Powder Properties and Mixing

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Questions and Answers

Which statement correctly describes the flow characteristics of lactose?

Lactose exhibits a greater volume drop compared to corn starch.

Lactose has a high angle of repose indicating poor flow.

Lactose particles are too large to form cohesive bonds. (correct)

Lactose is hygroscopic, leading to moisture interference.

What implication does a 35% drop in volume upon tapping corn starch suggest?

Corn starch has good flow characteristics.

Corn starch particles are larger than those of lactose.

Corn starch is unsuitable for applications requiring high density.

Corn starch displays signs of cohesion. (correct)

What is indicated by an angle of repose greater than 40°?

The material has excellent flow.

The material has good powder mixing capability.

The material exhibits poor flow characteristics. (correct)

The material experiences pass flow conditions.

What does a low tapped bulk density indicate about a powder?

It may not be suitable for certain applications. Signup and view all the answers

How is the angle of repose calculated in relation to a cone of powder?

By measuring the maximum angle between the pile surface and ground. Signup and view all the answers

What is a significant disadvantage of convective mixers?

They can lead to dead spaces with minimal powder movement. Signup and view all the answers

Which type of mixer is characterized by high rotational speeds and is used to mix powders with high energy input?

Impaction and high shear mixers Signup and view all the answers

What is a key advantage of using cube, cone, and V mixers?

They allow for better addition of lubricants and glidants. Signup and view all the answers

What potential issue is associated with the physical setup of planetary mixing?

They can create adhesion problems with blades and surfaces. Signup and view all the answers

What distinguishes high shear mixers from other types of mixers?

They significantly shatter powder particles during mixing. Signup and view all the answers

What characteristic of tightly packed powders results in minimal air entrapped?

Maximum interparticulate contact Signup and view all the answers

What is the porosity percentage of loosely packed powders?

48% Signup and view all the answers

What packing arrangement is characterized by the densest packing and a porosity of approximately 26%?

Rhombohedral packing Signup and view all the answers

Which statement about porosity is true?

It can be influenced by particle shape. Signup and view all the answers

What is the primary method to determine porosity in powders?

Measuring the poured bulk volume without disturbance. Signup and view all the answers

In powder characterization, what does 'bulk density' refer to?

Density of multiple particles together. Signup and view all the answers

What is the relationship between the 'true density' and 'particle density'?

True density is always higher than particle density. Signup and view all the answers

Which combination of coarse and fine particles results in the densest packing arrangement?

75% coarse and 25% fine Signup and view all the answers

What is indicated by a Carr's compressibility index greater than 33%?

Poor flow characteristics Signup and view all the answers

What happens to the final volume during the determination of tapped density?

It achieves a minimum bulk volume Signup and view all the answers

How does the Hausner ratio relate to powder flow properties?

Values less than 1.25 usually indicate good flow Signup and view all the answers

What is the primary purpose of measuring tapped density?

To evaluate dynamic powder packing over time Signup and view all the answers

What is the relationship between bulk density and tapped density?

Tapped density reflects maximum packing while bulk density represents minimum packing Signup and view all the answers

Which factor contributes to a larger difference between poured and tapped densities?

Increased interparticulate forces Signup and view all the answers

In powder flow characterization, what is the significance of added glidant?

It can enhance flow properties if needed based on Hausner ratio Signup and view all the answers

What does apparent porosity represent in the context of particles?

Estimated porosity that may not account for internal cracks or pores Signup and view all the answers

What is the primary aim of powder mixing in pharmaceutical processes?

To ensure each particle from one component contacts a particle from each additional component Signup and view all the answers

Which mixing technique involves adding a liquid phase to powders?

Wet mixing Signup and view all the answers

How do tumbler mixers primarily affect the mixing of powders?

By causing the powders to tumble without attrition Signup and view all the answers

Which of the following describes the process of pre-mixing?

Initial mixing of drug components with less than 5% w/w of the drug Signup and view all the answers

What is a key benefit of dry mixing compared to wet mixing?

Dry mixing avoids introducing moisture that can affect powder properties Signup and view all the answers

What role does mechanical screw feeding play in powder handling?

