Effects of microencapsulated APP-II on the microstructure and flame retardancy of PP/APP-II/PER composites

In this study, crystalline form II ammonium polyphosphate (APP-II) was microencapsulated with melamine-formaldehyde (MF) resin, which was prepared by in situ polymerization. The results of Fourier transform infrared spectra (FTIR), thermogravimetry (TG), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM) analyses demonstrated that APP-II was successfully microencapsulated with the MF resin. Polypropylene (PP)/APP-II/pentaerythritol (PER) and PP/MFAPP-II/PER composites were prepared and the flame retardancy, thermal stability, and microstructure of the corresponding composites were investigated based on the limiting oxygen index (LOI), UL-94 testing, TG, EDS, SEM, and cone calorimetry. Compared with PP/APP-II/PER composites, the PP/MFAPP-II/PER composites had a higher LOI value and passed the V-0 rating more easily. The results of the TG, EDS, SEM, and cone calorimetry analyses demonstrate that MFAPP-II is beneficial for forming a compact and strong intumescent char, thereby reducing the rates of the maximum-rate decomposition temperature (Tmax), heat release rate (HRR), total heat release rate (THR), and mass loss (ML) for the PP/MFAPP-II/PER composites, as well as improving the thermal stability, compatibility, and dispersion of MFAPP-II in PP/MFAPP-II/PER composites.