Permittivity of fiber polymer composites environmental effects: comparison of measurement and theory

The authors present the results of a study to determine the relative changes in fiber/organic resin composite permittivity after exposure to moisture, SO/sub 2/ and ultraviolet (UV) light. Effective medium theories are applied in an attempt to predict the permittivities of the composites given the permittivity of the constituent fiber and polymer. It is found that environmental changes due to moisture have severe effects on polyester composite permitivities. Changes near 400% in loss tangent and 20% in dielectric constant are observed. Effective medium theories are found useful for predicting permitivity in composite panels with fiber reinforcement. Moisture effects on the permittivity of these composites may also be predicted. The observed changes due to other environmental exposures are dominated by moisture pickup. Thus, no direct effects of UV and SO/sub 2/ can be determined from these measurements.<>