Aggregation Strength Testing Service

Aggregation Strength Testing Service – Accredited ISO/IEC 17025 Particle Cohesion and Mechanical Stability Assessment for the Croatian Market

Aggregation strength is a critical mechanical property that quantifies the resistance of particles, powders, granules, and agglomerates to breakage, attrition, and deformation under mechanical stress. This property is essential for ensuring the quality, performance, and handling characteristics of materials used in the pharmaceutical, chemical, food, agricultural, mining, ceramic, and additive manufacturing industries. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Ministarstvo gospodarstva i održivog razvoja, the Državni inspektorat, the Agencija za lijekove i medicinske proizvode (HALMED), and the Carinska uprava enforce strict quality, safety, and environmental standards aligned with EU directives and HRN EN (Croatian standards based on European norms), the accurate evaluation of aggregation strength is essential for product certification, supplier qualification, quality control in manufacturing, process optimization, and import-export processes. Our laboratory offers a comprehensive aggregation strength testing service, applying standardized methods that measure the resistance of particles and agglomerates to compression, impact, shear, and attrition under controlled conditions. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Croatian authorities and notified bodies, making them indispensable for regulatory compliance, material validation, and market access in Croatia and the European Union.

Materials and Samples We Regularly Test

Our laboratory receives a wide variety of particulate materials and agglomerates for aggregation strength testing. Typical samples include:

• Pharmaceutical powders and granules – active pharmaceutical ingredients (APIs), excipients, and granulated formulations for tablet compression.
• Chemical catalysts and adsorbents – catalyst pellets, extrudates, and beads for petrochemical and environmental applications.
• Food powders and ingredients – milk powders, flours, starches, spices, and instant beverage mixes.
• Agricultural granules and fertilizers – granular fertilizers, seed coatings, and pesticide granules.
• Ceramic powders and green bodies – for the production of tiles, refractories, and advanced ceramics.
• Mining and mineral products – ore concentrates, coal fines, and mineral agglomerates.
• Additive manufacturing powders – metal powders, polymer powders, and composite powders for 3D printing.
• Prototype and new material formulations – submitted by manufacturers for validation of aggregation strength before series production.
• Field-retrieved samples – for failure analysis and remaining life assessment.

Compression Strength Testing – Evaluating Resistance to Compressive Forces

Compression strength testing measures the force required to crush or fracture individual particles, granules, or agglomerates under a controlled compressive load. This test is essential for ensuring the mechanical integrity of materials during handling, transportation, and processing, and is widely used in the Croatian pharmaceutical, chemical, and agricultural industries.

• Single-particle compression test (ASTM D4179 / ISO 178 / NTC 5700 – for individual granules and pellets) – we place a single particle or granule between two parallel platens in a micro-compression testing machine. A compressive load is applied at a constant rate (e.g., 0.5 mm/min) until the particle fractures. The fracture force (in N) and the fracture stress (in MPa) are measured. We report the average fracture force, the fracture stress, and the deformation at fracture for a statistically significant number of particles (typically 20 to 50 particles).
• Granule bed compression test (NTC 5701 – for evaluating the strength of agglomerates in a bulk bed) – we place a known mass of granules or agglomerates in a cylindrical die and apply a compressive load (e.g., 0 to 100 kN) at a constant rate. The compaction curve (force vs. displacement) is recorded, and the yield pressure and the strength of the compact are determined. We report the yield pressure (in MPa), the compact strength (in MPa), and the compaction curve.
• Tablet and pellet crushing test (ASTM D617 / ISO 27368 / NTC 5702 – for pharmaceutical tablets and pellets) – we measure the force required to crush a tablet or a pellet using a tablet hardness tester (or a universal testing machine with a suitable fixture). The crushing strength (in N or kp) is recorded. We report the average crushing strength, the standard deviation, and the pass/fail status based on the specified limits.
• Burst strength of agglomerates (NTC 5703 – for evaluating the resistance to sudden rupture) – we apply a rapid compressive load (impact) to the agglomerate using a drop-weight tester or a pendulum impact tester. The impact energy required to fracture the particle is measured. We report the impact energy (in J) and the fracture mode.
• Temperature-dependent compression strength (NTC 5704 – for evaluating the effect of temperature) – we perform the compression test at different temperatures (e.g., -20 °C, 20 °C, 40 °C, 60 °C) to evaluate the effect of temperature on the aggregation strength. We report the fracture force and the fracture stress at each temperature.

Shear and Attrition Resistance Testing – Evaluating the Resistance to Frictional Forces

Shear and attrition resistance tests measure the ability of particles and agglomerates to withstand frictional forces and surface wear during handling, transport, and processing. These tests are essential for materials that are prone to dusting, degradation, or loss of flowability, and are widely used in the Croatian chemical, food, and mining industries.

