Integrated thermal conductive and charring effects of hexagonal boron nitride and polycarbosilane on flame retardancy of polyolefin/magnesium hydroxide composites

Halogen-free flame retardant polyolefin composites coupled with thermal conductivity are highly required to meet the challenges from thermal management and fire safety of wires and cables. The flame retardancy and thermal conductivity of polyolefin/magnesium hydroxide (PO/MH) composites were modulated by boron nitride (BN) and polycarbosilane (PCS). The synergistic effect between BN and PCS in PO/MH was demonstrated by the limiting oxygen index (LOI) of 42.9 % and the thermal conductivity of 0.66 W/(m·K). The results of cone calorimeter (CONE) evidenced the superior combustion behaviors with the reduced peak heat release rate (pHRR), total heat release (THR) and total smoke production (TSP) by 25 %, 28 % and 11 % in comparison with PO/MH, respectively. The thermal degradation by thermogravimetric analysis (TGA) revealed that PO/MH/PCS/BN took advantage of BN in stabilizing the side chain degradation and PCS in decreasing the main chain degradation rate to make for the enhanced char. And the results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) illustrated the structured char that was composed of the integrated surface char acting as a barrier to mass transfer and the foamed bulk char as a barrier to heat transfer. The proposed strategy would be prospective in developing polyolefin composites integrated with thermal conductivity and flame-retardant properties for wires and cables. • BN and PCS synergistically enhanced flame retardancy and thermal conductivity of PO/MH composites • The superior combustion behaviors of PO/MH/PCS/BN were evidenced with the reduced pHRR, THR and TSP in comparison with PO/MH. • Structured char: surface char blocks mass transfer, foamed bulk char impedes heat transfer.