Preparation And Study On Properties Of Ablation Resistant And Ceramizable Silicone Rubber Composites

In the process of pyrolysis,ceramifiable polymer composites can form a dense ceramic structure,which can effectively cut off the spread of O₂,heat transfer and reduce the actual temperature of internal materials.It has a good flame retardant effect.Ceramifiable polymer composites often used as thermal protection layer of wire and cable,and have broad application prospects.On the basis of others,we used methyl vinyl silicone rubber?VMQ?as matrix,fumed silica as reinforcing filler,muscovite as ceramic filler,low melting point glass frits as fluxing agent,thermosetting boron phenolic resin?BPF?for heat resistant fillers,good flame retardation ceramifiable silicone rubber composites were abtained with these fillers.Firstly,two different softening point glass frits A and B were choosed as fluxing agent.They were used to prepare muscovite/silicone rubber composites by physical blending method.The mechanical properties,structure,thermal decomposition properties and ceramic mechanism of both muscovite/silicone rubber composites were studied.The results show that tensile strength of both composites at room temperature is 3⁴MPa.Flexural strength of composites after pyrolysis is 0.5⁴.5MPa between 600?and 1200?,and glass frits is contribute to integrity of the structure.SEM results reveals that glass frits A can form more liquid bridge phase during pyrolysis,which is contribute to form a more continuous dense ceramic structure.Thermal pyrolysis properties was analysised by TG,it reveals that glass frits which contain more metal oxide can accelerate decomposition of silicone rubber,so it is necessary to control the amount of glass frits,and the amount of glass frits in 20phr is appropriate.Furthermore,the effect of the glass frits A is more effective than glass frits B.XRD results show that glass frit A is contribute to form potassium aluminum silicate?K₂O·Al₂O₃·6SiO₂?during pyrolysis,which has a positive effect on forming ceramic structure.In order to further enhance the strength of ceramic residue of muscovite/silicone rubber composites after pyrolysis,thermosetting boron phenolic resin was selected as heat resistant filler basing the above study.The curing properties,mechanical properties,ablation resistance,thermal properties,morphology and ceramic mechanism were studied.The results show that boron phenolic resin can delay vulcanization of silicone rubber,but it can increase the crosslinking point of silicone rubber and enhance cross link density in the thermal curing process.The tensile strength of the composites is increased from 3.33MPa to 5.61MPa,and the elongation at break is decreased from 170%to 85%when the content of boron phenolic resin vary from 0 to 40phr.Addition of boron phenolic resin can improve ablation resistance of muscovite/silicone rubber composites,and flexural strength of the pyrolysis products is also promoted,and the flexural strength of BPF40 after pyrosis at 1200?can reach to 11.25MPa.TG results also show that addition of boron phenolic resin can delay the decomposition of silicone rubber and increase its thermal stability.The microstructure of pyrolysis products was observed by SEM,it reveals that addition of boron phenolic resin can help to form more continuous structure,the resuides have a good combation between layers and form a monolithic ceramic structure.Through analysis and comparison,addition of boron phenolic resin in 30phr is more appropriate.Using XRD to analysis phase structure of pyrolysis products,it is found that boron phenolic resin can help to form SiC ceramics and more liquid phase in the pyrolysis products,in this way the fire resistant performance of muscovite/silicone rubber composites is improved.