Preparation and characterization of carboxymethyl cellulose from mechanically activated bagasse cellulose

Abstract: Carboxymethyl cellulose (CMC) is a kind of anion and aliphatic and water-soluble cellulose ether. It has been widely used in food, medicine, detergent etc because it has good performance in thickening, dispersion and suspension and so on. It is vividly regarded as the "Monosodium glutamate" in industry. In recent years, the CMC demand is stably growing. Improving quality and developing special type of CMC for specific user are becoming the development directions of CMC. Sugarcane bagasse (SCB), a kind of waste in the process of sugar extraction, is abundant and low-cost lignocelullosic material. SCB is mainly composed of cellulose, hemicellulose and lignin. Cellulose forms microfibril by intramolecular and intermolecular hydrogen bond, and hemicellulose and lignin are filling and adhering agent among the microfibril. Because of the special structure of SCB, chemical agents are difficult to penetrate and diffuse in it, which limits its application. Therefore, it is necessary to pretreat SCB to remove lignin and hemicellulose, reducing cellulose's crystallinity. To utilize SCB and prepare CMC with high degree of substitution (DS), SCB was mechanically activated by a stirring-type ball mill. Using monochloroacetate (MCA) as etherifying agent and sodium hydroxide (NaOH) as catalyst, CMC was synthesized from SCB with different activation time. The effects of mechanical activation time, reaction time, reaction temperature, solid-liquid ratio, NaOH-MCA molar ratio and water content on carboxymethylation of SCB were investigated respectively by using the DS of CMC as evaluating parameter. The structure of CMC from SCB was characterized by using Fourier transform infrared spectroscopy (FTIR),X-ray diffraction (XRD) and 1HNMR spectroscopy (1HNMR). The results indicated that mechanical activation considerably enhanced the carboxymethylation of SCB, the mechanically activated SCB was easier for carboxymethylation than the original SCB, and the DS increased first and then decreased with activation time. The reasons were that mechanical activation broke the sealing of cellulose by lignin, destroyed the crystalline structure and decreased the crystallinity of cellulose, which made etherification reagent more easily penetrate into the SCB and could increase reactivity and decrease the dependence on solid-liquid ratio, ratio of NaOH/MCA, H2O/substrate, reaction time and reaction temperature. The DS and viscosity of CMC obtained were 1.521 and 13 mPa.s respectively through carboxymethylation under the conditions which were reaction time of 2.0 h, solid-liquid ratio (mass/volume) of 1:18 g/mL, NaOH-MCA molar ratio of 2:1, H2O/substrate (volume/mass) of 1:1 mL/g and reaction temperature of 75℃. The research results would provide the reference for the preparation of CMC with high DS.