18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS PREPARATION AND ELECTROMAGNETIC PROPERTIES OF MULTIWALLED CARBON NANOTUBES BUCKYPAPER/EPOXY RESIN NANOCOMPOSITES TJ.Bao 1 , Y. Zhao 1 *, L Chen 2 , YX Duan 1 1 Department of Material Science and Engineering Beijing University of Aeronautics and Astronautics Xueyuan Road Beijing 100191 PR China 2 Composites Manufacturing Center of Commercial Aircraft. Shanghai aircraft manufacturing co.,Ltd. * Y. Zhao (correspondingauthor@iccm18.org) Keywords : buckypaper electromagnetic 2 Experiment Abstract A new technique involving buckypaper 2.1 preparation of buckypaper (prepared by mllipore filtration of MWCNTs Buckypapers are thin membranes or films suspension) /resin infiltration to prepare multiwalled formed with well controlled and dispersed porous carbon nanotubes (MWCNTs) reinforced network of MWCNTs. MWCNTs with different nanocomposites has been developed. aspect ration were purchased from Chengdu Organic MWCNTs with different aspect ratio are Chemicals Co.Ltd, and the purity was claimed to be investigated to fabricate buckypaper. The result 97% by the manufacturer. All of the buckypapers are shows that the MWCNTs with an aspect ratio of 200 prepared utilize a typical process [12] : A specific were easily to form buckypaper. The amount of MWCNTs was grinding with a little electromagnetic parameters of buckypaper water using a mortar and pestle. A selected composite and traditional composite are tested surfactant (X-100) and 1000 ml deioned water were comparatively. Since the uniformity of the added into the paste and conducted 1hour sonicating MWCNTs in buckypaper, the dielectric properties to form a stable suspension. The final concentration were greatly increased, and the buckypaper of the suspension was 10 – 60 mg /L. The suspension composite was demonstrated to be a potential was filtrated through a filter with the aid of vacuum absorbing material. to fabricate the buckypaper. Following filtration, the buckypaper were thoroughly washed with deionised 1 Introduction water to remove the dispersion surfactant. The Carbon nanotubes (CNTs) have attracted great buckypapers were carefully peeled off f rom the filter attention in the past decade due to their interesting after drying in a vacuum oven. properties [1-2] .Particularly, their extraordinary 2.2 Fabrication of composites electrical properties make CNTs have potential application as filler in microwave absorbing The buckypaper nanocomposite was prepared by materials [3-5] . However, fabricating CNTs-reinforced resin infiltration . Epoxy resin used for this research composites with uniform dispersion is a great was E-51 and the curing agent was tetraethylene challenge, since CNTs have a strong tendency to pentamine (TEPA) were mixed at a weight ratio of form agglomerates in matrix [6-8] . A new technique 100:12.After infiltration, the buckypaper with involving buckypaper/resin infiltration to prepare mixture of resin and curing agent were cured at multiwalled carbon nanotubes (MWCNTs) 70 ℃ for 1h and 120 ℃ for 2h. reinforced nanocomposites has been developed. The MWCNTs buckypaper [9-11] prepared by mllipore The conventional nanocomposite prepared by directly mixing MWCNTs into resin was also filtration of MWCNTs suspension is an entangled fabricated for comparison with buckypaper mat of MWCNTs, which is a highly porous mesh nanocomposites. The composite are cured at the structure. With the same concentration, same condition. nanocomposites prepared by buckypaper possess better dispersion than the composites manufactured 2.3 Characterization by the traditional mixing processing. Therefore, it will show higher electromagnetic properties.
The morphology of MWCNTs was observed by traditional MWCNTs composites and buckypaper FETEM (Tecnai G2 F20).The microstructures of composite, which represents the typical dielectric treated MWNTs are observed with FESEM (Apollo- properties of the samples investigated in this work. 300 OXFORD Corporation). The complex relative CNTs have high conductivity which tends to form permeability and relative permittivity of buckypaper conducting network in the composite based on its special morphology [13] which leads to the increase of composites and conventional composites in the frequency range of 8.2~12.4GHz are tested by the dielectrical properties in composites. In Fig3.3, 8722ES vector network analyzer for the further compare with the MWCNTs composite, the calculation and analysis of their absorbing properties. dielectrical properties of buckypaper composite was greatly enlarged, especially the imaginary part of 3 Result and discussion permittivity, which implied the buckypaper 3.1 Technological parameters of mllipore composite possessed better microwave absorbing property. The result could easily explained by the filtration micrograph of the buckypaper. From the SEM image The buckypapers prepared with different aspect of buckypaper, it can be seen that the MWCNTs ratio are observed with FESEM as shown in have a uniformed distribution, which could be Figure3.1. In Fig.3.1, it was the micrograph of the maintained when fabricating the composite [14] . The surface of buckypaper made by MWCNTs with conducting network was perfect in buckypaper different aspect ratio, which was 2000 for Fig.3.1a, composite, and the electron could run smoothly 1000 for Fig.3.1b and 200 for Fig.3.1c, respectly. through the conductive path of buckypaper The differences of aspect ratio were clearly shown in composites. On the other hand, in the traditional the HRTEM images of MWCNTs in the top right composite, the MWCNTs were inclined to corner of the SEM images. As it is shown in agglomerate in the resin as reported by other articles. Figure.3.1a, there are obvious cavities on the surface Therefore, the conductivity network was not of buckypaper made by MWCNTs with a high complete for the concentration of fillers in some aspect ratio of 2000. Moreover, it was so fragile that places and the deficiency in other places. it hardly can be peeled off from the millipore filter. 3.3 The microwave absorbing properties of However, with the reducing of aspect ratio, the composites surface of buckypaper turns to be smoother. When For further investigation of the microwave the aspect ratio was as low as 200, there was absorption, the reflection loss of traditional scarcely any pores on the surface and the surface MWCNTs composite (2wt %) and buckypaper was uniform and dense. This result might be due to composite (2wt %) are calculated, and the reflection the MWCNTs with high aspect ratio was easier to be loss curves are shown in Fig.3.4. entangled into agglomerates, even with the existence The reflection loss of a microwave absorbing layer of the surfactant. is given by [15] Therefore, MWCNTs with low aspect ratio are selected to make buckypaper in this work. The Z 1 buckypaper made by optimized nanotubes are shown in …… (3.3) R ( dB ) 20 log in Figure.2.It shown that the film was very integrity Z 1 in and the nanotubes are distributed uniformly in the film. π 2 r …… (3. 4) 3.2 The electromagnetic properties of composites Z tanh j fd in r r c r MWCNTs buckypaper composites are prepared based on optimized nanotubes. The electromagnetic where Z in is the normalized input impedance, c is the parameters of both the MWCNTs composite and velocity of electromagnetic waves in free space, f is MWCNTs buckypaper composite are analyzed the microwave frequency, and d is the thickness of comparatively. For both of the composites, the the absorbing layer. Therefore, microwave complex permeability is negligibly small as propagation in electromagnetic media is largely compared with complex permittivity, indicating that determined by the complex relative permeability and the dielectric loss mainly contributes to the permittivity of the absorbing materials. All the reflection loss of composites. As a result, the data of calculated values were predicted based on a constant the complex permeability was not displayed in this thickness d = 2.0 mm. article. Fig.3.3 manifests the complex permittivity of
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