Various factors affecting strength of tablets by kailash vilegave
Seminar on… Various Factors affecting strength of Tablets By… Mr. Kailash V Vilegave
Contents Introduction Definition Of Tablet Various Factors affecting Strength of Tablet References
Introduction Tablets require certain amount of Strength to withstand Mechanical shocks of Handling during Manufacturing, Packaging & Shipping. In order to show desired response each Tablet should posses optimum Strength.
Definition Tablets are unit solid dosage form containing Medicament/Medicaments with or without suitable excipients.
Moisture Content A small proportion of Moisture content is desirable for the formation of a coherent Tablet. The amount of moisture present on the Powder surface is just sufficient to fill the remaining voids in the bed. Further increase in Compression force results in this water being squeeze out to the surface of Tablet. This expelled Moisture may act as a lubricant at die wall, but It causes material to stick to punch forces.
At low moisture content there will be increase in die wall friction due to increased stress, hence the Tablet hardness will be poor. At high moisture level the die wall friction is reduced owing to lubricating effect of moisture. At further increase in moisture content there will be decrease in Compact strength due to reduction in Interparticulate bond.
Generalised plot of Tablet Strength Vs Moisture content of granules
Lubrication Lubricants are commonly included in Tablet formulations in order to reduce. Die wall friction. To improve flow properties & Antiadherant properties. However their presence may cause undesirable changes in Tablet properties.
Effect of Lubrication on TabletStrength Shotton & Lewis investigated the effect of Mg. Stearate on the strength of Tablet of crystalline materials & two simple granulation without binders. They found that Lubricant decrease the strength of all Tablets. The softening of Tablet by lubricants has been reported by Strickland who observed that Mg. Stearate & other Lubricants added as dry powder to granules, They appeared to adhere & form a coat around individual granules.
Bolhuir showed that Mg. Stearate forms an adsorbed lubricant film around host particles during the mixing process. The Lubricant film interfere with the bonding properties of host particle by acting as a physical barrier. This can be seen when the Tablet crushing strength is plotted as a function of the Log of the mixing time with the Lubricant.
Film formation of Lubricant on the Host particle.
The magnitude of the effect of Lubricants on crushing strength is depended on large no. of factors. Nature & properties of the Tablet ingredients & Processing condition.
Film formation of Lubricants duringmixing When a powdered Lubricant is added to a Tableting blend & submitted to a mixing action it is distributed as free fraction. Prolonged mixing time will transfer more Lubricant from free fraction to the surface film. The phenomenon of decrease in strength with an increase mixing time of Tablet ingredients with Lubricants is caused by formation of this Lubricant film, which interfere with the binding of the particles. The in crushing strength has been attributed to weaker bonds after compression between Lubricant – Lubricant molecules rather than strong excipients bonds.
A significant reduction in crushing strength has been found during mixing of excipients with hydrogenated oils, glycerides & PEG. Lubricants are Hydrophobic materials, poor selection or excessive amounts can result in water proofing the Tablets. Lubricants have been added to the granulating agent in the form of Suspension or Emulsion.
Material Type Conc In Granule s w/wBoric Acid E,L 1-5Collodial E,G 0.1-0.5SilicaMagnesium E,L,I 0.1-1SterateStearic Acid E,I,L 0.1-2Talc E,G 1-5
Effect of Particle Size on strengthof Tablet The shape of a particle is a complex characteristic and its importance in relation to powder properties is therefore difficult to assess. Generally particles with optimum size will give good strength for tablets. If the particle size is large(200-250µm)then they have a tendency to flow better than the smaller particles because they have greater mass.
Where as smaller particles may create mixing problems because surface area is more &may give rise to strong electrostatic forces as a result of processing and or Interparticulate friction from movement.These may prevent the desired distribution of these smaller particles. As the particle size approaches 10µ & below weak polarsing electrical forces called vandarwalls force or cohesive forces affect the flow of powder.
Smaller particles have larger surface area &when these are expose to atmosphere may prone to oxidation, moisture adsorption take place which effect the strength of tablet. Very large particles often exist as agglomerates of a small crystals on compression these agglomerates breakdown into small units.
EFFECT OF PARTICLE SHAPEON STENGTH OF TABLETS Particle shape affects powder inter- particulate friction &consequently the flow properties of powder General particle shapes and their effect on powder flow as follows Spherical particles Ablong shaped particles Cubical shaped particles Irregular shaped particles
REFERENCES The Theory and practice of industrial pharmacy by Leon lachman.Herbert a Lieberman Joseph kiang third edition. Pharmaceutics: The science of dosage form design by a Michael E. Aulton. Remington “The science &practice of pharmacy volume1,19th edition 1995 Physical pharmacy By Alfred martin, james Warrick Varghese Publications. www.google.com