Development and characterization of novel tannin-modified konjac glucomannan hydrogels with optimized crosslinking features

Konjac glucomannan (KGM) is a non-toxic, biodegradable polysaccharide known for its excellent gel-forming properties and high water retention. This study presents a novel tannin-enhanced KGM hydrogel, tailored for controlled solvent release and improved surface adaptability in artwork cleaning applications. Hydrogel formulation consisting of KGM crosslinked with borax was optimized generating borax through the reaction of boric acid and sodium hydroxide. This resulted in uniformly crosslinked gels with improved tensile strength and high moisture retention, essential for controlled cleaning. Moreover, tannins were incorporated in the optimised KGM-based polymer matrices. This modification was introduced as a novel and sustainable strategy to enhance crosslinking, leveraging natural polyphenols to add functional properties. Two tannins were tested: a condensed tannin isolated from Vitis vinifera, and a hydrolyzable tannin isolated from oak, tannic acid. Tannins were incorporated either through hydrogen bonding or covalently. Covalent attachment was achieved using epichlorohydrin (ECH) to add an epoxide motif to the tannin, enabling covalent binding with KGM. The resulting gels were thoroughly characterized for their chemical, rheological and morphological properties, showing that novel crosslinking via in situ borax formation improved moisture retention and surface adaptability, while the incorporation of tannins enhanced water absorption, maintaining high retention and favorable mechanical properties.