Bendable transparent films from cellulose nanocrystals–Study of surface and microstructure-property relationship

Journal article, 2023

The presented work focuses on preparing transparent bendable films from nanocellulose. In comparison to cellulose nanofibrils and bacterial cellulose, nanocrystalline cellulose are shorter and have higher crystallinity (CI<95 %). Sulfated CNC (CNCIH-OSO3H) were prepared, and by changing their counter ions from H+ to Na+ and Et4N+ (Tetraethyl ammonium) flexible films were prepared with a strength of 70.5 MPa and 2.6 % elongation at break. The CNC suspensions showed excellent dispersibility in DI water with Zeta-potential (ζ) values > -35 mV. In the preparation of films, pre-sonication was key in improving the tensile strength and improved elongation (>30 % increase compared to films prepared without sonication) and hydrophobicity. The change of counter ion, H+ to Na+ or Et4N+, improved the thermal and mechanical properties of CNC films. The films were investigated with UV–Vis spectroscopy and optical polarized spectroscopy to explain the arrangement of nanocellulose crystals in correlation with the mechanical properties. The wettability of CNC samples was also studied and explained in detail. CNC from CelluForce was also studied as commercial reference samples. The modified CNC films have adequate properties for application in flexible electronics, energy storage, and biodegradable smart packaging.