Preparation of dispersible TEMPO-CNF ultrafine powder and its application in achieving superhydrophobicity

Nanocellulose, which can be derived from abundant renewable plant sources, possesses outstanding properties such as nano-size, high strength, and high reactivity, rendering it a promising alternative to fossil-based materials in the future. However, the conventional drying of nanocellulose aqueous suspensions tends to result in significant aggregation, which substantially impedes the functionalization of nanocellulose by organic modifying reagents. This study presents an innovative method for drying nanocellulose from aqueous suspension into ultrafine powders while preserving its nanoscale properties. Ammonium bicarbonate was introduced into the aqueous suspension of cellulose nanofibrils (CNFs) to precipitate CNFs that were then dispersed in n-butanol. During the evaporation process, the ammonium bicarbonate decomposed, and the water evaporated, leading to the drying of CNFs in pure n-butanol into an ultrafine powder with high dispersibility. When prepared with a large amount of n-butanol, these ultrafine powders demonstrate enhanced redispersibility in water, with the ability to form a stable suspension through simple agitation. Our research in this paper centers on elucidating the dispersion mechanism of CNF ultrafine powders. We suggest that CNF ultrafine powders dried from n-butanol form a loosely porous mesoporous structure. In the absence of significant changes in crystallinity, the substantial reduction in the inaccessible area of the amorphous regions is likely responsible for their enhanced redispersibility in water. Additionally, by capitalizing on the micro- and nano-structural characteristics of CNF ultrafine powders, we have successfully developed a superhydrophobic coating by applying hydrophobic modification and adhering the treated powder to the surface of filter paper. This outcome not only substantiates the practical applicability of CNF ultrafine powders but also affirms their micro- and nano-dimensional structural attributes. This paper proposes a straightforward and viable approach for the reaction of functionalized organic reagents with nanocellulose, thereby significantly broadening its potential applications.