Intumescence in poly(butylene terephthalate): the effect of 2-methyl-1,2-oxaphospholan-5-one 2-oxide and ammonium polyphosphate

The flame-retardant effect of 2-methyl-1,2-oxaphospholan-5-one 2-oxide (OP) and ammonium polyphosphate (APP) in poly(butylene tcrephthalate) (PBT) was studied by the limiting oxygen index and the UL94 test. A self-extinguishing formulation (V-0 rating) was achieved by the addition of 15 wt% APP and 10wt% OP. The fire-retardant effect was attributed to the condensed-phase mechanism of intumescence. Mechanistic studies were performed using thermogravimetry, IR characterization of solid residues and GC-MS characterization of the gaseous and high-boiling products. OP-APP was shown to cause ammonolysis of PBT, formation of aromatic nitriles in the high-boiling products and phosphorus ester groups and polyphosphoric acid-phosphorus pentaoxide in the solid residue. (C) 2003 Society of Chemical Industry.