Effect of Ammonium Polyphosphate and Melamine Pyrophosphate on Fire Behavior and Thermal Stability of Unsaturated Polyester Synthesized from Poly(ethylene terephthalate) Waste

The fire behavior and thermal stability of unsaturated polyester prepared from recycled poly(ethylene terephthalate) (RUP) in the present of two phosphorus-nitrogen flame retardants (FRs) including ammonium polyphosphate (APP) and melamine polyphosphate (MPP) have been investigated. The effectiveness of FRs on the fire proofing of material was test by UL-94 vertical classification and limiting oxygen index (LOI). The obtained data showed that the fire retardancy and thermal stability were remarkably enhanced with addition of FRs. The best grade of UL-94V standard, V-0 ranking was attained as loading of 25 wt% of APP or 30 wt% of MPP. LOI significantly were enhanced from 20 to 36%. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Scanning electron microscope (SEM) were applied to determine the structure and morphology of char layers of RUP and RUP/FR mixtures. Thermogravimetric analysis (TGA) method was applied to investigate thermal stability of neat RUP, FRs, and RUP/FR and to evaluate kinetic parameters of the decomposition of RUP/FR. The mechanism of action of FRs, schemes for the possible decomposition mechanism RUP and FRs, and the cooperation of matrix and additives were also discussed.