Introduction: The increasing production of bananas in tropical and subtropical regions generates substantial amounts of lignocellulosic residues, particularly banana pseudostems. These residues are often discarded or burned without effective utilization, despite containing significant amounts of cellulose, hemicelluloses, lignin, and fibrous constituents that can serve as renewable resources for the production of bio-based materials. Therefore, the objective of this study was to extract high-purity cellulose from banana pseudostem waste and to comprehensively evaluate its chemical composition, structural characteristics, crystallinity, thermal behavior, and degree of polymerization.
Method: Banana pseudostem fibers were collected, washed, dried, and mechanically processed prior to treatment. The fibers were subjected to a mild alkaline treatment using a 4 wt. % sodium hydroxide solution at 75-80°C. Subsequently, a three-stage oxidative bleaching sequence was applied to further remove hemicelluloses, lignin, and extractive substances. Chemical composition and ash content were determined using standard analytical methods. Structural changes were investigated by Fourier-transform infrared spectroscopy (FTIR), crystallinity was evaluated using X-ray diffraction (XRD), thermal stability was assessed through thermogravimetric analysis (TGA), and the degree of polymerization was determined by viscometric measurements in cuprammonium hydroxide solution.
Results: Chemical composition analysis revealed that the raw banana pseudostem fibers contained 35.5% cellulose, 28.9% hemicelluloses, 16.0% lignin, and 19.6% extractives. Ash content decreased from 14.94% in the raw fibers to 8.75% after alkaline pulping and further to 3.70% after bleaching, indicating the effective removal of mineral constituents and inorganic impurities. FTIR analysis confirmed the elimination of characteristic hemicellulose- and lignin-related absorption bands, while the bands associated with the β-(1→4)-glucan backbone of cellulose remained intact, demonstrating the preservation of the fundamental cellulose structure throughout the treatment process. XRD results showed a substantial increase in the relative crystalline fraction, with the crystallinity index rising from 57.87% in the raw fibers to 86.4% in the bleached fibers, which was attributed to the removal of amorphous components during pulping and bleaching. Furthermore, the degree of polymerization increased from 395 in the raw fibers to 1100 in the purified cellulose product. TGA analysis revealed enhanced thermal stability in the treated samples. In the DTG curves, the degradation peak associated with hemicelluloses within the temperature range of approximately 220–320 °C was markedly reduced and nearly eliminated, confirming the predominance of the cellulose phase in the final material.
Conclusion: The findings demonstrated that the combination of mild alkaline treatment and oxidative bleaching is an effective approach for removing non-cellulosic constituents from banana pseudostem fibers and producing cellulose with high purity, crystallinity, thermal stability, and degree of polymerization. Accordingly, banana pseudostem waste can be considered a low-cost, renewable, and valuable feedstock for the production of cellulose fibers and bio-based materials within the framework of a circular bioeconomy.