Preparation Of High Efficient Flame Retardant System Based On PCS/Mg（OH）₂ And Its Flame Retardant Mechanism In Eva

With the technological development of flame retardants,the requirements for flame retardant materials with high performances are increasing,and more attention is paid to the impact of flame retardant materials on environment and health during the manufacture and applications.Under the background of low-carbon and sustainable development,the research of flame retardant system with high efficiency and environment-friendly characteristics has become a hot topic in the field of flame retardant.Magnesium hydroxide（MH）,as a traditional environment-friendly flame retardant,is widely used in the field of flame retardant polymers.Flame retardant ethylene-vinyl acetate copolymer（EVA）composites with MH are a kind of halogen-free flame retardant materials widely used in the field of wire and cable.However,due to the low flame retardant efficiency of MH,high loading levels are always the challenge in the application of EVA/MH composites.In facing the needs of wire and cable compounds with high-performances and diversified requirements of the application scenarios,as well as the low-carbon policy and environmental protection,the research was carried out to develop a synergistic system of MH with high flame retardant efficiency for EVA and solve the problems in balancing the flame retardant properties and mechanical properties.Hence,the high-efficient halogen-free flame retardant EVA composites were investigated by using MH as flame retardant and polycarbosilane（PCS）as ceramic synergistic in collaboration with flame retardant compounding,nano sheet enhancing and catalytic carbonization techniques.The thermal degradation process and the evolution of char structure were analyzed to reveal the flame retardant mechanism.The synergistic flame retardancy of MH was studied by taking PCS,aluminum hydroxide（ATH）,modified layered inorganic materials（CTAB-MMT and SDS-LDH）,transition metal oxides（Fe₂O₃and NiO）as synergistic flame retardants and by using oxygen index（LOI）as evaluation means.The results show that MH and PCS have better synergistic flame retardancy.EVA/MH/PCS composites with oxygen index up to 53.0 vol.%can be obtained by using 2 wt.%PCS and 48 wt.%MH.Compared with EVA/MH composites with 50 wt.%MH content,the oxygen index increases by 108%.The synergistic flame retardant effects of MH/PCS with modified layered inorganic materials and transition metal oxides were further studied.The efficient synergistic flame retardant effect of MH/PCS with Fe₂O₃and NiO are revealed.EVA/MH/PCS/Fe₂O₃and EVA/MH/PCS/NiO composites with oxygen index up to 65.0 vol.%and 60.0 vol.%were obtained.The combustion behaviors of different synergistic flame retardant EVA composites were studied by Cone.The results show that the synergistic flame retardant systems have lower heat release rate（HRR）and smoke production rate（SPR）,lower total heat release（THR）and increased total smoke production（TSP）during the combustion process.Compared with other synergistic systems,MH/PCS synergistic flame retardant system can better inhibit the behaviors of heat release and smoke release.Compared with EVA/MH,the p HRR of EVA/MH/PCS is reduced by 46%,the THR is reduced by 29%,and the TSP is increased by 45%.According to the fire risk parameters,the fire risk comprehensive index was calculated to comprehensively evaluate the effects related to heat,smoke and toxic gases during the combustion of the synergistic flame retardant systems.The research shows that EVA/MH/PCS/NiO and EVA/MH/PCS are of low fire risk with high comprehensive index,which show the characteristics of low heat release,low smoke release and low toxic gas release during the combustion,and the fire risk is low.The thermal degradation process and gaseous products of the flame retardant system were studied by TG-FTIR and GC-MS.The results show that the synergistic flame retardant systems present the similar degradation mechanism of EVA with two characteristic degradation stages during the thermal degradation.The introduction of ATH,modified layered inorganic materials and transition metal oxides leads to the degradation of the side chain at lower temperature while little effect is found on the degradation of the main chain.The synergistic effect of PCS and MH improves the thermal stability of the composite and inhibits the formation of acetic acid and acetic anhydride during EVA degradation.Compared with EVA/MH,EVA/MH/PCS has better thermal stability and generates more residual char by inhibiting the thermal degradation of the composite and the generation of hydrocarbon gas.A new gaseous product of CH₄is found due to the introduction of PCS.The structure of char is an important factor in affecting the flame retardant performances and combustion behaviors of flame retardant materials.A dense and continuous char can effectively inhibit the heat and mass transfer during combustion,and reduce the heat release rate and mass loss rate.Scanning electron microscopy（SEM）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）were used to study the char structure after combustion.The results showed that the char layer is mainly composed of magnesium oxide（MgO）particles.During the degradation of EVA,it interacts with MH,making the hexagonal lamellar structure of MH particles change into spherical structure.PCS has obvious migration phenomenon in the residual carbon.The content of Si element on the surface of char layer is much higher than that in the char layer.The crosslinking and degradation of PCS are in favor of the formation of a multi-layered char with dense surface and porous interior.The two-dimensional inorganic fillers,CTAB-MMT and SDS-LDH,inhibit the surface migration of PCS due to the nano layered structure.The content of Si element on the surface of char decreases,and cracks appear in the char structure.PCS inhibits the surface migration of metal oxides.The content of Si on the surface char of EVA/MH/PCS/Fe₂O₃and EVA/MH/PCS/NiO is more than that in the interior,while the contents of Fe and Ni are lower.Fe₂O₃and NiO promote the carbonization of EVA and the formation of a compact and continuous char.