• Shear cell test (ASTM D6128 / ISO 5722 / NTC 5710 – for powder flow and shear strength) – we place a sample of the powder or granules in a shear cell (e.g., a Jenike shear cell or a ring shear tester) and apply a normal load. The shear force required to initiate and maintain flow is measured at various normal loads. The effective angle of internal friction and the cohesive strength are determined. We report the angle of internal friction (in °), the cohesive strength (in kPa), and the flow function.
• Attrition and abrasion test (ASTM D4324 / NTC 5711 – for evaluating the wear resistance) – we place a sample of the granules or agglomerates in a rotating drum (or a fluidized bed) and subject them to a controlled amount of mechanical agitation. The amount of fines generated (particles smaller than a specified size) is measured. We report the attrition index (the percentage of fines generated) and the attrition rate (in % per hour).
• Friability test (ASTM D4167 / ISO 1214 / NTC 5712 – for pharmaceutical tablets and granules) – we place a known mass of tablets or granules in a rotating drum (a friabilator) and rotate it for a specified number of revolutions. The weight loss (in %) is measured. We report the friability (in %) and the pass/fail status based on the specified limits (typically less than 1 %).
• Wear index measurement (NTC 5713 – for evaluating the surface wear) – we measure the change in the particle size distribution and the surface morphology (using SEM) of the granules after the attrition test. The wear index (the increase in fines) and the surface damage are assessed. We report the wear index and the surface condition.
• Attrition at different humidity levels (NTC 5714 – for evaluating the effect of moisture) – we perform the attrition test at different relative humidity levels (e.g., 20 %, 50 %, 80 % RH) to evaluate the effect of moisture on the aggregation strength. We report the attrition index at each humidity level.

Impact and Drop-Weight Testing – Evaluating Resistance to Shock and Impact

Impact and drop-weight testing measures the resistance of particles and agglomerates to sudden impact forces, such as those experienced during drop loading, pneumatic conveying, and high-velocity processing. These tests are essential for materials used in the Croatian mining, agricultural, and construction sectors.

• Drop-weight impact test (NTC 5720 – for evaluating the impact resistance) – we drop a known mass (e.g., 1 kg, 5 kg) from a specified height onto a bed of granules or onto individual agglomerates. The impact energy (in J) and the percentage of broken particles are measured. We report the impact energy, the percentage of breakage, and the fracture mode.
• Impact fragmentation test (NTC 5721 – for evaluating the fragmentation behavior) – we use a split Hopkinson pressure bar (SHPB) or a drop tower to subject the agglomerate to a controlled impact load. The fragmentation energy and the fragment size distribution are measured. We report the fragmentation energy (in J/g) and the fragment size distribution.
• Drop test for bulk packages (NTC 5722 – for evaluating the impact resistance during transport) – we drop the packaged granules (e.g., bags, boxes) from a specified height (e.g., 1 m) onto a hard surface and then assess the degree of breakage and the dust generation. We report the package integrity and the product condition.
• Impact attrition test (NTC 5723 – for evaluating the combined effect of impact and attrition) – we use a jet mill or an impact mill to subject the granules to repeated impacts and attrition. The change in particle size and the generation of fines are measured. We report the impact attrition index and the particle size distribution.
• Impact resistance at different temperatures (NTC 5724 – for evaluating the effect of temperature) – we perform the impact test at different temperatures (e.g., -20 °C, 20 °C, 60 °C) to evaluate the effect of temperature on the brittleness of the material. We report the impact energy and the breakage percentage at each temperature.

Flowability and Cohesion Testing – Evaluating the Bulk Behavior of Powders and Granules

The flowability and cohesion of powders and granules are directly related to the aggregation strength. Our flowability and cohesion tests measure the ease with which the material flows and the forces required to initiate flow, which are essential for the design of hoppers, feeders, and pneumatic conveying systems in the Croatian food, pharmaceutical, and chemical industries.

• Angle of repose measurement (ASTM D6393 / NTC 5730 – for the flowability assessment) – we pour a sample of the powder or granules onto a flat surface and measure the angle of the cone formed. A lower angle of repose indicates better flowability. We report the angle of repose (in °).
• Flowability index (NTC 5731 – for the combined flowability assessment) – we combine the angle of repose, the compressibility, and the cohesiveness (from the shear cell test) to calculate a flowability index (or a flow function). The flowability index is classified from very good to very poor. We report the flowability index and the classification.
• Cohesion measurement (NTC 5732 – for evaluating the cohesive strength) – we use the shear cell test (or a tensile strength test) to measure the cohesive strength (the force required to separate particles). We report the cohesive strength (in kPa) and the classification.
• Bulk and tapped density measurement (ASTM D7481 / NTC 5733 – for the packing behavior) – we measure the bulk density (the loose-poured density) and the tapped density (the density after a specified number of taps). The compressibility index (Carr index) and the Hausner ratio are calculated. We report the bulk density, the tapped density, the Carr index, and the Hausner ratio.
• Flow through an orifice test (NTC 5734 – for the practical flowability evaluation) – we allow the powder or granules to flow through an orifice of a specified diameter and measure the flow rate (in g/s). The flow rate is correlated with the flowability. We report the flow rate and the flowability rating.

Moisture and Environmental Effects on Aggregation Strength – Evaluating the Durability under Various Conditions

The aggregation strength of many materials is highly dependent on the moisture content and the environmental conditions. Our moisture and environmental tests simulate the effects of humidity, temperature, and chemical exposure on the aggregation strength, providing a realistic assessment of the material's performance in the diverse Croatian climate (coastal, continental, and mountainous regions).

