The flame resistance properties of expandable polystyrene foams coated with a cheap and effective barrier layer

A cheap and effective flame retarded EPS system was developed by using a high silica content based fly ash (FA) synergistic with aluminum hydroxide (ATH) in the thermosetting phenolic resin (PF) coating layer. In this study, scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analyses confirmed the formation of a barrier layer which uniformly encapsulated each EPS microsphere. The flammability of EPS-PF/ATH/FA foam with different compositions were characterized by the limited oxygen index (LOI) and UL-94 vertical burning tests, an evident flame retardant effect has been observed with up to 29.6% LOI value and UL-94 V-0 rating. The cone calorimetric analysis (CONE) indicated that the heat release rate (HRR), total heat release (THR) and smoke production rate (SPR) of the resulting EPS-PF/ATH/FA foam decreased obviously, and the foam maintained structural integrity after combustion. The thermal stability of EPS-PF/ATH/FA foams has been evaluated by the thermogravimetric analysis (TGA). It is obvious that the presence of PF-ATH/FA flame retarded binder has delayed the pyrolysis process of EPS matrix by about 10 °C. From analysis conducted on the combusted residues, it can be inferred that the dominant flame retardant action of EPS-PF/ATH/FA foam occurred in the compact char layer, which acted as an effective fire-proofing and heat shielding barrier in the condensed phase.