Cellulose Nanofibrils from Black Wattle ( <i>Acacia mearnsii</i> De Wild.) Residues Produced by High-Intensity Ultrasonication: Production and Characterization

This study investigates the production of cellulose nanofibrils (CNF) from black wattle bark residues using high-intensity ultrasound (HIUS) as an environmentally friendly mechanical process. The residues were subjected to alkaline delignification and bleaching to obtain cellulose microfibers (CMF), which were subsequently ultrasonicated at different concentrations (1 and 2 wt %) and temperatures (4 and 25 °C). The resulting CNF suspension was characterized by atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and thermogravimetric analysis (TGA). Only the 1 wt % CMF suspension treated at 25 °C exhibited effective fibrillation, yielding CNF with a diameter of 11.93 ± 4.83 nm. The CNF displayed characteristic functional groups, a crystallinity index of 52.21%, and thermal behavior consistent with that of lignocellulosic-derived nanomaterials. These findings confirm the suitability of black wattle bark residues as precursors for CNF production. Furthermore, utilizing these residues as a raw material represents a promising alternative to conventional cellulose sources, providing a more environmentally sustainable route for obtaining nanofibrils through an eco-friendly ultrasonication-based methodology.