Incorporating Microspheres of Phenolic Resin and MXene to Improve Efficiently the Flame Retardancy, Crosslinking, and Mechanical Properties of the Epoxy Composites

Abstract In order to prepare halogen-free flame-retardant epoxy composites with high performances and solve the shortcomings of ammonium polyphosphate in this application, the phenolic resin microspheres (PF) were prepared, and an intumescent flame-retardant system was constructed using ammonium polyphosphate (APP) and PF and MXene. The flame-retardant system was then added into epoxy resin to prepare the flame-retardant composites. The E5A1.5P1.5M composite, containing 5% APP, 1.5% PF, and 1.5% MXene, exhibited a limiting oxygen index (LOI) of 28.5 and achieved a UL-94 vertical burning rating of V-0. Compared with neat EP, the peak heat release rate (PHRR), total heat release (THR), and total smoke release (TSR) of E5A1.5P1.5M were reduced by 69.9%, 38.9%, and 23.4%, respectively. Furthermore, hydroxyl groups on the surfaces of the PF microspheres and MXene formed hydrogen bonds with the hydroxyl groups in the EP matrix, increasing the crosslinking density of E5A1.5P1.5M by 22.7% compared with neat EP. Meanwhile, the incorporation of PF and MXene effectively compensated for the deterioration in mechanical properties caused by APP. Compared with E5A containing 5 wt % APP, the tensile strength and impact strength of E5A1.5P1.5M were improved by 16.5% and 13.4%, respectively.