Fabrication of Transparent Nanocellulose Paper from Plant Sources for Energy Devices

Abstract

Over the past decades, electronic waste has accumulated and has increased by 21% in the last five years. Recently, a UN report founded that the world dumped a gross record of 53.6 million tonnes of e-waste across last year. In the past, electronics had limitations due to their size constraint but with technological growth, electronics have now become a prominent part of the waste stream. Plastic substrates such as polyethylene (PET) and polycarbonate (PC) has been used pervasively in electronic devices. But due to their low co-efficient of thermal expansion (CTE), low recyclability and immense levels of pollution, a new state-of-art technology the cellulose nanopaper (CNP) has shown immense potential to replace plastic as a substrate in optoelectronics. Bio-derived decomposable electronics have exhibited great prospective to reduce the environmental footprint and avoid the surplus amounts of plastic based waste. This project reports about a nanopaper fabricated from self-assembled network structure from nanoscale building blocks known as cellulose nanofibers (CNF). Nanofibers from two distinct sources were tested – (a) Cannabis sativa - Hemp (b) Softwood – Pine. Hemp CNFs provided by IND Hemp, United States in association with Tangho Green Inc., Canada was prepared via alkaline and acid hydrolysis along with high compression grinding and a cellulose purity of 97% was obtained. Pine CNFs were purchased from Forestry Department of University of Maine, USA had a >98% purity spectrum. A comprehensive study of CNP’sstructure-property relationship has been established under different processing conditions such as temperature of drying and CNF grammage, through characterization analyses. Two main nanopaper fabrication techniques of Solution Casting and Vacuum Filtration were studied in detail. Secondary objective comprised of optimizing optical properties of CNPs by adding polymers like Poly (vinyl alcohol) (PVA) and Polymethyl methacrylate (PMMA). Both PVA and PMMA showed considerable compatibility with CNF as a way of making them transparent. The project was rounded off by incorporating Silver Nanowires (AgNWs) which was chosen as a conductive nano-filler due to its well-expressed aspect ratio. AgNWs showed high conductivity with increasing its loading density (mg/cm2 ) or grammage. The films showed a resistivity as low as 9.45 ohm.µm with higher grammage of nanowire added. The results showed that nanocellulose changed their nature from insulator to conductor after addition of conductive materials. Moreover, iv the highest conductivity around 1.05 kS/cm was obtained with maximum amounts of nanowire deposited. This work solely presents a trend for the application of this conductive nanopaper in foldable or flexible electronics such as solar cells, OLEDS, electrodes or electronic skin for electrophysiological monitoring.