The preparation of ZIF-67 and its synergistic effect on fire performance of intumescent flame retardant polypropylene

Herein, zeolite imidazolate frameworks-67 defined as ZIF-67 was prepared and confirmed. The obtained ZIF-67 was served as a synergist in intumescent flame-retarded polypropylene (PP) composites to improve the flame retardant efficiency and smoke suppression performance. The results of thermogravimetric analysis indicated that the residual char of IFR/ZIF-67 with the mass ratio of 95:5 greatly enhanced from 24.9 mass% for IFR to 63.5 mass%, and increased by 155.0%. It was ascribed the complexation effect of cobalt ion in ZIF-67 for IFR system. With the incorporation of 18 mass% IFR/ZIF-67, the PP/IFR/ZIF-67 samples (PP-4) achieved UL-94V-0 rating during vertical burning tests and the limiting oxygen index (LOI) value was as high as 31.1%. Compared with PP/IFR (PP-1) containing 18 mass% IFR, the peak heat release rate (peak-HRR), total heat release (THR), peak smoke production rate (peak-SPR) and total smoke production (TSP) of PP-4 were decreased by 33.1%, 33.8%, 31.0% and 21.1%, respectively. The char residue of PP-4 was as high as 27.4 mass% at the end of cone calorimeter test (CCT). The more expanded, sufficient and dense char layer were generated during combustion, and the flame retardancy and smoke suppression of PP-4 were significantly improved. Meanwhile, the pyrolysis gaseous products were inhibited to enter into combustion zone due to the isolation effect of the generated intumescent char layer. Consequently, the PP/IFR/ZIF-67 composites with excellent flame retardant performance and smoke suppression were obtained.