Synthesis and characterization of a novel organic-inorganic hybrid char-forming agent and its flame-retardant application in polypropylene composites

A novel organic-inorganic hybrid char-forming agent (SCTCFA-ZnO) was synthesized and characterized by Fourier transform infrared spectrometry (FTIR) and solid state nuclear magnetic resonance (SSNMR). SCTCFA-ZnO was combined with ammonium polyphosphate (APP) to prepare intumescent flame retardant polypropylene (PP) composites. The flame retardancy and thermal degradation behaviour of composites were investigated by the means of limited oxygen index (LOI), vertical burning test (UL-94), cone calorimeter test (CONE) and thermogravimetric analysis (TGA). The flame retardant pattern and mechanism of PP composites were studied by thermogravimetric analysis/infrared spectrometry (TG-IR), scanning electron microscopy (SEM), laser Raman spectroscopy analysis (LRS), FTIR and X-ray photoelectron spectroscopy (XPS). The results indicated APP/SCTCFA-ZnO system with the mass ratio of 2:1 showed the best flame retardant properties and smoke suppression performance in PP composites. TGA results showed that APP/SCTCFA-ZnO could clearly improve the thermal stability of composites and promote the char residue formation. The residue analysis results further revealed higher graphitic cross-linking structures containing more P, O, N and Si in PP/APP/SCTCFA-ZnO consequently resulted in more obvious reduction of the combustion and smoke production than PP/APP/SCTCFA/ZnO.