Fire retardant and charring effect of poly(sulfonyldiphenylene phenylphosphonate) in poly(butylene terephthalate)

Poly(sulfonyldiphenylene phenylphosphonate) (PSPPP) alone or together with polyphenylene oxide PPO, triphenylphosphate TPP or 2-methyl-1,2-oxaphospholan-5-one 2-oxide (OP) was mixed with poly(butylene terephthalate) (PBT). The combustion behavior of the formulations was studied by limiting oxygen index and Underwriters Laboratories UL94 test. The mechanism of the fire-retardant action of PSPPP was elucidated by thermogravimetry, IR characterization of solid residues and GC/MS characterization of the gaseous and high-boiling products. The UL94 test V-0 rating was achieved by addition of 10 wt.% PSPPP, 10 wt.% PPO and 10 wt.% OP. The fire retardant effect was attributed to promoting the char yield by involving the polymer in charring. PSPPP was shown to induce the formation of thermally stable polyarylates and phenolic functionalities in PBT. The additive is likely to react with these functionalities and crosslink macromolecules. (C) 2002 Elsevier Science Ltd. All rights reserved.