The effect of ammonium polyphosphate on the mechanism of phosphorous-containing hydrotalcite synergism of flame retardation of polypropylene

Ammonium polyphosphate (APP) is well known to have a synergistic action with phosphorus-based flame retardants in enhancing the flame retardant performance of matrix polymers, but the effect of APP and phosphorous-containing hydrotalcite on synergistic effect and degradation mechanism of polypropylene (PP) has not been thoroughly studied. In the present work, a synergistic flame retardant containing P3O105- intercalated Mg/Al hydrotalcite modified by rare-earth coupling agent (W-LDH-P) and APP were prepared and used as compounded flame retardant (W-LDH-P/APP) for PP matrix. The W-LDH-P/APP and PP composites(PP/W-LDH-P/APP) possess a limiting oxygen index (LOI) value of 27.8% and achieves the V-0 standard of the flame retardant plastic. Additionally, the heat release rate (HRR), total heat release (THR) and total smoke release (TSR) for the PP/W-LDH-P/APP composites were decreased by 44.0%, 21% and 75% compared with PP/W-LDH-P. These results demonstrate that APP dramatically enhances the flame retardancy of the PP. The synergistic effect and degradation mechanism of APP and W-LDH-P are confirmed by SEM and TGA analysis. These analyses reveal that the APP and W-LDH-P promoted the formation of a more continuous and compact char layer during the burning process for PP matrix.