Synthesis and performance of three flame retardant additives containing diethyl phosphite/phenyl phosphonic moieties

Three novel intumescent flame retardants (IFRs) containing phosphorus and nitrogen based on Schiff bases, poly(phosphonate ester(s)) (designated as PAB, PEB, and PPB), were synthesized and characterized. Thermal stability and flammability properties of ethylene-vinyl acetate copolymer (EVA)/30% IFRs blends were investigated by thermogravimetric analysis (TGA), limited oxygen index (LOI), vertical burning test (UL-94) and microscale combustion calorimetry (MCC). The results from UL-94 showed that EVA/IFRs blends all could reach V-2 rating. The addition of PAB into EVA reduced the PHRR value by 31%, and the LOI value increased from 19 to 24. Scanning electron microscope (SEM) observation results indicated that the existence of the cohesive charred layer on the surface of the residue was responsible for the improvement of the flame retardancy of EVA.