The team’s strategy was to build a composite rather than rely on PTFE alone. They reinforced the polymer matrix with two very different additives: polyimide pulp, a mat of fine, heat-resistant organic fibers, and graphitized carbon nanotubes, cylindrical carbon structures whose graphitic walls combine excellent lubricity with remarkable mechanical strength. The composites were manufactured through a cold-press sintering process, in which the blended powders are compacted at room temperature and then heated below their melting point so the particles fuse into a dense, coherent solid. This route is industrially attractive because it avoids the high pressures and complex tooling associated with melt processing of highly crystalline fluoropolymers, which are notoriously difficult to shape by conventional techniques.

To judge how well the new materials performed, the researchers used a ball-on-disk tribometer, the workhorse instrument of friction science. In this configuration, a hard ball slides repeatedly across the flat surface of the composite disk under controlled conditions, while sensors continuously record the tangential force needed to keep it moving. Dividing that force by the applied normal load yields the coefficient of friction, a dimensionless number that describes how easily the surfaces slide past one another. The team tested their samples under two normal loads, 2 newtons and 10 newtons, and two sliding frequencies, 1 hertz and 4 hertz, allowing them to probe how the materials respond as contact pressure and sliding speed increase together.

The standout formulation, designated #3 in the study, contained 5 percent by weight of polyimide pulp and just 1 percent by weight of graphitized carbon nanotubes. At the gentle end of the test range, 2 newtons and 1 hertz, this composite achieved a coefficient of friction of 0.025, a value that places it among the lowest ever reported for solid self-lubricating materials. For comparison, the same measurement on pure PTFE gave a coefficient roughly 69.3 percent higher. In practical terms, the composite allowed a steel counterface to slide across it with barely a quarter of the resistance offered by the unfilled polymer, which translates directly into lower energy losses, less heat generation, and quieter operation in real machinery.

Friction, however, is only half of the tribological story. A material can be slippery and still vanish under load if it wears away quickly, and wear resistance is precisely where pure PTFE fails most dramatically. The wear rate, typically expressed as the volume of material removed per unit of sliding distance and per unit of applied load, tells engineers how long a component will survive. Under the harshest conditions tested, 10 newtons and 4 hertz, the optimized composite reduced the wear rate by up to 75 percent relative to pure PTFE. That improvement means a bearing or seal made from the composite could theoretically last several times longer before needing replacement, a difference that matters enormously in applications where maintenance is costly or access is difficult.

To understand why the composite performed so well, the researchers turned to scanning electron microscopy and energy-dispersive X-ray spectroscopy. SEM produces high-resolution images of surface topography by sweeping a focused electron beam across the sample, revealing features far too small for optical microscopes to resolve. EDS complements this by detecting the characteristic X-rays emitted when the beam strikes atoms in the sample, mapping which chemical elements are present and where. Together, these techniques let the team examine both the worn composite surfaces and the steel counterfaces they had slid against, hunting for the microscopic signatures of the wear mechanisms at work.

The analysis pointed to a single decisive mechanism: the formation of a continuous and uniform transfer film on the steel counterface. When a PTFE-based material slides against metal, thin layers of polymer are sheared off and deposited onto the metal surface, and the subsequent sliding actually occurs between the polymer surface and this deposited film rather than between the original pair of materials. When the transfer film is patchy or easily removed, fresh polymer is continually exposed and scraped away, producing high wear. When the film is continuous and adherent, however, the contact effectively changes from composite against steel to film against steel, and the film itself acts as a low-shear solid lubricant that protects both surfaces.

The two additives earned their place by playing complementary roles in stabilizing that film. The polyimide pulp forms a load-bearing fibrous network woven through the composite, boosting its mechanical strength and creep resistance so the material does not simply deform and extrude under pressure. The graphitized carbon nanotubes, meanwhile, promote the adhesion and stability of the transfer film, anchoring the sheared polymer layers to the steel so they persist across thousands of sliding cycles. The EDS maps confirmed that the film covered the counterface uniformly, and the SEM images showed smoother, less damaged wear tracks on the best composites, consistent with a stable, protective third body mediating the contact. In effect, the researchers engineered the interface rather than just the bulk material, and the interface is where friction and wear are ultimately decided.

Beyond the specific numbers, the study offers a broader lesson in composite design philosophy. Rather than chasing ever-larger quantities of filler, the team found that a modest 6 percent total loading, split between a fibrous reinforcement and a nanoscale lubricant, delivered the best balance of mechanical and tribological properties. This matters because excessive fillers can embrittle a polymer, raise its cost, and complicate processing, so identifying the sweet spot is essential for any technology transfer from laboratory to factory floor. The cold-press sintering route also means the approach could be adopted with relatively conventional equipment, lowering the barrier to commercialization for self-lubricating components in automotive, aerospace, and industrial machinery.

The implications extend to any application where lubricating oils are impractical or undesirable, from food processing equipment and vacuum systems to spacecraft mechanisms where liquid lubricants evaporate or freeze. A PTFE composite that combines a coefficient of friction near 0.025 with a wear rate reduced by three quarters could extend the life of dry-running bearings, bushings, piston rings, and sliding seals while cutting maintenance intervals. As the authors note, their work provides a practical route toward PTFE-based self-lubricating composites with balanced mechanical and tribological properties, and it demonstrates that with the right fibrous scaffold and a dash of graphitized carbon, even the slipperiest polymer can finally learn to endure.

Subject of Research: Tribological performance of PTFE composites reinforced with polyimide pulp and graphitized carbon nanotubes

Article Title: Tribological performance of PTFE/polyimide pulp/GCNT composites

Article References: Zhou, J., Sun, X., Zhao, D., Si, C., & Wu, S. (2026). Tribological performance of PTFE/polyimide pulp/GCNT composites. Scientific Reports. https://doi.org/10.1038/s41598-026-74310-z

Image Credits: AI Generated

DOI: 10.1038/s41598-026-74310-z

Keywords: PTFE, polyimide pulp, graphitized carbon nanotubes, tribology, wear resistance, coefficient of friction, transfer film, self-lubricating composites, cold-press sintering, materials science, nanocomposites, Tribological