Synthesis And Characterization Of MWNTs/Co_0.5 Ni_0.5 Fe₂ O₄ /PI Microwave Absorbing Nanocomposites

Polyimide (PI) functions as an important high temperature polymer materials. It is important to develop polyimide matrix composites combining carbon nanotubes/ferrite composite powder for meeting the demand of light, thin, wide, strong for microwave absorbing materials served at high temperatures.In this thesis, multiwalled carbon nanotubes (MWNTs) were surface-modified by Ar plasma. The morphologies and structure of plasma modified MWNTs (denoted as L-MWNTs) were characterized by Fourier transform infrared spectroscopy (FT-IR),X-photoelectron spectrometer (XPS), X-ray diffraction (XRD) and Raman spectroscopy. The reaction between the Ar plasma and the MWNTs was illustrated. L-MWNTs/Co_0.5Ni_0.5Fe₂O₄ composite powder was obtained via chemical coprecipitation, the distribution and phase of ferrite nano particles on the surface of L-MWNTs were investigated by transmission electron microscope (TEM) and XRD. L-MWNTs/Co_0.5Ni_0.5Fe₂O₄/PI composites were prepared by Sol-Gel method in different contents and the absorbing properties were compared. Dispersity and morphology of L-MWNTs in the composites was characterized by scanning electron microscope (SEM) and TEM. The thermal and mechanical properties of the obtained nancomposites were also investigated.The results show that the proportions of functional groups on L-MWNTs have changed after Ar plasma treatment, which was carried out at 50 V with a current of 0.3 A, lasted for 10 min. Increase of carboxyl group is help to improve interfacial bonding between the MWNTs and PI matrix. Meanwhile, the reflection loss (RL) of the nanocomposites increases with the content of L-MWNTs increasing. When the content of L-MWNTs increased to 0.75 wt%, the reflection loss value of L-MWNTs/Co_0.5Ni_0.5Fe₂O₄/PI nanocomposites increases to -24.37 dB, the frequency range of RL value (dB) less than -10 dB is 5 GHz. When the content of L-MWNTs is 1 wt%, the reflection loss value of nanocomposites drops to -12.23 dB, and moves to high frequency range. It is obvious that tensile strength of nanocomposite increases with the content of L-MWNTs increasing from 0.25 wt% to 0.75 wt%, and when the content of L-MWNTs increases to 0.75 wt%, the tensile strength reaches 105 MPa. Besides, the results show that the glass transition temperature of nanocomposites was 261℃,and the thermostability is preserved at 500℃.