An investigation into synergistic effects of rare earth oxides on intumescent flame retardancy of polypropylene/poly (octylene-co-ethylene) blends

Synergistic effects of two kinds of rare earth oxides (REOs), neodymium oxide (Nd2O3) or lanthanum oxide (La2O3) on the intumescent flame retardancy of thermoplastic polyolefin (TPO) made by polypropylene/poly (octylene-co-ethylene) blends were investigated systemically by various methods. The limiting oxygen index (LOI) of flame retardant TPO (FRTPO) filled by 30 wt% intumescent flame retardants (IFR) composed of ammonium polyphosphate (APP) and pentaerythritol (PER) has been increased from 30 to 32.5 and 33.5 when 0.5 wt% of IFR was substituted by La2O3 and Nd2O3, respectively. Cone calorimetry tests also reveal the existence of synergistic effects. Thermalgravimetric analyses (TGA) demonstrate that the presence of REOs promotes the esterification and carbonization process in low-temperature range while enhances the thermal stability of IFR and FRTPO in high-temperature range. X-ray diffraction (XRD) reveals that the interaction of Nd2O3 with IFR results in the formation of neodymium phosphate (NdP5O14) with high-thermal stability. Thermal scanning rheological tests show that the presence of REOs increases complex viscosity of FRTPO in the temperature range of 190∼300°C so as to suppress melt dripping but decreases the complex viscosity and increases the loss factors tan δ in temperature range of 300∼400°C to make the carbonaceous strucuture more flexible and viscous to resist stress, expand better and keep intact