A novel P/N synergistic hydrogen-bonded organic framework for improving flame retardancy of epoxy resin
Yingbing Zou, Kui Niu, Yunbin Li, Xueyan Yang, Zhehang Shi, Fubin Luo, Hongzhou Li
Abstract
Epoxy resins (EP) are widely used in building materials and daily life applications; however, their inherent flammability severely limits their broader use. In this study, a novel phosphorus/nitrogen (P/N) synergistic hydrogen-bonded organic framework (HOF) was successfully synthesized via a one-step self-assembly strategy using 4,4′-biphenylenebis(phosphonic acid) (BPA) and dimethylamine. Structural characterization confirmed both the chemical composition and crystalline nature of the material. When incorporated into the EP matrix, BPA-HOF significantly enhanced the flame retardancy, and notably, the mechanical properties were also improved at a 3 wt% loading. At a 9 wt% BPA-HOF content, the limiting oxygen index (LOI) increased to 27.7 %, and a V-1 rating was achieved in the UL-94 test. Meanwhile, the peak heat release rate (pHRR), total heat release (THR), and smoke production rate (SPR) decreased by 62.0 %, 44.8 %, and 51.7 %, respectively. Furthermore, the char residue of the EP composite increased from 7.0 % to 45.9 %, contributing to enhanced fire resistance. Mechanistic studies revealed that BPA-HOF inhibits flame propagation through gas-phase radical quenching and promotes char formation in the condensed phase. This work offers valuable insights into the rational design of efficient HOF-based flame retardants and represents a promising strategy for developing high-performance EP composites.