Study On Pyrolysis Mechanism And Modification Of Wet Paper Based Friction Material

When the clutch is engaged,the friction heat causes the temperature of the friction pair to rise,and the components with poor heat resistance pyrolyzes and causes the heat to decline,resulting in the decrease of friction and wear performance and material failure.Nano materials such as nano-SiO₂ and carbon nanotubes have excellent thermal conductivity and/or heat resistance,which can improve the thermal degradation resistance of friction materials.In this paper,the pyrolysis characteristics of organic components of friction materials and the modification of nano particles were studied,which provided theoretical and practical basis for improving the thermal degradation resistance of wet paper-based friction materials.In this study,sisal fibers(SF),phenol resin(PR),Kevlar fibers(KF),friction powder(FP)were selected.Thermogravimetric analysis(TG),thermogravimetric infrared spectrometer(TG-IR)and infrared spectrum(FTIR)were used to analyze the changes of mass,volatile matter and solid residue during pyrolysis.The results show that the TG characteristic temperature of sisal fiber such as starting temperature,inflection point temperature and ending temperature are lower than the other three components.TG-IR analysis showed that when the temperature reached 200?,sisal fiber and friction powder released CO₂,phenolic resin began to release CO₂ and CH₄,aramid fiber did not pyrolysis.Based on Coats-Redfern(C-R)equation,the pyrolysis kinetic model of each component was established.The results show that the pyrolysis reaction conforms to the first-order reaction.When the heating rate is 10?/min,the activation energy of sisal fiber at 270?400?is 166.5 kJ/mol,that of phenolic resin at 500?640?is 77.7kJ/mol,that of friction powder at 500?640?is 82.6 kJ/mol,and that of aramid fiber at544?700?is 306.6 kJ/mol.Therefore,the thermal stability of the four organic components is sisal fiber<phenolic resin<friction powder<Kevlar fiber.In order to improve the heat decay resistance of sisal fibers,nano-SiO₂ and CNTs were used to modify sisal fibers.Firstly,the nano-SiO₂(particle size 266 nm)is deposited on the surface of sisal fibers by sol-gel method.When the amount of nano-SiO₂ is 60%,the temperature of the sisal fibers increases from 329.6?to 334.4?.SF@SiO₂ composite that is obtained by dipping of the maximum weight loss rate decreases from 9.25%/min to 5.65%/min,the initial pyrolysis temperature T_10%increases from 352.2?to 366.0?.And the thermal conductivity increases from 0.346 W/(m·K)to 0.526 W/(m·K).Secondly,the effects of CNTs deposition on sisal fibers and SF@CNTs composites of properties were investigated.When the deposition amount of CNTs is 2%,the results show that T_10%rises from 309.0?to 324.0?,and the maximum weight loss temperature rises from 360.0?to 360.7?.The SF@CNTs composites that are obtained by dipping of the maximum weight loss rate and T_5%are basically unchanged,T_10%increases from 330.0?to 337.0?,and thermal conductivity increases from0.355 W/(m·K)to 0.777 W/(m·K).