Pore Direction in Relation to Anisotropy of Mechanical Strength in a Cubic Starch Compact |
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Authors: | Yu San Wu Lucas J van Vliet Henderik W Frijlink Ietse Stokroos Kees van der Voort Maarschalk |
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Institution: | Department of Pharmaceutical Technology and Biopharmacy, University of Groningen, Groningen, The Netherlands. Yu-San.Wu@solvay.com |
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Abstract: | The purpose of this research was to evaluate the relation between preferential direction of pores and mechanical strength
of cubic starch compacts. The preferential pore direction was quantified in SEM images of cross sections of starch compacts
using a previously described algorithm for determination of the quotient of transitions (Q). This parameter and the mechanical
strength were evaluated in compacts of different porosities. Starch was chosen as a model compound for materials with ductile
behaviour of which tablets with low porosities can be made and which shows some elastic recovery after compaction. At medium
and high porosity Q was significantly higher in the images providing a side view of the compact than in the images providing
a top view (0.973 vs. 0.927 and 0.958 vs. 0.874 at 0 mm from the side of the compact and 0.956 vs. 0.854 and 0.951 vs. 0.862 at 3.5 mm), indicating that the pores were mainly oriented in the direction perpendicular to the direction of compression.
This was accompanied by a lower crushing force in this direction. This could be explained by considering the pores as cracks
which propagate through the sample during crushing. For both directions the crushing force decreased with increasing porosity.
The yield strength of the compacts also decreased with increasing porosity, but this parameter was not dependent on the direction
of crushing when the porosity was below 10%. The results show that pore direction significantly influences the crushing force
but does not influence the yield strength, at porosities below 10%. |
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Keywords: | anisotropy compact fracture mechanical strength pore direction |
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