The influence of entanglements of macromolecules on the mechanical and thermal properties of polylactide composites with carbon nanotubes

The influence of the reduction of macromolecular entanglements on the thermal and mechanical properties of polylactide composites containing 0.1–1.0 wt% of carbon nanotubes was investigated. Partial disentangling of the macromolecules improved the dispersion of the filler during composite fabrication. Greater mobility of less entangled polylactide macromolecules affected the crystallization of nanocomposites, which occurred already during the cooling of the melt and not only as a cold crystallization. Isothermal crystallization studies showed a beneficial combination of matrix disentanglement and increased nanotube nucleation, leading to much faster crystallization. In the entangled composite, crystallization at 120 °C was completed after 14 min, while in the partially disentangled composite only after 9 min. The reduction of entanglements of macromolecules also affected the mechanical properties. The plastic deformation was more easily initiated, and stresses in the strain-hardening phase increased more slowly during the deformation of disentangled homopolymers. In composites, the strain-hardening effect depended not only on the content of nanotubes but also on their dispersion, which was better in the less entangled polylactide matrix.