Highly aligned dense carbon nanotube sheets induced by multiple stretching and pressing

The CNT sheet fabricated by the floating catalyst chemical vapor deposition (CVD) method has attracted great attention due to its easy fabrication process and promising mass production at low cost. However, the randomly oriented CNT sheet with a loose stacking density shows relatively poor mechanical properties. In this work, a highly aligned dense CNT sheet was successfully fabricated by a simple process of two-time stretching and pressing of a multilayered CVD-grown CNT sheet. Drastic nanotube rearrangements occurred during stretching and pressing processes. A polymer-like tensile necking behavior was observed during the stretching process, accompanied by inter-tube junction breakage due to long-distance slippage. Simultaneously the CNT sheet was thickened after the stretching process due to the increase of the inter-layer space, which could be effectively eliminated by the following pressing treatment. After two-time stretching and pressing, a highly aligned dense CNT sheet was fabricated with the volume density increasing to 0.98 g cm^-3 (by 109%) and the tensile strength increasing to 598 MPa (by 221%) compared to the as-prepared CNT sheet.