In this work we attempt to improve the dispersion of multi wall carbon nanotubes (MWCNT) by means of surface functionalization with carboxyl groups. In this way, crystallization behaviour of Poly (L-lactide) and subsequent melting behaviour has been investigated in nanocomposites containing as-received MWCNT or carboxyl functionalized nanotubes (MWCNT-COOH) by means of differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM).
The results indicate that multi wall carbon nanotubes act as nucleating agents to speed up the crystallization process, yielding an enlarged crystalline fraction. The single bell-shaped crystallization peak in PLLA/ MWCNT-COOH nanocomposites may be associated to the good dispersion level achieved. The presence of a critical concentration of MWCNT that provides the maximum changes in crystallization behaviour of PLLA suggests the existence of bundles that reduce the efficiency of MWCNT as nucleation points.
It was found that the more stable PLLA crystals are achieved in the presence of functionalized nanotubes, where the provided nanotube surfaces are more efficient as sites for heterogeneous crystallization of PLLA. Morphological observations carried out by means of polarized light optical microscopy are in good agreement with the results obtained from the DSC experiments in which the crystallization time is reduced by the nucleating effect of nanotubes. Obtained results reveal that good dispersion of nanotubes can effectively influences the crystallization behaviour of PLLA.