Bahir Dar University, Ethiopia 2024 GC. Page v ABSTRACT The production of carboxymethyl cellulose (CMC) from water hyacinth, which is a cellulose-rich floating weed, was the main goal of this work. The change of this weed into useful product has economic advantages and environmental protection. The synthesis process of CMC included drying, grinding, cellulose extraction, alkalization, and carboxymethylation. The alkali treatment was carried out at 100 oC for 3 hours using 10% (w/v) NaOH, followed by bleaching at 30 oC using 17% (w/v) H2O2. The extracted cellulose was treated with 40% (w/v) NaOH for 15 minutes at room temperature to complete the alkalization process. In addition, this research studied the effect of parameters, namely chloroacetic acid concentration (0.76–1.1M), temperature (40–500C), and time (0.5–1hr) of carboxymethylation on the purity and yield of carboxymethyl cellulose. According to this work, at optimum conditions of chloroacetic acid concentration (0.972 M), temperature (45.035 oC), and time (0.796 hrs.), which were done using the central composite design of response surface methodology analysis, purity (93.553%) and yield (136.744%) of CMC were obtained. The proximate, namely moisture (7.75± 0.48%), ash (20.3±2.5%), volatile matter (58.5±1.73%), fixed carbon (21.2±2.3%), and chemical composition, namely, lignin (7.72± 0.5%), hemicellulose (34.2±0.4%), cellulose (58.08±0.9%), and extractive (5.3± 0.5%) of water hyacinth, were investigated and compared with standards. The DS (1.84±0.39), PH (7.3±0.2), water solubility (46.67±1.5% residue), color (white), viscosity (12±0.6 mPa.s), TGA (65.8% weight loss at 600oC), and SEM (smoother surface) of the optimized CMC product were recorded. The Fourier transform infrared spectroscopy (FTIR) peaks of 1600 (COO-), 1419 (CH2), and 3364 cm-1 (OH) indicate the successful production of carboxymethyl cellulose. This research revealed that CMC was synthesized from water hyacinth, which can be used as a thickener for paint, and carboxymethylation at optimum conditions gives maximum purity and yield of CMC. Keywords: Cellulose, CMC, thickener, alkalization, Carboxymethylation, paint