Combination of Carbon Nanotubes with Ni₂O₃ for simultaneously improving the flame retardancy and mechanical properties of polyethylene

Effects of multiwalled carbon nanotubes (MWCNTs) and Ni₂O ₃ on the flame retardancy of linear low density polyethylene (LLDPE) have been studied. A combination of MWCNTs and Ni₂O₃ showed a synergistic effect in improving the flame retardancy of LLDPE compared with LLDPE composites containing MWCNTs or Ni₂O₃ alone. As a result, the peak value of heat release rate measured by cone calorimeter was obviously decreased in the LLDPE/MWCNTs/Ni₂O₃ composites. According to the results from rheological tests, carbonization experiments, and structural characterization of residual char, the improved flame retardancy was partially attributed to the formation of a networklike structure due to the good dispersion of MWCNTs in LLDPE matrix, and partially to the carbonization of degradation products of LLDPE catalyzed by Ni catalyst originated from Ni ₂O₃. More importantly, both viscoelastic characteristics and catalytic carbonization behavior of LLDPE/MWCNTs/Ni₂O₃ composites acted in concert to result in a synergistic effect in improving the flame retardancy. Although both MWCNTs and Ni₂O₃ were not organically modified, LLDPE composites incorporating both the fillers showed higher mechanical properties compared with those of pure LLDPE.