Analysis of the state of water in polyvinylpyrrolidone aqueous solutions using DSC method

The states of water in polyvinylpyrrolidone aqueous solutions were investigated by using DSC methods. First, the glass transition was attributed from frequency dependent of temperature modulated DSC (TMDSC) measurements. Then, it was analyzed quantitatively using Couchman's approach. Two types of water exist in the concentration of PVP above 50 wt%. One shows glass transition, and other is liquid state at above −60 °C. On the other hand, in the concentration of PVP below 50 wt%, glass transition and phase transition from ice to liquid were observed. The glass transition analysis revealed that local part of PVP aqueous solution with constant composition shows glass transition. The concentration of water calculated from heat of fusion is lower than that derived from drying a sample after DSC measurement. Finally, in the concentration of PVP below 50 wt%, three types of water were clarified by means of quantitative discussions using impurity analysis, Couchman's approach and heat of fusion. One shows glass transition at around −25 °C, another is freezable and the other is liquid state at above −60 °C.

► The states of water in PVP aqueous solutions were investigated using DSC methods.
► Glass transition of PVP aqueous solution was attributed from TMDSC measurements.
► Impurity analysis, glass transition analysis and heat of fusion were discussed.
► Three types of water have been clarified.