High-intensity ultrasound and mechanical homogenization for extracting rice-straw cellulose fibers: effects on morphology, crystallinity, and thermal properties

Abstract In this study, the extraction of cellulose from rice straw was systematically investigated to evaluate the effects of different mechanical treatments, namely, ultrasonication bath (UB), high shear homogenization (HSH), and high intensity ultrasonication (HIU), on the morphology, crystallinity, and thermal properties of cellulose fibers. Cellulose fibers were initially isolated through alkali (12% NaOH), followed by bleaching treatment with 10% acidified NaClO 2 at pH 3–5, and subsequently subjected to ultrasonication and mechanical homogenization for 1 h under controlled temperature (below 30 °C) conditions. Field Emission Scanning Electron Microscopy (FE-SEM) revealed distinct modifications in surface morphology and an increased fibrillation, with HIU-treated fibers exhibiting superior dispersion. X-ray diffraction analysis indicated an enhancement in crystallinity, with the highest crystallinity index of 74.58% observed for HIU-treated cellulose fibers (HIU-CF). In contrast, the whiteness index measured by chromameter slightly decreased in HIU-CF, whereas UB-treated fibers (UB-CF) demonstrated improved whiteness, suggesting more effective removal of colored impurities and surface cleaning. Fourier Transform Infrared (FTIR) spectroscopy confirmed the preservation of the fundamental cellulose structure across all mechanical treatments, while the HIU-treated fibers exhibited increased peak intensity, indicative of enhanced porosity and fibrillation. Thermogravimetric analysis (TGA) further revealed that ultrasonic treatments improved the thermal stability of cellulose fibers relative to high shear homogenization. These findings demonstrate that the mechanical treatment method significantly influences the structural, morphological, and thermal characteristics of cellulose fibers. The findings indicate that the properties of mechanically treated cellulose highlight their potential as sustainable alternatives to synthetic fibers, with promising applications across diverse industrial sectors.