Effect of vacuum annealing on characteristics of the HCl-doped polyaniline pellets

Powders of HCl-doped polyanilines were prepared by using a solution polymerization process and then were pressed to the polyaniline pellets. The pellets were annealed in vacuum at 140, 200 and 260 °C for times up to 120 min, respectively. Electrical property and micromorphology of the pellets were studied by using a four-point probe technique and a scanning electron microscopy. The conductivity of the pellets decreases sharply when the annealing time reaches 30 min and then decreases gradually with further increasing annealing time. When the pellets are annealed under the conditions of 200 °C/120 min, 260 °C/90 min and 260 °C/120 min, the resistance of the pellets could not be measured by the four-point probe technique and the pellets show an insulating characteristic. The breakdown voltage increases with increasing annealing temperature and time. The maximum breakdown voltage is about 875 V/cm. The degradation of the conductivity is mainly attributed to the loss of chlorine in the polyaniline pellets. The micromorphology of the pellets becomes heterogeneous with thermal aging.