Flame retardancy and smoke suppression effect of an organic–inorganic hybrid containing phosphaphenanthrene‐modified magnesium hydroxide/zinc borate on epoxy resin

Abstract To improve the flame retardancy and smoke suppression effect of epoxy resin (EP), a new organic–inorganic hybrid (MH@ZB‐ODOPB) was fabricated. First, hierarchical‐structured particles (MH@ZB) were prepared by gradually depositing zinc borate (ZB) on the surface of magnesium hydroxide (MH) via a heterogeneous deposition process. Second, MH@ZB was modified with 10‐(2,5‐dihydroxyphenyl)‐10‐hydro‐9‐oxa‐10‐phospha‐phenanthrene‐10‐oxide (ODOPB) to obtain MH@ZB‐ODOPB. Finally, the chemical structure and form of MH@ZB‐ODOPB were analyzed via X‐ray diffraction, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and scanning electron microscopy. The characterization results show that ZB was loaded onto the surface of MH, and ODOPB was grafted on the surface of MH@ZB. The cone calorimetry test results show that when 7.5 wt% MH@ZB‐ODOPB was added into EP, the peak heat release rates, total heat release, total smoke production, and peak smoke production rates decreased by 51.8%, 42.4%, 58.1%, and 66.1%, respectively. Moreover, EP/MH@ZB‐ODOPB exhibited a limiting oxygen index of 33%. These results show that the incorporation of MH@ZB‐ODOPB into EP composites considerably improved the flame retardancy and smoke suppression properties of EP composites. The double action of MH@ZB‐ODOPB in condensed and gas phases was investigated by analyzing the carbon residue and pyrolysis gas. Furthermore, the implementation of ODOPB improves the mechanical properties of EP composites.