• Moisture absorption and its effect on strength (NTC 5740 – for evaluating the hygroscopicity) – we condition the granules at different relative humidity levels (e.g., 20 %, 50 %, 80 % RH) and measure the change in the compression strength and the attrition resistance. We report the strength retention (in %) and the moisture uptake (in %).
• Wetting and drying cycle test (NTC 5741 – for evaluating the durability under moisture cycles) – we subject the granules to repeated cycles of wetting (e.g., immersion in water) and drying (e.g., in an oven at 50 °C). The change in the aggregation strength is measured after each cycle. We report the strength retention after each cycle.
• Effect of chemical exposure (NTC 5742 – for evaluating the chemical resistance) – we expose the granules to various chemicals (e.g., acids, bases, solvents) at a controlled temperature and then measure the compression strength and the attrition resistance. We report the chemical resistance and the change in the strength.
• Storage stability test (NTC 5743 – for evaluating the aging effect) – we store the granules at a specified temperature (e.g., 40 °C) and humidity (e.g., 50 % RH) for a specified duration (e.g., 1 month, 3 months) and then re-measure the aggregation strength. We report the strength retention and the aging effect.
• Freeze-thaw test (NTC 5744 – for evaluating the resistance to frost) – we subject the granules to cycles of freezing (e.g., -20 °C) and thawing (e.g., 20 °C) and then measure the change in the aggregation strength. We report the strength retention and the freeze-thaw resistance.

Complementary Tests – Particle Size Distribution, Surface Morphology, and Chemical Composition

To fully understand the aggregation strength and the factors that influence it, we perform complementary tests, including particle size distribution analysis, surface morphology examination, and chemical composition analysis. These tests are essential for a comprehensive quality assessment and for the optimization of the material formulation and the manufacturing process.

• Particle size distribution analysis (ASTM D4464 / ISO 13320 / NTC 5750 – by laser diffraction or sieving) – we measure the particle size distribution (D10, D50, D90) of the granules before and after the aggregation strength tests. The change in the distribution indicates the extent of breakage. We report the particle size distribution and the change in the D50.
• Surface morphology examination (SEM – ASTM E1508 / NTC 5751 – for the structural analysis) – we use scanning electron microscopy (SEM) to examine the surface of the granules, the fracture surfaces (after the compression test), and the wear surfaces (after the attrition test). The morphology reveals the fracture mechanism (e.g., brittle fracture, plastic deformation, or intergranular failure). We report the SEM images and the fracture analysis.
• Chemical composition analysis (XRF / NTC 5752 – for the elemental composition) – we use X-ray fluorescence (XRF) or other spectroscopic techniques to determine the chemical composition of the material, which can influence the aggregation strength. We report the chemical composition and the presence of any impurities.
• BET surface area and porosity (ASTM D3663 / NTC 5753 – for the surface area and the pore structure) – we measure the specific surface area (in m²/g) and the pore size distribution (by nitrogen adsorption). The surface area and the porosity can affect the cohesion and the strength of the agglomerates. We report the BET surface area and the pore size distribution.
• Density and true density measurement (ASTM D792 / NTC 5754 – for the material density) – we measure the bulk density, the tapped density, and the true density (by helium pycnometry) of the material. The density is correlated with the porosity and the strength of the agglomerates. We report the density values.

Test Report and Recognition in the Croatian Pharmaceutical, Chemical, and Industrial Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (compression test machines, shear cells, attrition testers, and particle size analyzers) and traceability to international standards (NIST, PTB). Our test reports are issued in English (with a Croatian summary available on request) and include:

• Full identification of the material (manufacturer, product name, lot number, formulation, and particle size).
• Detailed description of the test methods applied (ASTM/ISO/HRN EN/NTC standards, test conditions, and measurement parameters).
• Numerical results: fracture force (N), fracture stress (MPa), attrition index (%), friability (%), angle of repose (°), flowability index, shear strength (kPa), and moisture uptake (%).
• Graphical data: compression curves, shear stress vs. normal stress curves, and particle size distribution curves.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ASTM D4179, ISO 5722, HRN EN 12241, and the requirements of the HZN, HALMED, and Državni inspektorat).
• SEM images of the particle surfaces and the fracture surfaces.
• Recommendations for material formulation optimization, process improvement, and quality control measures to achieve the required aggregation strength.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98-3 Guide.

These reports are fully accepted by the Hrvatski zavod za norme (HZN) for the verification of product conformity, by the Ministarstvo gospodarstva i održivog razvoja for industrial material compliance, by the Državni inspektorat for market surveillance, by the Agencija za lijekove i medicinske proizvode (HALMED) for pharmaceutical product certification, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of particulate materials and agglomerates. Additionally, we offer consulting services for the optimization of granulation processes, the selection of appropriate binders and additives, and the implementation of quality control programs for aggregation strength, contributing to the safety, reliability, and efficiency of industrial processes in the diverse and growing Croatian market, from the pharmaceutical and food sectors to the chemical, mining, and advanced manufacturing industries.