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 carboxymethylchitosan-g-poly(acrylic acid-co-trimethylallyl ammonium chloride) (CMCTS-g-(PAA-co-PTMAAC)) hydrogel and the properties of water in the hydrogel wereinvestigated by DSC measurement. The freezing water and non-freezing watercontents of the hydrogel were determined quantitatively by examining their relationshipwith the structure and constitutive parameters of the polyampholyte hydrogel. Theexperimental results showed that higher swelling ratio of the hydrogel could decreasethe content of the non-freezing water. It was found that the shape of the exothermic orendothermic curves and the peak temperature were strongly influenced by theheating/cooling rate or heating/cooling cycling. A hysteresis loop was evident during theprocess of heating/cooling cycling and the temperature interval between Tmax+ andTmax- was increased by higher heating/cooling rate. The cross-linking degree of thehydrogel, molar ratio of two monomers and the neutralization degree of the anionicacrylic acid also have a great influence on the water content at various states. Theresults showed that the amount of non-freezing water in the hydrogel increasedgradually as the cross-linking degree increased, but it was reduced while the molarratio of TMAAC increased. By increasing the neutralization degree of acrylic acid, theamount of the non-freezing water was also increased.