SHRINKING AND SWELLING PROPERTIES OF PELLETS CONTAINING MICROCRYSTALLINE CELLULOSE AND LOW SUBSTITUTED HYDROXYPROPYLCELLULOSE .2. SHRINKING PROPERTIES

From a previous study it is known that pellets obtained from extrusion/spheronization containing microcrystalline cellulose (MCC) and/or low-substituted hydroxypropylcellulose (L-HPC) are able to shrink during drying. This phenomenon has important consequences for pellet properties. The pellet size is reduced while the shape remains constant. Densification during shrinking leads to a lower porosity. In the actual study, shrinking and swelling phenomena were analysed quantitatively. This paper (part I) describes the manufacturing of the pellets and their shrinking properties together with their porosities, friabilities and liquid saturations. The accompanying article (part II) investigates the swelling and dissolution properties of the resulting pellets. Drying methods are of great importance for the properties of resulting pellets. Parts of the same formulations were dried alternatively by fluid-bed, oven or freeze-drying techniques and analysed with the aid of image analysis. Additionally, image analysis of the wet pellets was performed before drying. Freeze-drying almost suppressed shrinking of pellets. The size distributions of freeze-dried pellets are comparable to those of wet (undried) pellets and their porosities are very high. Fluid-bed and oven drying led to identical shrinking phenomena. The influence of the presence of L-HPC in the formulation on the shrinking process was studied. The extent of shrinking is influenced by the amount of excipients which are able to absorb water, the water content of the extrudate and the manner of drying. Freeze-drying prevents shrinking.