Effects of Sorbitol Addition on Sheared Cellulose Nanocrystal Films

ABSTRACT Cellulose nanocrystals (CNCs) are an exciting material for making high strength biodegradable films. However, films solely comprised of CNCs often crack. Sorbitol has shown promise for mitigating cracking in drop‐cast CNC films, but sorbitol's effects on shear‐cast films have not been investigated. This work contributes to scientific understanding of the effects of sorbitol on aqueous sulfated CNC dispersions and shear‐cast films. Sorbitol concentrations up to 1.61 wt.% do not prevent cholesteric liquid crystal phase formation in ~6.5 wt.% aqueous sulfated CNC dispersions, but sorbitol's presence reduces CNC dispersions' low shear viscosity as well as storage and loss moduli. While sorbitol does not affect CNC crystallinity, it slightly improves film thermal stability. This is attributed to changes in inter‐ and intramolecular hydrogen bonding as evidenced by Fourier transform infrared spectroscopy. Most notably, sorbitol mitigates cracking and curling in ~50 μm thick films produced at shear rates of 5, 25, and 50 s −1 without significantly affecting CNC orientation or mechanical strength. These results highlight that sorbitol is a promising additive for maintaining the desirable properties of sheared CNC films while mitigating cracking tendency.