Investigating the moisture-induced crystallization kinetics of spray-dried lactose.
Gravimetric water sorption experiments were performed to study the crystallization behavior of amorphous spray-dried lactose over a wide range of temperature and humidity conditions. Experiments performed at 25 degrees C between 48 and 60% relative humidity (RH) showed that the onset time to crystallization increased dramatically with decreasing humidity. At 55% RH and above, crystallization occurred in a single detectable step, while below a two-step process was observed. Experiments performed at 51% RH between 22 and 32 degrees C indicated the induction time to crystallization onset increased with decreasing temperature. Above 25 degrees C at 51% RH, crystallization occurred in one measurable step, while below crystallization occurred in two steps. The constant RH with varying temperature results were modeled to determine the crystallization mechanism. Above 25 degrees C a mechanism consisting of two competing reaction sequences fit the data with a 0.9997 correlation coefficient. Both reaction sequences have two steps: an auto-catalytic first step is followed by a three-dimensional diffusion controlled water loss step.
Burnett
D J
DJ
Surface Measurement Systems Ltd., 2222 South 12th Street, Suite D, Allentown, PA 18103, USA. burnett@smsna.com
Thielmann
F
F
Sokoloski
T
T
Brum
J
J
D003460:Crystallization; D003890:Desiccation; D006813:Humidity; D007700:Kinetics; D007785:Lactose / Q000737:chemistry*; D008956:Models, Chemical; D044367:Phase Transition; D013678:Technology, Pharmaceutical / Q000379:methods; D013696:Temperature; D014867:Water / Q000737:chemistry
D014867:Water; D007785:Lactose