Effect of silicone masterbatch on the electrical and flame-retardant properties of halogen-free cable materials

Halogen-free low-smoke flame retardant polyolefin cable materials were prepared by melt blending method with linear low-density polyethylene (LLDPE)/ethylene-vinyl acetate copolymer (EVA)/compatibilizer as matrix and aluminum hydroxide (ATH) as flame retardant. The effect of silicone masterbatch (SM) on ATH dispersion in matrix was observed by SEM, the melt index, density, electrical conductivity-temperature characteristics, breakdown field strength, and thermal stability were tested. The flame retardant performance of the samples was characterized by limiting oxygen index, vertical burning, and cone calorimetry. The results showed that the samples 6.58SM-EVA/LLDPE had the best comprehensive performance. Silicone masterbatch forms chemical bonds with polymers and fillers surface treatment agents to form a type of interpenetrating network structure, which increases the interface bonding force between the flame retardant and the matrix and introduces deep traps, raising the potential barrier and increasing the activation energy of the composite materials to 0.92 eV; the addition of silicone masterbatch optimizes the dispersion state of ATH and improves the internal structure of the samples, shortening the journey of free electrons and raising the dielectric breakdown strength of the composite materials. Silicone masterbatch, when heated in conjunction with ATH, decompose to form oxide solid solutions, which could catalyze and participate in the formation of carbon layers, generating stable carbon layers, reducing the dripping phenomenon during the combustion process and improve the flame retardant performance of the sample. After aging, samples are affected by thermal oxidation and thermal cracking reaction, causing partial molecular chain breakdown, deterioration of the interface between the filler and the matrix, led to the decrease of the electrical properties.