Synthesis of silicic poly carbonyl urea and its flame-retardant effect on polypropylene for char forming

Abstract

This paper researches the char forming and flame-retardant effect of silicic poly carbonyl urea (Si-PCU) in company with ammonium polyphosphate (APP) on polypropylene (PP). Si-PCU was firstly synthesized and represented by Fourier transform infrared spectroscopy, energy-dispersive analysis, thermogravimetric analysis and water contact angle. Then, the intumescent flame retardants, Si-PCU + APP, were added into PP. Their flame-retardant effects were studied by limiting oxygen index (LOI) test, UL-94 vertical burning and micro-combustion calorimetry (MCC). When the amount additions of PP, APP and Si-PCU were 70, 20 and 10%, the LOI value of these PP composites (PP-6) was reached 29.5 and UL-94 testing grade was V-0, besides the PHRR decreased 66% and THR decreased 34% compared with pure PP. Furthermore, the residual char layers’ microstructure and strength were researched by field-emission scanning electron microscope, wide-angle X-ray diffraction and laser Raman spectroscopy. They showed that PP-6’s char layer was denser and had higher strength than other PP composites. Finally, tensile tests illustrated that the addition of Si-PCU + APP could decrease the break strength and toughness of pure PP, but Si-PCU + APP/PP had better toughness than APP/PP.