Effect of zeolites on morphology and properties of water-blown semi-rigid ammonium polyphosphate intumescent flame-retarding polyurethane foam

Water-blown semi-rigid polyurethane foams (SPFs) were prepared by a one-shot, free-rise method. Effect of zeolites (ZEO) on morphology, flame retardancy, mechanical properties, damping properties, and thermal properties of ammonium polyphosphate (APP) intumescent flame-retarding SPFs was studied through the analysis of rotary viscosity test, limiting oxygen index (LOI), horizontal-vertical burning test, scanning electron microscopy (SEM) and mechanical test etc. Rotary viscosity test found that viscosity just enhanced a little when zeolites were added to the reaction matrix containing APP. With zeolites added, internal defects foams caused by the high loading of flame retardants could be effectively eliminated because the reaction heat could be partly taken by zeolites’ crystal water. The addition of zeolites did not increase the density of the APP intumescent flame-retarding SPFs. Meanwhile, with the presence of zeolites the APP intumescent flame-retarding SPFs exhibited better flame retardant property when APP content is high. Mechanical test showed that with the introduction of ZEO, compression strength and compression modulus of SPFs stably enhanced with the increasing APP loading and reached a maximum value when the APP content was 45 pphp. At a certain ZEO content (ZEO = 15 pphp), the APP intumescent flame-retarding SPFs with zeolites exhibited higher compression strength and modulus when the APP loading was over than 45 pphp.