Preparation And Properties Of Multi-walled Carbon Nanotubes/Poly(Ether Ether Ketone) Composite Films

Poly(ether ether ketone)(PEEK), which has been widely used inaerospace technology as well as the energy and chemical industries, isa semi-crystalline thermoplastic polymer with outstandingcharacteristics such as superior mechanical properties, thermalstability, and solvent resistance. The high dielectric constantcomposites films and conductive composites films based on polymer havegained great attentions owing to the importance of applications.Multi-walled carbon nanotubes (MWCNTs) are the excellent fillers for thepreparation of the high dielectric constant composites and conductivecomposites due to the small diameters, high aspect ratio, the uniquethermal and conductive electrical properties. This thesis, focuses on thepreparation and performance of composite films (high dielectric constantcomposite films and conductive composites films) based on multi-walledcarbon nanotubes and poly(ether ether ketone)In order to prepare the MWCNT/PEEK composite films with highdielectric constant, MWCNTs were first wrapped by poly(ether sulfone)(PES). And then MWCNT-PEEK composite films were prepared by melt blendingfollowed by melt extrusion. The dielectric constant, dielectric loss,mechanical properties and thermal stability of MWCNT-PEEK composite filmswere characterized. It could be found that the fillers (the wrapped MWCNTs)of the wrapped-MWCNT-PEEK composite film were more uniformly dispersedin the matrix (PEEK). It is also worth mentioning that the dielectricconstant of the PEEK composite film with0.68vol%of wrapped MWCNTs wasthe highest among the six samples. The value of the dielectric constant was around370, which was about100times higher than that of the purePEEK film. The dielectric loss of the wrapped-MWCNT-PEEK composite filmswas less than0.3at room temperature and103Hz, the value of dielectricloss is very low. The phenomenon should be ascribed that multi-walledcarbon nanotubes (MWCNTs) have small diameters, high aspect ratio and highconductivity. On the other hand, the existence of the PES coatingprevented the agglomeration of MWCNTs and resulted in more uniformdispersion of MWCNTs in the PEEK. As a result, the wrapped MWCNTs incomposite films can be regarded as a microcapacitor network, leading tovery high values of dielectric constant. In general, a composite film witha high dielectric constant, low dielectric loss, low percolationthreshold, and good mechanical and thermal properties was obtained. Thiscomposite film, which integrates structure and function, is particularlysuitable for some of the harsh operating environments in the electricalpower industry.Multi-walled carbon nanotubes (MWCNTs) are ideal conductivityfillers. Now that the high dielectric constant composites films can beprepared at the lower amount of filler, the conductive composite filmscan also be prepared at higher amount of filler. According to the aboveanalysis, a series of studies around the preparation and performance ofMWCNTs/PEEK conductive composite films were carried out. Multi-walledcarbon nanotubes (MWCNTs) were not wrapped in the part of the work, inorder to obtain the high conductivity. The high-temperature lubricant wasadded to composite film to improve the processability and the dispersionof MWCNTs. The electrical properties of the prepared MWCNTs/PEEKcomposite film were studied using a4294A Precision Impedance Analyzer.The electrical conductivity of the MWCNTs/PEEK composite films was4×10-4S/cm when the volume fraction of fillers was4.76vol%. As we all known,the preparation method of melt extrusion makes the MWCNTs be arranged in PEEK matrix along the extrusion direction. These composite films were hotpressed processing to eliminate the effect of the processing direction.It is obvious that the electrical conductivity of these hot pressed filmswas improved significantly. The electrical conductivity of the hotpressed MWCNTs/PEEK composite films was2.2×10-2S/cm for the volumefraction of fillers was4.76vol%. Based on the result of the mechanicaland thermal properties of composite films, it could be found thatMWCNTs/PEEK conductive composite films have excellent mechanical andthermal stability. In general, MWCNTs/PEEK conductive composite film isa kind of excellent conductive films.