Abstract: To improve the flame retardant properties of PP, melamine phosphate was used as an acid source and a gas source, dipentaerythritol was used as a carbon source to form an intumescent flame retardant system, and different proportions of ZIF-8/BC created by ZIF-8 material and BC were added into the system as synergist. The combustion properties, mechanical properties and thermal stability of the new halogen-free intumescent flame retardant composite were studied. The results indicate that the intumescent flame retardant system could effectively improve the flame retardancy of PP, and without the addition of ZIF-8/BC the oxygen index increases to 31.4%, while the tensile strength decreases to 17.37 MPa, that the addition of ZIF-8/BC slightly reduces the oxygen index of the composites, but improves the mechanical properties of the composites, that when ZIF-8/BC with a ratio of ZIF-8∶BC of 1∶2 is added, the oxygen index and tensile strength of the material are 27.2% and 19.87 MPa respectively, and that addition of ZIF-8/BC could increase the carbon content of composites, and it increases with the BC content, and that ZIF-8/BC as the synergistic agent has a positive effect on formation of dense carbon layer structure and smoke suppression.

Key words: polypropylene(PP), zeolitic imidazolate frameworks(ZIF-8), biochar(BC), intumescent flame retardant, oxygen index