Flammability of polystyrene/aluminim phosphinate composites containing modified ammonium polyphosphate

Abstract

Polystyrene (PS) composites with different loading level and proportions of CNAPP20 [i.e., ammonium polyphosphate (APP) wrapped graphitic carbon nitride (g-C3N4), where mass ratio of g-C3N4 to the CNAPP was 20%] to aluminim phosphinates were fabricated. The results indicated that the additives had good interfacial interaction with PS matrix. It is noted that only the PS-1 achieved the UL-94 V-0 rating, and value of limited oxygen index was also the highest among all the composites. The peak of heat release rate (pHRR) and total heat release of all the composites were greatly reduced as compared to those of virgin PS (77.5% decrease in pHRR for PS-1). Combining CNAPP20 with DAHPi (i.e., aluminim diethylphosphinate) induced the formation of a cohesive and uniform carbonaceous residue. In addition, the concentration of carbon dioxide, smoke and carbon monoxide was reduced upon incorporation of CNAPP20 and DAHPi. The property improvements were attributed to the explanations that the formed continuous and dense char residues acted as protecting layers to prevent the heat and mass permeation, and that the evolved gas diluted the oxygen, which retarded the further combustion of flammable compounds. Also, the generated free-radical scavengers retarded polymeric chain breakage.