Polylactide/cellulose nanocrystals : The in situ polymerization approach to improved nanocomposites

The in situ polymerization of L-lactide in the presence of various amounts of cellulose nanocrystals (CNC) is described. CNC was prepared efficiently by acidic hydrolysis of cotton linters. Molecular weight, morphology, thermal, mechanical and crystallization properties of the PLA-CNC nanocomposites were evaluated. From size-exclusion chromatography (SEC) analysis, the actual occurrence of chemical bond between CNC and PLA can be assessed. The effect of CNC has been evaluated through differential scanning calorimetry (DSC) analysis, which highlights the probable formation of α′ crystals in the obtained materials. More importantly, from thermogravimetric analysis (TGA) a marked improvement in thermal stability of nanocomposites has been demonstrated, with respect to standard PLA and to previously described PLA-CNC blends. Nanocomposites show also an improvement in rheological properties with respect to standard PLA. In particular, storage modulus greatly increases, indicating a reinforcing effect of CNC. The described in situ synthetic methodology allows an optimal compatibilization between the two entities (PLA and CNC), facing one of the major problems inherent to the preparation of nanocomposites. It leads furthermore to remarkably improved thermal and rheological properties of the obtained materials.