Powder Exploration: Unraveling Basics, Technology, and Batch-to-Batch Reproducibility in the Pharma Industry

Powders are bulk assemblies containing particles, but they encompass more than just particles. The terms 'particle' and 'powder' are often used interchangeably, which can be misleading. Powders also include gases, typically air, and liquids, usually water, either on the particle surface or within its structure. The properties and interactions of these phases define bulk powder behavior. This complexity arises from the numerous variables and potential interactions influencing powder behavior.

Powder behavior is influenced by both particle characteristics and external variables, making it complex and challenging to predict based on physical properties alone. The multitude of variables affecting powder behavior renders accurate mathematical modeling impractical. Additionally, we do not yet fully understand all potential interactions, nor can we measure many influencing factors directly. [1]

Cohesion

Cohesion, crucial for powder flow, results from particles bonding due to electrostatic charges and Van der Waals forces. While insignificant in consolidated powders, it dominates in loose packing states, impacting process performance significantly. Hence, cohesive properties are vital in low-stress packing processes.

Adhesion

Adhesion of particles refers to the force that causes particles to stick to surfaces they come into contact with. The strength and nature of adhesion can vary widely depending on the materials involved, the surface roughness, the presence of moisture, temperature, and other environmental factors.

Flowability

Flowability refers to the ease with which particles or powders move and flow. This property is crucial in various industries, such as pharmaceuticals, food processing, and materials engineering, where the handling and processing of particulate materials are common.

Several factors influence the flowability of particles: Particle Size and Distribution, Particle Shape, Surface Texture, Moisture Content, Density, Interparticle Forces, Bulk Density and Packing, and Environmental Factors.

Mechanisms that define the ease of the relative movement between the particles:

1) Liquid bridging

2) Cohesion

3) Inter-particulate interactions

4) Gravitational effects

5) Friction

6) Mechanical interlocking

Electrostatic charging

Electrostatic charging is a critical aspect of powder behavior that can significantly affect the handling, processing, and performance of particulate materials. This phenomenon occurs when particles gain or lose electrical charges, leading to the generation of electrostatic forces.

Permeability

Permeability of powders refers to the ability of a fluid (such as air, gas, or liquid) to pass through a packed bed of powder particles. This property is crucial in various applications, including filtration, catalysis, and material processing. Permeability is influenced by factors like particle size, shape, distribution, and packing density.

Compressibility
The compressibility of powders refers to the ability of a powder to decrease in volume under an applied pressure. This property is vital in various industries, such as pharmaceuticals (for tablet formation), metallurgy (for powder compaction), and food processing (for forming compacted food products). Compressibility affects the flowability, density, and mechanical properties of the final product

When discussing batch-to-batch variability, it's essential to examine several properties thoroughly before arriving at a definitive conclusion regarding why our product varies despite using the same raw material. By meticulously observing these properties, we can uncover valuable insights that shed light on the underlying factors contributing to the differences in our product outcomes, even when starting from identical source materials.

Shear stress

When discussing batch-to-batch variability, one critical property to examine is the shear stress of powders. Understanding and analyzing the shear stress can provide valuable insights into why our product exhibits differences even when using the same raw material.

Shear stress is a measure of the force per unit area exerted parallel to the surface of a material. It describes how a material responds to forces that cause it to deform by sliding along a plane. In the context of powders, shear stress is crucial for understanding flowability, compaction, and handling characteristics.

By carefully studying the shear stress, along with other relevant properties, we can better pinpoint the factors contributing to these variations and work towards achieving consistent product quality.


Basic Flowability Energy

Basic flowability energy (BFE) is a measure used to quantify the ease with which a powder flows. It represents the energy required to rotate a blade or impeller through a powder sample under specific conditions. BFE is an important parameter in powder technology, providing insights into the powder's handling and processing characteristics.

High BFE is a consequence of a more efficiently packed powder bed, meaning that the blade is required to displace more powder as it moves and with less available space for particles to move into. This results in more energy being required to mobilize the bed suggesting that the powder may be problematic under dynamic, forced flow conditions, such as those experienced in a screw feeder. [2]


Permeability

Permeability in powders refers to the ability of a gas or liquid to pass through a packed bed of powder particles. A higher Pressure Drop indicates greater resistance to airflow through the sample, i.e. lower Permeability. The lower Pressure Drop (higher permeability) is typical for the uniform structure created by an efficiently packed bed is often associated with improved gravitational flow in low-stress environments (such as filling operations). [2]

Understanding the fundamental behaviors of powders is essential for maintaining consistent product quality and optimizing manufacturing processes.

By thoroughly evaluating powderproperties, manufacturers can detect and address sources of variability, such as differences in particle size distribution, shape, moisture content, or packing density. This comprehensive understanding enables better control over the manufacturing process, leading to improved product consistency, efficiency, and reduced waste.

Understanding and managing batch-to-batch variability in powders is critical for ensuring consistent product quality and performance across various industries. By rigorously testing and analyzing key properties such as Shear stress, Basic Flowability Energy (BFE), and Permeability, manufacturers can gain valuable insights into the behavior of their powders and identify potential sources of variability.

[1] Freeman Technologies, Defining a Role for Powder Testing in Pharmaceuticals, Available to view at: https://www.freemantech.co.uk/ebooks/pflip-defining-a-role-for-powder-testing-in-pharmaceuticals_en/

[2] Freeman Technologies app note: "Assessing Batch-to-Batch variability of bulk chemicals", Available to view at: https://www.freemantech.co.uk/uploads/news/app9_assessing-batch-to-batch-variability-of-bulk-chemicals.pdf