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The influence of rolling friction on the shear behaviour of non-cohesive pharmaceutical granules: An experimental and numerical investigation
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
2013 (English)In: European Journal of Pharmaceutical Sciences, ISSN 0928-0987, E-ISSN 1879-0720, Vol. 49, no 2, 241-250 p.Article in journal (Refereed) Published
Abstract [en]

Granule shear behaviour was investigated experimentally and numerically to evaluate the reliability of the numerical model. Additionally, parameters affecting the ensuing flow regimes - elastic quasi-static and inertial non-collisional - were highlighted. Furthermore, the influence of using the Lees-Edwards periodic boundary conditions or the standard boundary conditions was studied. Experiments were performed with microcrystalline cellulose granules of three size distributions using the FT4 powder rheometer. The numerical parameters, particle size, effective density, and particle stiffness were selected to match the experimental conditions. Experimentally, an unexpected particle size effect was evident where the resistance to shear increased with particle size. Numerically, combining rolling friction. and increased shear rate enabled a transition from the inertial non-collisional to the elastic quasi-static regime at a reduced sliding friction coefficient. Presumably, this is an effect of increased particle overlap creating stronger contacts and facilitating force chain formation. Both boundary conditions provided comparable results provided a correction of system size was made, where larger systems were required for the standard boundary conditions. A satisfactory qualitative agreement between the experimentally and numerically determined yield loci emphasised the predictive capacity of the DEM. Rolling friction was in addition concluded to be an essential model parameter for obtaining an improved quantitative agreement.

Place, publisher, year, edition, pages
2013. Vol. 49, no 2, 241-250 p.
Keyword [en]
Shear, Discrete element method, Flow regimes, Rolling friction, Shear rate
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-204131DOI: 10.1016/j.ejps.2013.02.022ISI: 000319639800017OAI: oai:DiVA.org:uu-204131DiVA: diva2:637736
Available from: 2013-07-22 Created: 2013-07-22 Last updated: 2014-04-15Bibliographically approved
In thesis
1. Flow and Compression of Granulated Powders: The Accuracy of Discrete Element Simulations and Assessment of Tablet Microstructure
Open this publication in new window or tab >>Flow and Compression of Granulated Powders: The Accuracy of Discrete Element Simulations and Assessment of Tablet Microstructure
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Simulations are powerful and important tools for gaining insight into powder processes. Ultimately, simulations have the potential to replace experiments. Thus, accurate models and insight into the essential factors for descriptions of powder behaviour are required. In this thesis, discrete element method (DEM) simulations of granule flow and compression were evaluated to deduce parameters and potential models essential for the experimental and numerical correspondence. In addition, the evolution in tablet microstructure during compression was studied using mercury porosimetry.

Granule flow was measured using angle of repose, discharge rate, and shear. The granular flow depended primarily on particle shape and surface texture due to the mutual influence of these two parameters on the inter-particle forces. Rolling friction stabilised both the heap formation and promoted shear in the elastic quasi-static flow regime. Thus, rolling friction was established to be an essential simulation parameter for the correspondence to experiments.

Current compression models often neglect the elastic compact deformation during particle loading. In this thesis, two fundamentally different models were evaluated with focus of including the elastic deformation. The first model comprised a maximal particle overlap, where elastic deformation commences. The second model accounted for the contact dependence and impingement at high relative densities. This model was based on a truncated-sphere followed by a Voronoi extension. The validity of the models was demonstrated by the elastic qualitative correspondence to experimental compressions for ductile materials.

In tablets, the void (inter-granular pore) diameter was dependent on the degree of compression. Thus, the degree of compression provides an indication of the tablet microstructure. The microstructure was subsequently observed to be related to the tablet tensile strength as inferred from a percolation threshold required for formation of coherent tablets.

In summary, this thesis has shed light onto the potential of simulating flow and compression of granulated pharmaceutical powders using DEM. Continuous work in the area are required to further improve the models to increase the experimental and numerical correspondence.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 65 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 180
Keyword
Discrete Element Method, Granule, Flow, Angle of Repose, Discharge Rate, Shear, Rolling friction, Compression, Elastic deformation, Microstructure, Degree of compression, Tensile strength
National Category
Pharmaceutical Sciences
Research subject
Pharmaceutics
Identifiers
urn:nbn:se:uu:diva-208808 (URN)978-91-554-8769-0 (ISBN)
Public defence
2013-11-22, B42, BMC, Husargatan 3, Uppsala, 09:15 (Swedish)
Opponent
Supervisors
Available from: 2013-10-30 Created: 2013-10-08 Last updated: 2014-01-23

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