Preparation and film properties of carboxymethyl cellulose from leafstalk waste of Okra: Comparative study of conventional and deep eutectic solvent pulping methods

This study valorized okra plant leafstalk (OKS), a lignocellulosic waste that accumulates on farm fields after harvesting its edible okra pods. In this context, acidic-/alkaline-based deep eutectic solvents (DES) pulping methods were compared with the conventional pulping method (NA-C) as a simple and greener isolation process of cellulose from OKS lignocellulose. Subsequently, as an initial attempt, CMCs were synthesized from celluloses obtained from OKS, and their film-forming properties were evaluated. The results showed that one-pot DES pulping expedited the isolation process by simultaneously degrading lignin, hemicelluloses, and other impurities in OKS, retaining cellulose as an unsolubilized residue. Regardless of the pulping methods, isolated celluloses exhibited a typical structure and crystalline pattern of cellulose-I. Moreover, DES-pulped celluloses had similar crystallinity and higher recovery (∼50%) than NA-C. The derived-CMCs exhibited variations in physicochemical properties, such as degree of substitution (0.62–0.76) and molecular weights (30.41–60.52 × 103 g/mol) according to cellulose pulping methods, which impacted unique film properties. Films prepared using CMC synthesized from alkaline DES-pulped cellulose exhibited superior water barrier and mechanical properties essential for films intended for food packaging purposes. Overall, this study successfully valorized OKS into a value-added polymer and suggested a new strategy for isolating cellulose from lignocellulosic wastes.