162.0 °C which was obviously higher than that of neat CFEP-DDM (95.2 °C) and comparable to that of commercial DGEBA-DDM (154.1 °C) under DMA test, and DSC test presented similar trend of Tg results. Moreover, CFEP-DPDM possessed the highest crosslinking density (νe), indicating excellent mechanical property, which was further verified by tensile analysis that CFEP-DPDM displayed significantly enhanced tensile strength (44.6 MPa) and tensile modulus (3.2 GPa) which 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, in cone test, the peak of heat release rate (PHRR), total heat release (THR), CO2P and the fire growth rate (FIGRA) of CFEP-DPDM were declined by 41.0%, 37.6%, 60.0% and 39.8%, respectively, as compared to those of CFEP-DDM. Ultimately, the flame-retardant mechanism of CFEP-DPDM was investigated by further condensed and gas phases analyses.

Keywords: Bio-based epoxy resin, cardanol, DOPO-based curing agent, intrinsically flame-retardant