Study On Structure And Flame Retardant Properties Of Ceramizable PE/EVA/MH/PCS Composites

Polyethylene(PE)and ethylene vinyl acetate copolymer(EVA)are one of the important insulating or sheathing materials in the field of wires and cables because of their excellent mechanical and insulation properties.Magnesium hydroxide(MH)is widely applied in halogen free flame retardant PE/EVA material to meet the requirements for environment-friendly and flame retardant insulation or sheath materials.However,due to the low flame retardant efficiency of MH,it needs to be added in a higher amount,which leads to the deterioration of the comprehensive performances of flame retardant materials and brings great difficulties to the design of cable materials.Polycarbosilane(PCS),a ceramic precursor material,is used as ceramic binder in the process of organic-inorganic transformation.MH/PCS with ceramicized carbon layer structure is designed to improve the flame retardant efficiency of the flame retardant and improve the flame retardant performance of the material.Therefore,PCS is used to cooperate with MH in flame retardant PE/EVA blends to study the effects of the microstructure of PE/EVA/MH/PCS on the flame retardant performance,combustion behaviors and insulation properties.The composition and phase structure of PE/EVA Blends were studied.The distribution structures of MH and PCs in PE/EVA Blends with co-continuous structure and sea-island structure were analyzed.The results showed that PCS dispersed evenly in two phases,while MH showed selective distribution structure.The structure of selective distribution of MH in EVA phase and uniform dispersion of MH in two phases could be obtained by adjusting the preparation method.The flame retardant performances,combustion behaviors and insulation properties of PE/EVA/MH/PCS composites with co-continuous and sea-island structure were studied.The results showed that PCS and MH had synergistic flame retardant effect,which improved the oxygen index of the composites,reduced heat release and mass loss,and promoted the formation of compact char layer.The composites with selective distribution structure had better flame retardant properties,while the composites with uniform distribution structure had better insulation properties.The effects of the amount of flame retardant in PE/EVA/MH/PCS composites on the flame retardant properties and char layer structure were studied.The results showed that the increase of the amount of flame retardant was favor of the formation of char layer structure with good barrier effect,which lead to the improvement of flame retardant properties.The condensed phase flame retardant mechanism of MH/PCS was revealed.PCS decomposed at high temperature and amorphous phase wrapped magnesium oxide particles formed,which contributed to the ceramic surface char layer and the internal residual carbon structure.