Question

Discuss heat and mass transfer phenomena involved in freeze, spray and spray freeze drying. Discuss the mechanism behind the role of hygroscopicity in the pharmaceutical product ?

Answer 1

Heat and Mass Transfer Phenomenon involved in Freeze Drying:

During freeze drying,heat and mass transfer occur simultaneously.The material is first frozen at a low temperature, forming ice crystals and then these crystals are sublimed from the solid state directly into the vapor phase below triple point of water in a vacuum chamber.Heat is transferred from the absorbent to the surface of the product by internal conduction and the water vapor are captured by absorbent.This process can take long time.

Heat and Mass Transfer Phenomenon involved in Spray Drying:

In case of Spray Drying,Heat and mass transfer occur when hot air flows through a chamber and evaporating water from the atomized particles and transforming the product into a dry powdered product.It is a fast paced process.

Heat and Mass Transfer Phenomenon involved in Spray Freeze Drying:

SFD involves 3 processes namely atomization of solution into droplets, freezing it by cold fluid, and drying by sublimation.Heat transfer occurs when the atomised droplets come in contact with cryogen fluid and at the time of sublimation water vapors are captured by absorbent similar to Freeze Drying.

Hygroscopicity occurs when a pharmaceutical chemical bonds with water molecule from the atmospheric air.Hygroscopicity in the pharmaceutical product can occur at the time of manufacturing and packaging.The physical and chemical stability of the solid dosage forms, excipients, and polymers for controlled release formulations have been predominantly influenced by Moisture adsorption.