Abstract
The microbial degradation of electronic insulation polyimides was monitored and evaluated using electrochemical impedance spectroscopy (EIS). The microbial inoculum, comprising Aspergillus versicolor, Chaetomium species, Cladosporium cladosporioides, and Tricoderma viride, was isolated previously from deteriorated polyimides. After inoculation, fungal growth on the polyimides resulted in distinctive EIS spectra indicative of polymer insulation failure, which directly related to polymer integrity. Degradation appeared to progress in a number of steps and two distinctive stages in the decline of film resistance were detected in the EIS cells within 24 and 72 days after inoculation. The early stage of the decrease in resistance may be related to the ingress of water molecules and ionic species into the polymeric materials, while the second stage probably resulted from partial degradation of the polymers by fungal growth on the polymer film. The relationship between changes of impedance spectra and microbial degradation of the polymer was further supported by scanning electron microscopy (SEM) of fungi growing on the surface of the inoculated polyimides. Our data indicate that the EIS technique can be used to detect the early degradation of resistant polymers and that polyimides are susceptible to biodegradation by fungi.
