Study On The Flame Retardant Mechanism Of Double Oii-Resistant Low-Smoke Halogen-Free Polyolefin Cable Compound

With the rapid development of urban transportation systems such as subway and light rail in China,the demand for locomotive cables has gradually increased.In order to reduce the risk of fire in railway lines,it is necessary to strengthen the safety of rolling stock cables.Therefore,the development of low-smoke halogen-free flame-retardant cable materials with excellent oil resistance,high temperature resistance,mechanical and electrical properties has become the development direction of locomotive and vehicle cables.In this paper,halogen-free flame-retardant polyolefin cable material was prepared by melting blending method.The effects of matrix resin composition,flame retardant,crosslinking agent and antioxidant on the mechanical properties,electrical properties,and flame retardancy of composites were studied.The composite materials were tested for mechanical,thermal aging,oil resistance,and hot elongation properties.The results show that the material has good mechanical properties,heat aging resistance,oil resistance,and high temperature creep resistance,when the flame retardants are uniformly dispersed in the matrix and closely combined.The mechanical properties show that the radiation cross-linking increases the tensile strength and decreases the elongation at break of the material.After thermal aging,the tensile strength of the material is slightly increased and the elongation at break is reduced;With the increase of the amount of crosslinking agent,the material's heat aging resistance is improved.The heat resistance aging effect of the 12~#sample antioxidant system is better,and the changes in tensile strength and elongation at break are only-4.2%and-24.4%,respectively.It's found that the higher the vinyl acetate(VA)content in the matrix resin,the better the oil resistance in oil resistance experiments.It was found that the crosslinking degree of the system increased with the increase of the amount of crosslinking agent by thermal extension experiment,and the high temperature creep resistance is better.Too much antioxidant will inhibit the cross-linking of materials and reduce the degree of cross-linking.The volume resistivity and breakdown field strength tests found that the large amount of flame retardant filling is easy to aggregate into large particles,the carrier concentration increases,the defects increase,which reduces the volume resistivity and breakdown field strength.The volume resistivity and breakdown field strength of the material increase as the degree of crosslinking increases.Too much antioxidant content will inhibit the cross-linking reaction of the material,the carrier mobility is larger,the volume resistivity and the breakdown field strength are reduced.In the process of thermal aging,the materials continue to be cross-linked,the binding force to the carriers is increased,the carrier mobility is reduced,and the resistivity is increased.The influence of aluminum hydroxide/magnesium hydroxide flame retardant system on flame retardancy of halogen-free flame retardant materials is also studied in this paper.Oxygen index of the material improves with the increase of flame-retardant.Compared with ATH single-filled flame-retardant system,thermal degradation temperature and thermal stability of ATH/MDH composites are improved.With the addition of ATH/MDH,the peak heat release rate and smoke production rate of materials are reduced,the fire performance index is improved,carbon layer structure is better,and carbon residue is up to42.74%.