Optimization of cellulose nanocrystals extraction from teff straw using acid hydrolysis followed by ultrasound sonication

Abstract

• Teff straw is highly rich in cellulose fiber and it is a good source of cellulose nanocrystals. • Cellulose nanocrystals (CNCs) are effectively extracted using ultrasound assisted acid hydrolysis and optimized with the Box Behnken Design. • This research introduces a novel approach that combines a two-stage alkali treatment with a bleaching and ultrasound assisted acid hydrolysis process to significantly improve CNCs qualities. Its novelty is optimizing of acid hydrolysis process conditions to maximize the CNCs’ yields and improve its purity. • In the present work, the key findings are successfully isolated high yields and very fine size of CNCs with excellent properties. Maximum yields (93.8 %) and minimum CNCs’ size (31 nm) are obtained from optimum conditions of acid concentration, temperature and reaction times. • Cellulose nanocrystals extracted from teff straw has a high specific surface area (125 m 2 ), high crystallinity index (87.56 %), high strength and high aspect ratio due to its sulfate groups (40 mmol/Kg). Those properties are making it attractive for various applications including food packaging as reinforced nanomaterials. This study presents a novel approach to optimizing the extraction of cellulose nanocrystals (CNCs) from teff straw, addressing the challenge of utilizing agricultural waste effectively. Employing a novel two-stage alkali treatment and bleaching process, enhanced cellulose purity from 39.27 % to 89.75 % while removing lignin. The optimized conditions for the acid hydrolysis were sulfuric acid a concentration of 63.8 %, temperature of 60 °C, and reaction time of 90 mins. This resulted with a minimum CNCs’ size of 31 nm and a maximum yield of 93.8 % w/w. Dynamic light scattering (DLS) analysis revealed the particle size distribution of the CNCs. FTIR and TGA confirmed the functional groups and thermal stability of the CNCs respectively. Scanning electron microscopy (SEM) showed the rod-like or whisker-like morphology of the CNCs. Moreover, X-ray diffraction (XRD) demonstrated that the acid hydrolysis highly affected the amorphous regions of the cellulose. The higher specific surface area, 125 m 2 , and improved cross-linking potential of the CNCs make them attractive for packaging applications. Furthermore, the CNCs exhibited excellent mechanical, thermal, and barrier properties. A statistical analysis supports the robustness of the extraction model, with R-squared values indicating strong predictive capability (R² = 0.992, adjusted R² = 0.983, predicted R² = 0.903).

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