Quantitative determination of bound water in cardboard by measurement of dielectric permittivity

In this study we investigated the complex dielectric permittivity of cardboard with different water contents using a coaxial transmission/reflection technique from 10 MHz to 1.5 GHz. A relaxation process was analyzed to identify the bonding forms that exist in cardboard; this analysis was accompanied by a selective direct thermo-coulometric method. Two different types of bonding of water are found in cardboard (free and bound water) and both can be eliminated at 105 °C. The novelty of this work is the experimental correlation between the relaxation frequency situated in the radio-frequency band and the fraction of bound water in cardboard with a low water content.