Specimens of an aromatic polyimide paper, Aramid paper, which were subjected to various degrees of moisture adsorption were investigated both dielectrically and thermoanalytically in order to estimate how much the adsorbed moisture affects the dielectric and thermoanalytical behaviors. It was clarified that, while in the humid specimens the dielectric properties did not change so much and there were no endothermic and exothermic peaks, in the soaked specimens the dielectric properties changed remarkably and there were large endothermic and exothermic peaks due to free water recognized at about 0 degrees C. It was found that the dielectric properties of Aramid paper are rather stable to the moisture adsorption because its polyamide linkage bonds tightly with the adsorbed water, but when the adsorption reaches a value greater than the water content of 7.3%, a remarkable increase in the dielectric properties takes place because the free water is kept intact in the paper structure.
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