Preparation Of Nano-al₂ O₃ Modified Ptfe Composites And Investigation On Friction And Wear Properties Of Ptfe Composites.

As an ideal self-lubricating material, Polytetrafluoroethylene (PTFE) is of very low friction coefficient, high thermal stability and chemical stability. However, due to the poor thermal mechanical properties and the high wear rate, PTFE can not be used as anti-wear material alone. For the small-dimension, volume, surface and cooperative effect, nano-Al₂O₃ particles are widely used as fillers in reinforcing the polymer matrix to form high performance composite materials. However, the effects of reinforcement were largely limited by the high surface energy and the aggregated structure of the nano-particles, especially in mechanical mixing process. The targets of this thesis are aimed at eliminating the aggregation tendency of the nano-particles and improving the compatibility between the nano-particles and PTFE matrix. The composites of the modified or unmodified nano-Al₂O₃ particles and PTFE matrix were prepared following the mechanical mixing, molding and sintering process. The influences of the nano-particles on the hardness, the friction coefficient and the wear scar width of the composites were investigated. The effect of agglomerate structure and the possible wear mechanism with the introduction of the nanometer particles were discussed.Firstly, two crystal tapes of five dimension size of nano-Al₂O₃ particles were surface-modified by using silane coupling agent KH570. The results show that the hardness of the obtained PTFE composites was improved after filling with nano-particles. The friction coefficient of PTFE composite materials filled withαcrystalline nano-Al₂O₃ is larger than that ofγcrystalline nano-Al₂O₃; the wear of PTFE composite materials filled withαcrystalline nano-Al₂O₃ is less than that ofγcrystalline nano-Al₂O₃.Secondly,αcrystalline nano-Al₂O₃ particle of 70nm was treated with KH570, and then grafted with BA polymer and HFBA polymers separately. The corresponding PTFE composites of these three surface-modifiedαcrystalline nano-Al₂O₃, including the untreated nano-Al₂O₃, were prepared separately and their tribological properties were studied. The results show that the tribological properties of PTFE composite materials filled with polymer grafted nano-Al₂O₃ is better than that of those PTFE composites filled with the KH570 surface-modified and untreated nano-Al₂O₃.Thirdly, PTFE composites filled with calcium sulfate (CaSO4) whisker alone and in combination with the nano-Al₂O₃ particles were prepared. Their tribological performances were also studied. The results show that CaSO4 whiskers are effective in improving the wear resistant of the corresponding composites and the large-scale fragmentation of PTFE matrix was prevented. The anti-wear properties of PTFE composites filled with CaSO4/nano-Al₂O₃ combination fillers is better than that of PTFE composites filled with CaSO4 whisker alone.