Preparation And Electrical Properties Of PI/MWNTs Nano-hybrid Films

Polyimide (PI), as one of the highest performance engineering materials, exhibits excellent physical and chemical properties at a large temperature range. It was used widely in aerospace, electric and electronic industries. Along with the development and application of the new technologies, prefer a more rigid claim to polyimide, demand high performance and functionalized polyimide. Great attentions were focused on the preparation of the polyimide/inorganic nano-hybrid films. Due to the desirable mechanical and electrical properties, multi-walled carbon nanotubes (MWNTs) deserved attention greatly as one kind of nano-particles, their high aspect ratio made them possible to possess percolation threshold at low MWNTs loading in hybrid films.In this work, MWNTs were functionalized with two different way at first, and then were dispersed in solvent to prepare polyamide acid via In-Situ polymerization. By casting the PAA/MWNTs resin onto a clean glass plate, then the thermal imidization followed by stepwise curing, the PI/MWNTs nano-hybrid films were obtained.The dispersion of MWNTs was observed by SEM, the morphology of the surfaces the cross-section of PI/MWNTs nano-hybrid films were investigated by SEM. The electrical properties of PI/MWNTs films were tested using corona-resistance tester, withstand voltage tester and Precision Impedance Analyzer respectively. The experimental results indicated that functionalization of MWNTs effectively improved the dispersion in solvent and PI matrix. The FT-IR test results proved that there were functionalized MWNTs components in the PI/MWNTs hybrid films. As a whole, the corona-resistance property of PI/MWNTs hybrid films(series A,B and C films) was obviously enhanced at first, and then decreased significantly with the MWNTs contents increased continuously. The corona-resistance reached 7.75 hours in series A films at the MWNTs content of 0.34wt%, 5.75 hours in series B films at the MWNTs content of 0.43wt% and 9.5 hours in series C films at the MWNTs content of 0.31wt%, reached the maximum value respectively. The dielectric constantεr of PI/MWNTs hybrid films increased significantly with the MWNTs content increased, but decreased slightly as the frequency increased. The dielectric loss tanδincreased monotonically along with the increasing frequencies, with the increased of MWNTs doping quantity, the dielectric loss of PI/MWNTs hybrid films always greatened. The breakdown strength of three series hybrid films decreased with the MWNTs content increased, at the same circumstances, the dielectric strength of series A films was the strongest and series C films was the weakest. Taken all together, the corona-resistance property of PI films was obviously enhanced with the addition of MWNTs, all results showed that the electrical properties of PI/MWNTs hybrid films presented definite disciplinarian as the MWNTs content was changed.