Shear Flow and Mixing of Cohesive and Lubricated Granular Material

Abstract

The grains of the pharmaceutical powder have frictional and cohesive interaction between them. This creates problems during tablet ejection, reduces the flow properties and increases the losses due to particle sticking to the surface. To overcome these difficulties a small concentration of powder lubricant is added to the blend. The lubricant powder sticks to the surface of the grain to reduce the friction and cohesion and thereby improving the flow properties. The Objective of this work is to analyze the coating of the lubricant particle around the drug particles and to understand the role of the lubricant in the improving the flow properties using DEM simulations of spherical particles. The DEM simulations are carried out using open source LIGGGHTS software, which allows for the independent choices of particle size, cohesion strength and coefficient of friction. The blend particles and lubricant particles were modeled as large sized, rough (mu = 0:5), spherical and small-sized, spherical with lesser frictional interaction (mu = 0:05) respectively. We studied two mechanisms of lubrication viz, lubrication by reducing friction between large particles and lubrication by reducing cohesion between large particles in the parallel plate shear geometry in the presence as well as the absence of gravitational eld for the range of lubricant concentration and lubricant size. The modified shear behavior was quanti ed in terms of granular flux for the constant applied torque to the system. In the latter mechanism of lubrication, for a range of particle number ratio and size ratio studied, the flux shows an increase with the increase in number ratio and decrease in size ratio. Both variations seem to increase the number of lubricant particles between large particles, thereby preventing the contact which results in less cohesive interaction in the flow as a result flow behavior gets modified.