Regenerated Nanochitin Formed via Self-Assembly during Aqueous Reacetylation of Chitosan

<jats:p>Regenerated nanochitin was prepared in water through the reacetylation of chitosan using a simple stirring process. Limiting acetic acid to one equivalent markedly enhanced acetylation efficiency, enabling regenerated chitin formation without organic solvents. Systematic variation of acetic anhydride equivalents, together with time‑course analysis, revealed that nanochitin formation occurs after the degree of acetylation (DA) exceeds a threshold of approximately 90%, at which point a sharp increase in viscosity—arising from fiber entanglement—is observed. Dynamic force microscopy revealed that regenerated nanochitin forms short fibrils, and their length increases as molecular weight, chitosan concentration, and reaction temperature rise. X‑ray diffraction confirmed α‑chitin‑type crystallinity, while crystallinity index values strongly correlated with DA. Regenerated nanochitin exhibited irregularly curved fibrous morphologies distinct from natural nanochitin, suggesting structural disorder in the (110) plane. Strong correlations between DA, crystallinity indices, and fiber length indicate that DA is a key parameter governing self‑assembly and structural development. This aqueous method, which requires no specialized equipment, provides an accessible route for producing regenerated nanochitin and offers opportunities for designing nanomaterials and applications that leverage its unique structural characteristics.</jats:p>