Predicting melt rheology for hot-melt extrusion by means of a simpleTg-measurement
The feasibility of predicting melt rheology by using the glass transition temperature (Tg) of a desired amorphous solid dispersion (ASD) for hot-melt extrusion (HME) and other melt based processes is presented. Three groups of three different active pharmaceutical ingredients (APIs) or plasticizer/copovidone mixtures, with identical glass transition in rheological testing, were used. Their rheological behavior as a function of temperature and frequency were analyzed by means of small amplitude oscillatory shear (SAOS) on an oscillatory rheometer. The zero-shear viscosity (η0) identified at 150 °C was compared to Tg, measured by differential scanning calorimetry (DSC) and SAOS. A strong correlation between η0 and Tg was identified, independent of the API or plasticizer used to achieve Tg of the mixture. To evaluate and rate the discrepancy in η0 of the different mixtures at same Tg, hot-melt extrusion trials were conducted to measure torque and mean residence time. In this paper, carbamazepine, dipyridamole, indomethacin, ibuprofen, polyethylene glycol (PEG 1500) in vinylpyrrolidone-vinyl acetate copolymer (copovidone) as matrix polymer were used.