The combined effects of electrolyte addition and mechanical shearing on cellulose nanocrystal alignment

Abstract This research investigated the combined effects of electrolyte addition and mechanical shearing on the alignment, optical properties, and rheological characteristics of cellulose nanocrystal (CNC) films. Changes in aqueous CNC gels’ rheological properties due to electrolyte addition were correlated to the properties of the dried films. The alignment in dried CNC films was measured using the order parameter computed by UV-Vis transmission spectroscopy and qualitatively through cross-polarized optical microscopy. In the absence of electrolytes, a single stroke of mechanical shearing at a shear rate of 100 s⁻¹ is insufficient to significantly align CNC in CNC gel. However, the addition of electrolytes improves the alignment of CNC, resulting in an increase of order parameters, such as from 0.31 to 0.88 for NaCl addition, even at a lower shear rate of 20s⁻¹. This work shows the addition of electrolytes combined with mechanical shearing is a more effective approach to tuning CNC alignment to produce transparent and less hazy CNC films from CNC gel.