Design and fabrication of nanocellulose-based microfibers by wet spinning

Fiber materials, especially high-performance microfibers, play an essential role in the development of human society. In particular, advanced bio-based microfiber materials that can replace petroleum resources are receiving increasing attention for better sustainable development. Nanocellulose has excellent physical and chemical properties such as light weight, high strength, good biocompatibility, and biodegradability. Combined with wet spinning, the most widely used continuous spinning strategy, nanocellulose-based microfibers have become an emerging class of high-performance and high value-added biological fiber materials. This review comprehensively summarizes the design and fabrication strategies of nanocellulose-based microfibers by wet spinning to achieve high-quality, controllable, and predictable performance. The impacts of diverse spinning processes and material compositions on microfiber properties are elaborated. First, we outline diverse wet spinning processes involving conventional wet spinning, dry-jet wet spinning, and microfluidic wet spinning. The process parameters related to fiber structure and performance are mainly discussed. Subsequently, various types of nanocellulose-based microfibers are presented, including all-nanocellulose microfibers, natural composite microfibers, synthetic composite microfibers, and functional additive-containing microfibers. Finally, the application potential and present challenges of nanocellulose-based microfibers in the field of functional composites are proposed.