Co-microencapsulation of biomass-based char source and melamine polyphosphate and investigation for their synergistic action in flame-retarding polypropylene

In this article, co-microencapsulation technology was utilized for decorating the surface of dialdehyde starch (DAS) and melamine polyphosphate (MPP) via one-step process. The aim for this design was to improve the dispersion for DAS and MPP in polypropylene (PP) and employ DAS as sustainable char-forming agent, which lied in enhancing the flame retardancy of PP. In view of chemical composition, morphology and surface wettability, the changes for DAS and MPP after modification were confirmed by energy dispersive spectrometer (EDS), scanning electron microscope (SEM) and water contact angle (WCA) tests, respectively. Most of all, the results for flame retardant tests demonstrated limiting oxygen index (LOI) value and vertical burning tests (UL94) rating of PP/30 ph M[M&D] were 28.2% and V-1. Along with the synergistic effect, the homogeneous dispersion of DAS and MPP in PP after co-microencapsulation modification was also one of main reasons for the increased flame retardant properties. Except that, the chemical interaction between DAS and MPP in producing the char layer was also certified by TGA curves. After systematic analysis on char residue, the possible intumescent flame retardant mechanism was primarily proposed.