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Renin Angiotensin Mechanism.

Size Reduction.

 Size Reduction

Contents:

  1. Definition of Size Reduction.

  2. Importance of Size Reduction.

  3. Factors affecting Size Reduction.

  4. Mechanisms of Size Reduction.

Definition:  

  • Size Reduction or Comminution is a pharmaceutical process where bigger drug particles are converted into smaller drug particles as per requirement.

Importance of Size reduction:

  • To increase the rate of a solution: Size reduction reduces particle size and increases effective surface area which in turn increases the rate of solution.

  • To increase the rate of extraction: Rate of extraction is directly proportional to Size reduction. Smaller particle size allows faster penetration of menstruum and hence fastens the extraction process.

  • Mixing: Smaller particle size ensures effective mixing which is an essential thing for many pharmaceutical dosage forms.

  • Bioavailability: As particle size decreases the rate of absorption increases. Hence size reduction ensures good bioavailability e.g Griseofulvin.

  • Drying: Reduction in particle size increases effective surface area and fastens the process of drying.

  • To facilitate Filtration: Rate of filtration depends upon the size of particles to be separated.

  • Stability: Reduction in particle size increases the stability of certain pharmaceutical preparations such as suspensions and emulsions.

Factors Affecting Size Reduction:

  1. Hardness: It is easy to reduce the size of soft materials as compared to hard materials.

  2. Toughness: The crude drugs having fibrous nature containing more moisture content are more difficult for size reduction than hard but brittle substances.

  3. Stickiness: The gummy materials such as resins tend to adhere to grinding surfaces or sieves of the mill and produce a lot of problems during operation. In such cases complete drying of materials is useful.

  4. Material Structure: Materials with a special structure such as plant materials and minerals with weakness lines produce fibers and flakes during operation and produce problems.

  5. Moisture Content: The moisture content of material influences many properties like hardness, toughness, stickiness etc.. Usually 5% moisture in dry grinding and 50% moisture in wet grinding is considered good for size reduction.

  6. Softening Temperature: The fatty or waxy drugs softens during the process due to heat generation by process and jams the mill. However, this can be avoided by employing a cooling mechanism in the mill.

  7. Purity Required: The grinding surfaces of mills may wear off and appear in the final product and compromise the purity of the final product. This can be avoided by proper selection of mills and cleaning of mills between batches.

  8. Physiological Effect of Material: Some drugs are very potent, their dusting during operation may harm the operator this can be avoided by enclosing the mill completely.

  9. Flammability - Under certain conditions fine dust such as dextrin,  starch,  sulphur  are  potential  explosive  mixtures. All electrical switches should be explosive proof and mill should be well grounded

Mechanisms of Size Reduction:

  • Size reduction is the process of conversion of bigger particles into smaller particles.

  • Mechanisms of Size Reduction:

1) Cutting:

2) Compression:

3) Impact:

4) Attrition.

5) Combined impact and attrition.


1) Cutting:

  • The material is size reduced when it comes between sharp edges of the blades.

  • e.g Cutter Mill.

2) Compression:

  • The material is reduced by crushing when comes between a stationary platform and a moving heavy platform.

  • e.g. Mortar and pestle, Roller Mill.

3) Impact:

  • The material is size reduced when hit by a moving platform or material at a high speed.

  • e.g Dis-integrator, hammer mill.

4) Attrition:

  • The material is reduced by application of pressure and the shear force generated when it comes between the platforms moving relative to each other.

  • e.g Mortar and pestle and Roller mill.

5) Combined Impact and Attrition:

  • The material is size reduced by combined action of impact and attrition to get better results.

  • e.g. Ball Mill, Fluid energy mill.

Commonly Asked Questions.

  1. Define Size Reduction. Give its importance in pharmacy.

  2. Define Size Reduction. Give its objectives.

  3. Define Size Reduction. Write a note on various factors affecting rate of size reduction.

  4. Discuss different mechanisms of Size Reduction.
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