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. [ABSTRACT FROM AUTHOR]