Understanding the thermodynamic micro-environment inside a pan coater using a data logging device.

OBJECTIVE: The objective of the current study was to establish the use of PyroButton data-logging device to monitor and quantify the thermodynamic environment (temperature and humidity) of a pan coating process. MATERIAL AND METHODS: PyroButtons were placed (fixed) at various locations in a pan coater, including exhaust plenum, spray-gun bar, baffles and were also allowed to freely move with the tablet-bed. A full factorial design of experiments (DOE) study on three process parameters, exhaust temperature, pan speed and spray rate was conducted on a 24 inch pan coater, using a coating system and a core tablet combination expected to have a narrow process operating space. RESULTS: It was shown that the PyroButtons can provide a detailed and useful signature of the coating process. PyroButton data showed that the tablet-bed temperature was always lower than exhaust temperature and that the difference was a function of the operating conditions such as spray rate. Similarly, the tablet-bed humidity was found to always be higher than exhaust humidity. Some of the DOE batches showed coating defects (logo-bridging). It was shown that the relative humidity (RH), as measured by the freely-moving PyroButtons in the tablet-bed, correlated well with the logo-bridging events. A critical RH value (30%) was established, above which logo-bridging was observed for the selected formulation. CONCLUSIONS: This study showed that PyroButtons can provide very meaningful micro-environmental data that can be correlated to coating defects, and can aid in establishing a process design space for a given coating and tablet formulation.

Effect of powder substrate on foaml drainage and collapse: implications to foam granulation.

Foam granulation is a relatively newer wet granulation process whereby foamed binder solutions are added to powders in a mixer. It is essential to understand the effect of powder substrate on foam drainage and half-life, which are relevant to nucleation and agglomeration during foam granulation. Hydroxypropyl methylcellulose (HPMC) and hydroxypropyl cellulose (HPC) foams were characterized. Anhydrous lactose and stearic acid were selected as model soluble and insoluble substrates, respectively. The effect of these substrates on foam stability was measured by foam drainage and collapse time and microscopic observations. Both HPMC and HPC foams were similar in foam quality and foam density. Lactose destabilized both HPMC and HPC foams and foam drainage and collapse times were reduced two to four times in the presence of lactose. On the contrary, stearic acid did not significantly change foam drainage and collapse times. Microscopically, lactose exhibited rapid wetting within 15 s upon contacting the HPMC and HPC foam beds, whereas stearic acid remained unwetted even after 8 min and collapse of the foam beds. Substrate solubility can influence foam-substrate interaction. On the basis of this, we suggest potential mechanisms of nucleation and agglomeration of soluble and insoluble substrates during foam granulation.