Flame retardant polyester by combination of organophosphorus compounds and an NOR radical forming agent

Polymer materials with different surface‐to‐volume ratios require different mechanisms of flame retardants regarding condensed phase and gas phase activity. The flame retardant formulations in poly(ethylene terephthalate) (PET) are investigated regarding a condensed phase and gas phase activity by using thermogravimetric analysis (TGA), TG‐mass spectrometry (MS), TG‐Fourier transform infrared (FTIR), UL94, cone calorimeter and scanning electron microscopy–energy‐dispersive X‐ray spectrometer measurements. The flame retardant formulations containing phosphates, phosphonates, and phosphinates as flame retardants are analyzed by using a simultaneous analysis consisting of a differential thermal analysis‐TGA device which is in situ coupled to FTIR and MS. All analysis methods show a gas phase activity for the phosphonate (PCO 910), a condensed phase activity for the phosphate (3,9‐bis(phenoxy)‐2,4,8,10‐tetraoxa‐3,9‐diphosphaspiro‐5,5‐undecane‐3,9‐dioxide, (SPDPP) and a mixed condensed and gas phase activity for the new synthesized phosphate and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide containing flame retardant 3,9‐bis(phenoxy)‐2,4,8,10‐tetraoxa‐3,9‐diphosphaspiro‐5,5‐undecane‐3,9‐dioxide (SPDPDOM). The fire behavior of PCO 910 can be improved by adding O,O'‐Terephthaloyl‐bis‐N,N'‐naphthalimide ester as NOR radical‐forming agent (NOR‐RF) reaching a total amount of 3 wt % of both active agents for a UL94 V‐0 classification in PET.