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

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.

Polylactide cellulose-based nanocomposites.

Among biopolymers, polylactide (PLA) is considered as the most appropriate substitute for the petroleum-based polymers which are widely used in various commodity and engineering applications. PLA, however, also suffers from series of shortcomings such as slow crystallization rate and low melt strength which result in poor processability, formability and foamability which substantially limit its production and usage. Recently, the use of biobased/biodegradable cellulose nanoparticles such as cellulose nanocrystals (CNC), cellulose nanofibers (CNF), and bacterial nanocellulose (BC) have been proposed to manufacture fully green PLA-based biocomposites while they could resolve some of the noted drawbacks of PLA. However, due to their high hydrophilicity and the presence of hydrogen bonding cellulose nanoparticles are not compatible with hydrophobic polymers. Therefore, the dispersion of these nanoparticles in thermoplastics still remains as the main challenge to process/develop their nanocomposites. This article reviews the studies conducted on these challenges of developing PLA cellulose-based nanocomposites including the difficulties of their processing and possible enhancements of their rheological, thermal, and mechanical properties. The investigations that have been conducted on PLA-CNC, PLA-CNF, and PLA-BC nanocomposites are separately discussed in this review article, while the studies on the development of PLA-nanocellulose blend nanocomposites and PLA-nanocellulose microcellular foams are also highlighted.