Influence Of Reconstruction Of Expangable Graphite Flame Retardant System On Flame Retardant And Smoke Suppression Of Silicone Rubber Foam

Silicone rubber foam once ignited,it will continue to burn and release a large amount of heat and smoke,limiting its application in cutting-edge fields.This paper aiming at the problems of low strength,poor compatibility,and insufficient carbon formation rate in the flame retardant of silicone rubber foams,three different EG flame retardant systems which using green,environment-friendly,and economical expandable graphite(EG)as carrier were constructed from molecular,nano,and micron scale by chemical grafting technology,coating technology,and self-assembly technology.Silicone rubber foams were prepared by using the three kinds of reconstituted flame retardant systems,and the effects of different EG flame retardant systems on the physical properties,mechanical properties,flame retardant,and smoke suppression properties of silicone rubber foams were analyzed and compared,the mechanism of flame retardant and smoke suppression of EG reconstituted flame retardant system were revealed.This study has important theoretical and practical significance for improving EG flame retardant system and developing new flame retardant silicone rubber foam materials.The main research results of this paper are as follows:(1)Using EG as carrier,hexachlorocyclotriphosphazene(HCCT),carbon fiber(CF),halloysite(HNTs),and chitosan(CTS)as reconstruction components,EG-g-HCCT,CF@A-171,and HNTs@CTS were prepared by chemical grafting,coating,and self-assembly.The reconstructed products were characterized by scanning electron microscopy(SEM),comprehensive thermal analyzer(TG),fourier transform infrared spectroscopy(FT-IR),and X-ray diffraction(XRD).Then three EG flame retardant systems(EG-g-HCCT,EG/CF@A-171,and EG/HNTs@CTS)were obtained by compounded the reconstructed products with EG.The expansion properties of EG-g-HCCT,EG/CF@A-171 and EG/HNTs@CTS were evaluated.The EG-g-HCCT flame retardant system was helpful to increase the expansion rate,while EG/CF@A-171 and EG/HNTs@CTS flame retardant system had inhibitory effect on the expansion rate.(2)EG,EG-g-HCCT,EG/CF@A-171,and EG/HNTs@CTS were applied to silicone rubber foam system.The combustion properties,flame retardancy,and smoke suppression properties of silicone rubber foam were studied.The test results of limiting oxygen index(LOI),vertical combustion meter,and cone calorimeter showed that the flame retardant performance of EG/HNTs@CTS was the best,followed by EG-g-HCCT,EG/CF@A-171,and EG.When the proportion of EG/HNTs@CTS is EG10wt%+HNTs@CTS5wt%,the LOI is 35.7%and the flame retardant grade reaches V0.Ignition time(TTI)decreased to 61S,peak heat release rate(PHRR),total heat release(THR),peak smoke production rate(SPR),total smoke production rate(TSP),CO yield,and CO2 yield of flame retardant silicone rubber foam were 20.40 kW/m2,19.6 MJ/m2,0.020 m2/s,9.3 m2/m2,0.003%,and 0.087%respectively,decreased by 70.51%,45.32%,47.37%,44.97%,50.00%,and 59.72%compared with the blank sample.(3)The physical and mechanical properties of the EG reconstituted flame retardant system/silicone rubber foam were studied.The results of physical properties indicated that the EG/HNTs@CTS had no significant effect on the physical properties of silicone rubber foam,the EG-g-HCCT flame retardant system could improve the uniformity of silicone rubber foam and lower its density,silicone rubber foam with EG/CF@A-171 flame retardant system had higher density and hardness.The results of mechanical properties showed that the EG/HNTs@CTS flame retardant system had the best effect,followed by EG/CF@A-171 and EG-g-HCCT.When the ratio of EG/HNTs@CTS was EG10wt%+HNTs@CTS5wt%,the tensile strength could reached to 190KPa,the elongation at break was 127.79%,and the compressive strength was 449KPa,which increased by 171.43%,27.04%and 103.17%respectively compared with the blank sample.(4)The flame retardant and smoke suppression mechanism of reconstitued EG flame retardant system was explored.Thermal decomposition process,carbon slag structure,carbon slag composition and thermal degradation volatile products of EG/silicone rubber foam were analyzed by TG,SEM,XPS and TG-FTIR.The results showed that the carbon formation of CTS could improve the compactness of the "worm"-like carbon layer.HNTs not only built a three-dimensional structure in the residual carbon,but also formed the ceramic structure of SiAlON,which improves the strength of carbon layer and flame retardant effect of EG.In the EG-g-HCCT flame retardant system,the existence of HCCT accelerated the fracture of the silicone-oxygen bond,promoted the formation of a three-dimensional network structure of the main chain of silicon oxygen,and improved the strength of the EG carbon layer.The presence of P and N elements improved the compactness of the EG carbon layer and improved the flame retardant performance of silicone rubber foam.It was mainly based on the condensed phase flame retardant mechanism,supplemented by gas phase flame retardant.EG/CF@A-171 flame retardant system formed a three-dimensional structure during combustion,inhibited EG expansion and migration,increased the strength of the carbon layer,and improved the flame retardant performance of EG,which was mainly based on the flame retardant mechanism of condensed phase.