Abstract:In view of the problem that the strength of carbon layer formed by intumescent flame retardant (IFR) composed of ammonium polyphosphate (APP) and zinc borate-linear triazine hybrid char-forming agent (MCA-K-ZB) was not high enough in flame retarding PP, which was easy to be broken through by gaseous material flow in combustion. In this paper, 4A zeolite was added into IFR (m(APP):m(MCA-K-ZB)=3:1) as synergistic char-formingagent. The synergistic effect of catalytic carbon and mechanism of PP/IFR catalyzed by 4A zeolite were studied by limiting oxygen index (LOI), vertical combustion test (UL- 94), cone calorimetry test (CCT), thermogravimetric analysis (TGA), scanning electron microscope energy spectrum analysis (SEM- EDX), FT- IR and laser Raman spectroscopy (LRS). The results show that 4A zeolite can prevent the expansion carbon layer from being broken through by heat flow or air flow during PP/IFR combustion, and effectively reduces the intensity of PP combustion. 4A zeolite could promote APP and MCA-K-ZB to form aromatic ring crosslinked structural carbon residue and more graphitized carbon residue during combustion, and improve the thickness of dense carbon layer, so as to improve the strength and flame retardant effect of carbon layer. When the mass fraction of 4A zeolite and IFR is 1% and 22% respectively, the LOI value of PP reaches 33.1% and passes V-0 grade without dropping, achieving the expected goal of low IFR amount and high flame retardancy.