Abstract
Recently, woody biomass has been used in multiple ways as a carbon-neutral and renewable resource. Among them, cellulose nanofibers (CNFs) are attracting attention as a new nanomaterial derived from cellulose, which is one of the major components of trees. We established a unique CNF production method by introducing phosphate groups to the hydroxyl groups in the wood pulp. The obtained phosphorylated CNFs were completely nanofibrillated (approximately 3 nm in width) with high yield, and their aqueous dispersion was highly transparent, viscous, and stable at pH 3−11. An aqueous dispersion of phosphorylated CNFs can be dehydrated and dried to form transparent CNFs sheet with densely-packed CNFs. This sheet has high transparency, strength, and thermal dimensional stability, and at the same time, it has paper-like flexibility. To promote the practical use of this technology, we have currently been operating a demonstration plant for the production of CNFs aqueous dispersion and CNFs sheet.By using CNF, which have excellent water retention and film-forming properties, we developed a nanocellulose PEM that is weakly acidic, has low environmental impact, and has high proton conductivity. The PEM using cellulose nanofibers showed a high proton conductivity of >7×10-2Scm-1 under 95% RH at 80 ℃. By combining a PVPA filler in a CNF suspension, it has become possible to easily create a self-supporting membrane using CNF as a binder. This composite membrane showed an especially high proton conductivity of 9×10-2 Scm-1 under 95% RH at 80 ℃. These results suggest that CNF presents a high potential substitute for perfluorosulfonic acid polymers and serves as a pivotal component of environmentally sustainable PEMs.
Published Version
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