A New Model of DC Conductivity of Hygroscopic Solids

We investigate the DC conductivity of cotton, viscose, and wood and develop a quantitative theory. We propose that conduction occurs by exchange of protons within a hydrogen-bonded network of water molecules, in a manner analogous to that in liquid water and ice. According to this model, the very strong dependence of conductivity on regain, which is characteristic of these materials, arises from its dependence on the average distance between adjacent water molecules. We derive expressions for DC conductivity as a function of regain, which provide very good agreement with experimental data. With independent experimental evidence, we confirm a prediction by the theory that a similar conduction process occurs in dry cellulose.