Fire retardant effect of 2-methyl-1,2-oxaphospholan-5-one 2-oxide in the PPO/HIPS blend

A phosphorus-rich compound 2-methyl-1,2-oxaphospholan-5-one 2-oxide (OP) (Clariant, Germany), and poly(2,6-dimethylphenylene oxide) (PPO) were mixed with high impact polystyrene (HIPS). The combustion behavior of the formulations was studied by limiting oxygen index (LOI) and Underwriters Laboratories UL94 test. The mechanism of the fire-retardant action of the additives was studied by thermogravimetry, IR characterization of the solid residues and high boiling degradation products (HBPs) and GC/MS characterization of the HBPs. OP was found to improve fire retardant performance of the PPO/HIPS blend providing the UL94 V-0 rating. Upon pyrolysis, it evaporates and forms phosphorus-containing volatiles. Thermogravimetry and FT-IR provide evidence of an interaction between PPO and OP. The synergistic fire retardant effect is mostly attributed to the condensed- and vapor-phase activity of OP and condensed-phase effect of PPO.