Influence of antimony oxide on flammability of polypropylene/intumescent flame retardant system

An intumescent system consisting of ammonium polyphosphate (APP) as an acid source and blowing agent, pentaerythritol (PER) as a carbonific agent and antimony oxide (Sb2O3) as a synergistic agent was used in this work to enhance flame retardancy of polypropylene (FR-PP). Sb2O3 was incorporated into flame retardant formulation at different concentrations to investigate the synergistic mechanism of Sb2O3 with the flame retardant materials. The content of APP and PER was fixed at 25 wt% of total amounts of flame retardant-PP composite. The synergistic effects of Sb2O3 on novel intumescent flame retardant-PP composites were evaluated by limited oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Results show that LOI is increased from 27.8 to 36.6% in the presence of Sb2O3 and meets the UL-94 V-0 standard at the loading of 2 wt% Sb2O3. The SEM, and FT-IR results indicated that Sb2O3 could react with APP and form the stable charred layer which can inhabit the oxygen and heat transfer. (c) 2012 Elsevier Ltd. All rights reserved.