Detailed investigation of gel–sol transition temperature of κ-carrageenan studied by DSC, TMA and FBM

A broad temperature range of the gel–sol transition of κ-carrageenan was precisely examined by differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and the falling ball method (FBM). κ-Carrageenan the transition temperature of which ranged from 290 to 350 K was used as a representative sample of a thermo-reversible hydrogel. The starting of transition attributed to dissociation of the weak cross-linking zone of aggregated double helices was detected as a change of expansion coefficient by TMA and as an endothermic deviation by DSC. Peak temperature of endotherm by DSC agreed well with the temperature where expansion changed from positive to negative value and this temperature was attributed to gel–sol transition caused by dissociation of double helices’ assembly. Transition temperature measured by FBM was observed at a temperature higher than those obtained by DSC and TMA, which was attributed to decomposition of double helices.