In this chapter, a brief review on three-component composites comprised of a (micro) fibrous reinforcement and a thermoset polymer resin filled with nanoparticles is presented. For this type of composite, carbon nanotubes (CNT) and carbon nanofibers are more commonly used and the focus usually lies on resin-dominated properties, such as interlaminar shear strength, and interlaminar fracture toughness. Many three-component systems comprised of fiber/epoxy/CNT have been produced using resin transfer molding (RTM) or VARTM. However, there are major difficulties associated with the impregnation of a dry fibrous reinforcement using a highly viscous suspension of resin/nanofiller, especially for high content of nanofillers or highly packed fibrous systems. In such harsh circumstances, an alternative and recent approach to enable processing comprises the production/use of three-component prepregs containing nanofillers, although they are usually associated with high cost. The presented case study focused on an alternative route to produce glass-fiber composites with high content of CNT via RTM. A practical, low-cost and effective methodology for the direct deposition of an acetone/CNT/epoxy suspension on glass-fiber cloths was developed, achieving up to 4.15 % wt. in overall CNT content in the composite. The mechanical properties of the composites produced with non-functionalized CNT increased, in general, up to 10 % compared to the reference epoxy/glass-fiber composite. However, the high CNT content obtained was of uttermost importance for the development of electromagnetic characteristics on the material, absorbing much of the radiation in the microwave frequency range. The reflectivity properties reached a maximum of approximately - 14 dB (c.a. 95 % of electromagnetic absorption) and this excellent performance was obtained using a comparatively low cost (glass fiber) and thin (»2.2 mm) polymer composite material. Thus, the developed composites showed great potential to be used as microwave-absorption materials, replacing conventional ones employed for this aim. With further improvement in the manufacturing process, these materials could become of interest as high performance composites in a wide range of engineering applications, from telecommunications to aerospace.
