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Effect of spherical-agglomerate strength on the distribution of force during uniaxial compression
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.
2011 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 206, no 3, 283-290 p.Article in journal (Refereed) Published
Abstract [en]

We employ the carbon paper technique with the aim of investigating the effect of spherical-agglomerate (pellet) strength on force distributions, through confined compression of approximately 1 mm sized pellets formed from microcrystalline cellulose and polyethylene glycol. The carbon paper technique relies on the transference of imprints from compressed pellets onto white photo quality paper, which are digitised and processed via image processing software. The investigated pellets can both deform plastically and develop localised cracks in response to an applied stress, while remaining largely intact during confined compression. Our results indicate that such crack formation - henceforth referred to as fracture - has a decisive influence on force distributions. Previous work on non-fracturing systems has found that the distribution of normalized forces tends to narrow with increasing particle deformation. No narrowing is observed after the point of fracture in this study and the width of the distributions - as quantified by the standard deviation of non-normalized forces - is found to increase with the difference between non-normalized mean force and fracture force. Additional corroborative results show that spatial force-force correlations typically exhibit a marked change once the fracture force is exceeded.

Place, publisher, year, edition, pages
2011. Vol. 206, no 3, 283-290 p.
Keyword [en]
Granular materials, Compression, Force distributions, Carbon paper technique, Particle failure
National Category
Pharmaceutical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-147764DOI: 10.1016/j.powtec.2010.09.031ISI: 000286299200011OAI: oai:DiVA.org:uu-147764DiVA: diva2:401010
Available from: 2011-03-01 Created: 2011-02-28 Last updated: 2013-11-06Bibliographically approved
In thesis
1. Compression Mechanics of Powders and Granular Materials Probed by Force Distributions and a Micromechanically Based Compaction Equation
Open this publication in new window or tab >>Compression Mechanics of Powders and Granular Materials Probed by Force Distributions and a Micromechanically Based Compaction Equation
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The internal dynamics of powder systems under compression are as of yet not fully understood, and thus there is a necessity for approaches that can help in further clarifying and enhancing the level of understanding on this subject. To this end, the internal dynamics of powder systems under compression were probed by means of force distributions and a novel compaction equation.

The determination of force distributions hinged on the use of carbon paper as a force sensor, where the imprints transferred from it onto white paper where converted through calibration into forces. Through analysis of these imprints, it was found that the absence of friction and bonding capacity between the particles composing the powder bed had no effect on how the applied load was transferred through the system. Additionally, it was found that pellet strength had a role to play in the homogeneity of force distributions, where, upon the occurrence of fracture, force distributions became less homogenous.

A novel compaction equation was derived and tested on a series of systems composed of pellets with differing mechanical properties. The main value of the equation lay in its ability to predict compression behavior from single particle properties, and the agreement was especially good when a compact of zero porosity was formed.

The utility of the equation was tested in two further studies, using a series of pharmaceutically relevant powder materials. It was established that the A parameter of the equation was a measure of the deformability of the powder material, much like the Heckel 1/K parameter, and can be used as a means to rank powders according to deformability, i.e. to establish plasticity scale. The equation also provided insights into the dominating compression mechanisms through an invariance that could be exploited to determine the point, at which the powder system became constrained, i.e. the end of rearrangement. Additionally, the robustness of the equation was demonstrated through fruitful analysis of a set of diverse materials.

In summary, this thesis has provided insights and tools that can be translated into more efficient development and manufacturing of medicines in the form of tablets.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 56 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 159
Keyword
compression, powder, mechanical properties, pellet, tablet, compaction equation, force distribution
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-171874 (URN)978-91-554-8319-7 (ISBN)
Public defence
2012-05-16, B21, BMC, Husargatan 3, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2012-04-24 Created: 2012-03-28 Last updated: 2012-08-01Bibliographically approved

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