Synthesis of a novel organic–inorganic hybrid flame retardant based on Ca(H2PO4)2 and hexachlorocyclotriphosphazene and its performance in polyvinyl alcohol

To optimize the poor thermal stability and flammable of polyvinyl alcohol (PVA), a novel environmental-friendly organic–inorganic hybrid flame retardant Ca(H 2 PO 4 ) 2 @HCCP was successfully designed and synthesized via surface treatment technology and used to advance the flame retardancy of PVA. The thermogravimetric analysis implied that Ca(H 2 PO 4 ) 2 @HCCP can enhance significantly the thermal stability and char forming ability of PVA. Combustion results demonstrate that Ca(H 2 PO 4 ) 2 @HCCP could effectively suppress the melt dripping of PVA in the process of combustion. The presence of Ca(H 2 PO 4 ) 2 @HCCP can sharply reduce peak heat release rate and the total heat release up to 75% and 22.9%, respectively, in the microscale combustion calorimeter measurement. The results manifested that Ca(H 2 PO 4 ) 2 @HCCP could endow PVA with superior flame retardancy. Moreover, char residues analysis explained the flame retardant mechanism in condensed and gas phase, which is mainly attributed to the strong catalytic char formation, free radical trapping, and gas barrier effect. Therefore, the green flame retardant has great application s prospect in fire safety.