Tribological Properties Of Polytetrafluorethylene And Polyimide Modified With Nanometer Particles

Inorganic nanometer particles shows small-dimension, volume, surface and cooperative effect, once they are blended with polymer to make nanocomposites, then polymer/inorganic nanocomposites will have some unique properties. Therefore, it has become a focus in tribology research field to modify tribological properties of polymer through blending with nanometer particles. Until now, however, it has not been studied systemically about nanometer particles modifying tribological properties of polymer. Especially, it has not been reported about the effect of category, shape, size and surface properties of nanometer particles on agglomerate structure and tribological properties. Hence, it is important in this paper to systemically study nanometer particles fillers' modification on tribological properites of polymer.First, we took polytetrafluorethylene (PTFE) as the matrix, which has good tribological properties and has been studied widely and sufficiently, and fiber-like attapulgite (AT) and high-hardness ultrafine diamond (UFD) as fillers. PTFE/AT and PTFE/UFD composites were made by conventional methods, and we investigated the effects of pre-treatment and dispersive methods of nanometer partices on agglomerate structure, mechanical and tribological properties of PTFE composites.In addition, for the permission of adding some agents containing water to the synthetic reaction of polyimide, we made polyimide/SiO₂ (PI/SiO₂) nanocomposites with different size SiO₂ (diameter ranging from 50 to 500nm) by sol-gel reaction. The polyimide/fiber-like attapulgite (PI/AT) and were prepared by in-situ polymerization. We compared the two systems and studied effects of the size and shape of nanometer particles on mechanical and tribological properties of amorphous composites.On the basis of the tribological rules of PTFE and PI nanocomposites concluded above and with the aid of SEM, TEM, EDS, FT-IR, DSC, and so on, we studied themorphology of composites matrix, debris and wear track, and discussed the effect of agglomerate structure and the possible wear mechanism with the introduction of the nanometer particles.There are some innovative conclusions below:1) When the content of AT in PTFE matrix was less than 5wt%, there was no variation of friction coefficient, but the wear rate of PTFE composites was 1-2 orders of magnitude less than that of pure PTFE and the crystallity was improved 10%²0%. The purified AT by acid and thermal treatment was superior to AT untreated in enhancing the wear rate of PTFE.2) 5wt% globular ultra-fine diamond (UFD) particles could obviously improve 10-20% in the crystallity degree and decreased 1-2 orders of magnitude in the wear rate of PTFE/UFD composites, but its effect was less effective than fiber-like attapulgite nanometer particles.3) As for PTFE, one possible reason that may account for the decreasing wear rate is that the crystal nuclear effect of nanometer filler was helpful to form smaller crystal units of PTFE, which decreased frictional failure unit of composites. Moreover, AT was superior to ultrafine diamond in decreasing wear rate of PTFE, and it can be explained by the thermal chemical action between AT and PTFE, which was helpful for transfer films exhibiting more reducing-friction effect.4) PI/SiC>2 nanocomposites were prepared successfully by sol-gel reaction. As the content of nanometer SiC>2 was less than 10wt%, the tensile strength and elongation increased 30-50% and 200%³00% respectively. There was no obvious variation in the friction coefficient of the PI/SiC>2 nanocomposites, but wear rates changed remarkably with the different content and the different size of SiC>2. The wear rate of PI nanocomposites was improved 50-70% when diameter of SiC>2 in PI matrix was 80nm.5) PI/AT nanocomposites were prepared successfully by in-stiu polymerization. When nanometer AT content was less than 5wt%, the tensile strength and elongation of the PI/AT nanocomposites increased 10% and 100% respectively. The friction coefficient and wear rate of PI/AT nanocomposites decreased 10-30% and 70-80% respectively in comparsion.6) As for amorphous PI, fiber-like AT was better than globular SiO2 in improving the wear rate of PI. The reason can be that fiber-like nanometer...