Podcast
Questions and Answers
What is a common consequence of poor powder flow during tabletting?
What is a common consequence of poor powder flow during tabletting?
- Improved reproducibility of dosage forms
- Reduced particle-die-wall friction
- Increased risk of capping and lamination (correct)
- Enhanced homogeneity of the powder mixture
Which of the following factors contribute to the resistance of powder flow due to cohesion?
Which of the following factors contribute to the resistance of powder flow due to cohesion?
- High particle size
- Weak Van-der-Waals forces (correct)
- Low relative humidity
- Strong adhesion between particles and container walls
What is the main reason for the risks of dust contamination with fine particles?
What is the main reason for the risks of dust contamination with fine particles?
- Higher relative humidity
- Improved powder flow
- Increased particle-die-wall friction (correct)
- Reduced cohesion between particles
Which of the following is NOT a common method of powder transfer in manufacturing?
Which of the following is NOT a common method of powder transfer in manufacturing?
Why is it important to consider powder flow in various pharmaceutical processes?
Why is it important to consider powder flow in various pharmaceutical processes?
What is the range of the Carr Index for a powder that has 'excellent' flowability?
What is the range of the Carr Index for a powder that has 'excellent' flowability?
What is NOT a factor affecting powder flow, according to the text?
What is NOT a factor affecting powder flow, according to the text?
How does the text describe the relationship between particle size and powder flow?
How does the text describe the relationship between particle size and powder flow?
What is the purpose of a tapped density tester, as described in the text?
What is the purpose of a tapped density tester, as described in the text?
Which of the following is NOT mentioned as a factor affecting powder flow, according to the text?
Which of the following is NOT mentioned as a factor affecting powder flow, according to the text?
Flashcards
Factors affecting powder flow
Factors affecting powder flow
Cohesion, adhesion, particle size, and shape influence how powders flow.
Carr Index
Carr Index
A measure used to evaluate the flowability of powders based on compressibility percentages.
Tapped density tester
Tapped density tester
A device that measures the density of a powder by tapping it a specific number of times.
Bulk density measurements
Bulk density measurements
Assessing the density of a powder when lightly tapped or packed versus maximum packing.
Signup and view all the flashcards
Powder flowability categories
Powder flowability categories
Classifications of powders based on Carr Index: excellent to extremely poor flow.
Signup and view all the flashcards
Importance of Powder Flow
Importance of Powder Flow
Powder flow is crucial for processes like tabletting, granulation, and capsulation, affecting product quality.
Signup and view all the flashcards
Consequences of Poor Powder Flow
Consequences of Poor Powder Flow
Poor powder flow can lead to uneven mixtures, risk of segregation, and non-uniform dosage.
Signup and view all the flashcards
Cohesion
Cohesion
Cohesion refers to attractive forces between particles, often due to Van-der-Waals forces and moisture.
Signup and view all the flashcards
Adhesion
Adhesion
Adhesion is the attractive force between different surfaces, impacting powder flow and transfer.
Signup and view all the flashcards
Parameters Affecting Powder Flow
Parameters Affecting Powder Flow
Factors like particle size, moisture content, and cohesive forces influence how powders flow.
Signup and view all the flashcardsStudy Notes
Powder Flow
- Powder flow is important in various manufacturing processes, including tabletting, granulation, and encapsulation.
- Powder flow is also crucial for transfer within the manufacturing process, such as pneumatic, hydraulic, and gravity- or mechanically- assisted feeding.
Intended Learning Outcomes
- Students will understand the importance of powder flow.
- Students will identify parameters that affect powder flow.
- Students will understand the differences between various bulk densities, as well as how to measure them.
Importance of Powder Flow
- Poor powder flow can lead to uneven mixtures
- It can lead to issues with segregation.
- Non-uniformity of doses is a potential consequence
- Manufacturing processes requiring powder transfer (e.g., granulation, tabletting, encapsulation) can be problematic.
- Risks of capping and lamination (in tabletting) can emerge due to trapped air.
- Increased particle-die-wall friction and dust contamination issues.
- Particles smaller than 10 micrometers are extremely adhesive and cohesive.
