FTIR and dielectric studies of electrical aging in polyimide under AC voltage

The Kapton 100HN polyimide films were aged under 3 kV ac voltage (50 Hz), and the aging evolution were studied by the Fourier transform infrared spectroscopy (FTIR) and the dielectric measurement. The FTIR spectra show that the ether linkage, and some of C-H bonds in aromatic rings and C-N-C bonds transverse stretching vibration in imide are firstly broken by corona discharge. Then, with the increase of aging time, the cleavage of the imide group including C-N-C and C=O vibrations occurs. At the same time, the oxidative degradation produces compounds such as carboxylic acid, ketones, and aldehydes. Accordingly, the variations of dielectric constant ε ₁ and the dissipation factor tan δ are dependent on the formation of the polar groups and the breakage of some polar bonds in polyimide.