Friday, 22 November 2013

Granulation and its importance in tablet manufacturing process






Granulation process is an inevitable step in tablet manufacturing as it improves flow property and compressibility of powder mass intended for compression. Granulation prevents segregation of the constituents of the powder mix.


 Granulation is the process in which primary powder particles are made to adhere to form larger, multi particle entities called granules. Pharmaceutical granules typically have a size range between 0.2 and 4.0 mm, depending on their subsequent use.
Granulation is so important in tablet manufacturing process because it

1. Improve fluidity

2. Degrease segregation of the powder components

3. Degrease dusting

4. Improve compressibility of the material

An ideal granulation will contain all the constituents of the mix in the correct proportion in each granule, and segregation of the ingredients will not occur.

Types of granulation

There are two types of granulation technique

1.Dry granulation   2. Wet Granulation

Dry granulation

In dry granulation the primary powder particles are aggregated under high pressure. There are two main processes. Either a large tablet (known as a ‘slug’) is produced in a heavy-duty tabletting press (a process known as ‘slugging’) or the powder is squeezed between two rollers to produce a sheet of material (‘roller compaction’).

In both cases these intermediate products are broken using a suitable milling technique to produce granular material, which is usually sieved to separate the desired size fraction. Dry granulation technique is applicable  for drugs which do not compress well after wet granulation, or those which are sensitive to moisture.

Wet granulation

Wet granulation involves the massing of a mix of dry primary powder particles using a granulating fluid. The fluid contains a solvent which must be volatile so that it can be removed by drying, and be non-toxic. Typical liquids include water, ethanol and isopropanol, either alone or in combination. The granulation liquid may be used alone or, more usually, as a solvent containing a dissolved adhesive (also referred to as a binder or binding agent) which is used to ensure particle adhesion once the granule is dry. Water is commonly used for economical and ecological reasons. Its disadvantages as a solvent are that it may adversely affect drug stability, causing hydrolysis of susceptible products, and it needs a longer drying time than do organic solvents. This increases the length of the process and again may affect stability because of the extended exposure to heat. The primary advantage of water is that it is non-flammable, which means that expensive safety precautions such as the use of flameproof equipment need not be taken. Organic solvents are used when water-sensitive drugs are processed, as an alternative to dry granulation, or when a rapid drying time is required. In the traditional wet granulation method the wet mass is forced through a sieve to produce wet granules which are then dried. A subsequent screening stage breaks agglomerates of granules and removes the fine material, which can than be recycled. Variations of this traditional method depend on the equipment used, but the general principle of initial particle aggregation using a liquid remains in all of  the processes.

 Glossary of Terms

Compressibility – Compressibility is the ability of powder to decrease in volume under pressure.