The effects of lag-time and dwell-time on the compaction properties of 1:1 paracetamol/microcrystalline cellulose tablets prepared by pre-compression and main compression.

The effects of lag-time and dwell-time on the compaction properties of tablets compressed from a 1:1 blend of paracetamol and microcrystalline cellulose have been examined using a compaction simulator. Increases in lag-times (from 0.06 to 0.53 s) resulted in small increases in the tensile strengths of the tablets when combinations of 80 and 160 MPa were used as the compression pressures. Further increases in lag-time did not alter the tablet strengths. When combinations of 240 and 320 MPa were used for pre-compression and main compression, the effects on the tensile strengths were more complex, partly because the high elastic recoveries of the tablets resulted in greater variability in the data. Increases in lag-times from 0.06 to 0.97 s resulted in an increase of between 12 and 28% in tensile strength. Longer lag-times (1.24 or 1.52 s) did not result in further increases in tensile strength. The application of a dwell-time of 0.26 s during pre-compression or main compression pressures of 80 and 160 MPa generally led to a decrease (14-22%) in tensile strength compared with tablets where no dwell-time was used. This was because of increases in both the elastic recoveries and elastic energies. Subsequent increases in dwell-time from 0.26 to 0.9 s resulted in increases in tablet strength compared with that obtained when no dwell-time was applied. The tensile strengths of tablets made with a pre-compression of 160 MPa then a main compression of 80 MPa were 11-33% higher than those of tablets made with a pre-compression of 80 MPa then a main compression of 160 MPa. This was because higher plastic energies and more plastic deformation occurred at the higher pre-compression. Generally, the application of dwell-time resulted in greater increases in tensile strengths than lag-time, which had less effect on the compaction properties.