Research On Phenolic Resin Matrix Friction Material Added Carbon Nanotubes

The selection of reinforcement is crucial to friction material.The traditional asbestos for being harmful to human,metal fiber for high density and cor:rosion,hybrid-fiber for high cost,are not ideal.Carbon nanotubes(CNTs)with excellent mechanical and thermal performances provide a new way for enhancement.In this research,multi-walled carbon nanotubes(MWCNTs)were added into phenolic resin(PF)for combination of their advantages to develop out new practical PF matrix friction material.PF matrix friction materials added MWCNTs were prepared via dry mixing of ball-milling and hot press,and their frictional behavior was investigated on Chase-type friction tester.First,the composite with purified MWCNTs was compared with the without MWCNTs on friction and wear properties.Second,the surface of MWCNTs was modified by sulfonation,dipping of silane coupling agent KH-550 or coverage of sodium dodecyl sulfate to improve dispersion and the interface compatibility with PF.These MWCNTs were added into PF by dry or wet mixing of ultrasonic oscillation in ethanol,and specimens were prepared.Then the effect of surface state and content of MWCNTs on mechanical(hardness,impact strength)and tribological properties were analysed contrastively,whose mechanism was discussed through the characterization for surface states of MWCNTs by Fourier transform infrared spectrometer(FTIR),observation for micro-morphology by field emission scanning electron microscope(FESEM),and measurement for heat resistance and thermal conductivity by simultaneous and laserflash thermal analyzer.The results of research were shown as follows.The friction performance of PF matrix friction material added MWCNTs by dry mixing was better than the without MWCNTs,and so was the material added MWCNTs by wet mixing than the by dry.When the content of purified MWCNTs was 0.4 wt%,the friction coefficient(μ)of the by dry mixing was 0.25 as large of 0.07 as the without MWCNTs,and the wear rate(V),7.34×10-8 cm3/(Nm),was decreased by 25.3%.The μ of the by wet mixing was 0.35 as large of 0.1 as the by dry,and V,6.32×10-8 cm3/(Nm),was decreased by 13.9%.And the comprehensive friction properties of PF matrix friction materials with modified MWCNTs were better than the with purified MWCNTs.The recommending content of MWCNTs ranged from 0.4 to 0.8 wt%for mechanical performance,and the materials tended to brittle fracture with the increase of MWCNTs content.For tribological properties,the PF matrix friction material added 0.4 wt%sulfonated MWCNTs by wet mixing was the best,whose μ and V were 0.32 and 0.84×10-8 cm3/(Nm)respectively,and the frictional stability and fade resistance were good.The material added MWCNTs effectively converted damaging shear into "compaction"because of the decreased hardness of surface layer and high impact strength to increase the compactness of worn surface,shorten the distance and largen the contact area between sliding surface and counterpart,which in return was favorable to the exertion for lubrication and buffering of MWCNTs.Besides,MWCNTs improved the heat resistance and thermal conductivity of material,so that could protect the worn surface of materials.The dispersion of modified MWCNTs and interface compatibility with PF were better than the purified MWCNTs and the hardness of the by wet mixing was smaller,which suggested that the modification and adoption of wet mixing were more beneficial for PF matrix friction material added CNTs.