Download Mixing of Powders

Mixing
Importance:
1.
2.
3.
Ensure an even distribution of the active
component(s)
Ensure an even appearance of the DF
Ensure that the DF releases the drug at the correct
site and at the desired rate
Mechanisms of Mixing:
1.Diffusion:Movement of single particles
2.Convection:Movement of groups of particles
3.Shear
:Sliding of particles in planes over each
other
Mixing of powders
Large-Scale Mixing Equipment
The ideal mixer should
1- produce a complete blend rapidly to avoid
product damage.
2- It should be cleaned and discharged easily
3- be dust-tight
4 require low maintenance and low power
consumption.
Mixers for Powders
Tumbling Mixers/Blenders
Barrel blender
V-shape blender
Tumbling Blenders
• Cube blender
Double cone blender
Tumbling Blenders
Factors affecting mixing efficiency by
tumbling mixers
1. Too high a rotation speed will cause the
material to be held on the mixer walls by
centrifugal force, and too low a speed will
generate insufficient bed expansion and little
shear mixing.
2. The addition of baffles or rotating bars will also
cause convective mixing, for example the
V-mixer with agitator bar.
3. Presence of significant difference in particle
size, as segregation is likely to occur.
Mixing of Powders
Extemporaneous Methods
1- Spatulation
2- Trituration
3-Levigation
Small-Scale Mixing Equipment
1- Spatulation
The blending of powders with a spatula on a tile or
paper used sometimes for small quantities or when
the mortar and pestle technique is undesirable.
It is not suitable for large quantities of powders or for
powders containing one or more potent substance
because homogenous blending may
not occur.
2- Trituration:
.
is used to comminute( reduce particle size) & to mix
powders.
1-A porcelin preferred than glass morter.
2- A glass morter is preferrable for chemicals that stain
a porcelin. When granular or crystalline materials
are to be incorporated in to powdered product ,these
materials are comminuted individually and then
blended together in the morter.
3- Levigation
In this process
A- paste is first formed by the addition of a
suitable non solvent to the solid material.
B-Particle-size reduction then accomplished
by rubbing the paste in a mortar with a
pestle or on an ointment’ slab using a
spatula.