Humidity Dependence of the Dielectric Constant of a Thermosetting Polyurethane

Dielectric elastomer actuators (DEA) have gained an increasing importance in research and development studies. As dielectric elastomers (DE) novel electroactive polymers such as polyurethane, chloroprene, or nitrile rubber are currently attracting increasing interest due to their higher dielectric constant compared to established materials on the basis of silicones or acrylics. The dielectric properties of any polymer depend on extrinsic factors such as temperature and humidity. Therefore, material characterization should always be followed by information about the measurement conditions. In this work, a thermosetting polyurethane rubber (PUR) is compression-molded into elastomer films. The PUR films are stored at different humidities and the effect of moisture exposure on the electrical properties is explored at a constant temperature. The dielectric constant and loss increases significantly with an increase of humidity.