Conductivity percolation in loosely compacted microcrystalline cellulose: An in situ study by dielectric spectroscopy during densification
2006 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 41, 20502-20506 p.Article in journal (Refereed) Published
The present study aims at contributing to a complete understanding of the water-induced ionic charge transport in cellulose. The behavior of this transport in loosely compacted microcrystalline cellulose (MCC) powder was investigated as a function of density utilizing a new type of measurement setup, allowing for dielectric spectroscopy measurement in situ during compaction. The ionic conductivity in MCC was found to increase with increasing density until a leveling-out was observed for densities above similar to 0.7 g/cm(3). Further, it was shown that the ionic conductivity vs density followed a percolation type behavior signifying the percolation of conductive paths in a 3D conducting network. The density percolation threshold was found to be between similar to 0.2 and 0.4 g/cm(3), depending strongly on the cellulose moisture content. The observed percolation behavior was attributed to the forming of interparticulate bonds in the MCC and the percolation threshold dependence on moisture was linked to the moisture dependence of particle rearrangement and plastic deformation in MCC during compaction. The obtained results add to the understanding of the density-dependent water-induced ionic transport in cellulose showing that, at given moisture content, the two major parameters determining the magnitude of the conductivity are the connectedness of the interparticluate bonds and the connectedness of pores with a diameter in the 5-20 nm size range. At densities between similar to 0.7 and 1.2 g/cm(3) both the bond and the pore networks have percolated, facilitating charge transport through the MCC compact.
Place, publisher, year, edition, pages
2006. Vol. 110, no 41, 20502-20506 p.
Pharmaceutical Sciences Engineering and Technology
IdentifiersURN: urn:nbn:se:uu:diva-94366DOI: 10.1021/jp063835qISI: 000241192200064PubMedID: 17034236OAI: oai:DiVA.org:uu-94366DiVA: diva2:168192