Design of novel double-layer wrapped ammonium polyphosphate and its application in aging-resistant and flame retardant crosslinked polyethylene composites

In this study, double-layer wrapped ammonium polyphosphate (APP) is designed to enhance the mechanical properties, resistance and flame retardancy of crosslinked polyethylene (XLPE) composites. APP was wrapped with silica and then grafted with hindered phenol antioxidant 3-(3,5-di-tert-butyl-4 hydroxyphenyl) (AO) to prepare double-layer wrapped flame retardants (MCAPP). Due to the excellent compatibility between the MCAPP and XLPE matrix, the tensile strength and elongation at break of XLPE/MCAPP/CFA (XLPE-4) were improved. Moreover, the retention rate of elongation at break for the XLPE-4 composite reached 61.1%, significantly higher than that of XLPE-1 (2.6%) at 135 °C after aging for 14 d. This demonstrates that MCAPP could improve the aging resistance of XLPE cable composites. Compared with XLPE-1, the maximum smoke density and the peak heat release rate were reduced by 54.9% and 89.7%, respectively. Thus, the double-layer wrapping antioxidant strategy provides an excellent approach to obtain high-performance XLPE composites.