Influence of phosphorus-grafted expandable graphite on the flame-retardant property of UHMWPE composite

In this paper, an efficient flame retardant, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was covalently grafted onto the surface of expandable graphite (EG). The resultant DOPO-grafted expandable graphite (EG-g-DOPO) was characterized by Fourier transform infrared spectroscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy (XPS), respectively. The thermal stability of EG-g-DOPO was also evaluated by thermogravimetric analysis (TGA). Moreover, a series of flame-retardant ultra-high-molecular-weight polyethylene (UHMWPE) composites with various concentrations of EG-g-DOPO were prepared and evaluated. The results show that the UHMWPE composite with 20 wt% EG-g-DOPO possesses a satisfactory UL-94 flame-retardant grade (V-0) and a high limiting oxygen index (30.6%). The residual char of the UHMWPE composite with higher EG-g-DOPO concentration shows more compact and integrated, providing an efficient barrier for heat release.