Study of carboxymethyl chitosan-based polyampholyte superabsorbent polymer (Part II): Investigating the state of water in CMCTS-g-(PAA-co-PTMAAC) hydrogel

Some specific structure-properties relationship of a polyampholyte carboxymethyl chitosan-g-poly(acrylic acid-co-trimethylallyl ammonium chloride) (CMCTS-g-(PAA-co-PTMAAC)) hydrogel and the properties of water in the hydrogel were investigated by DSC measurement. The freezing water and non-freezing water contents of the hydrogel were determined quantitatively by examining their relationship with the structure and constitutive parameters of the polyampholyte hydrogel. The experimental results showed that higher swelling ratio of the hydrogel could decrease the content of the non-freezing water. It was found that the shape of the exothermic or endothermic curves and the peak temperature were strongly influenced by the heating/cooling rate or heating/cooling cycling. A hysteresis loop was evident during the process of heating/cooling cycling and the temperature interval between T_max⁺ and T _max^- was increased by higher heating/cooling rate. The cross-linking degree of the hydrogel, molar ratio of two monomers and the neutralization degree of the anionic acrylic acid also have a great influence on the water content at various states. The results showed that the amount of non-freezing water in the hydrogel increased gradually as the cross-linking degree increased, but it was reduced while the molar ratio of TMAAC increased. By increasing the neutralization degree of acrylic acid, the amount of the non-freezing water was also increased.