Dielectric spectra of natural cork and derivatives

Cork is a cellular biomaterial that has unique characteristics that make it suitable for many types of applications. Since it is also an electrical insulator, the study of its electrical and dielectric properties can lead to new interesting applications. The moisture present in cork and derivatives has a very important role on the dielectric properties. In this work a composite made of both recycled cork and TetraPak® used containers was studied and compared with other cork products. The dielectric relaxation spectra of natural cork (as received), commercial cork agglomerate and of a composite cork/TetraPak® was investigated in the temperature range of −50 to 120 °C and in the frequency range of 10−1 Hz–2 MHz. For some samples of the composite a small amount of paraffin was added. The highest values for the imaginary part of the dielectric permittivity were found for the commercial material and the composite without paraffin. The lowest was found for the cork/TetraPak®/paraffin composite. The influence of humidity content was investigated for the composite with wax. Natural cork shows a peak around 80 °C (not seen in the derivative materials). The commercial agglomerate and the cork/TetraPak®/paraffin composite show a peak around 40–50 °C. In the composite this peak becomes smaller as humidity is removed.