Comparative production of cellulose nanocrystals from sea mango (Cerbera odollam) fibre waste : Taguchi-optimized conventional hydrolysis, ultrasound-assisted processing, and kinetic analysis

The growing demand for sustainable bio-based nanomaterials has intensified interest in utilizing non-food industrial crop residues for cellulose nanocrystal (CNC) production. In this study, sea mango (Cerbera odollam) fibre waste (SMFW), non-edible lignocellulosic biomass, was introduced as a novel precursor for CNC production. CNCs were produced via sulfuric acid hydrolysis using both conventional and ultrasound-assisted approaches. Process parameters for conventional hydrolysis were optimized using a Taguchi experimental design, yielding a maximum CNC recovery of 72.09% under optimal conditions of 60 • C, 45 wt% sulfuric acid, a 20 mg/mL solidto-liquid ratio, and 60 min reaction time. The optimized conditions were subsequently applied to ultrasoundassisted hydrolysis to evaluate the effects of process intensification. Kinetic analysis using the Saeman firstorder and two-fraction models demonstrated that ultrasound markedly accelerated CNC formation, increasing the apparent rate constant from 0.0864 min-1 (conventional) to 0.1213 min-1 , and promoting a dominant fastreacting fraction associated with enhanced removal of amorphous cellulose domains. Structural and physicochemical characterization confirmed the successful formation of sulfate ester groups on CNC surfaces, preserving cellulose Iβ structure. Ultrasound-assisted CNCs exhibited slightly higher crystallinity (82.23%), reduced aggregation, smaller lateral dimensions, and narrower particle size distributions (80-800 nm) compared to conventionally produced CNCs. Thermogravimetric analysis indicated reduced thermal stability relative to raw biomass, consistent with sulfation and increased surface area. This work establishes SMFW as a new, sustainable biomass resource for CNC production and demonstrates that ultrasound-assisted hydrolysis is an effective strategy to enhance reaction kinetics and nanocellulose quality.