Mechanical and electrical characterization of epoxy nanocomposites for electromagnetic shielding devices in aerospace applications

Abstract

Polymer-based composites are popular in electronic applications due to their light weight, low cost, high strength and easy processing. The major part of these is used to insulate electrical circuits against atmospheric agents uniquely. Many polymeric materials are transparent to electromagnetic radiation and provide no shielding against electromagnetic interference (EMI). In electronic and communication applications, the EMI pickups by electronic components give rise to serious problems, such as noise enhancement and malfunction of electronic instruments. In order to avoid such drawbacks, the developing of materials with both typical composite and EMI shielding properties is thus required. Since their discovery in 1991 by Iijima carbon nanotubes (CNTs) attracted attention of researchers worldwide for their novel mechanical, thermal and electrical properties; an extensive research in CNT/nanocomposites field thus soon started. Essentially two families of CNTs exist: single-walled nanotubes (SWNTs), made up by only one rectilinear tubular unity (a "graphite sheet" rolled into a cylinder) and multi-walled nanotubes (MWNTs), that are constituted by a series of coaxial SWNTs. Though generally both types have high aspect ratio, high tensile strength, low mass density, etc. the actual values can be different, depending on whether it is SWNT or MWNT. Besides the type of nanotube, the synthesis mode (arc discharge, laser, CVD) is an important variable since it affects the perfection of the structure and the surface reactivity. Early theoretical works and recent experiments have confirmed that introducing CNTs as structural element in composites should improve material properties, therefore promising a large variety of applications in different fields: nanoelectronic devices, reinforcing materials, bio-medicine, aerospace and so forth. A prospective application in aerospace that is widely studied, including our work reported here, is the improvement of electrical properties of composites made of CNTs and epoxy resin. The key factors in preparing a good composite rest on good filler dispersion, control of nanotubes-matrix bonding, and density of the composite material; the main problem is in creating a good interface between nanotubes and the polymer matrix and attaining good load transfer from the matrix to the nanotubes during loading. Many companies have started to sell products that contain CNTs, by now. The progress in bulk synthesis and purification make CNTs available in larger quantities at lower prices; recent advances in developing nanocomposites with CNTs gives them the function of reinforcing structural elements and yields new electrical and thermal conductivity materials.