Sustainable Extraction and Comprehensive Characterization of Bast Fibers from Egyptian Molokhia (Corchorus olitorius) Stems Using Biological, Chemical, and Mechanical Methods

The valorization of agricultural plant waste as a sustainable source of natural fibers has gained increasing attention due to environmental and economic concerns. This study investigates the feasibility of extracting bast fibers from Egyptian Corchorus olitorius L. (Molokhia) plant residues and evaluates the influence of different extraction methods on fiber properties. Fibers were extracted using biological retting, cold al-kaline chemical treatment (4% NaOH), and manual scraping, followed by comprehensive characterization of their morphological, chemical, crystalline, mechanical, thermal, and environmental properties. The results showed that the extraction method significantly affected fiber performance. Chemically extracted fibers exhibited the smallest average diameter (13.76 ± 0.44 μm), the highest cellulose content (72.23%), and the lowest lignin content (3.20%), indicating effective removal of amorphous components. XRD analysis revealed the highest crystallinity index for chemically extracted fibers (70.0%), compared to bi-ological (60.0%) and manual extraction (64.0%). These structural improvements resulted in superior mechanical properties, with tensile strength and Young’s modulus reaching 600.67 ± 11.73 MPa and 38.96 ± 0.64 GPa, respectively, compared to lower values for biologically and manually extracted fibers. Weight loss analysis indicated optimal extraction durations of 21 days for biological retting and 9 days for chemical treatment. ICP-MS analysis confirmed that heavy metal contents were well below Oeko-Tex® Standard 100 limits. Overall, the findings demonstrate that Molokhia plant waste is a promising and environmentally safe source of natural fibers, with cold chemical extraction offering the most effective route for producing high-quality fibers suitable for bio-based composite applications.