Study On Halogen-Free Flame Retarded Nanocomposites Of Ethylene-Vinyl Acetate Copolymer

The development of nano technology and nanocomposite materials provides a new perspective for the development of flame retardant science and technology.Therefore,it is an important research area to improve the flame-retardant properties of the polymer by introducing nano flame retardant,so as to prepare flame retardant polymeric composites with better comprehensive properties.Montmorillonite nanocomposites?MMT?have good thermal stability,especially the nano-dispersed montmorillonite layer,which has excellent gas barrier effect and flame retardant effect.The effects and mechanism of MMT,Sol-Gel Silica and ammonium polyphosphate?APP?coating with TiO₂ on properties of ethylene-vinyl acetate copolymer?EVA?/aluminum hydroxide?ATH?composites were investigated.Meanwhile,the effect of hydromagnesite?HM?on performance of EVA was studied.The main research works were as follows:?1?The effect of organic modified montmorillonite powder?OMMT?and its montmorillonite ethylene-butyl acrylate masterbatch?OMMT-MB?on property of EVA/ATH was compared for the research of OMMT's adding method.The tensile strength of EVA/ATH with addition of OMMT powder was significantly higher than that of OMMT-MB.The initial thermal decomposition temperature of EVA composites increased by 8?and the temperature of the first thermal decomposition peak was delayed by about 14?,which means that the thermal decomposition process is delayed and the thermal stability is improved.The ignition time?TTI?was delayed and the heat release decreased during combustion.The compatibility between EVA and OMMT is better than that of EBA and OMMT-MB,which was in accordance with the simulation results and the micro-morphological characterization results.With the improvement of compatibility,the dispersion distribution of MMT is more uniform,and the exfoliated degree is improved.?2?The low cost of montmorillonite containing Ca²⁺?Ca-MMT?and OMMT were compared.The tensile strength of EVA/ATH with addition of Ca-MMT was significantly higher than that of OMMT.The decomposition of the second phase was delayed.Heat release reduced and fire performance index?FPI?increased significantly.Ca-MMT improves the comprehensive properties of EVA/ATH composites because of the exfoliation of Ca-MMT which was conducive to barrier effect and the catalytic effect of calcium ions to promote the charring.?3?The preparation method had significant effect on the morphology and properties of EVA nanocomposites.Two step extrusion method can improve the mechanical properties,the heat release behavior and the carbon layer quality of the high filled EVA composites with MMT.?4?The effect of HM and OMMT on performance of EVA was studied.The addition of HM decreased the initial decomposition temperature and slowed down the decomposition rate of EVA composites obviously in nitrogen or air atmosphere.Besides,the addition of OMMT could delay the thermal decomposition of EVA.Thermal oxidation leads to decomposition of pure EVA in advance,but had little effect on EVA composites with HM and OMMT,which showed that HM and OMMT could inhibit the decomposition of EVA effectively and play a role in reducing the thermal degradation rate and reducing gas release.The adding of HM could increase the LOI values of EVA composites.In addition,EVA/55%HM/5%OMMT reached V-0 classication in the UL-94 test.The THR,MLR and TSP of the EVA/HM composites decreased obviously with the increase of OMMT content.All the evidences indicated that the addition of OMMT could make the carbon layer denser.Furthermore,the internal residual carbon formed fluffy sponge structure similar to the non decomposed polymer,which was benefit for HM to release non flammable gas and to dilute combustible gas.?5?Inorganic high filled EVA nanocomposites based on sol-gel reaction technology was investigated.The heat release of EVA composites reduced significantly and carbon residue was more compact and complete with the addition of Sol-Gel.The surface temperature of EVA composites was significantly lower using Sol-Gel to replace HM,indicating that the uniformly distributed sol-gel SiO₂ could promote the formation of carbon.The addition of Sol-Gel significantly reduced the amount of carboxylic acid and aliphatic hydrocarbons released from the thermal decomposition of EVA composites.The interaction between Sol-Gel and EVA chain led to the weakening of EVA van Edward force and the reduction of the complex viscosity,which is helpful to improve the fluidity of EVA composites in the process.?6?In situ APP-nTiO₂ had better dispersibility and could improve its compatibility with EVA matrix.Both the tensile strength and elongation at break of EVA/ATH/APP-nTiO₂ were improved.The EVA/ATH/APP-nTiO₂ composites reached V-1 classication in the UL-94 test and the TSP decreased obviously.Studies on the char residues showed that the presence of APP-nTiO₂ enhanced the char-forming behavior of EVA during combustion.More dense and isolated char was formed,which could protect the internal organic structure from damage and prevent or delay the release of combustible gas with small molecules.EVA substrate was protected,which was also related to the formation of titanium pyrophosphate.