The effect of speed of compression on the properties of compacts.
A high speed hydraulic press has been developed into a computer
controlled high speed compression Simulator, capable of reproducing
displacement time profiles seen on any production tabletting machine.
The system has been validated to monitor punch displacements to ±12pm
and loads to ±O.05% of full scale. Confidence in the results obtained
using the Simulator were enhanced by comparison with other operational
Simulators. The established Simulator was then used to investigate the
effects of compression on ibuprofen.
Ibuprofen was found to consolidate mainly by plastic
deformation with a lesser contribution from the melting of asperities.
A significant amount of pressure induced melting and subsequent fusion
bonding occurred at higher pressures. Ibuprofen was found to be
sensitive to the magnitude and rate of application of the compression
pressure. The extent of plastic flow exhibited by ibuprofen during
compression was, found to decrease as the compression speed increased.
Lamination and capping of ibuprofen compacts at high compression
speeds was considered to be due to a combination of air entrapment and
the inability of the compact to withstand the stresses of
When ibuprofen was mixed with a second material and compressed,
the consolidation mechanism and properties of the compacts formed were
found to follow complex relationships. The relationships were
dependant on the proportion of each material and the speed of
compression. For ibuprofen microcrystalline cellulose mixtures
positive interactions were considered to occur due to bonding between
the two materials. For ibuprofen and lactose mixtures the interactions
observed were considered to be a balance between the plastic
deformation by the ibuprofen relieving the applied load preventing the
cri tical force required for fracture of the lactose being attained,
and the lactose fragments bearing the applied load reducing plastic
flow by ibuprofen.
The Simulator was then employed to investigate different
aspects of tabletting machine design. A simple ibuprofen
microcrystalline cellulose mixture and a commercial ibuprofen
formulation were compressed to a constant load and then to a constant
thickness and the properties of the compacts compared. Tablets
prepared under a constant maximum applied load, with fill weights
varied over the B.P uniformity of weight limits, had relatively
constant disintegration times and radial tensile strengths. This was
considered an advantage over the tablets prepared to a constant
thickness which showed considerable varia•tion under the same conditions.
The second aspect of tabletting machine design to be
investigated was the use of relatively high precompression pressures
using a commercially available paracetamol granulation. The maximum
compression pressure exerted during the tableting cycle was found to
be the major factor contributing to the tensile strength of the
tablets. The use of a second compression either before or after the
main compression was found to produce a significant increase in tablet
tensile strength. The greater the magnitude of the second compression,
the greater its effect on tensile strength. The contribution of a
second compression towards the tablet tensile strength was attributed
to the effective increase in dwell time it generated. The orientation
of the greater and lesser compression pressures during tableting was
found to influence the tablet tensile strength. Stronger tablets
resulted if the greater pressure was exerted first. This was
considered to be a function of temperature increases within the tablet
and the disruptive effects of the second compression.