Effect of Commercial Halloysite Nanotube Grade on the Tribo‐Mechanical Performance and Structural Evolution of Polytetrafluoroethylene Composites

The aim of this work was to establish how the grade of commercial halloysite nanotubes affects the structure, mechanical properties, and tribological behavior of polytetrafluoroethylene (PTFE) composites. Three grades of halloysite, ANT 811, ANT 1108, and ANT 3810, differing in phase composition and textural characteristics, were used as fillers at 1, 2, and 5 wt.%. The addition of 5 wt.% ANT 811 halloysite, which had the highest specific surface area and the smallest crystallite size, reduced the wear rate by 100% compared to initial PTFE, from (496 ± 32) × 10 −6 to (1.2 ± 0.6) × 10 −6 mm 3 /(N·m), while a low coefficient of friction of 0.20 was maintained. The degree of crystallinity increased from 64% for initial PTFE to 73% for the ANT 811 composite. These improvements were achieved at the cost of reduced ductility. The elongation at break decreased by 55%, although it remained 9 times higher than that of the composite with ANT 3810. FTIR spectroscopy, XPS, and SEM revealed that the halloysite particles acted as a solid lubricant at the initial stage of friction and then initiated the formation of a secondary tribo‐layer enriched with tribo‐oxidation products. The resulting composites can be recommended as anti‐friction materials for dry sliding units.