It provides a controlled flow of powders from one vessel to another Signup and view all the answers

Which property of the powder mixture is most affected by the mixing process?

The homogeneity of drug distribution within the dosage form Signup and view all the answers

In the context of powder transport, what is the purpose of using a vacuum?

To induce a flow of powder from one vessel to another Signup and view all the answers

What is the primary purpose of an impaction mixer?

To break up agglomerates in dry powders Signup and view all the answers

What is a primary concern when selecting a mixer for powder materials?

The size of the mixing vessel relative to the batch Signup and view all the answers

Which of the following mixing mechanisms is primarily responsible for the movement of entire groups of particles?

Convection Signup and view all the answers

What is a potential safety hazard associated with mixing powders?

Dust emissions from the powders Signup and view all the answers

Which type of mixer is best suited for free-flowing powders?

Tumbling mixers Signup and view all the answers

What loading ratio is typically optimal for convective mixers?

50-80% Signup and view all the answers

In which scenario would electrostatic charging be a significant concern during mixing?

When mixing dry, fine powders Signup and view all the answers

What is the effect of particle size, shape, and density differences during mixing?

Increased separation or segregation Signup and view all the answers

Study Notes

Preformulation - Bulk Powder Properties

Powders can exist in various packing states, from loosely packed (maximum airspace) to tightly packed (minimum airspace).
Particle size and shape influence packing density, with smaller particles filling voids between larger ones.
Porosity, the amount of air space between particles, is inversely related to packing density.
Loose packing has approximately 48% porosity, and dense packing has approximately 26% porosity.
Coarse and fine particles have approximately 55% porosity.

Determination of Porosity

Powder is placed in a measuring cylinder without vibration to determine the poured bulk volume (V₁).
The poured bulk density (ρ♭) is the reciprocal of the poured bulk volume.
The void volume (Vp) is the difference between the poured bulk volume and the particle volume.
Porosity is calculated by dividing the void volume by the total bulk volume.

Determination of Tapped Density

Powder is placed in a cylinder and tapped to determine the tapped volume (Vt).
The tapped density (ρt) is the reciprocal of the tapped volume.
Tapping increases packing density and reduces porosity.
This measurement is used to evaluate the dynamic powder packing characteristics.

Flow Properties

Interparticulate forces (e.g., Van der Waals, electrostatic) influence packing and flow.
Difference between poured and tapped densities indicates cohesion.
Increased tapping requires more energy for tighter packing.
Carr's compressibility index and Hausner ratio metrics predict flow properties from packing characteristics.

Hopper Design and Flow

Funnel flow - some powder remains stationary, while mass flow involves all powder in motion.
Funnel flow and rat holing are associated with shallow angle orifices and can cause segregation.
Mass flow is superior, and offers uniform flow with constant density.
Steep orifice angles minimize rat holing problems.

Flow Improvement

Particle size, shape, charge, and moisture influence flow.
Glidants are utilized to improve flow by smoothing particle surfaces.
Hoppers, aeration, and force feed mechanisms improve powder flow.

Powder Mixing

Mixing is essential to produce homogeneous distributions of powder components.
Components mixing variables include: particle size, shape, and density.
Mixing's outcome influences subsequent processes like granulation, tabletting, and capsule filling.
Mixing involves dry mixing (without liquid) and wet mixing (with liquid binder, such as granulation).
Different mixing methods (e.g., tumbler, convective, planetary) have differing efficiency for various particle types.

Interactive Powder Mixtures

Interactive/ordered powder mixtures result from cohesive, fine particles forming ordered units, improving homogeneity.
Factors like particle size and density affect segregation, while vibration and segregation (including different types) relate to stability.

Segregation as a Problem

Segregation is a problematic issue in powder mixtures due to particle differences in size and shape, potentially leading to uneven or non-homogenous mixtures.
Strategies for mitigating segregation include the careful selection of components with similar particle size and density, and/or improved mixer/process design.

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Description

Test your knowledge on the flow characteristics of lactose, mixing techniques, and the properties of powders. This quiz covers various types of mixers, density measures, and the significance of porosity in powders. Ensure you understand the distinctions between high shear mixers and other mixing methods.