Effect of water content on tensile fracture force and deformability of ram extruded cylinders

Abstract Wetted powder masses with varying amounts of water were used to study mechanistically the extrusion process in terms of brittleness and deformability of ram extruded cylinders. Mixtures of dicalcium phosphatedihydrate (DCPD) and Avicel PH 101 (70/30%) were massed with water (moisture contents 50, 60, 70, 80 w/w%). The masses were extruded in a ram extruder (25.0 mm in diameter) with a 10.0 mm diameter and 10 mm long die. The moist extrudates were cut to isodiametrical cylinders. The porosity and degree of liquid saturation were determined. The extruded, isodiametrical cylinders were glued on to small brass cylinders and connected to a material testing instrument. The force as a function of displacement was recorded during tensile testing of the extruded cylinders at a loading rate of 1 mm/min. The tensile fracture force (force at failure) and the deformability during the measurement, i.e. an inverse number of the slope of the force displacement curves, were determined. The tensile fracture force of the extruded cylinders decreased with increased porosity. At the same time the deformability of the cylinders increased for all the extruded masses, except the one with the highest porosity.