27 Lab 2: Milling Aram I. Ibrahim 30/oct./2018

Outline Introduction Mechanisms of size reduction Applications Disadvantages Factors affecting particle size reduction procedure

Introduction Milling is the process of reducing the particle size of a substance by using external forces, its also called comminution. Size reduction increases particle surface area, which affects particles wetting, drying, extraction, dissolution, surface adsorption as well as bioavailability of active ingredients.

Mechanisms of size reduction Compression or crushing: particle disintegration by two rigid forces. Impact or hammer: particle concussion by a single rigid force. Attrition or rubbing: arising from particles scraping against one another or against a rigid surface. Cutting or shear: cutting of particles by a sharp object.

Applications particle size reduction plays important role in preparation of solutions, emulsions, suspensions, ointments or pastes, as well as in granulation, pelleting, tablet compaction. All the preparations meant for external application to the skin must be free from gritty particles to avoid irritation of the area to which they are applied.

Disadvantages On grinding the aromatic and volatile constituents of crude drugs may be lost, like cinnamon, clove and cardamom. Since on size reduction the surface area is increased which when exposed to atmospheric conditions may result in oxidation and hydrolysis.

Factors affect size reduction Physical properties of drugs such as hardness, toughness, moisture content etc. Melting and softening point of the material. The quantity of the material to be reduced.

Procedure 1. Weigh 50 g of a substance and put it in a mortar and mill it for 15, 30, 45, 60 and 120 sec. 2. Sieve it with 710 mm mesh 3. Weigh the passed fine particles on electronic balance. 4. Plot a figure indicating the effect of milling time on the particle size distribution.

Thank you

Lab. rules Punctuality is highly required Cell-phones are forbidden Always wear lab. Coat, gloves, and eye glasses etc. Clean your work area when finished Respect your friends and teachers