Research On Halogen-free Flame Retardancy And Foaming Properties Of The Composites Based On EVM

With the development of the technology and the improvement of the level ofpeople’s living, polymer materials have been used widely. But most of them are easy toignite under continuous heat, release some toxic gases and smoke, which cause the firejeopardizing to increase. So the study on the halogen-free flame retardant(HFFR)polymeric materials continue to be of great concern. In addition, rubber foamingmaterials have been widely used in packaging, heat insulation, shock absorption and insome other applications because of their good properties such as low density, lightweight, excellent heat/sound insulation and damping properties. In recent yearsethylene-vinyl acetate(EVM) rubber has been one of the popular rubbers, which hasexcellent heat/oil/weather resistant, filler acceptance, and easy to foam. Therefore,EVM has been used as the matrix to obtain the high-performance HFFR EVM/NBRcomposites with the high addition of inorganic flame retardant magnesium hydroxide(MDH). At the same time, the low density EVM foam which has fine pore structurewas made, with the addition of the peroxide as curing agent, the azodicarbonamide(AC)as blowing agent.The difference among three kinds of flame retardants (micro-aluminumhydroxide(ATH), micro-MDH and nano-MDH) on flame retardancy of the EVM/NBRcomposites was investigated by the limiting oxygen index (LOI),cone calorimeter andsome other measurement. It can be found that the three flame retardants at sameloading have no obvious influence on LOI. The addition of ATH can obviously prolongthe time to ignition (TTI). The micro-MDH system showed a better flame retardancyeffect than nano-MDH system in the later period of combustion.The effect of different loading of MDH, synergistic flame retardant zincborate(ZB) and fillers on the flame retandancy, thermal stability and mechanical properties of EVM/NBR composites have been also investigated in this paper. Theresults indicate that the flame retardancy of EVM/NBR vulcanizates is improved andthe fire jeopardizing is dramatically reduced due to the addition of MDH. With theamount of MDH increasing, the peak of heat release rate(PHRR), the total heat releaseand mass loss deduced, the thermal stability of material increased, while the elongationat break was dramatically declined. The content of flame retardant MDH reached to180phr to gain the highest fire performance index(FPI) and the best flame retardance.The adding of zinc borate can decrease the PHRR, extend the TTI, which is beneficialfor improvement of flame retardancy. Moreover, the use of zinc borate just cause aslight loss of mechanical properties. For the EVM/NBR composite with140phr MDH,the content of zinc borate reached to20phr to gain the best synergistic flameretardance effect. The addition of silica, talc and CaCO3would decrease the LOI of thecomposites and affect the strength of charring layers in the combustion process.Finally, the effect of processing parameters, the match between foaming agent andcuring agent, the difference of fillers on foaming behavior, pore quality and physicalproperties of foam were studied by the moving die rheometer (MDR),stereomicroscope, rubber processing analyzer (RPA) and some other measurements.Also we explored the influence of foam density on compression behavior and dynamicmechanical properties of EVM foams. The results exhibited that the overfilling intomould is beneficial for foams to obtain good physical properties and pore quality. Alsowe can obtain the optimum adjustment of processing parameter and formula for lowdensity EVM foams: cure temperature of165~170℃, time of4~6min, higher pressure,DCP content of6~8phr, AC content of3.5~7phr. And it can be found that there is agood correlation between foam density and tensile strength. The higher the foamdensity, the better tensile strength was. The EVM foam filled with silica showed thebetter pore quality than the ones with carbon black. From the compressive stress-straincurve analysis, with the foam density increasing, the linear elastic region is graduallynarrowed. Besides, when the foam density increased, the storage modulus of foammaterial gradually enlarged in high-elastic state.