Synergism of Phytic Acid Modified Piperazine Pyrophosphate and Zinc Borate in Flame-Retardant Polypropylene

Based on the synergistic effects among phosphorus, nitrogen, and boron elements, this study developed a novel and highly efficient flame-retardant system to enhance the fire safety of polypropylene (PP) during its application. An integrated intumescent flame retardant (IFR) was prepared via supramolecular self-assembly by surface-modifying piperazine phosphate (PAPP) with phytic acid (PA) and melamine (MEL), and was named PM@PAPP. Subsequently, it was combined with zinc borate (ZB) to prepare flame-retardant PP composites. The PM@PAPP/ZB/PP composite exhibited excellent flame retardancy and smoke suppression performance. Specifically, the limiting oxygen index (LOI) of PP5 reached 35.3%, and its vertical burning test (UL-94) rating was V-0 level. The peak heat release rate (pHRR) was 91% lower than that of pure PP. The peak smoke production rate (pSPR) of PP5 decreased from 0.097 m 2 /s for pure PP to 0.007 m 2 /s, representing a reduction of 93%. Furthermore, thermogravimetric analysis (TGA) and Raman spectroscopy results confirmed that the synergistic effect of ZB and PM@PAPP promoted the formation of continuous and dense carbon layers. This study provides a new strategy for improving the flame-retardant properties of PP and expanding its application in fields with strict fire safety requirements.