Calibration of a compaction simulator for the measurement of tablet thickness during compression

Development and evaluation of a miniaturized procedure for determining the bonding index: a novel prototype for solid dosage formulation development

The purpose of this study was a comparative evaluation of miniaturized vs. University of Minnesota's (i.e., U of Minn. = Hiestand's) procedures for determining the tensile strength, indentation hardness, and bonding index (BI), one out of three Indices of Tableting Performance (ITP). Tableting properties of six direct compression placebo formulations were determined by using a compaction simulator and a Texture Analyser TA-XT2I, or by following the U of Minn. method, which included a specially designed triaxial compression device, a computer-controlled mechanical stress-strain analyzer, and a dynamic pendulum impact apparatus. Miniaturization of the procedures to determine the ITP, as well as the ability to differentiate between materials while operating compaction cycles more comparable to standard tablet production conditions, enabled proper evaluation of each material's inherent tableting properties. Indentation diameter calculated via an empirical equation appeared to correlate well with, and provided acceptable precision of accuracy to, the determination of indentation diameter via standard optical microscopy methods. The miniaturized and U of Minn. procedure exhibited a significant degree of correlation when comparing the BI. However, the tensile strength and indentation hardness values were somewhat different due to the use of triaxial decompression for the U of Minn. procedure vs. standard compaction profiling for the miniaturized procedure. The present direct compression placebo formulation data gathered from the miniaturized procedures and compared with the U of Minn. method for determining the ITP suggest that both techniques yield similar conclusions. However, discrimination of out-of-die compaction properties determined via the miniaturized procedures, such as tensile strength and indentation hardness, appeared to associate more precisely with changes in strain rate, thus allowing better discrimination of particle-particle interactions and ductile-to-brittle characteristics as a function of compaction speed and pressure.

Thermodynamic analysis of compact formation; compaction, unloading, and ejection. I. Design and development of a compaction calorimeter and mechanical and thermal energy determinations of powder compaction

The aim of this investigation was to determine and evaluate the thermodynamic properties, i.e. heat, work, and internal energy change, of the compaction process by developing a 'Compaction Calorimeter'. Compaction of common excipients and acetaminophen was performed by a double-ended, constant-strain tableting waveform utilizing an instrumented 'Compaction Simulator.' A constant-strain waveform provides a specific quantity of applied compaction work. A calorimeter, built around the dies, used a metal oxide thermistor to measure the temperature of the system. A resolution of 0.0001 degrees C with a sampling time of 5 s was used to monitor the temperature. An aluminum die within a plastic insulating die, in conjunction with fiberglass punches, comprised the calorimeter. Mechanical (work) and thermal (heat) calibrations of the elastic punch deformation were performed. An energy correction method was outlined to account for system heat effects and mechanical work of the punches. Compaction simulator transducers measured upper and lower punch forces and displacements. Measurements of the effective heat capacity of the samples were performed utilizing an electrical resistance heater. Specific heat capacities of the samples were determined by differential scanning calorimetry. The calibration techniques were utilized to determine heat, work, and the change in internal energies of powder compaction. Future publications will address the thermodynamic evaluation of the tablet sub-processes of unloading and ejection.

Deformation of the Stokes B2 rotary tablet press: quantitation and influence on tablet compaction

Deformations that affect the vertical punch displacement of a Stokes B2 rotary tablet press were characterized with a cathetometer. The press deformation was found to be elastic for both the upper and lower compression roller assemblies. However, the upper and lower compression roller assemblies have different Hookian spring constants: 8.58 x 10(4) and 5.18 x 10(4) kN/m for the upper and lower assemblies, respectively. Using two-way analysis of variance, the Hookian spring constants were shown to be independent of compaction phases and lower punch penetration setting. To study the influence of press deformation on tablet compaction, the Hookian spring constants were factored into the caculation of the incremental work of compaction for dibasic calcium phosphate dihydrate and microcrystalline cellulose. As the peak compression pressure increases, the force-displacement work done on the tablet during the loading phase decreases relative to calculations that neglect press deformation. This decrease in force-displacement work was attributed to elastic press deformation, which absorbs energy during the loading phase and then releases this energy later in the compaction cycle, altering the punch-displacement profile. The rate at which the press stores and releases elastic energy depends in part upon the viscoelastic properties of the tablet. Based upon these results, the coupling between press elasticity and a tablet's viscoelastic properties should be accounted for when analyzing tablet compaction or trying to simulate the punch-displacement profile of a tablet press that deforms during compaction.