1st Year • ER20-11T
Pharmaceutics (ER20-11T): Unit 2 - Size Reduction & Separation
Compiled by Pharmacist365 Academic Council
Unit 2 • ER20-11T
Size Reduction & Milling Technologies
Pharmacy Council of India (PCI) ER-2020 Standard Lecture Notes
1. Introduction to Size Reduction (Comminution)
Size reduction or comminution is the process of reducing large solid pharmaceutical masses, crystals, or vegetable crude drugs into smaller fractions, coarse powders, or microfine particles.
Key Objectives of Particle Size Reduction:
- Enhanced Dissolution Rate: According to the Noyes-Whitney equation, dissolution rate $(dC/dt)$ is directly proportional to surface area $(A)$.
- Uniform Content Distribution: Crucial for potent drugs formulated as tablets or suspensions.
- Improved Absorption: Finer particles dissolve rapidly in gastrointestinal fluids, improving oral bioavailability.
- Stabilization of Suspensions: Follows Stokes' law; smaller particles exhibit lower sedimentation velocity.
2. Mechanisms of Comminution
| Mechanism | Physical Action | Industrial Equipment |
|---|---|---|
| Impact | Material stationary, struck by high-speed kinetic striker | Hammer Mill, Disintegrator |
| Attrition | Shearing & rubbing between moving abrasive surfaces | Roller Mill, Colloidal Mill |
| Combined Impact & Attrition | Simultaneous impact and particle-to-particle attrition | Ball Mill, Fluid Energy Mill |
| Compression | Heavy compressive mechanical crushing | End Runner & Edge Runner Mills |