Die wall pressure measurement for evaluation of compaction property of pharmaceutical materials

The aim of this study was to evaluate the compaction property of several pharmaceutical materials by measuring the die wall pressure. The profile of die wall force during tabletting process was measured with the compaction process analyzer (TabAll). Several compaction parameters such as maximum die wall pressure (MDP), residual die wall pressure (RDP) and pressure transmission ratio (PTR) from upper punch to lower punch were calculated. The ejection pressure (EP) of tablet compacted was also measured as a parameter for sticking property of the compacts. The profile of die wall force observed was classified to the typical two types, a small type and a large one. Partly pre-gelatinized starch (PCS), cornstarch and low substituted hydroxypropylcellulose (L-HPC) were the small type, while crystalline lactose, ascorbic acid and potassium chloride were the large type. The die wall force of crystalline lactose remarkably increased at the ejection of tablet and then capping was observed. RDP value of PCS, cornstarch, L-HPC was smaller than that of crystalline lactose, ascorbic acid, potassium chloride. As the higher pressure transmission ratio from upper punch to lower punch means a good compressing property of the powder, we proposed that RDP/MDP is a useful parameter for evaluating the compaction property of powders. Although potassium chloride which is strongly plastic deformable powder showed the highest RDP value among the powders tested, the RDP/MDP value was lower than that of crystalline lactose or ascorbic acid and the tensile strength of resultant tablet of potassium chloride was much higher than these powders.