Interface-Driven Carbon Fiber Reinforcement in Graphite Packing Rings for Enhanced Service Stability

Flexible graphite packing rings are widely employed in high-temperature and high-pressure valve sealing systems owing to their intrinsic lubricity and thermal stability, yet their service reliability is often compromised by low mechanical strength, pronounced creep, and unstable tribological behavior under extreme conditions. Here, we present an interface-engineered strategy to enhance the service performance of graphite packing rings via reinforcement with surface-functionalized PAN-based carbon fibers (PAN-CFs; carbonized fibers derived from polyacrylonitrile precursors). Through controlled oxidative modification of carbon fibers combined with high-temperature graphite expansion, a three-dimensional reinforced graphite network with uniform fiber dispersion was constructed. The influence of PAN-based carbon fiber (PAN-CF) content (0-7 wt%) on compressive strength, thermal stability, friction behavior, and long-term durability was systematically evaluated. An optimal performance was achieved at 5 wt% PAN-CF, featuring a ~58% increase in compressive strength, a stable friction coefficient of 0.15-0.18, and enhanced creep resistance, while retaining over 78% of the initial strength after 1000 h of sustained loading. Microstructural and complementary structural analyses suggest that these improvements are associated with interfacial mechanical anchoring, fiber embedding, and load-transfer reinforcement enabled by fiber surface functionalization and the expanded graphite architecture. This work offers a practical material-level approach to improving the long-term reliability of graphite-based sealing components in demanding industrial environments.