Role of dwell on compact deformation during tableting: an overview

Abstract

Tablet compaction is an important unit operation in the pharmaceutical industry. Among the compaction parameters, dwell time is a key parameter that has been consistently been shown to impact the mechanical quality of tablets. Compacts experience a state of relatively constant strain during the dwell phase and this allows time dependent reactions such as viscoelastic flow to take place within the tablet microstructure. The importance of time dependent compact deformation during the dwell phase has been extensively researched over the years. The amount of plastic flow during the dwell phase has been quantified by researchers by calculating the amount of compaction force decay from stress relaxation curves and by determining certain deformation parameters from compaction force–time profiles during high speed tableting. Dwell time prolongation often led to significant enhancements in the mechanical strength of the tablets, due to a favorable time-dependent shift in the elastic–plastic equilibrium in the compact. The influence of dwell phase on tablet properties is governed by the predominant deformation properties of constituents being compressed along with other coexisting compaction parameters such as strain rate during the consolidation phase of the compaction cycle. Research work on the impact of dwell time on tablet compaction in conjunction with formulation and process variables are useful as the findings that are representative of manufacturing conditions would be useful for understanding of the compaction process especially in high speed tableting. Press or tool designs may also be accentuated at increasing dwell time without compromising tablet production rate.