Cellulose Nanopaper: A Study of Composition and Surface Modifications to Develop Sustainably-Sourced Alternatives to Plastics

Pollution from the fossil-fuel-powered production of plastics presents a serious threat to the planet’s environmental health. To address this issue, cellulose nanopaper (CNP) has been pushed as an abundant, sustainably-sourced potential alternative. Initially derived from wood pulp, CNP is comprised of a network of nanosized cellulose fibers. Although CNP has exhibited remarkable optical transparency, porosity, and stiffness, the need for improvement in its chemical and electrical properties has been identified. Optimizing these properties would allow CNP to function in flexible electronic systems. By altering the paper through several surface processing experiments, the most effective treatments to increase CNP’s functionality were identified. These treatments included altering the source of cellulose, performing atomic layer deposition (ALD) with Al2O3, conducting surface esterification reactions, and applying transparent, conductive coatings. Along with conventional pine fibers, CNP with longer cellulose fibers from the jute plant was developed. Sequential, uniform deposition of Al2O3 films via ALD was also implemented for added stability. The surface of the CNP was treated with organic acids to yield nonpolar ester groups, with the goal of increasing water resistance. Finally, conductive ink coatings consisting of carbon nanotubes and cellulose nanofibers demonstrated improved electrical conductivity of CNP for optoelectronic applications. After the treatments, material properties were characterized, including strength, flexibility, water resistance, conductivity, surface smoothness, and transparency. Improvements in hydrophobicity, conductivity, and surface smoothness were observed. These treatments and their corresponding findings represent promising ways of improving the functionality of CNP without dramatically altering its high transparency and flexibility.