Study On Carbon Nanotubes/cyanate Ester Composites

High dielectric constant (high K)polymer matrx composites have a significant future in electron and electric industry, so it is important to enhance the dielectric constant. Carbon nanotubes (CNTs) with large aspect ration and high electric conducitivity have been pursued with the hope of delivering CNTs properties to a processable and synergistic host. In the past years, dielectric performance and percolation effect were studied, but the law of polarization under the alternating current field, the mechanism of dielectric performance and percolation effect under the different interface of CNTs and CE matrix, higher frequency (GHz), changed temperature conditions remains unclear.In this thesis, the preparation and properties of multi-walled carbon nanotubes/ cyanate ester (MWCNTs/CE) nanocomposites were studied. In order to enhance the compatibility and improve the property of interface between the filler and the matrix resin, MWCNTs were modified by Fenton reagent, the corresponding modified MWCNTs coded as MWCNTs-OH. MWCNTs-OH were characterized by Fourier transform infrared spectrum(FTIR), Raman spectrum(RM), etc. The results indicated that a large number of hydroxyl were grafted on the surface of MWCNTs. And then, MWCNTs/CE and MWCNTs-OH/CE nanocomposites were prepared by in-situ polymerization.The thermal properties of MWCNTs/CE and MWCNTs-OH/CE composites were studied. The results showed that the addition of 1wt% MWCNTs into CE decreased the glass transition temperature (Tg) and thermal stability, while the incorporation of 1wt% MWCNTs-OH did not decline Tg and significantly improved the thermal stability of CE. The dielectric properties of MWCNTs/CE and MWCNTs-OH/CE composites were studied. The results showed that the percolation thresholds of the two kinds of composites were approximately equal, about 0.62wt%. The dielectric constants increased remarkably after the percolation threshold. However, the largest dielectric constant of the two kinds of composites was different. 1 KHz, the largest dielectric constant of MWCNTs/CE composites was 114 with 1wt% MWCNTs, while it reached 165 for MWCNTs-OH/CE composites with about 1.5wt% MWCNTs-OH. The different interface of fillers and matrix made great influence on the dielectric constants of composites. The dielectric loss of both kinds of composites increased non-linear as the dielectric constant when the percolation occurred. 101-3.25×109Hz, when the content of MWCNTs was lower than the percolation threshold, the dielectric constants and dielectric loss of both kinds of composites changed little with the increase of the test frequency, however, when the content of MWCNTs was more than the percolation threshold, the dielectric constants and dielectric loss of both kinds of composite decreased quickly with the increase of the test frequency. 1KHz, -50-200℃, the content of CNTs was lower than the percolation threshold, the dielectric constants and dielectric loss were independence on temperature; The content of CNTs was more than the percolation threshold, the dielectric constants decreased with increasing temperature while the dielectric loss increased with increasing temperature.