Synergistic effect of p-type semiconductor n-Co3O4@C-N on the flame retardancy, smoke suppression, and toxicity reduction of linear low-density polyethylene composites

Linear low-density polyethylene (LLDPE) is flammable and produces severe molten droplets and toxic smoke, posing a great threat to life and property safety. To address these challenges, ZIF−67-derived nano-carbon-nitrogen-coated Co 3 O 4 (n-Co 3 O 4 @C-N) was synthesized and employed as a synergist for an intumescent flame retardant (IFR) in LLDPE. When IFR/n-Co 3 O 4 @C-N was introduced, LLDPE composites achieved a UL−94 V−0 rating and the limiting oxygen index of 26.8%. Cone calorimeter test results further demonstrated that the total heat release of LLDPE/IFR/n-Co 3 O 4 @C-N−3 decreased by 23.2% compared with pure LLDPE, indicating remarkable suppression of fire intensity. Compared with LLDPE/IFR and LLDPE/commercial-Co 3 O 4 , LLDPE/IFR/n-Co 3 O 4 @C-N−3 exhibited a reduction in total smoke production by 50.3% and 37.2%. The high specific surface area of n-Co 3 O 4 @C-N facilitates sufficient contact with the polymer matrix, enhancing catalytic carbonization and forming a robust graphitized char layer. Furthermore, as a p-type semiconductor, n-Co 3 O 4 @C-N has a narrower band gap, reducing the energy required for electron transition, and its higher hole concentration helps to oxidize more CO to low-toxicity CO 2 , thereby lowering the concentration of toxic gases. This study presents a promising strategy to fabricate flame-retardant, smoke-suppressing, and low-toxic LLDPE composites, thus effectively overcoming the existing technical limitations in wire and cable application fields.