Expanded polystyrene foams containing ammonium polyphosphate and nano-zirconia with improved flame retardancy and mechanical properties

Abstract

Expanded polystyrene (EPS) foams were flame retarded using ammonium polyphosphate (APP) and nano-zirconia (nano-ZrO2) by means of phenolic resin as a binder. It is found that the incorporation of a small amount (5 phr) of nano-ZrO2 into the APP flame-retarded EPS foams leads to 19% increase in flexural strength and 38% increase in compressive strength. Flame-retardant properties of the flame-retarded EPS foams were investigated by limiting oxygen index (LOI), UL-94 and cone calorimetry test (CCT). The LOI of the APP flame-retarded EPS foams in presence of nano-ZrO2 is above 31%, and the UL 94 V-0 rating can be reached. The CCT test results indicate that the APP flame-retarded EPS foams containing nano-ZrO2 have lower peak heat release rate, average effective heat of combustion and average specific extinction area. Moreover, thermal decomposition of the flame-retarded EPS foams was investigated by thermogravimetric analysis (TGA) and the TGA results illustrated clearly that the addition of nano-ZrO2 into the APP flame-retarded EPS foams leads to an increase in the residual char yield. The reason for the increase is possibly because ZrO2 may react during combustion process with pyrophosphoric acid produced from the thermal decomposition of APP to form zirconium pyrophosphate (ZrP2O7) confirmed by XRD studies of the char, which is helpful to improve the formation of the char. The XPS results showed that the ratio of oxidized carbons in the char increases with the presence of nano-ZrO2.