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The degree of compression of spherical granular solids controls the evolution of microstructure and bond probability during compaction
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.
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.
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2013 (English)In: International Journal of Pharmaceutics, ISSN 0378-5173, E-ISSN 1873-3476, Vol. 442, no 1-2, 3-12 p.Article in journal (Refereed) Published
Abstract [en]

The effect of degree of compression on the evolution of tablet microstructure and bond probability during compression of granular solids has been studied. Microcrystalline cellulose pellets of low (about 11%) and of high (about 32%) porosity were used. Tablets were compacted at 50, 100 and 150 MPa applied pressures and the degree of compression and the tensile strength of the tablets determined. The tablets were subjected to mercury intrusion measurements and from the pore size distributions, a void diameter and the porosities of the voids and the intra-granular pores were calculated. The pore size distributions of the tablets had peaks associated with the voids and the intra-granular pores. The void and intra-granular porosities of the tablets were dependent on the original pellet porosity while the total tablet porosity was independent. The separation distance between pellets was generally lower for tablets formed from high porosity pellets and the void size related linearly to the degree of compression. Tensile strength of tablets was higher for tablets of high porosity pellets and a scaled tablet tensile strength related linearly to the degree of compression above a percolation threshold. In conclusion, the degree of compression controlled the separation distance and the probability of forming bonds between pellets in the tablet. 

Place, publisher, year, edition, pages
2013. Vol. 442, no 1-2, 3-12 p.
Keyword [en]
Tablets, Pore structure, Microstructure, Degree of compression, Tensile strength, Percolation theory
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-196531DOI: 10.1016/j.ijpharm.2012.08.011ISI: 000314690200002OAI: oai:DiVA.org:uu-196531DiVA: diva2:610860
Available from: 2013-03-13 Created: 2013-03-11 Last updated: 2017-12-06Bibliographically 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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