Effect of carboxylated cellulose nanocrystals on konjac glucomannan/ κ-carrageenan composite hydrogels

Konjac glucomannan/kappa-carrageenan (KGM/KC) composite hydrogels often fail to meet industrial requirements due to their weak mechanical properties, while nanofillers are potential materials to address this challenge by taking advantage of their nano-size and filling effects. Herein, carboxylated cellulose nanocrystals (C-CNCs) were chosen as nanofillers to regulate the properties of KGM/KC composite hydrogels, with focus on the effect of C-CNCs concentration on the morphological and physicochemical properties. Meanwhile, an in-depth exploration of the possible mechanisms was also underlying. C-CNCs were well dispersed within the KGM/KC composite matrix, which positively enhanced the mechanical strength, as well as increased the apparent viscosity and modulus of the composite hydrogel greatly when the C-CNCs concentration was 10 % (w/w). This is mainly ascribed to the enhancement of hydrogen bond interaction among the KGM, KC, and C-CNCs, which were verified by Fourier transform infrared spectroscopy. Additionally, the results of low-field nuclear magnetic resonance confirmed the presence of C-CNCs in the hydrogel matrix reduced the water mobility of the hydrogel, which improved the freeze-thaw stability of the composite hydrogel. The fitting of the Power law model (R-2 > 0.98) showed that the swelling mechanism of KGM/KC composite hydrogels belonged to Fickian diffusion, and the swelling behavior could be regulated by adjusting the C-CNCs concentration. However, the excessive C-CNCs might weakened the interaction of composite hydrogels, which partially explains the reversal of the reinforcement effects seen at the lower additions of C-CNCs inclusion. These results provide a basis for the development and design of KGM/KC-based products with desirable attributes.