Study On Friction And Wear For The System Of Carbon Nanotube And Bismaleimide

Bismaleimide (BMI) is a kind of high-performance resin with high specific strength, high specific modulus ratio, excellent insulation and good heat resistance to and good anti-corrosion, which meets the new needs in the fields of aviation and astronavigation, electronic devices and also nuclear industry. However, the tribological study of this kind of resin is quite scarce, which is related with the final loss and failure of the material. In order to impeove this properties of BMI resin, two schemes are proposed to reduce the friction and wear of the resin:firstly, prepare bismaleimide nanocomposite solid lubricant to realize lubrication in nano-scale; secondly, add nano-lubricant into the contacting surface between BMI resin and the anti-wear metal to reduce friction and wear of the system.Firstly, combining the excellent thermal, mechanical and also lubricating properties of carbon nanotube with the wonderful properties of advanced BMI resin, MWCNTs/BMI nanocomposite has been prepared in order to reduce friction and wear of the material. For the further study of this nanocomposite to reduce friction and wear of the material, excluding the environmental effects (such as temperature and humidity), several main factors have been found out and studied.Using carbon nanotubes with different slenderness ratios to prepare MWCNTs/BMI nanocomposite, it is found that nanocomposite using MWCNTs with larger slenderness ratio processes lower friction coefficient and wear rate. However, the effect of the slenderness ratio of MWCNTs on the friction and wear of the composite is far less than the effect of functional groups attached to MWCNTs. When carbon nanotubes are aminated, the tubular structure is damaged and the friction coefficient decreases.The friction and wear of MWCNTs/BMI nanocomposite is also related with the crosslinking degree of the resin matrix. When carboxyl groups are attached to carbon nanotubes, the carboxyl groups can accelerate the curing of the resin and increase the crosslinking degree of the resin. And this kind of strengthening for the matrix is favored by the reduce of the friction and wear of the composite.With everything under the same circumatance, it is the most efficient method to improve the tribological properties of MWCNTs/BMI nanocomposite through improving the interface of the composite. Nanocomposite prepared with allyl bisphenol A modified carbon nanotube shows the best tribological properties with only one quarter of friction coefficient and one half of wear loss rate to the composite with unmodified carbon nanotube, which is related with the best dispersing state and best interfacial adhesion.Field emission scanning electronic microscope (FESEM) and dynamic mechanic analysis (DMA) are adopted to analyze the worn surface and wear mechanism of the composite. The factors mentioned above will all affect the worn surface of the material but the interfacial factor plays the key part. The addition of original carbon nanotube into the BMI resin can change the fatigue mechanism of the pure BMI resin with large numbers of cracks and flaws to adhesive mechanism with many roll marks. The addition of modified carbon nanotube into the BMI resin can change the mechanism to abrasive wear mechanism with regular straight grooves on the worn surface. When the worn mechanism meets the mechanism of abrasive wear mechanism, the relationship between wear rate and microhardness is as follows: dm/dl=-0.01498+0.0059/H, which means the microhardness can be the simple criterion of wear loss rate:the higher the microhardness, the lower the wear loss rate and also the better wear resistance of the material.Secondly, stearinic acid modified carbon nanotube dispersed in parafin oil can form the uniform lubricant between the BMI resin and steel anti-wear system. The friction coefficient is reduced significantly and the width and depth of the worn mark are also decreased. The modified carbon nanotube displays the effect of micro-bearings on the contact surface to reduce friction and wear. However, small amount of carbon nanotubes are found to insert into the surface of the resin and micro scratches are formed.In order to reduce these micro scratches on the worn surface, hydrolyzed styrene-maleic anhydride co-polymers are used to modify carbon nanotubes with tough carbon nanotubes as core and soft polymer as shell and dispersed in paraffin oil in spheral shape. This core-shell structured carbon nanotube can reduce the friction and wear of the system at low concentration and low contact temperature for the protecting film formed on the steel ball. However, at high carbon nantube concentration, the residue carbon nanotube with polymer soft shell interacts with the BMI resin, which will accelerate the formation of defects of the surface and deteriorate the friction and wear of the system.