Mechanistic study of the effect of roller compaction and lubricant on tablet mechanical strength.

Heckel analysis, tablet tensile strength, and indentation hardness were determined for a series of sieved and roller compacted microcrystalline cellulose mixtures under both unlubricated and lubricated conditions with magnesium stearate. These results have been used to evaluate the loss of reworkability following roller compaction for microcrystalline cellulose and show the extent of impact on tableting properties when magnesium stearate is added intragranularly prior to roller compaction. While results consistent with traditional work-hardening are observed as shown by a modest increase in dynamic hardness and mean yield pressure for unlubricated, roller compacted microcrystalline cellulose, it is overshadowed by the overlubrication effect seen during roller compaction and in particular, the subsequent milling step. The common practice of lubricating the feedstock with magnesium stearate to avoid sticking of the material to the compaction rolls appears to be the major cause of decreased mechanical strength of the final compressed tablets.