A high-shear granulator consists of a cylindrical or conical mixing bowl, a three-bladed impeller, a chopper, an auxiliary chopper, a motor to drive the blades and a discharge pot. By either circulating hot or cool liquid or steam through the jacket, the mixing bowl is jacketed for heating or cooling the contents of the bowl as the case may be.
The high-shear wet granulation process using high-shear granulator can be divided into 5 stages and they included;
- Powder mixing
- Binder addition or addition of granulating liquid.
- Wetting of powder and nucleation
- Growth of granules and densification of the powder.
- Granule attrition and breakage.
The impeller which is employed in mixing of the dry powder and spreading of the granulating fluid in high-shear granulator normally rotates at a speed ranging from 100rpm to 500rpm. The chopper forms part of high-shear granulator and is used to break down the wet lump to produce granules. The chopper rotates at a speed of 1000 to 3000rpm. Powder densification and/or agglomeration are by the in cooperation of a granulation fluid into the powder with high-power-per-unit mass, through rotating high-shear forces.
High-shear granulators can be subclassified into vertical high-shear granulator and horizontal high-shear granulator. These sub-classes are primarily distinguished by the geometric positioning and orientation of the primary impellers.
A vertical high-shear granulator is where the impeller shaft rotates in the vertical plane and the impellers are bladelike. The vertical high-shear granulator could be either a top-driven (example Colleter-Gral granulator) or a bottom-driven unit (example Diosna or Powrex granulators).
In the horizontal high-shear granulator, the impeller shaft rotates in the horizontal plane (or is said to be side driven).
Factors affecting the granulation process and granule properties of a high-shear granulator
- Formulation variables; that is the type and quantities of excipients used.
- The physical properties of the materials to be granulated.
- The type and amount of binder solution used in the process.
- Process variables which include;
- Load of the granulator bowl.
- Impeller speed
- Granulating solution addition method
- Granulating solution addition rate
- Chopper speed
- Wet-massing tire
- Granulator design.
Pharmaceutical uses of high-shear granulator
- Granulation of highly cohesive material containing hydrophilic polymers which is not achievable with low-shear granulation
Advantages of High-shear granulators
- Granulation process requires less binder solution.
- Granulation is achieved within a short time.
- Greater densification and production of less friable granules.
- The granulator produces reproducible less friable granules with a uniform particle size distribution.
- High-shear granulator minimizes the exposure of drug dust to workers due to reduced process dust generation.
- Granulation endpoint is predictable while using high-shear granulator.
- Requires short drying times.
Disadvantages of high-shear granulator
- High-shear granulator produces less compressible granules when compared to low-shear granulator.
- It has a narrow range of operating conditions.
- Over-wetting of the granules may lead to formation of large-sized lumps.
- Thermolabile materials could be chemically degraded due to increase in temperature.
- Mechanical degradation can take place in case of fragile particles.
- Dilip M. Parikh (2010). Handbook of Pharmaceutical Granulation Technology, Third Edition. CRC Press, Taylor and Francis Group, LLC.
- Jim Litster, and Bryan Ennis (2004). The Science and Engineering of Granulation Processes. Kluwer Academic Publishers, Dordrecht, Netherland.
- Larry, L. A. and Stephen, W. H. (2008), Pharmaceutical Dosage Form: Tablet. CRC Press, Taylor and Francis Group, LLC.
- Namdeo Shinde, Nagesh Aloorkar, Ajit Kulkarni, Bhaskar Bangar, Suyog Sulake, and Pratik Kumbhar (2014). Recent Advances in Granulation Techniques. Asian Journal of Pharmaceutical Sciences. 4(1): 38-47.