An investigation into the impact of magnesium stearate on powder feeding during roller compaction

Abstract

A systematic evaluation on the effect of magnesium stearate on the transmission of a placebo formulation from the hopper to the rolls during screw fed roller compaction has been carried out. It is demonstrated that, for a system with two ‘knurled’ rollers, addition of 0.5% w/w magnesium stearate can lead to a significant increase in ribbon mass throughput, with a consequential increase in roll gap, compared to an unlubricated formulation (manufactured at equivalent process conditions). However, this effect is reduced if one of the rollers is smooth. Roller compaction of a lubricated formulation using two smooth rollers was found to be ineffective due to a reduction in friction at the powder/roll interface, i.e. powder was not drawn through the rollers leading to a blockage in the feeding system. An increase in ribbon mass throughput could also be achieved if the equipment surfaces were pre-lubricated. However this increase was found to be temporary suggesting that the residual magnesium stearate layer was removed from the equipment surfaces. Powder sticking to the equipment surfaces, which is common during pharmaceutical manufacturing, was prevented if magnesium stearate was present either in the blend, or at the roll surface. It is further demonstrated that the influence of the hopper stirrer, which is primarily used to prevent bridge formation in the hopper and help draw powder more evenly into the auger chamber, can lead to further mixing of the formulation, and could therefore affect a change in the lubricity of the carefully blended input material.

Keywords::

• Roller compaction
• lubrication
• magnesium stearate
• powder flow

Acknowledgements

The authors would like to thank Prof. Mike Adams, Prof. Stuart Blackburn, Dr. Andy Ingram, Dr. Charley Wu (all University of Birmingham), Dr. John Grosso, Dr. Nancy Barbour, Dr. Michael Leane, Dr. Peter Timmins, Dr Wayne Sinclair, Ms. Helen Toale, Mr. Martin Vernon (all Bristol-Myers Squibb) for their support during this study. The authors would also like to acknowledge the Engineering and Physical Science Research Council (EPSRC).

Declaration of interest

The authors acknowledge Bristol-Myers Squibb for the financial support during this Engineering Doctorate project. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this paper.