Establishing correlations between process parameters and granule properties for optimal process control.
Dry granulation by roller compaction is a relatively low cost, energy efficient method of converting fine powders into uniform, more easily handled granules. Used throughout the pharmaceutical, food, and chemical industries it is particularly suitable for moisture or heat sensitive materials.
Secure correlations between process parameters and granule properties ensure the consistent manufacture of materials optimised for end-use application or subsequent processing but rely on relevant powder testing.
A collaborative study with Gerteis Maschinen + Processengineering (Jona, Switzerland), a market leader in the design and supply of premium roller compaction equipment, illustrates the value of measuring bulk and dynamic properties for establishing such correlations and for the optimisation of roller compaction processes.
Dynamic, shear and bulk powder properties were measured (FT4 Powder Rheometer®, Freeman Technology, Tewkesbury, England) for a series of granule samples produced using a representative, placebo pharmaceutical blend (Gerteis MINI-PACTOR roller compaction unit). The figures below show the strongest correlations observed between compaction force, a primary control parameter, and measured granule properties.
Dynamic and bulk properties both securely differentiate the samples, providing complementary insight into the effect of compaction force. In contrast, no strong correlations were observed with any shear properties, including wall friction data.
Increasing compaction force decreases the compressibility of the granules but increases permeability; conditioned bulk density also increases (data not shown). These trends indicate that higher compaction forces produce denser granules that pack more efficiently. Increasing permeability may additionally suggest more complete fines incorporation since fine particles tend to inhibit the passage of air by filling the interstices between larger particles.
Aerated energy (AE) also increases with compaction force, a trend consistent with increasing granule density. Denser particles are less influenced by the upward flow of air applied during aeration testing and therefore tend to generate higher AE values than less dense analogues.
Basic flowability energy (BFE) exhibits a more complex, non-linear trend that reflects its sensitivity to multiple particle properties including morphology and stiffness, as well as density.
While the rise in BFE is consistent with increasing density, since denser particles are more difficult to move under the forcing conditions applied during BFE measurement, the results suggest that particle size distribution or stiffness may begin to offset this trend at higher compaction pressures.
These results reliably quantify the impact of consolidation. They are useful in revealing which properties differentiate the granule samples but also demonstrate the unsuitability of shear testing for this application. However, the question of industrial relevance remains. For example, does a change in BFE affect downstream processing performance?
Many powder testing techniques lack industrial relevance, generating properties that cannot be robustly correlated with process performance. In contrast, dynamic and bulk powder properties have been correlated with behaviour across a range of applications.
Notably, the BFE of granulated blends has been strongly linked with tablet hardness, a critical quality attribute while permeability and compressibility influence the rate and consistency of filling operations and inform on performance within a tablet press. Controlling roller compaction to produce granules with specified dynamic and bulk properties can therefore be a productive strategy for quality control or downstream process optimisation.
Read on to learn about the effect of roller gap, an additional control parameter for dry granulation.
Freeman Technology
- +44 (0)1684 851 551
- info@freemantech.co.uk
- https://www.freemantech.co.uk
- 1 Miller Court Severn Drive Tewkesbury Gloucestershire GL20 8DN GB
About us
Freeman Technology specialises in systems for measuring the flow properties of powders and has nearly 20 years' experience in powder flow and powder characterisation.
The company invests significantly in R&D and applications development, and provides detailed know-how to support its range of products. Expert teams guide and support users around the world in addressing their individual powder challenges, focusing on delivering the most relevant information for the process. The result is world-leading solutions for understanding powder behaviour - in development, formulation, scale-up, processing, quality control, or anywhere that powders have a role.
Freeman Technology’s solutions include the FT4 Powder Rheometer®, a uniquely universal powder tester, and the Uniaxial Powder Tester, a complementary tool for quick and robust powder assessment. Systems are installed around the world in the chemical, pharmaceutical, toners, foods, powder coatings, metals, ceramics, cosmetics, and many other industries. They deliver data that maximise process and product understanding, accelerating R&D and formulation towards successful commercialisation, and supporting the long term optimisation of powder processes.
Founded in 1989 as a developer of automated testing systems for materials characterisation, the company has focused exclusively on powders since the late 1990s and in 2018 became part of Micromeritics Instrument Corporation. The company’s R&D, manufacturing and commercial headquarters are in Gloucestershire, UK, with operations and distribution partners in key global territories. In 2007 the company received the Queen’s Award for Enterprise in Innovation and in 2012 the Queen’s Award for Enterprise in International Trade.
Where we supply to
UK Ireland, Europe, Africa, Asia, Australia, South America, North America
Industries we supply to
Chemicals, Food and Beverage, Pharmaceutical Cosmetics Toiletries
