Optimizing the Mechanical and Tribological Properties of PTFE / PI Composites via Constructing Bicontinuous Structure

ABSTRACT To meet the synergistic demand for both load‐bearing and lubricating capabilities in rotary lip seals for heavy‐duty gearbox shafts, this study systematically investigates the co‐optimization mechanism of the mechanical and tribological properties of polytetrafluoroethylene (PTFE)/polyimide (PI) composites by controlling the PI content within the PTFE matrix to construct a bicontinuous structure. It was found that at a PI content of approximately 20 wt%, a unique bicontinuous structure (where both the PTFE matrix and the PI network are continuous) forms within the composite, resulting in optimal overall mechanical performance. Furthermore, under conditions of heavy‐duty dry sliding and oil‐starved lubrication simulating bearing oil‐mist environments, this specific composition exhibited the lowest and most stable coefficient of friction (an average of 0.012 under oil‐starved conditions) along with excellent anti‐wear ability. The synergy in properties stems from the continuous PTFE phase ensuring a sustained supply and transfer of lubricating film, while the continuous PI network constructs a robust load‐bearing skeleton. Their cooperative interaction stabilizes the friction interface. Deviation from this critical compositional window leads to structural imbalance and performance degradation. This work reveals that constructing a bicontinuous structure at a critical filler content is a key strategy for the synergistic enhancement of mechanical and tribological properties in self‐lubricating composites, offering a new perspective for developing high‐performance sealing materials for severe service conditions.