Abstract
Recent studies on thermal properties of thermo-irreversible polysaccharide hydrogels formed by physical and chemical cross-linking are reviewed. Aqueous solution of polysaccharides forms thermo-irreversible hydrogels via ionic linkage, hydrogen bonding formed by freezing-thawing and chemical linkage. Polysaccharide electrolyte solutions, such as low-methoxyl pectin and sodium alginate, form various kinds of hydrogels when divalent cations are added. Polysaccharide molecules wrap divalent cations and an unique cross-linking zone known as egg-box structure is formed. Viscoelastic properties of Ca-pectin and Ca-alginate hydrogels are measured by thermomechanical analysis (TMA) in water. Dynamic modulus of hydrogels increases with increasing the cross-linking zone. Locust bean gum (LBG), which has been accepted as a non-gelling polysaccharide, is found to form soft gel by freezing-thawing. DSC studies on water restrained by LBG hydrogels are briefly presented. Thermal characteristic of new type polysaccharide hydrogels obtained by chemically linking in water are also introduced. The above rigid and soft hydrogels are thermally stable regardless of preparation method.
https://ror.org/058h74p94 
