Mixing is a unit operation that involves manipulation of a heterogeneous physical system with the intent to make it more homogeneous. Mixing can be achieved by the following processes:
- Hand Mixing (Using Spatula)
- Mortar & Pestle (Trituration)
- Tumbling & Shaking (Diffusion)
- Shear Mixing (Low Shear: Planetary Mixer, High Shear- Mixer-Granulator)
- Fluid Bed Process
Objective of Mixing
- To produce a homgenous physical mixture
- To produce physical change
- To produce dispersion
- To promote chemical reaction
Type of Mixing
- Diffusion Mixing : by Random movement (Using Blender or Bin)
- Convection Mixing: Displacement of group of particles from one place to another (Auger Mixer, Ribbon Mixer)
- Shear Mixing: By effecting mechanical energy to change the configuration of ingredients (High Shear Intensive Mixer).
Danckwerts (Danckwerts, 1953) classified mixing as follows:
- Positive mixing: spontaneously and completely mix.
- Negative mixing: separation is occurred unless continuously agitated.
- Neutral mixing: neither mixing nor demixing takes place unless any force is applied.
Mode of Mixing
1. Geometric Dilution: In Pharmaceuticals this is mostly used for making an intermediate concentrate pre-mix for actives, colors or any other ingredient in a very small amount in the product composition.
2. Ordered Mixing: It is a non-randomized process. In this process materials are selectively mixed based on their physical characteristics (cohesive, adherence, ruggedness, irregular shape, coating, and/or flow properties) this process is widely used in the Pharma Industry and can be achieved in a number of ways.
3. Mechanical: By Dividing and Recombining, Mixing & Screening
- Selective mixing of the low drug load <5% API with a carrier with irregular surface area (e.g. Anhydrous Lactose, Mannitol etc.). Thus the career excipient due to its rugged irregular surface attaches the low amount drug substance forming an API-carrier mixture concentrate for ultimate BU and CU of the drug product.
- Selective mixing of high drug load >50% API of non-cohesive property with a cohesive ingredient to induce compaction for a Direct Compression (D.C) Process.
Mixing Equipment
- Diffusion Mixing: V-Blender, Slant-cone Mixer, Double-cone Mixer & Bin Blender
- Convection Mixing: Auger Mixer & Ribbon Mixer
- Shear Mixing: Low-shear Planetary Mixer, High-shear Intensive Mixer
