| Natural rubber (NR), which is widely used in transport, buildingmaterials, petrochemical industry, mechanical industry and many otherfields, is closely related with people’s daily life. Unfortunately,flammable NR with a low limited oxygen index value (16~18%) as wellas molten droplets produced during the combustion could easily trigger afire and lead to rapid spread of the fire, which extremely restricts its wideapplication, especially in automotive and electronics/electrical appliances.So, to develop flame retarded NR composites is particularly necessaryand important. Intumescent flame retardant (IFR), which have higherflame retarded efficiency and belonged to environment-friendly flameretardancy, is widely used in the field of flame retarded polymers.Polyhedral oligomeric silsesquioxane (POSS) has inorganic-organichybrid architecture and their structure contains a stable inorganic Si-Ocore, which have high thermal stability. Therefore, the thermal stability ofpolymer would be improved by incorporating POSS onto macromolecularchain. And as one kind of silicon-containing flame retardancy, POSScould obviously reduce polymers’ flammability when incorporated withIFR. In order to enhance the thermal stability and flame retardancy of NR,we prepared flame-retarded NR by introducing POSS to natural rubberchain and adding physical fillers respectively. And the effects of differentfillers on intumescent flame retarded NR composites were also studied.Based on limited oxygen index (LOI), heat release rate (HRR), riskanalysis for fire disaster and thermal stability, combustion performance ofIFR/NR composites composed of different mass ratio of APP/MEL/PERwere studied and compared by LOI, CONE and TGA. The result showsthat the optimal ratio of intumescent flame retardant APP/MEL/PER was4/1/1, and the limited LOI could reach28.5%, and heat release rate,maximum average heat release rate, index of heat release and smokerelease all reached the minimum level.In order to improve thermal property of NR, the modified NR wasprepared by melt reactive blending through Brabender inner mixer and byfree radical reaction in solution respectively. The structure and POSS contents of modified NR were characterized by FTIR and ICP-OESrespectively. The result shows that POSS could graft on the nature rubberby reactive blending. The thermal properties of POSS/NR hybrids wereinvestigated by TGA and DSC. The presence of POSS improves thethermal oxidative degradation temperature between380-800℃, and theglass temperature (Tg) of composites were improved slightly in contrastwith natural rubber. The modified NR prepared by free radical reaction insolution was characterized by FTIR and TGA. The result shows thatPOSS could incorporate onto NR macromolecular chain. The thermalstability and the volume of residue at600℃were all considerablyimproved.Effect of other additives, such as expandable graphite (EG),aluminium diethylphosphinate (ADP), zeolite and POSS on flameretardancy and mechanical properties of intumescent flame retarded NRcomposites were investigated respectively. The results show that ADP,zeolite and POSS have synergistic effect with IFR, and there exists anoptimal ratio between each type of flame retardant synergist and IFR. Thesynergism of POSS is most effective; mechanical properties and flameretardancy were all enhanced by adding POSS into intumescent flameretarded NR composites. When using the same amount fillers, addingPOSS could obviously reduce HRR, THR, SPR and the release rate ofCO/CO2. POSS could volatilize in lower temperature and convert to SiO2in higher temperature. So it could lead to different thermal degradationstages for NR/IFR/POSS composites, excellence thermal stabilization ofPOSS can only be obtained in high temperature. |
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