Ultrasonic-assisted synthesis for the production of green and sustainable hemp carboxymethyl cellulose

Hemp fiber (Cannabis sativa) is being widely used to produce carboxymethyl cellulose (CMC). This study focused on synthesizing carboxymethyl cellulose from bleached hemp fiber to investigate the impact of different factors, i.e., chemical concentration and synthesis time, on its characteristics. The fiber morphology analysis revealed desirable properties, which are essential for high-quality CMC production. Optimal condition for CMC synthesis were investigated, which involved using 20 % NaOH (w/v), the shortest total synthesis time (2.30 h), and using 0.9 g MCA (w/w). This resulted in a non-significantly high DS (0.80) in both nonspray-dried and spray-dried hemp carboxymethyl cellulose, representing a high CMC content around 96 %. Moreover, the use of ultrasonic assistance and spray drying techniques significantly improved the hemp carboxymethyl cellulose properties, indicating a decreased molecular weight (2.65 × 10⁴ g/mol) and a decreased particle size (7.82 μm). Thermal analysis revealed that spray-dried hemp carboxymethyl cellulose had lower thermal stability than hemp fiber and nonspray-dried hemp carboxymethyl cellulose. FTIR and ¹³C NMR analyses confirmed the successful CMC synthesis. Additionally, XRD and SEM analyses demonstrated changes in the crystalline structure and hemp carboxymethyl cellulose surface morphology. This revealed advanced techniques that could enhance hemp carboxymethyl cellulose quality and properties, making it suitable for various industrial applications.