Study On Conductive Response Behaviors And Ceramifiable Properties Of Silicone Rubber Composites

The methyl vinyl silicone rubber/carbon black composites wereprepared by mechanical mixing. The piezoresistive properties,thermoresistive properties, piezoresistive stability and repeatability undercompression cycles, and resistance relaxation properties were studied.Furthermore, the relations between the structural changes of conductivenetwork and conductive response behaviors were investigated.The experimental results showed that the composites have remarkablepiezoresistive effect near the percolation threshold; the piezoresistiveeffect appeared a critical pressure with the increasing CB content; thepressure resistance repeatability and stability were improved byprecompression and increasing compression cycles. In addition, a novelpiezoresistive mathematical model derived from tunnel current theorywas put forward. And the mathematical model can give a very good fit tothe positive pressure coefficient effect and negative pressure coefficienteffect. In analogy to the stress relaxation mathematical model, theresistance relaxation mathematical model was obtained, and fit well. Thetransition temperature from positive temperature coefficient effect tonegative temperature coefficient effect at40oC, and the apparentactivation energy of the composites obtained by Arrhenius equationdecreased with the increasing CB content.Addition of certain OMMT enhanced the mechanical properties ofMVQ/CB composites. The study showed that with the increase of OMMTcontent, the piezoresistive intensity decreased; the piezoresistive stability and repeatability increased; the transformation temperature from positivetemperature coefficient effect to negative temperature coefficient effectshifted to low temperature.The ceramifiable silicone rubber composites were prepared bymechanical mixing. The effects of mica, low softening point frit andplatinum compound on the thermal stability, flame retardation andceramifiable properties of composites were investigated. The eutecticreaction between mica and SiO₂can lower the ceramifiable temperature.At800℃, the melting effect and liquid phase were observed around theedges of the mica plates. The abundant localized melting of mica particlesat the edges and bridging between mica plates and pyrolysis productswere formed after sintering at1000℃for30min, which produced moreglass phase products and improved the continuity and strength of residue.Addition of mica from0to100phr, the thermal stability of compositesfirstly increased and then decreased according to the TGA analysis; andthe limiting oxygen index value increased from21.5%to35.5%. TheMVQ/SiO₂/Mica composites filled with40phr mica had the optimalthermal stability, residue performance and processability.Addition of low softening point frit increased the liquid phaseingredient, remarkably improved the strength and continuity of theresidue, and effectively lowered the ceramifiable temperature. However,the metal ions in frit acting as catalyzers accelerate the degradation ofsilicone rubber so as to lower the thermal stability of the composites tosome extent. MVQ/SiO₂/Mica/Frit composites filled with10phr frit hadthe largest silicone rubber residue rate.The effects of platinum compound on catalytic crosslinking ofsilicone rubber molecular chains and the residue performance werefurther studied. When100ppm phr platinum compound blended with other fillers, the silicone rubber residue rate of MVQ/SiO₂/Mica/Frit/Ptcomposites increased from1.68%to11.7%, and notably enhanced thestrength and continuity of the residue. What’s more, the compositesproduced some black residue containing Si、O、C in sintering, and thethermal stability and flame retardation were improved.