40 Questions
What is the primary mechanism of mixing in liquid-liquid mixing?
Application of shear
What is the function of rotating blades and paddles in mixing?
To facilitate bulk transport
What is the primary goal of the mixing process?
To treat two or more components so that each unit lies in contact with each of the other components
What type of mixing occurs in the granulation step of tablet and capsule production?
Wet mixing
What is the characteristic of turbulent flow in mixing?
Random fluctuation of fluid velocity
What is the result of molecular diffusion in mixing?
Mixing of liquids at a molecular level
What is a characteristic of positive mixtures?
They mix spontaneously and irreversibly by diffusion
What type of mixture is formed when materials tend to separate out?
Negative mixture
What is the purpose of a shaft in a mixing apparatus?
To mount the impeller
What is the classification of mixing mechanism that involves the movement of a large portion of material from one location to another?
Bulk transport
What is an application of mixing in pharmaceutical production?
Production of pellets for capsule
What is a characteristic of neutral mixtures?
The information is not provided in the content
What is the term used to describe the mixing of two dissimilar liquids through laminar flow?
Laminar mixing
What is the result of positive mixing?
A mix that approaches a perfect mix without input of energy
What is the device used to facilitate mixing in a mixing apparatus?
Impeller
What is an example of dry mixing in pharmaceutical production?
Dry blending of powder in capsule, dry syrup and compound powder
What is the primary cause of segregation in powder mixes?
Difference in particle sizes
What happens when powder mixes are subjected to vibration?
Particles with similar properties tend to congregate
What is the term for the phenomenon where smaller particles tend to fall through the voids between larger ones?
Percolation segregation
Why is segregation more likely to occur in powder mixes?
When particles have greater flowability
What is the result of segregation in powder mixes?
Regions with a higher concentration of a particular component
What is the consequence of segregation in powder mixes?
Increase in content variation
Why do particles tend to separate in powder mixes?
Due to differences in particle size and density
What is a common observation in cereal packets or jars of coffee?
Smaller particles tend to congregate towards the bottom
What is a key requirement for mixers in semisolid mixing?
Rotating elements with narrow clearances between themselves and the mixing vessel wall
What is a problem that occurs during semisolid mixing?
Materials finding their way to the dead spots and remaining there
What is the purpose of emulsifying agents or wetting agents in semisolid mixing?
To mix immiscible liquids and insoluble solids
What type of mixers are used for solid-solid mixing?
Triple roller mills
What is the main use of Sigma-blade mixers?
For semisolid preparation and wet granulation process in manufacturing tablets
Why are primary mixers often unable to completely disperse powder particles in a semisolid base?
Because it is difficult to completely disperse powder particles in a semisolid base
What is the purpose of subjecting the mix to a roller mill or colloidal mill after using a primary mixer?
To 'rub out' the particles by the intense shear generated by rollers or cones
What is a characteristic of Sigma-blade mixers?
They have close tolerances between blades and the sidewall
What is a characteristic of the ribbon mixer?
It is less likely to cause segregation
What type of mixing occurs in the Nautamixer?
Combination of convective, shear, and diffusive mixing
What is a limitation of the planetary mixer?
It has limited size and is useful for batch work only
What occurs in the ribbon mixer due to the rotation of helical blades?
The shearing action may be insufficient to break up drug aggregates
What is a characteristic of the Nautamixer's screw?
It conveys the material to near the top
What is not a characteristic of the ribbon mixer?
It can break down agglomerates rapidly
What is a use of the planetary mixer?
Wet granulation process
What is not a type of mixer mentioned in the content?
Tumbling mixer
Study Notes
Mixing Equipments
- The ribbon mixer: achieves mixing through the rotation of helical blades in a hemispherical trough, may have "dead spots" and may not be effective in breaking up drug aggregates.
- The Nautamixer: combines convective, shear, and diffusive mixing through the rotation of a screw and the cascading of material.
- The planetary mixer: uses low speeds for dry blending and fast speeds for wet granulation, can break down agglomerates rapidly, and is useful for batch work.
Mixing of Miscible Liquids and Suspensions
- Liquid-liquid mixing: the formation of a homogeneous system through the application of shear, classified into four mechanisms: bulk transport, turbulent, laminar, and molecular diffusion.
- Mixing equipments: consist of a container and a mixing device (impeller) mounted on a shaft driven by a motor.
Mixing Theory and Equipments
- Definition of mixing: a unit operation that aims to treat two or more components to bring them into close contact with each other.
- Application of mixing: an intermediate stage in the preparation of dosage forms, such as wet mixing in granulation and dry mixing in direct compression.
Types of Mixtures
- Positive mixtures: formed from materials that mix spontaneously and irreversibly by diffusion, requiring no input of energy.
- Negative mixtures: components tend to separate out, requiring mixers with rotating elements and narrow clearances to produce a high degree of shear mixing.
- Neutral mixtures: no categorization provided.
Semisolid Mixing
- Problems: poor flowability, materials finding their way to dead spots, and remaining there.
- Mixer requirements: rotating elements with narrow clearances and high degree of shear mixing.
- Equipment used: Sigma mixer, planetary mixer, triple roller mill, and colloidal mill.
Sigma-Blade Mixer
- Used for semi-solid preparation and wet granulation in manufacturing tablets.
- Difficult to disperse powder particles completely, requiring further action by roller mills or colloid mills.
- Close tolerances between blades and the sidewall and bottom of the mixer's shell.
- Segregation causes an increase in content variation in samples taken from the mix, leading to batch failure.
Powder Segregation (Demixing)
- Particles behave differently when forced to move, leading to segregation.
- Particles exhibiting similar properties tend to congregate together, causing regions in the powder bed with higher concentrations of a particular component.
- Segregation is more likely to occur with vibration and greater flowability.
Particle-Size Effects
- Difference in particle sizes of components is the main cause of segregation in powder mixes.
- Percolation segregation: smaller particles tend to fall through voids between larger ones and move to the bottom of the mass.
- Percolation segregation occurs when a powder bed containing particles of different sizes is disturbed, leading to particle rearrangement.
This quiz covers different types of mixers used in pharmaceutical industry, including the ribbon mixer, planetary mixer, and Nautamixer, and their characteristics.
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