Heterogeneous Acetylation of Plant Fibers into Micro- and Nanocelluloses for the Synthesis of Highly Stretchable, Tough, and Water-Resistant Co-continuous Filaments via Wet-Spinning

Heterogeneous acetylation of wood fibers is proposed for weakening their interfibrillar hydrogen bonding, which facilitates their processing into micro- and nanocelluloses that can be further used to synthesize filaments via wet-spinning. The structural (SEM, WAXD), molecular (SEC), and chemical (FTIR, titration) properties of the system are used to propose the associated reaction mechanism. Unlike the homogeneous acetylation, this method does not alter the main morphological features of cellulose fibrils. Thus, we show for the first time, the exploitation of synergies of compositions simultaneously comprising dissolved cellulose esters and suspended cellulose micro- and nanofibrils. Such colloidal suspension forms a co-continuous assembly with a matrix that interacts strongly with the micro- and nanofibrils in the dispersed phase. This facilitates uninterrupted and defect-free wet-spinning. Upon contact with an antisolvent (water), filaments are easily formed and display a set of properties that set them apart from those reported so far for nanocelluloses: a remarkable stretchability (30% strain) and ultrahigh toughness (33 MJ/m³), both surpassing the values of all reported nanocellulose-based filaments. All the while, they also exhibit competitive stiffness and strength (6 GPa and 143 MPa, respectively). Most remarkably, they retain 90% of these properties after long-term immersion in water, solving the main challenge of the lack of wet strength that is otherwise observed for filaments synthesized from nanocelluloses.