Microstructure and mechanical properties of polymer nanocomposites based on polylactic acid and carbon nanotubes

Abstract

The features of the formation and the influence of carbon nanotube (CNTs) clusters in a polylactic acid matrix on the mechanical characteristics of the obtained nanocomposites were analyzed. The dependence of the CNT clusters’ fractal dimension on their concentration was studied, and its critical values, which determined the percolation threshold of the material, were established. It is shown that increasing the CNT content to 1 wt.% makes the cluster structure more complex, thereby promoting the formation of a branched nanotube network and improving the functional characteristics of the nanocomposite. The mechanical parameters, which in particular include the tensile strength, Young’s modulus, and impact strength, change nonlinearly. An initial decrease of the composite strength is observed at low CNT concentrations (up to 0.5 wt.%) due to the formation of internal stress concentrators. However, a further increase in concentration improves interfacial interactions and increases the material’s overall mechanical strength. In particular, the optimal rigidity-to-plasticity ratio is achieved at a CNT concentration of 0.75–1 wt.%, thereby enabling effective dissipation of mechanical load.