Effects of molecular weight and crystallizability of polylactide on the cellulose nanocrystal dispersion quality in their nanocomposites

Abstract

This study investigated how cellulose nanocrystals (CNC) dispersion quality and its percolation network formation could be influenced when using polylactide (PLA) with various molecular weights and crystallizability. In this context, systematic rheological experiments were conducted on PLA/CNC nanocomposites prepared through solution casting method using dimethylformamide (DMF) as the solvent. It was found that lower CNC percolation concentrations could be obtained when a PLA matrix possesses lower molecular weight as the shorter chains and CNCs interpenetration could be facilitated during their dissolution in the solvent. On the other hand, the CNC percolation concentration was further lowered when the PLA with higher crystallizability was used. During the solvent evaporation step that occurred at 85 °C, the isothermal heterogeneous crystallization of PLA around the dispersed CNCs could prevent the driving force of the CNCs towards their re-agglomeration. Therefore, the finest CNC dispersion was appeared in the highly crystallizable low molecular weight PLA through which the rheological properties were dramatically improved and the thermal stability was significantly extended to higher temperatures. The crystallization behavior of the prepared nanocomposites was also analyzed using differential scanning calorimeter and X-ray diffractometer. The thermal degradation behavior of the PLA/CNC nanocomposites were examined through thermogravimetric and rheological analysis.

Keywords: Cellulose Nanocrystals; Crystallization; Molecular weight; Nanocomposites; Polylactide; Rheological properties.