Effect of Activated Carbon and Various Other Nanoparticle Fillers on PTFE Wear

Abstract

It has long been known that a breadth of materials in microscale filler form reduce wear of polytetrafluoroethylene nominally by a couple orders of magnitude through prevention of large plate-like debris delamination. Though hypothesized that this wear reduction mechanism should halt as particle size is reduced to the nanoscale, alumina fillers not only maintained their wear reducing capability at the microscale but improved when employed as nanoparticles. In a survey of other nanofiller materials it is found that improved performance at the nanoscale is special not only to this alumina but also to its alpha phase, as most other materials and phases of alumina at best maintained microcomposite levels of wear resistance, more often losing some and in several cases fully returning to prohibitively high wear rates of unfilled polytetrafluoroethylene (PTFE). However, activated carbon emerged as exceptional, providing levels of wear resistance as a nanofiller well beyond that of typical microcomposites and even alpha-alumina itself. Against polished steel countersurfaces this activated carbon nanofiller began showing sizeable reductions in PTFE wear at contents as low as 0.18%, attaining with 0.8% content reduced wear rates ∼3 * 10−7 mm3/Nm comparable to alpha-alumina nanofiller, further decreasing with increased content to ∼10−8 mm3/Nm levels at 20% filling. It is believed that exceptional filler materials such as alpha-alumina and activated carbon possess an additional wear reduction mechanism complementing that operating at the microscale, one involving their specific surface chemistry that triggers fibrillation deformation processes in neighboring PTFE and becomes increasingly active at reduced filler particle size where surface area and affected interfacial polymer are augmented.