LOW-FREQUENCY DIELECTRIC-SPECTROSCOPY CHARACTERIZATION OF MICROCRYSTALLINE CELLULOSE, TABLETS AND PAPER

Cellulose fibres and particles in the form of powder, tablets and pape r sheets have been investigated by very low frequency dielectric spect roscopy using a novel form of dielectric cell, in which two planar ele ctrodes have been mounted in fixed positions at right angles. The broa d pattern of response obtained from the samples is independent of the structural form of the cellulose sample, a loss peak in the 0.1-100 Hz range, and at lower frequencies a dispersion process which is dominat ed by an imperfect charge transport. Moisture has a significant influe nce on the rate of charge transport. In dry samples the dipolar loss p eak was not evident but as the moisture content increased it appeared. Using a humidity normalizing technique the dielectric response for mi crocrystalline cellulose has been characterized over the equivalent of 14 decades in frequency. It has also been shown that there is a linea r response between the capacitance and the density of microcrystalline cellulose samples. The consolidation of powder into tablets is discus sed with respect of the observations of changes in capacitance, loss p eak frequency and im perfect charge transport efficiency. Furthermore it was found possible to investigate differences between the dipolar r elaxation rate ''in'' and ''out'' of the plane of paper in the stack. The relaxation time for dipoles ''out'' of the paper plane is 7 to 8 t imes longer than for dipoles ''in'' the paper plane.