Synergistic modification of the tribological properties of polytetrafluoroethylene with polyimide and boron nitride
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Synergistic modification of the tribological properties of polytetrafluoroethylene with polyimide and boron nitride Chaojie XIE, Kejian WANG* College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing 100029, China Received: 29 April 2020 / Revised: 01 July 2020 / Accepted: 11 July 2020
© The author(s) 2020. Abstract: Polytetrafluoroethylene (PTFE) blended with polyimide (PI) and filled with boron nitride (BN) is prepared through cold pressing and sintering for composites with remarkable wear resistance and reduced coefficient of friction (COF). The characterizations show that BN and PI at different levels, improve the hardness, dynamic thermo-mechanical modulus, thermal conductivity, and tribological properties of PTFE. PI boosts the dispersion and bonding of BN in PTFE. In dry sliding friction of a block-on-ring tribometer, the wear rate and COF of 10:10:80 BN/PI/PTFE reduce to almost 1/300 and 80% of those of pure PTFE, respectively, as the wear mechanism transition from being adhesive to partially abrasive. This occurs only when the additives BN and PI induce a synergistic effect, that is, at concentrations that are not higher than ca. 10 wt% and 15 wt%, respectively. The obvious agglomeration at high percentages of added PI and severe conditions (400 N and 400 rpm) induce strong adhesive failure. The variations in the tensile properties, hardness, crystallization, and microstructure of the composites correspond to different effects. The multiple parameters of the plots of wear and friction are transformed into their contour curves. The mechanism transition maps aid in understanding the influence of various test conditions and composite compositions on the contact surfaces in the space-time framework of wear. Keywords: wear mechanism; coefficient of friction (COF); transition map; polytetrafluoroethylene (PTFE); polyimide (PI); boron nitride(BN)
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Introduction
In chemical industries [1], hydraulic engineering [2], and aerospace mechanisms [3], some dynamic mechanical transmissions require close sealing at the contacting interfaces between relative moving components to prevent liquid leakage. A long-standing, steady, and low abrasion sealing is necessary for the reliable operation of equipment throughout their service life. More importantly, many operational conditions involve corrosive environments, high temperatures, and long durations of continuous operation [1−3]. Thus, sealing rings must be fabricated from materials which are corrosion-resistant, abrasion-resistant,
thermostable, and with a low coefficient of friction (COF). These multiple and steep requirements can only be satisfied by employing composites. Therefore, the development of composite sealing materials with superior performances is significant to assure the reliability and improve the efficiency and increase the working life of machines and moving parts. Polytetrafluoroethylene (PTFE) is widely used in mechanical seal structures due to its chemical st
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