Modeling pharmaceutical compacts tensile strength based on viscoelastic properties

Although several researchers acknowledge the effects of viscoelasticity in pharmaceutical powder compaction, no models have been reported that relate compact mechanical properties to the powder viscoelastic properties. The tensile strength of a compact is largely influenced by contact area between deforming particles which depends on the viscoelastic properties and compaction variables. The objective of this research was to develop semi-mechanistic models based on viscoelastic contact area estimates, to predict tensile strength of Microcrystalline Cellulose (MCC) and Acetaminophen (APAP) compacts. Formulations with varying amounts of MCC, APAP and moisture contents corresponding to 50 and 70% RH were prepared. The powders were compressed in a Uniaxial testing machine (Instron) at a punch velocity of 2 mm/min to final pressures in the range of 12.5 to 44 MPa. The diametral tensile strength, compaction and viscoelastic properties were determined. The deformation contact area was estimated using equation by Lum and Duncan-Hewitt [22] based on the median particle size of MCC, compaction and viscoelastic properties as determined from the Maxwell model. It was found that the estimated contact area depended on the APAP composition, moisture content and on compaction pressure. The viscoelastic contact area, density and final compact tensile strength were found to increase with increasing compaction pressure, moisture content and MCC. A unified model that expresses the compact tensile strength as a function of viscoelastic contact area was successfully developed.

Viscoelastic properties, density and tensile strength of compacts were measured. Density and tensile strength increased with increasing MCC and moisture content. Viscoelastic contact area was estimated using the small deformation model. Contact area was influenced by raw material and process variables. Semi mechanistic models that predict density and tensile strength were proposed.Figure optionsDownload as PowerPoint slideHighlights
► Viscoelastic properties, density and tensile strength of compacts were measured.
► Density and tensile strength increased with increasing MCC and moisture content.
► Viscoelastic contact area was estimated using the small deformation model.
► Contact area was influenced by raw material and process variables.
► Semi mechanistic models that predict density and tensile strength were proposed.