Co-microencapsulation of ammonium polyphosphate and aluminum hydroxide in halogen-free and intumescent flame retarding polypropylene

In this article, co-microencapsulated ammonium polyphosphate (APP) and aluminum hydroxide (ATH) [M(A&A)] was prepared by using 4,4'-diphenylmethane diisocyanate (MDI) and melamine (MEL) via in situ surface polymerization method. The chemical composition of M(A&A) was confirmed by Fourier transform-infrared spectra (FT-IR). Thermal behavior and surface morphology of M(A&A) were systematically analyzed by thermogravimetric analysis (TGA) and scanning electron microscope (SEM), respectively. Water solubility tests indicate that water solubility of M(A&A) decreases greatly than un-microencapsulated ones. Besides, flame retardant properties of polypropylene (PP) compositing with M(A&A) were investigated by limiting oxygen index (LOI), vertical burning tests (UL-94) and cone calorimeter. The results demonstrate the LOI value of PP composites is improved after combining with co-microencapsulated flame retardants. Compared with PP/A&A, the peak heat release rate of PP/M(A&A) decreases from 210 to 120 kW/m2 at the same flame retardant loading level. Moreover, in order to investigate the flame retardant mechanism, the char residue of PP composites after combustion was studied by optical photos, X-ray photoelectron spectroscopy (XPS) spectra and FT-IR. POLYM. COMPOS., 35:715–729, 2014. © 2013 Society of Plastics Engineers