To achieve high mechanical strength electromagnetic interference (EMI) shielding materials for practical application, cellulose nanocrystals (CNC), as a reinforcing and dispersing agent, are intercalated into reduced graphene oxide (RGO) layers, forming an ultrathin, robust, flexible, and hydrophobic CNC/RGO film with a highly ordered nacre-like layered structure via a self-assembly process. The layered structure significantly shortens the reduction time and improves the mechanical strength and shielding effectiveness (SE) of the resultant CNC/RGO composite film. The controlled preparation of CNC with different aspect ratios is realized by using separated bamboo fiber and parenchyma. The CNC of the fiber with a higher aspect ratio and lower diameter results in a lower porosity, denser structure, and more uniform distribution in the composites, and therefore a higher electrical conductivity and SE. The highest SE (39.1 dB) and specific SE (11 367 dB cm² g⁻¹) with a high tensile strength (179 MPa) and water contact angle (106°) of the CNC/RGO film are obtained at 10 wt% CNC loading with a film thickness of 12 μm. The maximum tensile strength of the composite film reaches 227 MPa with 30–50% CNC. The ultrathin high-performance CNC/RGO film shows significant potential as an EMI shielding material in the aerospace and flexible electronics fields.

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.

The mechanical performance of bamboo is highly dependent on its structural arrangement and the properties of biomacromolecules within the cell wall. The relationship between carbohydrates topochemistry and gradient micromechanics of multilayered fiber along the diametric direction was visualized by combined microscopic techniques. Along the radius of bamboo culms, the concentration of xylan within the fiber sheath increased, while that of cellulose and lignin decreased gradually. At cellular level, although the consecutive broad layer (Bl) of fiber revealed a relatively uniform cellulose orientation and concentration, the outer Bl with higher lignification level has higher elastic modulus (19.59–20.31 GPa) than that of the inner Bl close to the lumen area (17.07–19.99 GPa). Comparatively, the cell corner displayed the highest lignification level, while its hardness and modulus were lower than that of fiber Bl, indicating the cellulose skeleton is the prerequisite of cell wall mechanics. The obtained cytological information is helpful to understand the origin of the anisotropic mechanical properties of bamboo.