Research on highly flame-retardant rigid PU foams by combination of nanostructured additives and phosphorus flame retardants

Abstract

Flame retardant rigid PU foams (RPUF) were prepared by using nanostructured zinc oxide (ZnO), Zeolite and montmorillonite (MMT) combined with traditional phosphorus flame retardants as flame retardant systems. Phosphorus flame retardants were ammonium phosphate (APP) and dimethyl methyl phosphonate (DMMP). The former mainly took effect in condensed phase and the latter mainly played role in gas phase. Nanostructured additives (Nanos) were used to reduce flammable gas release rate and to form highly protective char layer. Research results showed that RPUFs showed different combustion performances, when different Nanos added together with APP and DMMP. ZnO and MMT narrowed the heat release peak of RPUFs, but the intensity of the peak did not reduce. Heat release rate (HRR) of RPUF with Zeolite/DMMP/APP flame retardant system was only 91 kW/m2, which was 56% lower than that of pure RUPF and 26% lower than RPUF only with DMMP/APP flame retardant system, while the limiting oxygen index (LOI) of RPUF reached 29.5%. Further study indicated that structure of Nanos and the interaction between Nanos and phosphorus flame retardants was essential to the effect of flame retardant system.