Char-forming mechanism of a novel polymeric flame retardant with char agent

A novel phosphorus-containing compound, poly(2-hydroxy propylene spirocyclic pentaerythritol bisphosphonate) (PPPBP) has been proved to be an excellent flame retardant for polyethylene terephthalate (PET) fabrics. In order to understand its flame retardant mode, FT-IR and XPS are used to investigate the char-forming mechanism of PPPBP. FT-IR spectra results show that with the increase of temperature, P-O-C group of PPPBP breaks down gradually, and species containing CC double bond appear. XPS spectra indicate that PPPBP produces phosphoric or polyphosphoric acid during thermo-decomposition. In the high temperature range (>400 °C), CC and phosphorus-containing complexes become the major components of the charred residue of PPPBP. Data of XPS and FT-IR spectra give positive evidence that PPPBP yields high amount of carbonaceous chars by producing phosphoric or polyphosphoric acid, which inhibit the oxidation of carbon atoms, and simultaneously impel the formation of carbon and species containing carbon double bond with outstanding heat resistance.