Thermo-oxidative Degradation Kinetics of PMDA/ODA-type Polyimide Film

Polyimide films have been successfully applied as cable insulation layer, optical fiber coating, printed circuit board and flexible solar cell substrates, owing to their excellent heat resistance and mechanical properties. During the devices fabrication and application, the polyimide films are usually exposed to elevated temperature or thermal oxidation environment, which often causes material degradation and results in device failure. Therefore, it is necessary to understand the thermo-oxidative degradation behavior of polyimide films in order to improve the reliability of the materials. The thermo-oxidative degradation of polyimide film was a multi-step process. It can not be described by one kinetic triplet, i.e., the apparent activation energy E, reaction model f(a) and pre-exponential factor A. In this study, the multi-step thermo-oxidative degradation of polyimide film derived from PMDA and ODA was investigated based on its thermogravimetirc curves under different linear heating rates. The overlapped processes incorporated in the overall thermo-oxidative degradation were firstly separated by peak-fitting of the differential thermogravimetric curves of polyimide film using Fraser-Suzuki function. Kinetic analysis of each separated process was subsequently conducted by employing Friedman method and Master-plots to determine the E, f(a) and A. The kinetic result revealed that two overlapped processes were involved in the overall thermo-oxidative degradation of polyimide film. The E values for the two processes were 154.00 and 139.27 kJ/mol respectively. The corresponding lnA values were 18.55 and 16.74 s(-1). Both the two processes followed the Avrami-Erofeev model. Moreover, the validity of these kinetic parameters obtained were verified by reconstruction of original TGA curves and prediction of TGA curve not employed in the kinetic analysis.