Preparation of microencapsulated ammonium polyphosphate with carbon source- and blowing agent-containing shell and its flame retardance in polypropylene

In this paper, a novel and facile method was carried out to microencapsulate ammonium polyphosphate (APP) via two-step surface polymerization process, which introduces the carbon source and blowing agent into the microcapsules simultaneously. The chemical composition of microencapsulated APP (MAPP) was confirmed by fourier infrared spectra (FTIR). The surface morphology and thermal behavior of APP and MAPP were investigated by scanning electron microscope (SEM) and thermogravimetric analysis (TGA), respectively. Additionally, transmission electron microscopy (TEM) demonstrates that MAPP particles possess the obvious core/shell-like structure. Compared with APP, the water solubility of MAPP greatly decreases that can improve the water resistance of MAPP in polymer materials when exposed to water. Moreover, the flame retardant properties of polypropylene (PP) compositing with MAPP were systematically researched by limiting oxygen index (LOI), vertical burning tests (UL-94) and cone calorimeter. The results show the flame retardant properties of PP composites are enhanced by combining MAPP than that of APP. Besides, the water resistance of PP/MAPP is also enhanced. And the char residue of PP composites after combustion was analyzed by FTIR and X-ray photoelectron spectroscopy (XPS) spectra. Based on these facts, a possible flame retardant mechanism of MAPP in PP composites was proposed.