Evaluation of fine wear particles emission from styrene-butadiene rubber reinforced with aligned carbon nanotubes: A study based on unit wear mass analysis

Rubber filled with carbon nanotubes (CNTs) oriented along a specific direction exhibits excellent tribological performance owing to the unique directional structure of the CNTs, and offers significant application potential. However, when CNT-reinforced rubbers are worn, fine wear particles (WPs), including CNTs, are emitted, creating a potential respiratory health risk. This study explores the relationship between the emission of fine WPs (with sizes $\le 10\mu m$) against a frosted glass disc under sliding conditions and the tribological performance of styrene-butadiene rubber (SBR) reinforced by aligned CNTs. The number of WPs per unit worn mass (Q_wpS/uwm, where S is the upper limit to the particle size in μm), was defined to quantify the emissions after a unit mass was worn. Using a pin-on-disc test rig developed for this study, the results showed that SBR with CNTs oriented perpendicular to the wear surface (denoted as CNTs_-z-SBR) exhibited higher Q_wp3.0/uwm and Q_wp5.0/uwm values owing to its superior wear resistance. A greater worn mass resulted in larger amounts of WPs, but smaller Q_wp3.0/uwm and Q_wp5.0/uwm. Furthermore, both water lubrication and lower coefficients of friction (COF) increased the value of Q_wp3.0/uwm, whereas a larger load and velocity decreased the values of Q_wp3.0/uwm and Q_wp5.0/uwm.