Preparation and Application of Cellulose Nanofibers from Local Waste Biomass, Such as Orange Peels Rich in Primary Cell Walls

Cellulose nanofibers (CNFs), which can be prepared from various plant biomasses, are crystalline cellulose-based fibers with a width of 3–100 nm and have attracted attention as highly functional nanomaterials. Ehime Prefecture is a citrus-growing region in Japan, and its squeezed orange juice is well-known throughout the country. Massive amounts of peel waste are generated after juice processing, leading to waste management issue. Therefore, the effective use of citrus peel waste remains an issue, both locally and globally. The squeezed juice residue contains cellulose, which can serve as raw material for CNFs. Previous reports on the preparation and application of CNFs from citrus peels with primary cell walls are reviewed in this paper to summarize previous studies on CNFs derived from primary cell walls, which remain less well-known, and to discuss their potential development. This paper focuses on CNF preparation from citrus peels, analysis of their physical properties, development of applications, and discussion regarding CNFs from primary walls. This study suggests that the primary cell wall is novel raw material for producing highly advanced CNFs.