Determination of bound water content in polymers by DTA, DSC and TG

Various kinds of water sorbed on hydrophilic polymers were analysed using differential thermal analysis (DTA), differential scanning calorimetry (DSC) and thermogravimetry (TG). From the heat of melting or crystallization of water, the bound water content was calculated using the relationship Wt = Wf+Wb, where Wt is the total water content, Wf is the free water content whose phase transition temperatures are similar to those of ordinary water and Wb is bound water. In many hydrophilic polymers, Wb, is the sum of the non-freezing water Wnf and freezing bound water Wfb. From a DTA vaporization curve, the Wt value could be evaluated for a sample containing a large amount of water. At the same time, the Wb value was estimated using TG. In TG curves, a two-step weight loss corresponding to Wf and Wb, was observed. By combining DTA, DSC and TG, it becomes possible to evaluate the exact amount of bound water which is tightly attached to the polymer matrix.