How to measure compressibility / compactability

Compaction force and compactability are interrelated properties often measured in texture analysis, especially in industries like pharmaceuticals, food production, and materials science. These properties reveal how materials behave under compression, such as during tablet formation, powder compaction, material packing, or bulk material handling, reflecting a material's capacity to be compacted or compressed during a test.

Compactability is particularly desirable in applications like the formation of cosmetic or pharmaceutical tablets from granules. By analysing this property, scientists and manufacturers can optimise tablet formulations, improve manufacturing processes, and ensure consistent product quality. Data from texture analysis provides valuable insights for research and development, as well as quality control in tablet production.

In contrast, resistance to compression is preferred for packaging materials to protect products from external forces. This is essential for industries like food, electronics, and pharmaceuticals, where safe handling, secure transport, and efficient storage are priorities, especially when stacking is required. Testing the compaction force of materials like corrugated cardboard or packaging foams ensures they withstand stacking without deformation, maintaining product protection. In packaging, compressibility reflects a material's ability to resist permanent deformation or breakdown under compression - a key factor for materials that need to absorb shocks and preserve structural integrity.

Compactability in packaging also includes a material’s ability to reduce in volume under pressure for space efficiency. This property is important for flexible packaging materials, such as foams, bubble wraps, and certain plastics, where compacting aids in storage and shipment. High compactability also indicates whether the material can recover after compression, a vital attribute for protective packaging. Testing on foam inserts or cushioning materials, for example, ensures they can be compressed for storage but expand to protect contents upon unpacking.

Compactability testing using a Texture Analyser is essential across industries like pharmaceuticals, food processing, and materials science, where compaction characteristics are critical for product performance and quality. Here are some key applications:

• Pharmaceutical powder compression: Evaluating the compactability of pharmaceutical powders for tablet formulation by measuring the force applied during powder compaction to assess the cohesiveness of an active ingredient.
• Pharmaceutical powder rheology: Studying the flow and compaction behaviour of pharmaceutical powders under various pressure conditions as in a hopper feeder to optimise flow in pharmaceutical manufacturing.
• Pharmaceutical tablet compression: Assessing the force required to form tablets with the desired hardness and friability to evaluate the compactability of a drug formulation.
• Powder flow and compaction: Evaluating the compactability of powders used in pharmaceuticals, cosmetics, and food processing by measuring the force required to compress a powdered compact/block to assess its flow properties and compressibility.
• Food ingredient compaction: Testing the compactability of food ingredients like powders and granules during processing. For example, measuring the force needed to compact sugar granules into sugar cubes to evaluate processing efficiency.
• Soil compaction testing: Assessing soil compaction properties for construction and geotechnical applications by measuring the force required to compact a soil sample to a specified density to evaluate its compressibility/unconfined yield strength.
• Granular material compaction: Testing the compaction of granular materials like coffee grounds or detergents. For example, measuring the force required to compact coffee grounds into a puck for espresso preparation.
• Metal powder compaction: Assessing the compressibility of metal powders in manufacturing parts using powder metallurgy by measuring the force needed to compact the metal powder into a green compact before sintering.
• Paper and board compression: Evaluating the compressibility of paper and board for packaging and printing. For example, measuring the force required to compress a stack of paper to assess its resilience and compactability. In packaging, these tests ensure that materials meet performance standards for strength, resilience, and protective function. Compression tests on corrugated cardboard, cushioning foams, or moulded pulp trays, for example, help ensure that packaging can endure impacts and shocks without permanently compressing, which would reduce its protective capacity.

In these examples, a Texture Analyser applies controlled forces/distances to materials to assess their compaction characteristics. These measurements are crucial for process optimisation, product development, and quality control in industries where material density and compression are key factors.

In a typical compaction test, a compression probe/attachment that is larger than the sample is used to simulate the compressive action on a sample. The sample is either a single item e.g. a box, or a multiparticle contained sample, such as powder/granules located under the probe which pushes against it as the Texture Analyser records the force and distance throughout the test.

Cylinder Probes of all sizes

Rectangular Compression Platen

When measuring compaction properties, the force vs distance/time graph typically shows an increase in force with/without a drop in force (due to sample failure) representing the amount of force needed to compact the sample to a chosen force/distance. From the graph you can observe/obtain the following:

• Work of compaction
• Force to compact
• Ease of compression
• Point of non-recoverable failure
• Compression recovery 

A full explanation of these curves and their analysis can be accessed within Exponent Connect software. Existing Exponent users can upgrade to Exponent Connect specification.

Below is a video example of how we can help you understand curve analysis for an example property.

• Applied pressure: The magnitude of force applied to the material directly influences the degree of compaction achieved.
• Speed of compression: The rate at which pressure is applied can affect how the material responds, potentially leading to different compaction outcomes.
• Duration of force application: The length of time the compressive force is maintained can impact the final compaction state of the material.
• Moisture content: The amount of water present in a material can significantly impact its ability to be compacted, often acting as a binding agent.
• Material composition: The chemical and physical makeup of the material, including any additives or binders, can greatly influence its compactability.
• Cohesive properties: The tendency of particles to stick together affects how easily a powdered material can be compacted into a coherent mass.
• Initial porosity: The amount of void space in a powdered material before compression directly affects how much it can be compacted.
• Material elasticity: The ability of a material to return to its original shape after compression influences its overall compressibility.
• Presence of air voids: The amount and distribution of air pockets within a material can significantly affect its compressibility and final density after compression.

In general, a more-free flowing powder is less compressible (as the powder particles have already flowed into a more close-packed state). This corresponds to a small increase in bulk density with stress and a low compressibility. A more cohesive powder tends to show the opposite behaviour and a high compressibility.

Holes are present in the compression probe to allow for air pockets to be released during compression from the underlying powder column. Along with the measurement of Compressibility and Bulk Density, additional parameters can also be measured within this test after it has been split into three sections: Stiffness, Relaxation and Elastic Modulus.

The Stable Micro Systems Texture Analyser excels in optimising measurements of compaction force and compactability through its versatile capabilities and specialised features. It offers a comprehensive approach, utilising compression probes of various sizes and specially designed compaction attachments to accurately measure properties of solid and powdered/granulated materials such as cosmetic powders or packaging materials.

The Texture Analyser's advanced Exponent Connect software provides detailed force-time-distance profiles, capturing critical points and parameters such as relaxation/recovery behaviour. Backed by Stable Micro Systems' expertise in method development and data interpretation, the Texture Analyser delivers unparalleled accuracy and insight. These capabilities make it the ideal choice for researchers and manufacturers across various industries seeking to refine product formulations and optimise compaction processes.