Synthesis of a highly efficient charring agent and its application to intumescent flame‐retardant coatings for 3D‐printed polypropylene parts

To improve the flame retardancy of 3D‐printed polypropylene (PP) parts, cyclic triphosphonitrile‐based hyperbranched charring agent (DHCCP) was innovatively synthesized and applied in flame‐retardant coatings. Thermogravimetric analysis (TGA) indicated that the residual char rate of DHCCP reached 64.33% at 700°C. When 5 wt% DHCCP was added to the coating, the limiting oxygen index of the composite reached 29.1%, and the vertical combustion (UL‐94) could reach V‐0 rating. In addition, cone calorimetry test measured a 54.10% reduction in peak exothermic rate, and the tensile strength of coated PP was improved. The morphology and chemical composition of the char residues were investigated by scanning electron microscopy, infrared spectroscopy, and laser Raman spectroscopy. After combustion, the coated PP formed a continuous and dense char layer, which could play the role of heat and oxygen insulation and anti‐drip, effectively improving the flame‐retardant of 3D‐printed PP parts. Synthesis of charring agents and flame‐retardant mechanisms of coatings.