Caged pentaerythritol phosphate-expandable graphite synergistic flame retardant natural rubber

The synergistic flame retardant system consisting of cage pentaerythritol phosphate (PEPA) and expandable graphite (EG) was added to the natural rubber (NR) to prepare EG-PEPA/NR composites. The effects of PEPA and EG with different mass ratios on the flame retardancy and mechanical properties of EG-PEPA/NR composites were investigated by limiting oxygen index(LOI) and vertical combustion(UL-94) test, thermogravimetric analysis, cone calorimetry, tensile test and carbon residue SEM and FTIR. The results show that the flame retardancy and mechanical properties of EG-PEPA/NR composites perform the best when PEPA to EG with the mass ratio of 33:7 are added to NR. Its LOI reaches 28.1% and the UL-94 reaches V-0 level. The amount of carbon residue increases from 27.5% to 33.6% at 600℃. The peaks of total heat release and heat release rate are 96.2 MJ·m^-2 and 512.4 kW·m^-2, respectively, decreasing by 22.2% and 40.3% compared to the pure NR sample. The tensile strength and elongation of EG-PEPA/NR at break also reach 13.8 MPa and 368%, respectively.