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

The features of the formation and 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 fractal dimension of CNTs clusters on their concentration was studied and its critical values, which determined the percolation threshold of the material were established. It is shown that with an increase in the CNTs content to 1 mass%, the structure of the clusters becomes more complicated, which contributes to the formation of a branched nanotube network, which improves the functional characteristics of the nanocomposite. The mechanical parameters, in particular the tensile strength, Young’s modulus and impact strength, change nonlinearly. An initial decrease in the strength of the composite is observed at low CNTs concentrations (up to 0.5 mass%) due to the formation of internal stress concentrators, however, a further increase in the concentration leads to an improvement in the interfacial interaction and increase in the overall mechanical strength of the material. In particular, the optimal ratio between rigidity and plasticity is achieved at a CNTs concentration of 0.75–1 mass%, which allows for effective dissipation of mechanical load.