Effect of Partial Dehydration on Freeze-Drying of Aqueous Nanocellulose Suspension

The study on low-cost drying-redispersion process for the storage and transport of nanocellulose has been a great challenge in practical applications. The existence of abundant hydroxyl groups on the nanocellulose surface causes a strong tendency of agglomeration of the nanoparticles in the dry state. In this paper, we propose a new method to solve this problem by controlling the solid content of cellulose suspension to obtain a well-dispersed nanocellulose with reduced fibrillar alignment in the following freeze-drying treatment. The results show that when the solid content in the original suspension varied between 4 and 10 wt %, the morphology of the aerogel transformed from the membranous to fibrillar network with increasing specific surface area and redispersibility, and further dehydration was detrimental. This phenomenon is mainly attributed to the entanglement of cellulose fibrils in the cellulose network, which suppressed the growth of ice crystal during the dry-freezing process. In addition, the interaction between intra-/intermolecular hydrogen bonds is also proved to be responsible for the variation of the cellulose morphologies and the thermal decomposition temperature. This research will provide an effective and convenient way for the transportation and storage of nanocellulose, aiming at its large-scale industrial applications.