Eco-friendly cellulose nanofibrils with high surface charge and aspect ratio for nanopaper films with ultrahigh toughness and folding endurance

Abstract

Cellulose nanofibrils (CNFs) are a class of emerging sustainable nanomaterial. Among all their advantages, their high surface charge offers high colloidal stability, while their higher aspect ratio favors the mechanical properties of the corresponding network materials. In order to obtain such CNFs, harsh chemical pretreatments are usually applied, leading to inferior eco-friendly characteristics for CNFs. Herein, we report an eco-friendly pretreatment using maleic anhydride (MA) esterification at a low reaction temperature of less than 100 °C without the addition of any organic solvent or toxic catalyst. Up to 83% of unreacted MA in the pretreatment can be recovered. The resultant MA-CNFs have a high surface charge density (1.6 mmol g⁻¹) while maintaing a high aspect ratio of 390, which cannot be achieved using conventional chemical pretreatment. Moreover, the interfibrillar interaction can be well tuned through the surface MA groups, which translates to superior mechanical properties for nanopaper films possessing ultrahigh toughness (16.4 MJ m⁻³) and folding endurance (3.68), as well as a high transmittance of up to 88%. Altogether, this work enhances the performance of cellulosic materials in an eco-friendly manner, and provides a promising candidate for advanced nanofilm applications, which conventional materials based on pulp fibers or petroleum-based polymers will not be able to reach.