Effect of H bonds on thermal behavior and cohesion in polylactic acid nanocomposites and nitrogen-doped carbon nanotubes

In this work, we explain the filling effect of pristine carbon nanotubes (CNTs) and nitrogen-doped carbon nanotubes (N-CNTs) under the properties of polylactic acid (PLA) nanocomposites by combining molecular dynamics simulations and experimental results. We observed via computational analysis that the presence of nitrogen in the CNTs improves their integration with the polymer chains. An experimental study of these systems showed that the addition of N-CNT in the PLA matrix causes different phenomena: The PLA crystallinity decreases, crystalline domains form at the surface of the composites due to nanostructure doping, and the energy dissipates by an order of magnitude. In addition, the glass transition and melting temperatures of the PLA nanocomposites were calculated by molecular dynamics simulations, which were in good agreement with the obtained experimental results. The computational study also revealed a good integration of N-CNTs with PLA chains due to the generation of strong hydrogen bonds between the nanotubes and the polymer chains. This last result was also confirmed by the PLA radius of gyration and by the radial distribution function of C–H and N–H pairs between the nanotube and polymer, both indicating an approach of the polylactic acid chains toward doped carbon nanotubes.