Water movement evaluation during extrusion of wet powder masses by collecting extrudate fractions.
Water is normally the liquid of choice in extrusion/spheronisation systems. Its behaviour during the process is crucial to its success. In most extrusion formulations water moves under the pressures involved. It is important to understand how to control and limit water movement, and to understand its consequences. Five drug models were mixed with microcrystalline cellulose and with three different ratios of water and extruded at two different speeds using a ram extruder. Whilst extruding, the extrudates were collected to small fractions and dried to constant weight. Different parameters were calculated to quantify the extent of water movement that occurred. The same formulations were also extruded and than spheronised to pellets, for which size and shape factor were measured. The correlation between water level and extrusion force at the same given time was calculated. It was found that at the faster speed and in the wettest formulation there was less water movement. A significant correlation was found between extrusion force and water going through the die. The extrusion/spheronisation technique was found to be tolerant to some extent of water movement during the extrusion process. Nevertheless, excessive water movement is not appropriate.