Supramolecular self-assembly modification of ammonium polyphosphate and its flame retardant application in polypropylene

In order to improve its water resistance and compatibility with polymer matrix, ammonium polyphosphate (APP) is modified with melamine-trimesic acid (MEL-TA) aggregates by supramolecular self-assembly technology. Chemical structure and morphology of APP@MEL-TA are investigated by Fourier transform infrared spectroscopy and scanning electron microscopy (SEM), respectively. Intumescent flame retardant system of APP@MEL-TA and charring-foaming agent is introduced into polypropylene (PP) matrix. The flammability and combustion behavior of PP composites are investigated by limiting oxygen index (LOI), UL-94 vertical burning, and cone calorimetry tests. In terms of LOI values and cone combustion results, APP@MEL-TA performs better than pristine APP. Char residue of PP composites is investigated by SEM and Raman spectra. Flame retardant mechanisms are proposed based on thermal decomposition, combustion results, and analysis on char residue.