Synergistic flame retardancy of linear low-density polyethylene with surface modified intumescent flame retardant and zinc borate

Aluminum diethylphosphinate (ADP) was surface modified with the silane coupling agent KH-560, and mixed intumescent flame retardants (IFRs) were prepared with neopentyl glycol (NPG) and melamine (MEL). Then mixed IFRs and zinc borate (ZB) were compounded and added into linear low-density polyethylene (LLDPE) material. The morphology, composition, and structure of LLDPE/IFRs/ZB composites were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The maximum limiting oxygen index of LLDPE/IFRs/ZB composites is 28.7%, and the combustion grade is V0. The thermogravimetric analysis results showed that the thermal degradation rate of LLDPE/IFRs/ZB composites decreased, and the carbon residue reached 15.3 wt% at 700 ℃. The cone calorimeter test showed that peak heat release rate (PHRR), total heat release rate (THR), peak smoke release rate (PSPR), and total flue gas output (TSP) of LLDPE/IFRs/ZB composites decreased by 52.5%, 24.7%, 30%, and 15.5%, respectively, compared with pure LLDPE, significantly improving the flame retardant and smoke suppression performances of LLDPE. The residual carbon analysis shows that the CC and POC bonds in the modified mixed IFR strengthen the carbon layer structure and form a denser intumescent carbon layer, effectively hindering flame propagation. The experimental results show that the new intumescent flame retardant is a remarkable breakthrough in both flame retardancy and smoke suppression compared with ordinary intumescent flame retardants, and is more suitable for flame retardant polymer materials than traditional intumescent flame retardants.