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 V[sbnd]0. 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 C[dbnd]C and P[sbnd]O[sbnd]C 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.