Microwave activation of cellulose nanocrystals surface hydroxyls drives ordered reconstruction toward 2D cellulose nanosheets.

Since the discovery of cellulose nanosheets (CNSs), these two-dimensional (2D) nano-sized cellulose nanomaterials have demonstrated advantages in many applications such as barrier materials, reinforcing materials, and film materials, owing to their large lateral dimensions, thin sheet thickness, and continuous sheet-like structure. Although there is a certain structural correlation between CNSs and cellulose nanocrystals (CNCs), it still remains unclear whether CNCs can be directly assembled to obtain CNSs. Therefore, a nano-welding strategy based on microwave hydroxyl activation is proposed in this work, which realizes the reconstruction of 1D CNCs into 2D reconstructed CNSs (rCNSs) within a short reaction time of 15 min. The obtained 2D rCNSs possess sizes of several micrometers and possess structural origins and crystalline building units similar to those of naturally extracted CNSs. The results reveal that microwave treatment effectively activates the surface hydroxyl groups of CNCs, facilitates charge separation of hydroxyl groups, and increases interfacial dipole moment. Ordered hydrogen bond networks are induced via dipole interactions to further trigger the nano-welding, accomplishing the ordered reconstruction of 2D sheet structures. The O2 and CO2 barrier properties of the reconstructed lamellar rCNCs are 1.67 times and 1.12 times those of rod-like CNCs in the PBAT matrix, respectively. This work provides important theoretical support and technical routes for the controllable fabrication and functional application of high-performance 2D nanocellulose materials.