(337c) Why Do We Dwell on Dwell Time? a Compaction Simulator Study Investigating Tableting Attributes

Compaction of powders and granules into tablets with robust mechanical strength and absence of structural defects remains a significant formulation challenge in the pharmaceutical industry. Two compression process parameters, dwell time and press speed (ex. punch velocity), are discussed as principal variables that directly contribute to the tableting process performance and properties, such as density, tensile strength, and defects. Specifically, extended dwell time has been correlated to reduce the chance of capping and lamination, increase tablet density, and increase tensile strength. The proposed mechanism is longer dwell times allow for stress relaxation and release of entrapped air, making critical defects less likely. On the other hand, reduced punch velocity has been attributed to decreased air entrapment and thus lower incidence of tablet defects/cracking. Prior work is limited, and many studies do not independently control dwell time and punch velocity due to equipment limitations. In this study, we systematically investigate the independent influence of dwell time and punch velocity using a hydraulic compaction simulator. In anticipation of the impact of dwell time and punch velocity being material-dependent, we used a range of material classes such as: ductile materials (ex. microcrystalline cellulose), elastic materials (ex. polyethylene oxide), and brittle materials (ex. dicalcium phosphate). Measurements included tensile strength, tablet density, tablet ejection force, stress relaxation, and imaging of critical tablet defects like capping and lamination through visual inspection and x-ray microcomputed tomography. By understanding the individual effects of dwell time and punch velocity on powder compaction, researchers can avoid unexpected observations on high-speed rotary presses. Decoupling their effects may encourage appropriate reporting of the crucial process parameter(s) for each material and enable appropriate risk responses for tablet defects to improve mechanical property performance. Moreover, understanding of the mechanism responsible for tablet properties, compaction velocity or dwell time, will inform the development of more robust production equipment.