Highly foldable, robust and water-resistant cellulose specialty paper reinforced by aramid nanofibers

Mechanical strength and water resistance are typical issues with cellulose paper due to the nature of cellulose. Specialty papers that are highly foldable, such as banknotes and securities, must be able to withstand multiple folding actions while also providing exceptional durability. In this paper, a multi-approach strategy involving direct addition, in-situ growth, and coating is proposed for introducing aramid nanofibers (ANFs) as 1D nanofillers and 2D membranes to improve the overall properties of cellulose specialty paper. The flexible and fatigue-resistant ANFs with a large aspect ratio play the roles of filling and bridging between cellulose fibers and ANF via massive hydrogen bonds. The resulting 1.5 wt% ANF reinforced paper has a tensile index of 79.1 N m/g, an impressive folding endurance of over 3500 times, and strong water resistance (a water contact angle of 85.2°). Furthermore, SEM observation of paper during various folding periods reveals that the filling and bridging effects of ANFs, as well as their highly entangled nanofibrous network, contribute to paper's excellent foldability. This work facilitates promising candidates for simultaneously achieving robust, highly foldable, durable and water-resistant cellulose specialty paper.Graphical abstract