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

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.