Wet granulation is a common granulation technique in pharmaceutical industry. It’s used mainly to improve flow and compressibility of powders, and to prevent segregation of the blend components. Where particle size of the granules is affected by the quantity and feeding rate of granulating liquid.

Wet massing in a high-shear mixer or rapid mixer granulator is frequently compared to fluid bed mixing or granulator and to roller compaction technique, and the results seem to be formulation dependent. Compared to high shear granulation, low shear or fluid bed process requires less fluid binder, resulting in a shorter drying time, but also in a less cohesive material.

To achieve the more dense and granular particles and for rapid granulation high shear mixer or rapid mixer granulator is selected for most of the products. Where binder addition rate controls granule density, while impeller and chopper speed control granule size and granulation rate.

The process flow of granulation technique in RMG (Rapid mixing granulator)

Material charging/loading > Dry mixing > Granulating fluid addition > Wet mixing > Discharging > Sieving/Milling

To detect the end point of granulation a trial batch should be taken at a fixed speed and with a predetermined method of binder addition (for example, add water continuously at a fixed rate to a dry mix with a water-soluble binding agent). Before adding the binder solution, measure the baseline level of motor power consumption or impeller torque at the dry mix stage.

During the batch, stop the process frequently times to take samples and, for each sample, note the end-point values of power consumption or impeller torque.

Finally compress the tablet and find out the desired characteristics of tablet from the sample collected during granulation.

During this process optimization batch following critical parameters to be optimized – 

  • Granulating fluid amount
  • Granulating fluid addition time
  • Wet mixing time
  • Impeller speed
  • Chopper speed
  • Power consumption
  • Impeller torque

After successful optimization of the batch process validation batches can be taken as per recommendation of process optimization batch. Where batch size and machine capacity to be selected carefully. It is better to start with same batch size as like optimization batch. Then batch sizescale-up can be proceed with extra precaution and measurements.

Hopefully this brief guideline will be helpful for pharmaceutical professional and they can consider the critical issues of wet granulation in high shear mixer or rapid mixer granulator.

There are a list of parameters can be measured on a Rapid Mixer Granulator (RMG) - 

  • Current
  • Voltage
  • Capacitance
  • Conductivity
  • Probe vibration
  • Boots Diosna Probe
  • Chopper Speed
  • Impeller or Motor Shaft Speed
  • Motor Slip and Motor Load Analyzer
  • Impeller Tip Speed
  • Relative Swept Volume
  • Temperature
  • Binder Addition Rate
  • Power Consumption
  • Impeller Torque
  • Torque Rheometer
  • Reaction Torque