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. Decrease segregation of the powder components
3. Decrease 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
Basically two types of granulation technique, but also other technique is direct compression
1.Dry granulation 2. Wet
Granulation
N.B: Wet granulation mostly used in tableting process, but this also depend on that chemical nature which we used for tableting.....
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 tableting 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.
