Some electrical properties of wood pulp

The variation with temperature and frequency of the dielectric constant ε′ and the dielectric loss ε″ for sheet wood pulp and ground wood pulp were measured. Also, the effect of the relative humidity on the dielectric behavior was measured for the ground sample at 25°C. For the dry ground wood pulp, the dielectric constant is larger than that for the dry sheet sample. This may be a result of the increase in the surface area, of the decrease in the size of crystals and/or of the decrease in the degree of crystallinity on grinding of the sheet sample. The variation of ε″ with frequency passes through a maximum. From the shift of this maximum with temperature, it is found that the apparent activation energy ΔH for this relaxation is equal to 7.06 kcal/mole and it is attributed to the polarization of the OH groups in the cellulose molecule. From the relation between the dielectric constant and the specific resistivity Rs, the dissociation energy U0 for the ground wood pulp was calculated. U0 for this sample below and above 52% RH is 0.315 and 5.13 × 10−12 erg, respectively. Also, the dissociation energy of Egyptian Ashmouny cotton was calculated. The variation of the electrical conductivity σ with humidity for different types of cellulosic materials is represented graphically.