Research On Properties Of APP/EG Synergistic Flame Retardant PE/EVA Composite Cable Material

Various functional fillers have significant influence on the properties of cable insulation and sheath materials,and how to obtain composite materials with excellent comprehensive properties by adjusting the composition and ratio of fillers has been widely concerned by the research community.In this paper,the compound doping and performance improvement of polymer are realized by melt blending.With polyethylene(PE)and ethylene-vinyl acetate copolymer(EVA)as matrix materials,ammonium polyphosphate(APP)and expandable graphite(EG)as flame retardants,and compounded with other additives,a series of PE/EVA based halogen-free flame retardant composite cable materials were prepared.The structure and structure of APP/EG synergistic flame retardant PE/EVA composite cable materials caused by different composition ratios of APP and EG were studied.The results show that PE/EVA materials with different composition ratios have been successfully prepared by melt blending.By comparing their tensile strength and elongation at break,it is found that the mechanical properties are the best when the ratio of PE to EVA is 2/8.The effects of adding APP or EG to PE/EVA matrix alone on the dispersion of filler,mechanical properties,flame retardancy and thermal stability of the composites were studied.The cross-sectional morphology of the composites was characterized.The results showed that APP and EG showed different dispersion states of blocky particles and lamellar particles in the matrix with island-like phase structure,and the continuous phase formed by EVA in the matrix was destroyed with the increase of the filler content of these two flame retardants.The extent of the deterioration of the mechanical properties of the composites caused by the addition of EG is higher than that of APP.However,the addition of APP or EG alone will make the flame retardant properties of the composites increase at first and then decrease.The total amount of flame retardant was 20wt%,and APP/EG synergistic flame retardant PE/EVA composite cable materials with different ratios were prepared by melt blending method.The effects of flame retardant ratio on the morphology,mechanical properties and flame retardant properties of the composite materials were studied.It is found that when APP/EG is 3/2,the limiting oxygen index of the composite reaches32.5 %,and it can reach the V-0 level of UL-94 vertical combustion standard,showing excellent flame retardancy.At the same time,under the flame retardant ratio,the composite also showed good mechanical properties,with the tensile strength of 8.450 MPa and the elongation at break of 850 %.Thermogravimetric analysis was used to study the thermal stability of the composites in nitrogen atmosphere.It was found that the addition of synergistic flame retardant with APP/EG ratio of 3/2 affected all the indexes of the composites.The initial decomposition temperature of 2 % reached343.69 ℃,the maximum thermal weight loss temperature reached 508.18 ℃,the residual carbon rate at 600 ℃ reached 15.90 %,and the maximum thermal weight loss rate decreased to 1.36 %/℃.In addition,the insulation performance of the composite material is also investigated in this paper.It is expected that the breakdown field strength,all of which can meet the use standard of cable materials.By studying the combustion behavior and char morphology of the composite,the mechanism of its superior flame retardant performance was analyzed.