- Particles between 10 and 50 micrometers have irregular or no flow due to van der Waals forces.
- Particles larger than 50 micrometers exhibit free flow.
- Dense particles are less cohesive.
Resistance to Powder Flow
- Cohesion: Forces between particles, stemming from van der Waals forces (electrostatic), are dependent on the particle's composition. These forces intensify as particle size diminishes, and moisture (relative humidity -RH ) influences cohesion, with stronger forces above a critical humidity level.
- Adhesion: Adhesive forces occur between dissimilar surfaces, such as a particle and the hopper wall of a tabletting press.
Factors Affecting Powder Flow
- Resistance to flow due to cohesion and adhesion
- Particle size
- Particle density—dense particles tend to be less adhesive.
- Particle shape—spherical particles have less interparticulate contact compared to non-spherical particles.
- Particle size distribution—smaller particles settle below larger particles.
- Particle surface - electrostatic forces increase cohesion. Rough surfaces have more cohesiveness, and packing geometry plays a role.
- Humidity
- Processing conditions, such as hopper vibration needs to be controlled to minimize problems.
- Powder density
- Porosity of the powder
Powder Flow in the Hopper
- Requirements include a controlled and constant flow rate, along with seamless flow (no segregation).
- The two principal types of flow are mass flow and core flow.
- Hopper design (geometry and wall material) is often fixed, whereas powder properties can be modified.
Mass Flow
- All material is in motion during discharge.
- The bulk of the powder flows downward.
- The angle of repose is generally approximately 20 degrees.
- Wall friction angle needs to be considered.
Core Flow
- Materials outside the falling region remain stationary
- Some powders stay undisturbed.
- Dead space happens during discharge.
- The angle of repose is typically around 50 degrees.
- Wall friction angle must be considered.
Case Study: Design Variation
- Different hopper designs with varying angles (15–75 degrees) are used.
Problems of Core Flow
- Flow from the hopper may unexpectedly cease.
- Arching occurs between hopper walls, which may be strong enough to support material above.
- Piping, rat-holing, and funnelling can occur.
- Sudden and rapid powder discharge can result from arch or pipe collapse, creating flooding.
- Powder segregation leads to the loss of mixing uniformity, potentially causing irregularities in the dosage.
Bulk Density
- Bulk density refers to the density of a powder sample, encompassing both the particulate volume and inter-particulate pores.
- Minimum bulk density refers to the maximum volume occupied by the powder.
- Poured bulk density is determined after pouring the powder into a cylinder.
- Tapped bulk density represents the maximum theoretically achievable density without particle deformation.
- Relative density (also called packing fraction or fractional solid content), often denoted as 'k', is a ratio between bulk density and true density.
Porosity of Powder Bed
- Porosity indicates the proportion of a powder bed occupied by pores, effectively reflecting the packing efficiency of the powder.
- Porosity calculation: 1 – (Bulk density/True density)
Characterisation of Powder Flow
- The angle of repose is a critical factor for determining powder flow characteristics, with <30° suggesting good flow and >40° indicating problematic flow.
- Varying methods can affect measurement results, so caution must be exercised in interpretation.
Bulk Density Measurements
- Hausner ratio is calculated as Tapped bulk density/ Poured bulk density, offering insights into powder flowability.
- Free-flowing powders often have a Hausner ratio near 1.2, while cohesive powders usually exhibit ratios exceeding 1.6.
- Carr index, another measure of flowability, assesses the tendency of arch formation.
Tapped Density Tester
- Procedures for tapping at 10, 500, and 1250 counts are essential.
- The procedure must ensure the measurements are taken at consistent speed.
- Measurements enable calculations of Do and Df.
Summary of Powder Flow
- Key factors affecting powder flow include cohesion and adhesion, particle size and distribution, shape, texture, density, porosity, formulation, and hopper design.
- Understanding powder flow is crucial for effective manufacturing processes, particularly those that involve producing tablets.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz covers the essential aspects of powder flow in various manufacturing processes, such as tabletting and granulation. Students will learn about the significance of powder flow, the parameters affecting it, and the importance of bulk density measurements. Understanding these concepts is crucial for ensuring uniform mixtures and effective manufacturing outcomes.