THE EFFECT OF WATER-CONTENT ON THE POROSITY AND LIQUID SATURATION OF EXTRUDED CYLINDERS

The preparation of isodiametrical and nearly monodispersed pellets by extrusion-spheronization requires an extruded mass which shows a compl ex balance between deformability and its ability to break up into smal ler units. The possibility of extruding the mass through an orifice is mainly related to its plasticity or deformability. Such mechanical pr operties of moist compacts are related to both the porosity and the de gree of liquid saturation. In this study the effect of water addition has been studied in this context. Mixtures of dicalcium phosphate dihy drate (DCPD) and Avicel PH 101 (70:30%) were massed with water (moistu re contents of 50, 60, 70, 80 w/w %). The masses were extruded in a ra m extruder (25.0 mm in diameter), initially with a 10.0 mm die and the n without the die. The moist extrudates were cut to isodiametrical cyl inders and the porosity and the degree of liquid saturation were deter mined. An increased moisture content decreased the extrusion force and increased the porosity of the extrudates. The degrees of liquid satur ation were similar and high for all extruded masses. It is suggested t hat such a nearly complete filling of the pore space with a liquid com ponent is a prerequisite for the wet mass to yield and thus extrude. T he mechanism behind the yielding process is probably an enhanced possi bility for particle movement and rearrangement due to a reduced partic le-particle attraction when the pore space is filled with a liquid.