Overview of preparation, modification, and application of tunicate-derived nanocellulose

Cellulose extracted from the outer capsule of tunicates has received much attention from researchers because of its excellent physicochemical properties. In addition, its nanocellulose has high strength, high purity, high modulus, and versatile photoelectromagnetic properties, and is gradually becoming a novel biomaterial. However, the utilization of tunicate is extremely low, and its discarded outer capsules accumulate in large quantities, resulting in a huge environmental burden and waste of resources. Therefore, it has become imperative to fully exploit and reuse tunicates. This review highlights the different extraction methods (e.g., alkali treatment and kraft process, etc.) and the preparation techniques (e.g., acid hydrolysis, enzymatic treatment, TEMPO oxidation and spinning technique, etc.). The successful preparation and functional modification of tunicate nanocellulose provide the basis for the discovery of its new functions. The applications of tunicate and its composites in various fields (e.g., biomedical field, energy and electronics, polymer reinforcement, food packaging field, paper industry and environmental materials, etc.) are also discussed. Finally, this review concludes with further applications and future perspectives of tunicate cellulose, to provide new ideas and references for improving the high-value integrated utilization of the outer capsule of tunicates.