Development and characterization of sustainable cellulose nanofibers from passion fruit peel using citric and hydrochloric acids

Passion fruit peel is an abundant agro-industrial byproduct rich in lignocellulosic components, but its high pectin and lignin contents hinder cellulose valorization. This study produced cellulose nanofibers (CNFs) from passion fruit peel flour using three chemical extraction routes: citric acid (CA), hydrochloric acid (CL), and a sequential CA + CL treatment, followed by alkaline purification and mechanical fibrillation. Mass balance, yield analysis, preliminary life cycle assessment (LCA), and cost estimation were integrated with structural, chemical, thermal, and morphological characterization. CNF yields ranged from 24.8% to 29.4%, within values reported for agro-residue CNFs obtained under mild conditions. X-ray diffraction confirmed preservation of the cellulose Iβ crystalline structure with crystallinity indices above 80%. FTIR showed effective delignification and differences in hydrogen bonding. Thermogravimetric analysis indicated higher thermal stability for CL-derived CNFs, while SEM revealed nanofibers of 60–65 nm and some fibril bundling in CA + CL. Sustainability analysis showed CA used less water and produced fewer effluents, whereas CL achieved higher yields and lower production costs.