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Mesopore structure of microcrystalline cellulose tablets characterized by nitrogen adsorption and SEM: The influence on water-induced ionic conduction
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.ORCID iD: 0000-0002-5496-9664
2006 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 32, 15776-15781 p.Article in journal (Refereed) Published
Abstract [en]

Tablets of microcrystalline cellulose were formed at different compaction pressures and physical properties, such as pore size distribution, surface area, and pore surface fractality, were extracted from N-2 adsorption isotherms. These properties were compared to previously published data on the water-induced ionic conductivity of the tablets. The conduction process was shown to follow a percolation model with a percolation exponent of 2 and a porosity percolation threshold of similar to 0.1. The critical pore diameter for facilitated charge transport was shown to be in the 5-20 nm range. When the network of pores with a diameter in this interval is reduced to the point where it no longer forms a continuous passageway throughout the compact, the conduction process is dominated by charge transport on the surfaces of individual microfibrils mainly situated in the bulk of fibril aggregates. A fractal analysis of nitrogen adsorption isotherms showed that the dominant interface forces during adsorption is attributed to surface tensions between the gas and the adsorbed liquid phase. The extracted fractal dimension of the analyzed pore surfaces remained unaffected by the densification process at low compaction pressures (< similar to 200 MPa). At increased densification, however, pore-surface structures smaller than similar to 100 nm become smoother as the fractal dimension decreases from similar to 2.5 at high porosities to similar to 2.3 for the densest tablets under study.

Place, publisher, year, edition, pages
2006. Vol. 110, no 32, 15776-15781 p.
National Category
Engineering and Technology Pharmaceutical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-94365DOI: 10.1021/jp055858vISI: 000239656100023PubMedID: 16898725OAI: oai:DiVA.org:uu-94365DiVA: diva2:168191
Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Water-Induced Charge Transport in Microcrystalline Cellulose
Open this publication in new window or tab >>Water-Induced Charge Transport in Microcrystalline Cellulose
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Vatteninducerad laddningstransport i mikrokristallin cellulosa
Abstract [en]

Microcrystalline cellulose (MCC) is the most frequently used excipient for direct compaction of tablets within the pharmaceutical industry. It has earlier been indicated that the interactions between the hydration shell – surrounding the drug molecules in an MCC tablet – and the cellulose regulate the speed of the drug release process. These interactions, and the charge transport governed by moisture, are therefore important to analyze and understand to be able to tailor make new functional drug delivery systems.

In this thesis the physical parameters affecting the water-induced ionic transport have been studied with impedance spectroscopy, transient current measurements, nitrogen adsorption and scanning electron microscopy. Dielectric relaxation processes, pertaining to other processes, have also been assessed and analysed, and a generalized regular singular point model has been shown to be able to describe all features of the dielectric spectrum.

It has been shown that the ionic charge transport mechanism in humid MCC most likely is governed by two parallel processes: One involving water constituent ions diffusing between adjacent lowest energy sites (free OH- groups) in disordered regions of the cellulose and the other caused by impurity ions, such as Na+, and protons or H3O+ ions, jumping between neighboring cellulose OH- groups to which primary water molecules are attached. At relative humidities of ~ 37 % (representing monolayer coverage) and higher, the latter process is totally dominating the charge transport.

At a given moisture content, there are two parameters determining the magnitude of the water-induced ionic conductivity in MCC: The connectedness of the interparticulate bonds and the connectedness of pores with a diameter in the 5-20 nm size range.

The presented findings emphasize the importance of analysing and being able to control the nanostructure of a pharmaceutical cellulose-based system in order to tailor the drug transport properties. The presented results should also be significant for other areas where cellulose-water interactions are of key issue; such as for paper and sanitary product research and for food industries using cellulose-based gels.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 53 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 170
Keyword
Materials science, Materialvetenskap
Identifiers
urn:nbn:se:uu:diva-6815 (URN)91-554-6541-2 (ISBN)
Public defence
2006-05-12, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30
Opponent
Supervisors
Available from: 2006-04-21 Created: 2006-04-21Bibliographically approved

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Nilsson, MartinMihranyan, AlbertValizadeh, SimaStrömme, Maria

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