Chemical, Structural and Morphological Characteristics of Sugarcane Bagasse Fibers Under Different Alkaline Treatment Durations

Abstract

This study investigated the influence of alkaline treatment duration on the chemical composition, structural characteristics, and morphology of sugarcane bagasse (SCB) fiber, a widely available lignocellulosic byproduct of the sugar industry. SCB fibers were treated with 1.0 M sodium hydroxide (NaOH) for 30 min, 1 h, 2 h, and 4 h, with untreated fibers serving as the control. Changes in chemical composition were determined through analysis of extractives, Klason lignin, holocellulose, and cellulose contents, while structural and morphological modifications were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and optical microscopy. Increasing alkali treatment duration progressively reduced hemicellulose content from 19.39% to 15.09% after 2 h and Klason lignin content from 20.29% to 4.39% after 4 h, indicating effective removal of non-cellulosic constituents. In contrast, cellulose content increased slightly from 44.94% in the untreated fiber to 46.72% after 2 h of treatment. FTIR analysis revealed a marked attenuation of lignin- and hemicellulose-associated absorption bands at 1730, 1600, 1510, 1460, 1245, and 834 cm⁻¹, whereas cellulose-related bands at 1425 and 1030 cm⁻¹ remained largely unchanged. XRD results showed that the crystallinity index (CrI), calculated using the Segal method, increased from 37.78% for untreated SCB to a maximum of 49.80% after 2 h of treatment before decreasing to 45.65% after 4 h, suggesting that excessive alkali exposure may partially disrupt the ordered cellulose structure. Optical microscopy further confirmed progressive surface roughening and fiber defibrillation with increasing treatment duration. Although all measurements were conducted as single determinations and should therefore be interpreted as relative comparisons, the combined results indicate that a 2 h alkaline treatment provides the most favorable balance between non-cellulosic component removal and cellulose crystallinity enhancement. These findings highlight the potential of optimally treated SCB fibers for applications in biocomposites, papermaking, and biodegradable products, although further studies on mechanical, thermal, and end-use performance are required.