Study on the thermal degradation of mixtures of ammonium polyphosphate and a novel caged bicyclic phosphate and their flame retardant effect in polypropylene

The thermal degradation behaviour of a novel caged bicyclic phosphate (Trimer) and its mixture with ammonium polyphosphate (APP) was studied by TG, FTIR and TG-FTIR. The flame retardant effect of Trimer/APP (IFR) in polypropylene (PP) was evaluated by limiting oxygen index (LOI) and vertical burning test (UL-94) at different mass ratio of Trimer and APP. Obvious synergistic effect can be observed between Trimer and APP, which remarkably improves the flame retardant properties of PP/IFR system. A maximum LOI value of 28.8% and UL-94 V-0 rating were achieved when the mass ratio of Trimer and APP was 2:1 at a total IFR loading of 25 wt%. Different degradation behaviour of Trimer/APP (with the mass ratio of 2:1) from APP or Trimer was observed by TG. The experimental TG curve of Trimer/APP, compared with the theoretically calculated one, showed lower initial degradation temperature and higher char residue at 800 degrees C, demonstrating interactions of Trimer and APP during thermal degradation. Such interactions were shown by gaseous degradation products analyzed by TG-FTIR. APP can chemically interact with Trimer, which changes the degradation process of Trimer. In the condensed phase, dehydration, cross-linking and char formation dominated the Trimer/APP interactions. (C) 2012 Elsevier Ltd. All rights reserved.