Effect of the Crosslinker Introduction Stage on the Structure and Properties of Xanthan Gum–Acrylamide Graft Copolymer

TL;DR

This paper studies how introducing a crosslinker at different stages affects the structure and water absorption properties of a xanthan gum-acrylamide graft copolymer.

Contribution

The novel contribution is identifying how crosslinker introduction timing and acrylamide concentration influence sorption properties and network structure.

Findings

Spatial network density and interstitial molecular weight can be controlled by crosslinker stage and acrylamide concentration.

Water sorption increases up to 17.2 g/g with later MBA introduction and higher grafting degree.

Lower monomer concentration and early crosslinker introduction enhance equilibrium sorption.

Abstract

Graft copolymers of polysaccharides with side chains of carbon-chain monomers have significant potential for a variety of practical applications. In this work, the effect of the N,N-methylenebisacrylamide (MBA) introduction stage and acrylamide concentration in microwave-assisted radical copolymerization with xanthan gum on the structure and sorption properties of the cross-linked graft copolymer was studied. It has been found that the spatial network density and average molecular weight of interstitial fragments can be controlled by varying these factors. Moderate crystallinity (<50%) and a highly developed surface of our synthesized samples were revealed using XRD and SEM. The graft copolymer exhibits the Schroeder effect; its liquid water sorption obeys Fick’s law and increases with MBA introduction at later stages and with increasing grafting degree, reaching 17.2 g/g. Studying the methylene blue sorption kinetics using pseudo-first/pseudo-second order models, a combined model and an average pseudo-order model have shown that the lower the monomer concentration in the reaction mixture and the earlier (from the onset of the reaction) the cross-linking agent is introduced, the higher the equilibrium sorption. The observed “equilibrium degree of sorption on xanthan gum vs. pseudo-order” relationship, which passes through a minimum, is explained by chemisorption and the sorbate consumption effect. An assumption is made about the prospects of using our synthesized copolymers for designing selective sorbents and ion-exchange membranes.

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