The Preparation And Characterization Of Buckypapers And Their Composites

Carbon Nanotubes (CNT) have excellent electrical conductivity, thermal conductivity and mechanical strength. However, applications of carbon nanotubes are greatly restricted due to agglomerate of CNT. Fortunately, the invention of carbon nanotubes paper (buckypaper, BP) greatly expands its application. In this paper, composites were preparated using buckypaper fabricated by vacuum filtration as a filler and using polypropylene (PP) or epoxy resin (EP) as resin matrix. Structure and properties of the composites were investigated.The dispersion of MWCNT were studied and buckypaper was fabricated by vacuum filtration with three different diameters and lengths of MWCNT. Besides, the impacts of carbon nanotubes geometry on the structure and properties of buckypapers were investigated. The ideal parameters of ultrasonic disperse were determined by UV-vis spectra test and solution resistance test. The results demonstrate that the"thick and long" and "thin and long" MWCNT show better stability while triton X-100 can significantly improve the stability of the suspension. It is found that "thin and long" carbon nanotubes possess best film-forming properties, electrical conductivity (29.5 S/cm), thermal conductivity (81.4 W·m-1·K-1) and mechanical properties (strength of 3.3 MPa). On the microscopic pore structure, "thin and long" carbon nanotubes incline to form a more uniform pore structure and narrow pore distribution. Based on the above results, that "thin and long" carbon nanotubes have the best overall performance.PP/BP composite materials were prepared by hot-pressing using buckypaper and polypropylene. The morphology, self-heating properties, thermal properties and electromagnetic interference shielding effectiveness (EMI SE) were investigated. The results demonstrate that PP/BP composite surface temperature depends on the applied voltage and BP filling amount. In addition, as time went on, the current of composites under an applied voltage increases firstly and then gradually reaches equilibrium.The conductivity of BP decreases because of resin impregnation. The conductivity improves 2?3 orders in comparison with traditional blending material and increases with temperature increasing. Mechanical performance tests show that BP enhanced composite mechanical properties. Young's modulus and tensile strength of 3.7 wt% BP increase by 47.3% and 19.7% respectively. The primary mechanism of shielding of PP/BP composite is absorption in the 8.2?12.4 GHz (X band). The EMI SE depends on the thickness of the layer BP. With BP thickness increases, the shielding effectiveness improves. The shielding effectiveness reaches up to 40 dB when the thickness was 70?m. Noticeable improvements in the EMI SE of PP/BP composites are obtained by adjusting the space between BP layers. The shielding effectiveness reaches 44-51 dB with double layer BP (50?m thickness) at 1.5 mm spacing between two layers.EP/BP composites with single or multi-layer BP were prepared by solution casting method using epoxy as matrix. The EP/BP composite morphology, self-heating performance, electrical conductivity, and EMI SE were investigated. The thickness of impregnated BP increases about 120%, which shows a good permeability for BP. The surface heating temperature of composites increases with the applied voltage and BP thickness increase. The resistance value of the BP increases and the electrical conductivity decreases first and then increases with the temperature increasing. The storage modulus of EP/BP composites with 10.7 wt%BP is about twice value as pure epoxy resin, while glass transition temperature showes no obviously change. The primary mechanism of shielding of EP/BP composite is absorption. With BP thickness increasing, the shielding effectiveness improves.Besides, the increase of BP layers improves EMI SE and that reaches more than 50 dB with 5 layers BP (50?m).By properly adjusting the layer spacing between buckypapers, the shielding effectiveness reaches up to 52 dB with double layers BP (50?m thickness) at 1.7 mm spacing between two layers.