The Study of Electrical Conductivity of Cork

The normal cork contains more than 3.5% absorbed and adsorbed water at ambient relative humidity (RH). This amount is sufficient to produce significant modifications of the electrical properties. The electrical conduction of normal, partially dry and dry cork has been investigated in the temperature range from −100 to 105°C. Additional results were obtained using isothermal charging and discharging currents and dielectric relaxation spectroscopy (DRS) measurements. The conductivity of normal cork (ambient RH) at 25°C is σ = 1.2 × 10−10 S m−1 and the intrinsic conductivity of cork is σ = 1.67 × 10−13 S m−1 at 50°C. The dielectric relaxation revealed at least two relaxation processes. The diffusion of water in cork, as resulted from DC conductivity recovering, is a very slow process and it has two components: a first one with a characteristic time of about 20 days and a second one with a characteristic time of about one month.