One-pot solvent-free green quaternization of guar gum using betaine hydrochloride as a natural quaternizing agent

A green and robust dual functionality has been incorporated within the molecular structure of the sustainable agro-biopolymer guar gum via quaternization using naturally abundant betaine hydrochloride (BeHCl) as a quaternizing agent. This quaternization modifies guar gum into a cationic biopolymer with improved functionalities in addition to turning its microbial susceptibility into antimicrobial potential owing to the insertion of permanent quaternary ammonium groups. The environmentally benign, economical, and non-toxic reaction was performed at an optimized temperature of 60 °C ± 1 °C using varying molar concentrations of BeHCl (0.00163-0.0130 M) under solvent-free conditions. The developed methodology adheres to key green chemistry principles, including the use of renewable feedstocks, a solvent-free approach, non-toxic reagents, and energy-efficient processing. Notably, a detailed mechanism for the solvent-free green quaternization of this galactomannan has been proposed for the first time in the present work. The changes in swelling and solubility behavior and the physicochemical and structural properties of the quaternized guar gum (QGG) were studied using diverse techniques, such as FTIR spectroscopy, XRD, TGA-DTG, NMR (1D and 2D) spectroscopy, CHNS/O, and zeta potential analysis. Additionally, the antibacterial and antifungal potential of the developed cationic formulation was studied against E. coli and S. aureus (antibacterial) and A. niger (antifungal), respectively. Hence, the rational combination of naturally occurring betaine hydrochloride and guar gum exemplifies environmental stewardship, offering a green, biodegradable antimicrobial platform with minimized environmental impact.