Anisotropy in tribological performances of long aligned carbon nanotubes/polymer composites

A new continuously aligned carbon nanotubes (ACNTs) reinforced epoxy composite was fabricated by wetting as-grown arrays of ACNTs. The uniform distribution of ACNTs in the epoxy composites was confirmed by high magnification scanning electron microscopy observations. Owing to its load-transfer-favored structure, 1.1 vol.% ACNTs achieved orders of magnitude higher improvement in the wear resistance of epoxy composite compared to randomly dispersed CNTs in epoxy reported before. The research demonstrated for the first time that the use of ACNTs alone can achieve significant improvement in the wear resistance of epoxy for applications, and the specific wear rate under normal direction was stable at ∼10−6 mm3/Nm with the sliding conditions varying from 0.4 to 2.5 MPa m/s. Further, the experimental results showed that the wear performance of ACNT/epoxy composite is highly dependent on the orientation of the ACNTs relative to the sliding direction. In particular, it was found that ACNTs achieved the highest improvement in wear resistance under normal orientation whereas the least improvement was observed under parallel direction. The results are different from that of carbon fiber reinforced epoxy composites, indicating different wear mechanisms. Based on microscopic observations, new ACNTs related wear mechanisms were further proposed and discussed.