Dependence of bakelite resistivity on temperature and humidity

The use of bakelite as electrodes for resistive plate chambers is widespread. The performance of RPC's, in particular its rate capability, strongly depends on the bulk resistivity of the electrodes. Since the bakelite resistivity changes as a function of temperature and humidity, we have performed several resistivity measurements of a melaminic bakelite sample in order to investigate this dependence. Two sets of measurement at well controlled environmental conditions were performed: the former after relative humidity changes in the range from 80% to 20% at constant temperature, the latter varying the temperature from 15/spl deg/C to 35/spl deg/C at constant relative humidity.