Crospovidone interactions with water. II. Dynamic vapor sorption analysis of the effect of Polyplasdone particle size on its uptake and distribution of water.

Polyplasdone of different particle size was used to study the sorption, desorption, and distribution of water, and to seek evidence that larger particles can internalize water. The three samples were Polyplasdone® XL, XL-10, and INF-10. Moisture sorption and desorption isotherms at 25 °C at 5% intervals from 0 to 95% relative humidity (RH) were generated by dynamic vapor sorption analysis. The three products provided similar data, judged to be Type III with a small hysteresis that appears when RH is below 65%. An absent rounded knee in the sorption curve suggests that multilayers form before the monolayer is completed. The hysteresis indicates that internally absorbed moisture is trapped as the water is desorbed and the polymer sample shrinks, thus requiring a lower level of RH to continue desorption. The fit of the Guggenheim-Anderson-de Boer (GAB) and the Young and Nelson equations was accomplished in the data analysis. The W(m), C(G), and K values from GAB analysis are similar across the three samples, revealing 0.962 water molecules per repeating unit in the monolayer. A small amount of absorbed water is identified, but this is consistent across the three particle sizes.