Extraction and Comprehensive Characterization of Corchorus olitorius L. Bast Fibers Recovered from Egyptian Molokhia Stem Residues Using Biological, Chemical, and Manual Extraction Methods

The valorization of agricultural residues as alternative lignocellulosic fiber resources may improve biomass utilization. This study comparatively evaluated Corchorus olitorius L. bast fibers recovered from Egyptian Molokhia stem residues using biological water retting, cold alkaline extraction, and manual scraping. The fibers were characterized using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), chemical composition analysis, elongation-at-break measurements, moisture content determination, extraction-related weight-loss assessment, and thermogravimetric/derivative thermogravimetric analysis (TGA/DTG). Cold alkaline extraction produced the highest measured cellulose content (72.0 ± 3.98%) and the lowest measured lignin content (3.0 ± 1.98%). Biological retting produced the highest empirical Segal crystallinity index (75.2%), whereas chemically extracted fibers exhibited the highest elongation at break (1.8 ± 0.17%). Extraction-related weight loss reached 71.4 ± 0.4% after 21 days of biological retting and 80.7 ± 0.5% after 9 days of cold alkaline extraction; these values reflect overall mass reduction during extraction and should not be interpreted solely as removal of specific non-cellulosic constituents. TGA/DTG showed the highest measured onset degradation temperature and maximum degradation-rate temperature for biologically retted fibers (344.4 and 379.6 °C, respectively), while chemical extraction produced the highest residual mass at 600 °C (9.85%). Overall, the extraction route influenced the measured chemical, morphological, structural, mechanical, and thermal characteristics, with no single method exhibiting the highest values across all evaluated parameters. These findings provide comparative baseline data for further evaluation and optimization of Corchorus olitorius bast fibers recovered from Egyptian Molokhia stem residues.