Blending and Blend Assessment Flashcards
What is the significance of blending, and what are the effects of poor blending?
- produce unit doses of constant mass and volume.
- segregation or poor blending will cause issues of content uniformity.
Describe the theory of mixing.
Theory of mixing talks about the different types of mixing:
- Positive mix
- complete and spontaneous mixing with no input of energy required (e.g miscible liquids, gases and vapors) - Negative mix
- stirring is required otherwise phase separation will occur (e.g. insoluble solids in liquids, immiscible liquids) - Neutral mix
- stirring is required but demixing will not occur spontaneously (e.g. mixture of powders)
What is the ideal state of mix?
- particles are well distributed and in close contact with one another, alternating between one another.
- standard deviation in the composition is zero.
What are the different mixing mechanisms?
- Convective
- Particles move from one area to another in the mixture (usually when spatula is inserted) - Shear
- Slip planes are formed, unstable fractions collapse, shearing occurs. - Diffusive
- Body of powder is lifted beyond its angle of repose and avalanches, resulting in the redistribution of individual particles.
What is segregation caused by?
differences in particle size, shape and density
What are the different types of segregation?
- percolation segregation
- elutriation segregation
- projection segregation
- feed/heap segregation
- shear segregation
Describe the different types of segregation.
- Percolation segregation
- finer/denser particles will filter to the bottom when powder bed is subjected to movement or vibration (e.g. vibrating bin) - Elutriation segregation
- Air stream rushing through the powder bed will sift out lighter and/or finer particles ( e.g. empty tube filled with powder). - Projection segregation
- When a powder mix is projected into the air, heavier particles will be projected further (e.g. under a horizontal belt conveyor). - Feed/heap segregation
- Heavier/larger particles will roll further down a heap of powder (e.g. charging a hopper/bin) - Shear segregation
- When 2 planes in a powder shear, the finer particles on the top layer will fill the voids of the bottom layer (e.g. powder blend flowing down the slope).
Describe ordered mixing, and the forms that segregation may occur.
- process when fine particles are mixed with coarse particles and coat them to form a blend that will not segregate.
- ## termed “ordered” because constituents are not independent of one another.Segregation may occur as:
1. ordered unit segregation - due to size differences, larger carrier particles have more of the adsorbed component.
- displacement segregation
- addition of another component may compete for adsorbed component, displacing them. - saturation segregation
- limited active sites on carrier particles for adsorption.
- if saturated, additional fines will be prone to segregation by percolation.
What is geometric dilution?
Process where a small amount of powder is progressively and throughly mixed with a larger entity.
What are the different types of blending equipments?
Shaped bin blenders: V-cone, Y-cone, double cone
Common laboratory blender:
- drum/barrel hoop blender
- turbula mixer
Describe the mixing process (solid-solid mixing).
- expansion of the beds of solids
- application of 3D shear forces to the powder bed
- allow sufficient time for the powder to reach random state
- maintain random state
What are the factors affecting mixing?
- % of actives
- particle size
- particle size distribution
- particle shape
What are the factors affecting blend homogeneity?
- sample size
- no. of samples
- sampling device
What is a suitable sampling device and how does it operate?
- core sampler, contains 3-5 sampling points and can be sampled along the blend axis.
What are some process variables in blending for the loading method?
- layer excipients one on top of the other with API in the middle.
- lubricants normally do not require layering and are thus located on the top.
- when mixing the substances, using top-bottom/radial mixing.
- end point is determined by no. of revolutions, which is affected by fill level (60% is optimum figure) for mixing.