Functional organoclay with high thermal stability and its synergistic effect on intumescent flame retardant polypropylene

Abstract In this work a novel functional modifier for clay with increased thermal stability and synergistic effect on the flame retardancy of intumescent flame retardant polypropylene (IFR PP) composites was developed. First, triphenyl(undec-10-enyl)phosphonium bromide (TPB) was synthesized and characterized by FT-IR and 1H NMR spectroscopy. TPB has a high thermal stability with an initial decomposition temperature of about 270 °C. Subsequently, TPB was used to prepare functional organoclay (OC) by cation exchange reaction. OC was characterized by thermogravimetric analysis (TGA) and wide-angle X-ray scattering (WAXS). The interlayer distance of novel OC increased to 1.85 nm. OC was used in IFR PP nanocomposites prepared by melt mixing. The morphology, thermal stability and fire behavior of these IFR PP nanocomposites were investigated by SEM, TEM, TGA, limiting oxygen index (LOI), vertical burning test (UL94), and cone calorimeter (CC) test. In comparison to IFR (18 wt%) PP composites, IFR (16 wt%) + OC (2 wt%) PP nanocomposites passed the UL94 V-0 rating and showed no dripping. The LOI value decreased from 30.5 to 28.8 due to the use of low molar mass TBP. It was shown by cone calorimeter tests that the additional used of 1 or 2 wt% OC leads to a reduced heat release rate, smoke production rate and total smoke production. All these experimental results showed that this novel OC provided an excellent synergistic effect on the flame retardancy of IFR PP composites. Finally, electron beam treatment was used to enhance the thermal stability of flame retardant nanocomposites.