(97d) Convective Drying Kinetics of Polymer Strip Films

Polymer strip films are flexible platforms for oral delivery of drugs. They have shown superior performance compared to the traditional solid dosage forms¹. These films are extensively used as a delivery form for water-soluble drugs but they can be promising candidates for the delivery of poorly water-soluble drugs, which attracted attention in recent years¹. Drying of strip films is an important part of the manufacturing process. Drying process has significant effect on the final morphology of the strip films and consequently on their quality and performance. In this research, a comprehensive kinetic study is done based on design of experiments (DOE) and integral method of analysis to obtain models for convective drying of polymer strip films loaded with poorly water-soluble drug particles, at different process conditions. The major novelty of this work is in examining the drying kinetics and corresponding the model development that incorporate the impact of drug particles. These models can be used to analyze the effect of process parameters and optimally design the drying process to produce strip films with the desired moisture content and thickness. In the experimental part of this study, a polymer solution of hydroxypropyl methylcellulose (HPMC) E-15 and glycerin mixed with drug suspension (fenofibrate) was used in a doctor blade to cast films on a plastic substrate at a certain thickness. Drying data was collected using a batch set-up in which the air velocity and temperature were controlled by an air blower with a heating coil. The plastic substrate was placed on a heated metal plate with a fixed temperature. The plate was positioned on a digital scale connected to a computer system and the weight of the film was recorded every 2 s. The air temperature and velocity in the chamber were monitored throughout the process, using thermocouples and an anemometer to ensure steady-state operation. Data was collected based on a full factorial design (DOE) with center point for air temperature (40, 55 and 70 ̊C) and velocity (0.2, 0.6 and 1 m/s). A drying mechanism consisting of a constant-rate and a falling-rate period was assumed and based on that a rate model was used in the nonlinear regression to fit the experimental data. The model shows good agreement with the experimental data for the moisture content. At lower air temperature and velocity, shorter constant-rate period and lower drying rate are observed. By assuming moisture transport in the gas phase above the film as the limiting transport mechanism, the constant drying rate was also calculated using principles of heat transfer and available correlations for heat transfer coefficient. The result shows a difference between the estimated and calculated constant drying rates. Overall, this study presents a methodology for estimating the drying rates of wet polymeric strip films in a convective batch drying set-up, which is expected to help facilitate development of robust drying processes. Our study also demonstrates the need for a more detailed transport model to simulate the drying process, which is currently in progress.

1. Krull, Scott M., et al. "Polymer strip films as a robust, surfactant-free platform for delivery of BCS Class II drug nanoparticles." International journal of pharmaceutics 489.1 (2015): 45-57.