Rheological Studies of Hydrogels Based on Low- and High-Methoxylated Pectins and Dihydrazides of Dicarboxylic Acids

Abstract

The paper describes the synthesis of pectin-based hydrogels with different contents of methoxy groups. The pectin crosslinking has been carried out using acylhydrazone groups, the dicarboxylic acid dihydrazides being used as crosslinkers in the absence of any catalyst. It has been established that covalently crosslinked hydrogels are formed from highly methoxylated pectin even at low concentrations of the crosslinkers, whereas the formation of covalently crosslinked hydrogel occurs only at a high concentration of the cross-linker for low-methoxylated pectin. Rheological properties and network structure parameters of the pectin hydrogels as functions of the content of methoxy groups and the cross-linkers have been comprehensively studied. It has been shown that the shear modulus of the hydrogels increases slightly but regularly in the number of malonic–succinic–glutaric–adipic dihydrazide series of the cross–linkers and significantly depends on their concentration. It has been found that thermal stability of the pectin hydrogels increases with an increase in the content of the acylhydrazone bonds.