Effect of carbon nanotube reinforcement on the tribological behavior of fiber composites in vacuum environments

The tribological performance of fiber-reinforced polymer composites is strongly influenced by reinforcement design, interfacial interactions, and operating environment. While carbon nanotube (CNT) reinforcement has been widely reported to improve friction and wear behavior, most existing studies have been limited to ambient atmospheric conditions, leaving its effectiveness under vacuum environments insufficiently understood. In this study, the effect of CNT addition on the friction and wear behavior of glass fiber-reinforced polymer composites were systematically investigated under three distinct environmental conditions: ambient atmosphere, low vacuum, and high vacuum. Tribological tests were conducted using a ball-on-disk configuration under varying normal loads, and the resulting frictional response, wear behavior, and dominant wear mechanisms were analyzed. The results demonstrate that the influence of CNT reinforcement is highly dependent on both applied load and the surrounding environment. While CNT addition enhances wear resistance under atmospheric conditions at higher loads through improved load transfer and crack-bridging mechanisms, it does not provide a universal improvement across all environments. Under vacuum conditions, the absence of moisture-assisted tribochemical reactions and unstable tribofilm formation can diminish or reverse the beneficial effects of CNTs. These findings highlight that CNT reinforcement in fiber-reinforced polymer composites should be evaluated within an application-specific framework rather than assumed to yield generalized tribological improvements. The present study provides critical insights into the environment-dependent role of CNTs and contributes to the informed design of polymer composite systems for vacuum and space-related applications.