Crospovidone Interactions with Water. I. Calorimetric Study of the Effect of Polyplasdone Particle Size on Its Uptake and Distribution of Water

The ability of crospovidone to take up and distribute water in the polymer samples was studied using differential scanning calorimetry (DSC). Polyplasdone® is an example of crospovidone that, although insoluble in water, serves as a superdisintegrant. Three samples of Polyplasdone® with different mean particle size were studied to see the effect of particle size on the water uptake and distribution characteristics. Water was shown to plasticize Polyplasdone® samples by a reduction in the glass transition temperature as the water content was increased. Although the particle sizes covered a wide range, there was essentially no difference in the ability to take up or distribute water. Three types of water were observed, namely water closely associated with the polymer, water built up as multilayers, and bulk water. Although the water closely associated with the polymer could not be detected by DSC, it could be calculated by mass balance and by extrapolation of the data to the x-axis in a plot of freezable water content as a function of the actual water content. A split in the melting endotherm of water that freezes supported the premise of two forms of freezable water. The number of water molecules per repeating unit could be calculated.