Effects Of Environmental Temperature And Humidity On The Tribological Properties Of Filled PTFE Three Layer Composites

In various applications, temperature and humidity have great influence on the tribological properties and the service life of polymer based composites, because the polymer based composites are special sensitive to temperature and humidity. In this thesis, the tribological properties of polymer based composites were investigated systematically in different temperatures and humidities. The friction and wear mechanisms of the polymer based composites in different temperatures and humidities were also analyzed in detail. The results are good references and of great guidance significance for the research and engineering applications of polymer based composites.The filled PTFE three layer composites (FPLC) were selected as the study materials, and a kind of FPLC containing PI was self-prepared (named P02), and a commercial FPLC material without PI with high-performance (named P01) was chosen for comparison. In several environmental temperatures of 20℃, 60℃, 100℃, 150℃, 200℃, 250℃, 300℃, the tribological properties of the FPLC samples were studied. The results showed that: the friction coefficient of two samples are decreased with the temperature increased, and above 200℃, the friction coefficient decreased obviously. At 20℃, the wear of the two samples was unusual and slightly higher, which is related to the change of the crystalline form of PTFE at 19℃. After that, the wear increased significantly with the temperature increased. Though According to the test results, the P01 had slightly better performance than the P02. However, P02 showed stable wear at high temperatures, which indicates PI could improve the tribological properties of composites at high-temperatures. At different temperatures, the friction and wear mechanisms are as follows: the wear was abnormally slightly higher at 20℃due to the crystalline change of PTFE at 19℃, and the main wear mechanism is adhesive transfer + fatigue wear. From 20℃to 200℃, being normal wear, the main wear process was normal adhesive transfer + fatigue wear + small amount of peeling off. From 200 to 300℃, the main wear was a large number of adhesion and transfer with heavy deformation. Above 300℃, the wear mechanism is a large number of adhesion and transfer with melting and deformation of the composites. The tribological properties of the tested composites were also carried out in different humidities of 15%, 45%, 60%, 75%, 100%. The test results showed that in the humidity of 15% ~ 75%, the friction coefficient of composites increased with the humidity increases. At the humidity of 100%, the friction coefficient reduced significantly. With the increase of humidity, the wear of the composites decreased at first and then increased, the smallest wear appeared in the humidity was 45% or 60%, which is close to the atmospheric humidity during the test. The comparison of the results of P01 and P02 showed that P01 had slightly lower coefficient of friction, but its wear was larger, indicating its larger humidity sensitivity. And the results also revealed that PI is helpful to improve the wear stability of the composites in different humidities. The observations and analyses showed that the main wear mode is fatigue wear in different humidities. The existence of water vapor, on the one hand, has somewhat lubrication, on the other hand, could produce a negative impact to the matrix structure because of the water absorbance of semi-crystallines in the matrix and the fillers. Therefore, in low humidities, with the increase of humidity, the lubrication became significant, thus reducing the wear, but weakens the formation of transfer film, as a result, the coefficient of friction did not reduce. In high humidities, with the increase of humidity, the role of water-absorbance will cause obvious damage to the polymer structure, so it will increase the wear. At humidity of 100%, the lower friction coefficient maybe related to the lubrication of water in the interface.Our research obtains the effect rules of environmental temperature and humidity on the tribological properties of the FPLC, which had a certain significance on the development of high-performance FPLC. In addition, the effects of environmental temperature and humidity on the wear mechanism of FPLC need to be further studied.