Tablet Tensile Strength Role of Surface Free Energy

Keywords Ryshkewitch-Duckworth equation, compaction, tableting, surface free energy, adhesion, tablet porosity 

Mittal (ed.) Advances in Contact Angle, Wettabilty and Adhesion Volume 2, (397-418) 2015 Scrivener Publishing LLC 

Achieving adequate tensile strength can sometimes be a challenge, particularly when formulations contain large amounts of active ingredient or require special excipients to enhance dissolution or increase stability. Special excipients may have undesirable properties with regard to tableting. 

During tableting, powder is uniaxially compressed in the die. During the compression process the powder is densified under the applied pressure. Densification of the powder occurs through particle rearrangement, particle fracture and particle deformation. The relative extent of each of the three identified densification mechanisms that occurs in a specific instance is determined by the applied pressure, the rate of the increase of pressure, the duration of the applied pressure, and the mechanical properties of the materials that are being compressed. 

Adhesion strength depends on both the quality and quantity of intimate contact between the materials in question. The densification of the powder that occurs during tableting results in an increase in the contact area between the particles. The quality of interaction depends on the specific surface chemical properties and surface free energy of the materials in question. 

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