Study on the effect of PolyFR and its FR system on the flame retardancy and foaming behavior of polystyrene

Abstract

A new class of brominated polymeric flame retardant (PolyFR) which is a kind of environmental FR was researched. Hydrotalcite (HT), applied as an environmentally-friendly heat stabilizer for PolyFR, was investigated by thermogravimetric analysis (TGA). It presented the result that no more than 0.15% HT significantly improved the thermal stability during processing but excessive HT would weaken the flame retardancy of PolyFR because of the ability to absorb hydrogen bromide (HBr). Flame-retardant polystyrene (PS) was prepared via mixing PolyFR/BDDP/HT and then introducing inorganic particles such as antimonous oxide (Sb₂O₃), organo montmorillonite (OMMT) and graphite to study their effect on the PolyFR/BDDP/HT system. The PS foams were prepared by batch foaming of the PS composites. Meanwhile, the combustion properties of PS composites and PS composite foams were characterized by limiting oxygen index (LOI) and vertical flame test (UL-94). The results indicated that the 2.5%PolyFR/2.5%BDDP/0.15%HT/PS composite possessed 25.7% LOI and pass UL-94 V-2 rating, while its foam possessed 30.7% LOI and pass UL-94 V-2 rating. And the addition of Sb₂O₃, OMMT and graphite reduced the oxygen index and vertical burning performance of PS composites and PS composite foams to different degrees. Otherwise, the flame-retardant (FR) mechanism of each FR system was studied by TGA and cone calorimetry. This revealed that PolyFR/BDDP promoted decomposition and dripping of PS early to remove heat through droplets and released HBr to quench free radicals and dilute combustible gas and oxygen during combustion. These properties of PolyFR/BDDP helped reduce the burning intensity and extinguish the flame through droplets, thereby endowing PS and its foam with better fire-resistant properties. When the addition of Sb₂O₃, OMMT or graphite improved the thermal stability of PS, they weakened the droplet effect as well. Besides, PS foams were characterized by scanning electron microscopy (SEM). The results indicated PolyFR played an efficient heterogeneous cell nucleation role in the foaming process to reduce average cell size (from 110.5 μm to 38.4 μm) and narrow cell distribution (from 60–160 μm to 20–60 μm).