Microencapsulation of ammonium polyphosphate: Preparation, characterization, and its flame retardance in polypropylene

Microencapsulated ammonium polyphosphate (MCAPP) with a melamine-formaldehyde (MF) resin coating layer was prepared by in situ polymerization. MCAPP was characterized by Fourier transform infrared, X-ray photoelectron spectroscopy, and so on. The results show that the microencapsulation with MF resin leads to a decrease in the particles' size and water absorption. The flame retardant action and mechanism of MCAPP and ammonium polyphosphate (APP) in polypropylene are studied using limiting oxygen index (LOI) and UL 94 test, and their thermal stability is evaluated by thermogravimetric analysis. The LOI value of the PP/MCAPP composite at 30 wt% loading is 30.5%, whereas the corresponding value of the PP/APP composite is only 20%. Moreover, the LOI values of the PP/MCAPP/PER composites are higher than the ones of the PP/APP/PER composites. In the UL 94 test, the PP/MCAPP/PER composites with suitable ratios of MCAPP to PER can reach the V-0 rating, and the best rating of the PP/APP/PER composites is V-1.