Improving processability and mechanical properties of epoxy resins with biobased flame retardants

Integrating flame-retardant additives into epoxy resins is an essential strategy for improving their fire resistance. However, introducing flame-retardant groups often compromises the processability and mechanical integrity of such resins. In this research, we synthesized a novel, biobased flame retardant, referred to as DPN, using naringenin and chlorodiphenylphosphine as precursors via a straightforward single-step process. The addition of DPN markedly decreased the viscosity of hydantoin epoxy resin, from 7468 to 1285 mPa s. Furthermore, when cured with 4,4-diaminodiphenylmethane, the composite containing five equivalents of DPN (DPN-5) exhibited a marked improvement in mechanical strength, reaching 190 MPa, significantly outperforming the pure thermoset (DPN-0: 104 MPa), while preserving high transparency. Combustion tests further confirmed that DPN significantly boosts the flame resistance of the thermoset, with DPN-5 achieving a limiting oxygen index of 37% and securing a UL-94 V-0 rating. Cone calorimetry analysis showed that DPN-5 effectively reduced heat and smoke production during combustion, achieving a 13.4% reduction in peak heat release rate and a 28.2% decrease in total heat release compared to DPN-0. This study underscores the potential of multifunctional biobased flame retardants derived from renewable resources in advancing the development of high-performance materials. © 2024 Society of Industrial Chemistry.