Enhanced mechanical property and freeze-thaw stability of alkali-induced heat-set konjac glucomannan hydrogel through anchoring interface effects of carboxylated cellulose nanocrystals

Abstract

The alkali-induced heat-set konjac glucomannan (KGM) hydrogels have drawn increasing attention due to their high absorbency and thermal irreversibility ability, but pure KGM hydrogels generally have defects of low strength and high syneresis rate. Cellulose nanocrystals and their derivatives, which have a very high specific surface area, good biocompatibility, biodegradability, and low toxicity, are promising candidates to solve this challenge. In this work, we propose the use of carboxylated cellulose nanocrystals (C–CNCs) as nanofillers for the strengthening of KGM hydrogels. The effects of the C–CNCs content on the microstructure and physical properties of the KGM hydrogels and their possible mechanism were investigated. The compressive test results indicate great improvement in the mechanical properties upon the addition of the C–CNCs for the KGM hydrogel and reached a maximum value at 20% loading. The microstructure analyses of the KGM hydrogel revealed that the well-distributed C–CNCs can act as a physical cross-linker to connect the neighboring KGM chains to strengthen the resultant hydrogel, based on their strong interactions, including hydrogen bonding and chain entanglements. Moreover, adding 20% C–CNCs can significantly decrease the syneresis after five repeated freeze-thaw cycles of the KGM hydrogels. Compared to pure KGM hydrogels, KGM/C–CNCs nanocomposite hydrogels demonstrated higher water-binding capability based on Low-field nuclear magnetic resonance. These findings indicate that C–CNCs are considered anchors for KGM chains as well as reinforcement fillers in the polymer matrix, which contributes significantly to the mechanical property of the nanocomposite. Therefore, C–CNCs were a promising material to be applied for modulating the mechanical and freeze-thaw stability properties of the polysaccharide-based hydrogel in food and biomedical applications.