(201g) Characterization of Lubrication in a Continuous Powder Mixer
Lubricant blending is an important step in almost every tablet manufacturing process. Presence of lubricant prevents powder sticking to the tablet die and also improves granular flow properties. In the context of establishing the continuous tablet manufacturing technology, characterization of continuous lubricant mixing becomes important. In the present study, lubricant mixing was characterized in a continuous powder mixer (Gericke GCM 250) using a model formulation of acetaminophen, Avicel and Magnesium Stearate for various processing conditions. The parameters examined in this work are impeller rotation rate, impeller design, lubricant feed position and the concentration of lubricant.
For different experimental conditions samples were collected at the exit of the blender, which were further analyzed by NIR spectroscopy to determine the concentration of Magnesium Stearate in them. The extent of lubrication in the powder was characterized by the wettability measurement using Washburn's technique (Washburn, 1921). Micro-distribution of lubricant in the powder blends is affected by the total shear exposure, which subsequently affects its flowability, bulk density and tabletting properties (Mehrotra et. al, 2007). Residence time distribution measurements were used to estimate the total shear exposure (number of blade passes) in the blender. Powder samples were then compressed into tablets using a Carver Press at a constant compression force. Tablets were tested further for both lubricant micro-distribution as well as crushing hardness. Lubricant micro-distribution in the tablets was measured using LIBS (Laser-Induced Breakdown Spectroscopy) technique.
For intermediate rotation rates tablet hardness was found to be reduced. Feed position of MgSt was found to be an important parameter to control the shear exposure. To optimize the shear exposure using feed position, mixing profiles were calculated by sampling inside the blender at steady state. Two feed positions including the inlet and the center of the continuous blender were examined at different rotation rates. Thus, residence time and total shear were used to correlate tablet hardness, lubricant homogeneity and blend hydrophobicity with the processing parameters.
Mehrotra A., Llusa M., Faqih A., Levin M., Muzzio F. J., Influence of shear intensity and total shear on properties of blends and tablets of lactose and cellulose lubricated with magnesium stearate, International Journal of Pharmaceutics, 2007, 336, 284-291.
Washburn, E.W., 1921. Phys. Rev. 17, 273?283