Effects of Polymer Additives and Dispersion State on the Mechanical Properties of Cellulose Nanocrystal Films

Abstract

Films produced from colloidal and nanomaterial dispersions such as aqueous cellulose nanocrystal (CNC) dispersions tend to crack above a critical cracking thickness; this issue limits the ability to produce flow‐aligned CNC films at thicknesses above ≈50 μm. This research explores the effects of adding polyethylene oxide (PEO), flocculation with hydrochloric acid (HCl), and the combination of both methods on film cracking, mechanical properties, and mechanical anisotropy. Most research on CNC polymer composites focuses on composites where the polymer is the majority component. To the authors' knowledge there has been only one investigation of CNC films' mechanical anisotropy and no studies of using HCl flocculation to flocculate CNC dispersions prior to shear casting. PEO addition significantly reduces Young's modulus, tensile strength, and toughness, but enhances the Young's modulus anisotropy. Flocculation results in little property deterioration but nearly eliminates mechanical anisotropy. The combination of both techniques results in similar properties as flocculation alone. These findings highlight the trade‐offs between these two approaches and can be used to help guide further research on obtaining robust shear cast CNC films over a range of thicknesses. image