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Fractal dimension of cellulose powders analyzed by multilayer BET adsorption of water and nitrogen
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.ORCID iD: 0000-0002-5496-9664
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 Science and Technology, Technology, Department of Engineering Sciences.ORCID iD: 0000-0002-8279-5163
2003 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 107, no 51, 14378-14382 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to show that multilayer fractal Brunauer-Emmett-Teller (mfBET) theory can be used as a tool to obtain information about the distribution of water in cellulose powder particles of varying crystallinity. Microcrystalline cellulose, agglomerated micronized cellulose, low-crystallinity cellulose, and cellulose powders from green and brown algae were characterized by scanning electron microscopy and mfBET analysis on water and nitrogen adsorption isotherms. The distribution of water in the cellulose materials was found to be characterized by a fractal dimension smaller than 1.5 for all powders. The results showed that for highly crystalline cellulose materials, such as Cladophora cellulose, the cellulose-water interactions take place mainly on cellulose fibril surfaces adjacent to open pores without causing any significant swelling of the material. For less ordered celluloses the water interaction was found to take place inside the bulk material and the water uptake process caused the pore volume to swell between 1 and 2 orders in magnitude. For the Cladophora cellulose, the thickness of the adsorbed water layer at the outer cut off of the fractal region was found to coincide very well with the average pore size obtained from nitrogen adsorption measurements. The multilayer fractal BET analysis on nitrogen adsorption isotherms showed that the particles could be characterized by fractal dimensions between 2.13 and 2.50. We conclude that water adsorption has the ability to alter the structure of the studied material and reveal a sorption-induced, "apparent" fractal structure over a relatively narrow length scale interval, while nitrogen adsorption probes the substrate morphology over a wide range of length scales and reveals the "true" fractal structure.

Place, publisher, year, edition, pages
2003. Vol. 107, no 51, 14378-14382 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-92515DOI: 10.1021/jp034117wScopus ID: 2-s2.0-0345803800OAI: oai:DiVA.org:uu-92515DiVA: diva2:165627
Available from: 2005-01-20 Created: 2005-01-20 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Engineering of Native Cellulose Structure for Pharmaceutical Applications: Influence of Cellulose Crystallinity Index, Surface Area and Pore Volume on Sorption Phenomena
Open this publication in new window or tab >>Engineering of Native Cellulose Structure for Pharmaceutical Applications: Influence of Cellulose Crystallinity Index, Surface Area and Pore Volume on Sorption Phenomena
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cellulose powders from various sources were manufactured and characterized to investigate the influence of their crystallinity index, surface area, and pore volume on sorption phenomena and the relevant pharmaceutical functionality. The influence of the cellulose crystallinity index on moisture sorption was important at low and intermediate relative humidities. At high relative humidities, properties such as surface area and pore volume took precedence in governing the moisture sorption process.

The theory of physical adsorption of gases onto fractal surfaces was useful for understanding the distribution of water in cellulose and the inner nanoscale structure of cellulose particles. It was found that, as a consequence of swelling, moisture induces a fractal nanopore network in cellulose powders that have a low or intermediate degree of crystallinity. On the other hand, no swelling occurs in highly crystalline cellulose powders and moisture sorption is restricted to the walls of the open pores.

No correlation was found between the cellulose crystallinity index and the incorporation and release of nicotine in cellulose mixtures. By loading nicotine in highly porous matrices of the Cladophora sp. algae cellulose, higher stability against oxidative degradation, higher loading capacity, and more steady release into an air-stream was achieved than when commercially available microcrystalline cellulose was loaded.

It was also shown that, by manipulating the structure of cellulose, the undesired hydrolysis of acetylsalicylic acid in mixtures with cellulose can be avoided. It was suggested that a broad hysteresis loop between the moisture adsorption and desorption curves of isotherms at low relative humidities could be indicative of an improved compatibility between acetylsalicylic acid and cellulose.

In all, this thesis demonstrates how the pharmaceutical functionality of microcrystalline cellulose can be improved via engineering of the structure of native cellulose powders.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. 57 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 1
Keyword
Pharmaceutics, microcrystalline cellulose, Cladophora sp. algae, crystallinity index, surface area and pore volume, fractals, stability, Galenisk farmaci
National Category
Pharmaceutical Sciences
Identifiers
urn:nbn:se:uu:diva-4752 (URN)91-554-6130-1 (ISBN)
Public defence
2005-02-11, B41, Biomedical Center, Husargatan 3, Uppsala, 09:15
Opponent
Supervisors
Available from: 2005-01-20 Created: 2005-01-20Bibliographically approved

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Strömme, MariaMihranyan, AlbertEk, RagnarNiklasson, Gunnar A.

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