Tribological Properties Of High Performance Fabric Reinforced Polytetrafluoroethylene Composites

Polytetrafluoroethylene (PTFE) is an ideal solid lubricating material with excellent self-lubricating property, chemical stability and temperature tolerance. But the mechanical properties, bad capacity and wear resistance of pure PUFE are very poor, restricting its application. The inclusion of various fillers or reinforcing elements to PTFE is a common way to improve its properties. The tribological behaviours of PTFE composites are widely studied by the researchers. Fibers, nano materials and micron particles are frequently used to form PTFE composites in the researches. But there are still many problems. The mechanical properties, load capacity and interfacial adhesion of traditional PTFE composites are still poor. Furthermore, improvements are usually achieved at the cost of the declination of the excellent properties of PTFE.Compared with traditional fillers or reinforcing elements, the structure ordering, stiffness and integrity of fabric are much higher. Fabric reinforcement can improve the mechanical properties and load capacity of the composite significantly. Furthermore, self-reinforcement can improve the interfacial adhesion of the composite effectively because of the same chemical component. The properties can also be improved without the inclusion of other material so that the excellent properties of the material can be restored as much as possible.With those in mind, three kinds of high performance fabric, i.e. carbon fabric, aramid (Twaron) fabric and PTFE fabric were used to reinforce PTFE in this dissertation. The fabrication process of the composites was studied. The influences of fabric content on the mechanical and tribo logical properties were researched. The efficiency of fabric reinforcement and short fiber reinforcement was compared. Various modification methods such as fabric surface treatment and nano particle inclusion were used to further improve the tribological properties. The friction and wear mechanisms of the composites were discussed based on the observation and analysis on the fabric surface, worn surface, wear debris and tensile failure surface.The main results are summarized as follows:1. Carbon fabric, aramid fabric reinforced PTFE composites and PTFE homocomposites with a certain range of composition were fabricated succesfully with a dispersion impregnation technique and the composition can be controlled accurately. The mechanical and tribological properties of the the composites were very excellent. The compositions influenced the mechanical and tribological properties of the composites a lot. The comprehensive performances of the composites with medium fabric content were the best.2. The tensile strength of the composites were much higher that that of traditional PTFE composites. Carbon fabric reinforcement was the most effective on improving the tensile strength of PTFE and the highest value was387.7MPa. The friction coefficients of the composites were very low. Compared with corresponding short fiber reinforced PTFE composites with a traditional technical process, the wear resistance of three fabric composites was much superior. Aramid fabric reinforcement was the most effective on the wear reduction. Fabric self-reinforcement improved the mechanical and tribological properties of PTFE significantly without the inclusion of other material, so that the excellent properties of PTFE were restored as much as possible.3. Proper surface treatment of carbon fabric and aramid fabric changed the surface morphology and chemical component, improved the interfacial adhesion and finally improved the tribological behaviours of the composites. The inclusion of nano-TiO2also improved the interfacial adhesion and influenced on the band structure of the matrix, resulting in the improvement of the wear reistance. Combined surface treatment and inclusion of nano-TiO2had cooperative effects on improving the wear resistance of the composites. The inclusion of nano-TiO2improved the wear resistance of PTFE fabric homocomposite to some extent, but the improvement was limited. 4. In three fabric reinforced PTFE composites, continuous net structure of the fabric supported the load and influenced the formation of crystalline band in large scale. The two effects resulted in the excellent tribological behaviours of the composites and the load-supporting effect was more important. Proper composition was beneficial to the two effects of fabric. Proper fabric surface treatement and nano-TiO2inclusion improved the interfacial adhesion and were also beneficial to the load-supporting effect. Nano-TiO2inclusion further influenced the band structure of the matrix and inhibited the destruction of the crystalline structure in large scale.5. The different failure behviours of the three fabrics and their fibers influenced the load-supporting effect of corresponding fabric a lot. The brittle fracture of carbon fiber had a bad effect on the load-supporting effect of carbon fabric. The high strength and tenacity of aramid fiber resulted in the good load capacity of aramid fabric reinforced PTFE composites. The lowest strength and band structure of PTFE fiber resulted in the worst load-surpporting effect of PTFE fabric.Based on the studies on the tribological behaviours and mechanisms of three kinds of high performance fabric reinforced PTFE composites, this research expands the research field of tribolgy of PTFE composites and deepens the understanding of rules of wear and failure of fabric reinforced PTFE composites. The results of this research widen the basic date and theoretical understanding of polymer tribology and can instruct the development of high performance self-lubricating composites.