Synthesis and properties of polyphosphoester and diphenyl phosphoroxy derivative for flame retardant poly(ethylene terephthalate)

Abstract

A polyphosphoester flame retardant, polyphenylphosphonic acid (2- (diphenylphosphonyl)-1,4-phenol) (PPSFR) was synthesized and applied to flame retarded poly(ethylene terephthalate) (PET). The flame retardancy and thermal stability of the PET/PPSFR were investigated by limiting oxygen index (LOI), vertical burning test (UL-94) test and thermogravimetric analysis (TGA) in nitrogen and air. LOI values increased from 21 for pure PET to 40 for flame retardant PET, and UL-94 V-0 materials were obtained with the 5 wt% PPSFR. The TGA results indicated that incorporation of PPSFR significantly enhanced the char yield and the thermal stability of char layer at higher temperature. The thermal degradation behaviors of PET/PPSFR were analyzed by thermogravimetric analysis/infrared spectrometry (TGA-FTIR), pyrolysis gas chromatography-mass spectrometry (PY-GC/MS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). Although the addition of PPSFR does not change the degradation mechanism of PET, the contents of the deep pyrolysis products of PET are inhibited. Phosphorus in the form of phosphate compounds concentrates on the surface of aromatic carbon layer and promotes PET dehydration into protective charcoal. PPSFR plays a role of flame retardant in condensed phase and gas phase.