Green synthesis of cellulose acetate from corncob: Physicochemical properties and assessment of environmental impacts

Abstract The widespread availability and chemical constitution of agroindustrial residues have stood them out as a promising source of natural chemicals and polymers, such as cellulose. However, to date, green alternative routes developed to convert the agroindustrial residues into value-added products lack environmental performance regarding the impact’s quantification. In this work, promising green pretreatment (hydrothermal treatment followed by dilute sodium hydroxide reaction) and acetylation (solvent-free method catalyzed with iodine) techniques were applied to obtaining cellulose acetate (CA) from corncob. Physicochemical characterization revealed successful cellulose extraction and acetylation. CA synthesized by green and standard (acetic acid method) acetylation methods presented degree of substitutions of 2.68 and 2.89, and yield of 60 and 40%, respectively. The storage modulus of CA film produced via this green approach (green pretreatment and acetylation) was found to be 1.89 GPa, and its operating temperature was limited to 140 °C. The environmental performance of the green approach was modeled via life cycle assessment (LCA) and compared with a conventional approach (alkali-bleach pretreatment followed by standard acetylation). The LCA shows that the green approach is more advantageous than the conventional approach. The avoidance of chemicals (e.g. acetic acid, sulfuric acid, acetate buffer and aqueous chlorite) and the less use of energy throughout the pretreatment and acetylation steps of the green approach were critical to achieving environmental benefits. For instance, a reduction of 19 and 16% was attained for ionizing radiation and particulate matter emissions, respectively. Results also indicate that, for both approaches, the acetylation step was the main contributor to environmental impacts, as it accounts roughly 82 and 86% of the Global Warming Potential and Human toxicity impacts, respectively, of the green approach. The primary consumption of dichloromethane (DCM) in the purification step significantly influences this negative outlook. Moreover, sensitivity analysis demonstrates that the performance of the conventional approach only exhibits overall positive environmental effects, in comparison to the green approach, for scenarios with very high acetylation weight gains, higher than 70%.