Polylactide stereocomplex crystallization prompted by multiwall carbon nanotubes

摘要

Nanocomposites of equimolar enantiomeric polylactide blends with multiwall carbon nanotubes (MWCNTs) were prepared by a solvent casting/sonication procedure. The first objective of the study was to investigate the effect of MWCNTs as nucleating agents for the selective crystallization of the polylactide (PLA) stereocomplex to obtain PLA-based nanocomposites. Transmission Electron Microscopy (TEM) studies revealed large agglomerates and poor distribution of the non-functionalized MWCNTs within the matrix. To enhance the compatibility between PLA and MWCNTs, pyrene-end-functionalized PLLA (py-end-PLLA) nanocomposites were prepared because of the ability of the pyrene moieties to interact with the MWCNTs via π-π stacking, and were subsequently blended with poly(d-lactide) (PDLA) to investigate the possibility of achieving nanocomposites in which the enantiomeric blend crystallizes as stereocomplex. The resulting nanocomposites were characterized by Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), TEM, and Nuclear Magnetic Resonance Spectroscopy (NMR), revealing that MWCNTs were efficient nucleating agents for the overall crystallization of the blends. Interestingly, full stereocomplexation could be achieved with the aid of soft specific thermal treatments. According to these results, the addition of small amounts of MWCNTs combined with a mild thermal treatment might extend the processing window for the preparation of polylactides exclusively crystallized in the stereocomplex form.