Synergistic flame‐retardancy of lamellar cerium phenylphosphonate and aluminum diethylphosphinate towards suppressing “candlewick effect” of polyamide 6/carbon fiber composites

Abstract In order to improve the flame retardancy of carbon fiber reinforced polyamide 6 (PA6/CF) composites and eliminate the “candlewick effect” caused by CFs, a lamellar cerium phenylphosphonate (CeHPP) was synthetized through reflux method and combined with aluminum diethylphosphinate (ADP) to prepare flame retardant carbon fiber reinforced polyamide 6 (PA6/CF) composites. Transmission electron micrographs (TEM) showed that both CeHPPs and ADPs dispersed homogenously in PA6 matrix. Thermogravimetric analysis (TGA) indicated that CeHPPs had excellent thermal stability and abundant char residues. Compared to PA6/CF, the limiting oxygen index (LOI) of PA6/CF‐10ADP increased from 27.5% to 36.4%, with no melt droplets during burning. After replacing 2 wt% ADPs to CeHPPs, PA6/CF‐8ADP‐2CeHPP reached to UL‐94 V‐0 rating with a LOI of 35.6% and the total heat release (THR) decreased by 37.2% in cone calorimeter test. CeHPPs had good synergistic effect with ADPs, and CeHPPs could form a continuous and compact char layer in PA6/CF composites to block the combustible gas spillage and heat transfer along the CFs, thus significantly attenuating the “candlewick effect” and improving the flame retardancy of PA6/CF composites.