Dissolution of cellulose derivatives in NaOH/urea aqueous solvent and optimisation of a cationic cellulose/carboxymethyl cellulose hydrogel using response surface methodology

Abstract

This study presents the synthesis and optimisation of a cellulose-based hydrogel derived from oil palm empty fruit bunch (OPEFB) waste via a sustainable green chemistry approach. Cationic cellulose (CC) was prepared through a cationisation using diallyl dimethyl ammonium chloride (DADMAC), followed by dissolution in a NaOH/urea aqueous system. A hydrogel was then synthesised by blending CC with carboxymethyl cellulose (CMC) and crosslinked with epichlorohydrin (ECH). Response surface methodology with a design model of central composite design (RSM/CCD) was applied to statistically optimise three key variables of CC : CMC ratio, ECH concentration and reaction temperature, for enhanced gel content and degree of swelling. The variables were modelled and analysed using quadratic Analysis of Variance (ANOVA). The optimum hydrogel formulation achieved a gel content of 20.95% and swelling capacity of 116.94 g g⁻¹. FT-IR, XRD, TGA and FESEM-EDX were performed to characterize all samples in order to evaluate the success of the reaction optimisation. FT-IR spectroscopy confirmed successful chemical crosslinking of the hydrogel with ECH at 2913.07 cm⁻¹ and 2879.77 cm⁻¹, while XRD analysis revealed a transition from cellulose I to cellulose II with reduced crystallinity at 2θ = 20° and 2θ = 22° suggesting a higher degree of amorphous character. Thermal analysis of TGA demonstrated improved thermal stability in CC due to quaternary ammonium groups, whereas the hydrogel exhibited multi-stage degradation. FESEM-EDX micrographs revealed a highly porous morphology of the hydrogel with an average pore size of 81 µm. These findings validate the potential of cellulose for the development of biodegradable hydrogels with tunable physicochemical properties.