Turning trash into treasure: conversion of agroresidue rice straw into carboxymethylcellulose biopolymer

In the present study, rice straw-derived cellulose was converted into carboxymethylcellulose (CMC) using alkalization followed by an etherification reaction. The synthesis conditions for this chemical modification were optimized such that CMC with a high degree of substitution (1.02) was obtained. Infrared spectra of the synthesized CMC clearly showed an increased intensity of the C═O bond at 1600 cm⁻¹, confirming successful carboxymethylation. Further, X-ray diffraction analysis demonstrated a decrease in cellulose crystallinity owing to partial rearrangement from a crystalline to an amorphous phase during initial alkalization reaction. The obtained CMC biopolymer was subsequently cross-linked to form a composite hydrogel matrix reinforced with bentonite clay. The hydrogel showed about 91% adsorption capacity for methylene blue dye as a model contaminant in aqueous media. Therefore, this study shows that lignocellulosic agrowaste is a rich source of cellulose, and its derivatives such as CMC possess the potential to realize the waste to wealth sustainability goal.