Waterless production of cellulose nanofibrils adopting DBD oxygen plasma

Abstract Cellulose is a strong contender to become a raw material which can enable the development of new sustainably resourced biodegradable materials composites supporting circular economy. Almost limitless possibilities exist for functionalising the cellulose molecule via the highly reactive hydroxyl groups enabling easy modification of the material surface, leading to the generation of tailored compatibility with a wide variety of industrial applications. Cellulose nanofibrils (CNF) are one of the most promising such lignocellulose derivatives. Currently, their production capacity and economy are hindered by high chemical and energy consumption, the latter primarily during mechanical fibrillation of native fibre in aqueous suspension, and the negative limitation of very low solids content associated with the gel-like properties of the resulting final product. Eliminating the need for liquid water during process treatment could, therefore, be transformative in respect to production feasibility, end-product transportation and application. The work reported here illustrates the application of oxygen gas barrier discharge plasma on dry cellulose fibre. The example fibre comes from paper pulp manufacture, but in principle is not limited to wood source. The action of the oxygen plasma is to etch the microcellulose fibre structure, simultaneously oxidising the glue-functioning hemicellulose, rendering it potentially soluble, so that the nanopolymer crystalline-based cellulose fibrils can subsequently be readily delaminated from the initial microfiber, either under mild mechanical shearing forces or at the point of application using ultrasonication in aqueous medium, to form the commonly used nanocellulose gel-suspension, but newly at desired higher solids content. The absence of liquid water during this pretreatment process for CNF production can deliver significant reduction in cost and environmental load. In addition, transport of plasma treated dry product to the point of its transformation to nanocellulose gel can decrease fuel consumption drastically and so bring yet further environmental benefits.