Highly efficient multifunctional mono-component flame retardants comprising of sulfenamide and phosphate moieties for polypropylene

A strategy to enhance flame retardant properties of polypropylene (PP) has been investigated by the design of six multifunctional mono-component flame retardants denoted from NS1 to NS6, where sulfenamide and phosphate moieties have been integrated into a single molecule. Herein, the synthesis and characterization of six different mono-component flame retardants are presented. Thermal decomposition characteristics of the multifunctional flame retardants were studied by thermogravimetry analysis, and a 5% mass lose was recorded in the temperature range between 220 °C to 267 °C for the samples. Moreover, the flame retardant samples were oven aged up to 260 °C in the presence and absence of 9, 10-dihydroantracene and the formed decomposition products were analyzed using GC/MS, LC/MS, 13C NMR and 31P NMR. The results indicate that the sulfenamide bond dissociates before the phosphorus moiety for samples NS1, NS2, NS3 and NS6. Whereas the phosphorus moiety breaks first in case of NS4 and NS5. The prepared flame retardants were then admixed with polypropylene in a Haake Rheocord melt blender at loadings ranging from 0.5 to 4 wt%. Thereafter, polypropylene films and plaques were prepared by hot pressing and their flame retardant properties were evaluated according to DIN 4102-B2 and UL94V standards, respectively. All the PP film samples containing any of the different multifunctional flame retardants at the low loading of 0.5 wt% passed the DIN4102 B2 test and for NS1film sample no burning dripping nor ignition of paper were recorded. Noteworthy, is that NS2 and NS3 samples reached the UL94V2 classification as standalone flame retardants even at a loading of only 4 wt%. From this standpoint, it seems the multifunctional mono-component flame retardants may exhibit inherently an exceptionally high synergistic effect.