A novel halogen-free intumescent flame retardant containing phosphorus and nitrogen and its application in polypropylene systems

A novel halogen-free intumescent flame retardant, pentaerythritol spirobisphosphoryl-dicyandiamide (SPDC), was synthesized and characterized by FTIR, 1H NMR, and 31P NMR spectra. The new flame retardant was used in polypropylene (PP) to prepare flame-retardant materials whose flammability and thermal behavior were studied by the limiting oxygen index (LOI) method, thermogravimetric analysis (TGA), and cone calorimetry (CONE). The mechanical properties were also investigated. The results indicated that when the addition of SPDC reached 30 wt%, the material showed both excellent flame retardancy and anti-dripping abilities for PP. Moreover, the LOI value of the PP-IFR(30%) was 32.5, and it passed the UL-94 V-0 rating test. The CONE results revealed that in PP, SPDC(30%) significantly decreased the peak heat release, total heat release, and smoke relative to their values for pure PP. The morphological structures observed by SEM demonstrated that SPDC could promote the formation of a homogeneous and compact intumescent char layer. The TGA data showed that SPDC could enhance the thermal stability of PP and effectively increase the char residue formation. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers