Specific Water/Vapor Uptake of Ultrathin Films of Cellulose: Paving the Way for New Responsive Materials from Renewable Polymers

Cellulose is the main structural component of all plant fibers. Recent technology has enabled the top-down isolation of the nanosized supramolecular units from within the fiber and the possibilities of these nanocellulosic building blocks in applications of materials science were recently reviewed.1 In this presentation, we focus on the specific applications of nanocellulose in ultrathin films whose interactions with water and water vapor were scrutinized. Contrary to the common assertions, nanocellulose is not exclusively hydrophilic but in fact, amphiphilic (although it is highly hygroscopic) and this amphiphilicity leads to a distinct, controllable behavior with water, elaborated here from the physico-chemical perspective. Generally, the high water uptake of nanocellulose is viewed as a nuisance, resulting in, e.g., strength reduction of its composite materials. By contrast, we want to see the specific nature of its water interactions as an asset with nanocellulose.
Several aspects of this work have already been published2-4 whereas fresh data will also be presented, linking the data to general considerations on diffusion, porosity, and crystalline/amorphous characteristics of the cellulose in use. The results demonstrate the potential of ultrathin nanocellulose films in applications such as sensors and actuators. Overall, we advocate the vision where the specific properties of renewable polymers would be given more attention instead of the approach where renewability and sustainability are their sole assets in materials science