An investigation of water vapor uptake kinetics by different forms of lactose, poly(ethylene glycol) and poly(vinyl pyrrolidone)

Water vapor uptake by solids is an area of interest in the pharmaceutical sciences. It is of importance in formulation, packaging and storage. In this study, the kinetics of water vapor uptake by different solids were investigated under various conditions.; The focus of this research was to investigate the behavior of solids with respect to water vapor uptake, and the effects on their physico-chemical properties. Experiments were performed over timeframes for which the water vapor sorption/desorption processes were active, in order to reveal which properties and mechanisms were important.; Lactose, poly(ethylene glycol), PEG, and poly(vinyl-pyrrolidone), PVP, were chosen as model solids to be used in this research. These are solids commonly used in the pharmaceutical industry, and there is widespread interest in properties. The behavior of water vapor uptake differs significantly for each compound.; An experimental setup was designed and constructed, using an electrobalance in a controlled environment chamber, in order to conduct kinetic studies on water vapor uptake by solids. The experimental chamber was used to maintain the humidity and temperature conditions during the experimental runs. The setup was capable of continuously recording any changes in the solid sample weight due to moisture uptake.; The different forms of lactose that were studied exhibited different behaviors with respect to water vapor uptake. Anhydrous lactose showed fluctuating moisture uptake profiles. The β and monohydrate forms did not display the fluctuations, but the β form took up significantly more water than the monohydrate. Lyophilized lactose, which was almost completely amorphous at the start of the uptake runs, sorbed the largest amounts of water vapor, and showed a conversion in the sorption behavior due to crystallization. This resulted in a portion of the sorption profiles in which moisture was taken up, followed by a desorption phase in which moisture was given off. In each phase, the mass taken up or given off was linear with the square root of time. Mathematical models were postulated to describe the kinetics and mechanism of water vapor uptake by lyophilized lactose.; In the PEG studies, molecular weights of 3350 and 8000 were used. Comparisons of water vapor uptake by the various grades and forms of PEG were made. Moisture uptake profiles by PEG showed a two-phase uptake pattern. The first phase showed rapid uptake of moisture, followed by a second region in which the uptake showed a plateau in which the uptake rate nearly vanished. This second phase was characterized by the formation of a thin liquid layer on the surface of the polymer. (Abstract shortened by UMI.)...