Facile fabrication of starch-based, synergistic intumescent and halogen-free flame retardant strategy with expandable graphite in enhancing the fire safety of polypropylene

Aimed at improving the efficiency of bio-based flame retardants, a starch-based, chemical-physical synergistic intumescent and halogen-free flame retardant system has been prepared in polypropylene (PP). Besides, the starch-based flame retardants have been modified via surface hydrophobicity to enhance the interfacial compatibility with PP. Surprisingly, limiting oxygen index (LOI) value of PP composites can reach as high as 33.5% with UL-94 V-0 rating when the total flame retardant content is 30 phr. Definitely, the synergistic effect of starch-based flame retardants and expandable graphite (EG) endows the better flame retardancy and anti-dripping ability of PP, which can be attributed to the conjunct chemical-physical intumescence action in improving the quality of charring layer. Finally, systematic analysis on char residue has revealed the synergistic flame retardant mechanism. This work has opened up a new path for exploiting the bio-based flame retardant with high performance in actual applications.