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2 PHYSICS OF TABLET COMPRESSION BHARATI VIDYAPEETH COLLEGE OF PHARMACY, KOLHAPUR. 2012-13 Presenter - Mr. Pravin Manik Hajare B. Pharm. Department of Pharmaceutical Technology Seminar on Date: 11-10-2012


CONTENT Compressibility Bonding in tablet Force volume relationship Decompression Conclusion References 3

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Compression: The reduction in the bulk volume of a material as a result of the removal of the gaseous phase (air) by applied pressure. Consolidation: Involves an increase in the mechanical strength of a material resulting from particle-particle interactions. 4 COMPRESSIBILITY


1.COMPRESION When external mechanical forces are applied to a powder mass , there is reduction in bulk volume as follows , 1.Repacking 2.Particle deformation 3.Brittle fracture 4.Microquashing 5 Microquashing : Irrespective of behavior of larger particles, smaller particles may deform plastically .

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2.CONSOLIDATION Mechanism : Cold welding (particle distance < 50nm) Fusion welding (caused due to frictional heat) Consolidation process is influenced by : - Chemical nature of material - Extent of available surface - Presence of surface contaminants and interface distances. 7

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8 HOT WELDING : On macroscale, irregular particle shape ,there is no. of points of contact. Application of load under appriciable force, results in generation of frictional heat. If this heat is not dissipated, local rise in temperature. This heat is sufficient to melt the contact surfaces. Melt solidifies gives rise to fusion bonding. Which results in increasing mechanical strength of tablet.

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COLD WELDING Particles approach each other very closely (>50nm) Their free surface energies result in a strong attractive bond formation. This bond depends on interior nature of the particles. This phenomenon is called cold welding Cold welding results in increasing mechanical strength of tablet. 9

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Fig. : Effect of increasing compressional forces on specific surface area of powder mass , Increased surface area (from O to A), initial particle fracture due to increased compression point A. Particle rebonding predominates and then surface area decreases (from A to B). 10


COMPACTION OF POWDER The physics of compaction is simply stated as … “ The compression and consolidation of two phases due to applied forces ”. 11 Compaction Consolidation It is defined as formation of solid geometry by compression. The compaction takes place in a die by action of two punches, the lower and upper by which compression force is applied. It is in increasing in mechanical strength of material by particle- particle interaction.


EFFECT OF APPLIED FORCES 1. Deformation : Strain : The relative amount of deformation produced on a solid body due to applied force . It is dimensionless quantity . Compressive strain , Z = Δ H / H ο where, H- Thickness Stress ( σ ) : σ = F / A here , F is force required to produce strain in area A . 12

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13 a) Tensile strain b) Compressive strain c) Shear strain Fig. : Diagram shows changes in geometry (strain) of solid body resulting from various types of applied forces. *(In fig .dash line is original shape and solid line is deformed shape.)

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14 Elastic deformation Plastic deformation Brittle rearrangement Before force application During force application After removal of forces Fig. : Deformation mechanisms of material


ROLE OF MOISTURE As little as 0.02% moisture can affect the proportion of applied forces transmitted to lower punch. At 0.55% moisture the behavior is actually the reverse of that for totally dry material. 15


FORCE –VOLUME RELATIONSHIP Compression process ends when , bulk volume= tapped volume ( porosity = 0) Decrease in porosity is due to two process. Filling large spaces by Interparticulate slippage. Filling small voids by deformation or fragmentation at high load. 16

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17 Fig. : Decreasing porosity with increasing compressional forces 1. Initial repacking 2. Elastic deformation 3. Plastic deformation 4. Compression


DECOMPRESSION Occurs on removal of applied forces after compression. Plastoelasticity( γ ), γ = [H ο /H – (H -H )/H ο -H ] where, H ο , H , H = thickness of tablet mass at onset of loading , at max. applied pressure and on ejection from die. γ > 9 produce tablets that are laminated or capped. 18


CONCLUSION The physics of tablet compression gives knowledge of compatibility and flowability of pharmaceutical powder which is essential for formulation of tablets. The tendency of material for plastic deformation, fragmentation and elasticity could be expressed and are compared with different material. The bonding theories in tablet preparation is studied to increase the strength of tablet. The different parameters of powder like flow rates, effect of moisture etc. are studied with there effect on the compression of tablet. 19


REFERENCES Leon Lachman, Herbert A. Lieberman. The Theory and Practice of Industrial Pharmacy. Special Indian Edition 2009, 66-99. M. E. Aulton. Pharmaceutics: The Science Of Dosage Form Design. Second edition, 423-438. 20

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