Comparative assessment of the strain-sensing behaviors of polylactic acid nanocomposites: reduced graphene oxide or carbon nanotubes

Reduced graphene oxide (RGO)/polylactic acid (PLA) and carbon nanotubes (CNTs)/PLA nanocomposites were prepared by ultrasound-assisted dispersion and a hot-pressing method for comparative studies. The RGO and CNT nanofillers, which had a hydrogen-bonding interaction with the PLA matrix, were uniformly dispersed in the PLA matrix, and low percolation thresholds (0.11 wt% for RGO/PLA and 0.80 wt% for the CNTs/PLA nanocomposites) were achieved in the PLA nanocomposites. The addition of RGO resulted in weak crystallization ability and significant enhancement in thermal stability of the PLA matrix owing to the two-dimensional characteristic of RGO, while opposite results were obtained for the CNTs nanocomposites (the degree of crystallinity X-c is 49.82% for 0.8 wt% CNTs and 9.21% for 0.8 wt% RGO, respectively). During ten extension-retraction cycles, the values of the max and min Delta R/R-0 for the RGO/PLA nanocomposites shift upwards gradually with the increase of the cycle number, resulting from the breakdown of conductive networks caused by the slippage of overlapped RGO layers; while the values of the max and min Delta R/R-0 for CNTs/PLA nanocomposites decrease gradually owing to the formation of a better conductive network caused by the rearrangement of CNTs. This study is meaningful for the application of conductive polymer composite based strain sensors in many fields, such as structural health monitoring, wearable electronic devices, soft robotics, etc.