Synergistic effect of activated carbon and Ni_2O_3 in promoting the thermal stability and flame retardancy of polypropylene

摘要

A novel combined catalyst of activated carbon (AC) with Ni_2O_3 was demonstrated to be much more efficient than AC or Ni_2O_3 alone in enhancing the char yield of polypropylene (PP) and improving its char layer structure, which greatly improved the thermal stability and flame retardancy of PP. The results of X-ray diffraction, field-emission scanning electron microscope and transmission electron microscope revealed that the residual char mainly consisted of carbon nanotubes (CNTs). Thermal gravimetric analyses results indicated that the combination of AC and Ni_2O_3 dramatically enhanced the thermal stability of PP. The flame retardancy of PP and its composites was studied by cone calorimeter test. The heat release rate and total heat release of the ternary PP/7.5AC-7.5Ni_2O_3 composite decreased significantly in comparison with those of neat PP. The investigation of the synergetic mechanism showed that in the presence of both AC and Ni_2O_3, a large amount of CNTs were in situ formed from the degradation products of PP during combustion. This not only reduced the release of flammable degradation products of PP, but also acted as a thermal shield for energy feedback from the flame. In addition, the formation of a network-like structure of AC and Ni_2O_3 particles in PP matrix favored the formation of a more compacted protective layer, which enhanced the flame retardancy of PP.