RESUMO
Efficient design of electromagnetic (EM) shielding materials has emerged as a challenging research area in the past decade. To address this issue, we propose thin, lightweight, yet strong epoxy/carbon fiber (CF) composites modified with functionalized graphene oxide (GO) sheets as "interconnects". This strategy resulted in an impressive 175% improvement in the storage modulus, a 100% enhancement in the lap shear strength, and an extraordinary 200% improvement in the shielding effectiveness at a very low GO content (0.5 wt %). First, GO was functionalized with an epoxy prepolymer (namely E-f-GO) to improve the interfacial adhesion with the matrix polymer, epoxy. As a control, epoxy nanocomposites were also prepared with modified GO. It was followed by the fabrication of CF laminates impregnated with epoxy nanocomposites. Covalent functionalization of epoxy chains on GO sheets was confirmed using various techniques like X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, and thermogravimetric analysis. Epoxy nanocomposites were analyzed for thermal, mechanical, electrical, and adhesive strength behavior. CF laminates with epoxy nanocomposites were fabricated using vacuum-assisted resin transfer molding. The E-f-GO/epoxy/CF composite exhibited an excellent shielding effectiveness value of -70 dB, and the storage modulus was found to be >40 GPa. The modified composite showed absorption-driven shielding of EM waves and hence can be used as a highly effective EM absorber.
RESUMO
In this work, we have attempted to improve electromagnetic interference (EMI) shielding and mechanical behavior of epoxy/carbon fiber (CF) composite, simultaneously, in the presence of functionalized carbon nanotubes. It is well understood that properties of composite depend on the interface between the filler and matrix. Considering this basic understanding, functionalized carbon nanotubes/epoxy nanocomposites were impregnated into a bidirectional carbon fiber (CF) mat and, further, various mechanical and EMI shielding behaviors were studied. Multiwalled carbon nanotubes were functionalized with branched poly(ethyleneimine) (b-MWNT) to tailor the interface of epoxy/CF composites. Laminates with two layers of CF were fabricated with functional MWNT modified epoxy. Scanning electron microscopy was used to analyze the microstructure of epoxy/CF laminates. Lap shear test was performed to analyze adhesion between the modified epoxy and carbon fiber. Further dynamic mechanical analysis in the temperature range of 30-160 °C was performed. Thermal degradation of composites was studied using a thermogravimetric analyzer. Electrical conductivity of laminates was measured using a four-point method on an Agilent probe station. EMI shielding effectiveness (SE) was measured for 0.5 mm-thin laminates in the Ku band. The b-MWNT modified epoxy/CF composites showed excellent SET of ca. -60 dB and SEA of ca. -50 dB, which are of commercial importance. Compared to unmodified epoxy/CF, b-MWNTs/epoxy/CF exhibited 200% increment in EMI SET and 35% enhancement in storage modulus due to the improved interface between the epoxy matrix and carbon fiber.
RESUMO
In this study, branched poly(ethyleneimine), BPEI, was synthesized from carboxylic acid terminated multi-walled carbon nanotubes (c-MWNTs) and characterized using FTIR, TEM and TGA. The BPEI was then chemically grafted onto MWNTs to enhance the interfacial adhesion with the epoxy matrix. The epoxy composites with c-MWNTs and the BPEI-g-MWNTs were prepared using a sonication and mechanical stirring method, followed by curing at 100 °C and post-curing at 120 °C. The dynamic mechanical thermal analysis showed an impressive 49% increment in the storage elastic modulus in the composites. In addition, the nanoindentation on the composites exhibited significant improvement in the hardness and decrease in the plasticity index in the presence of the BPEI-g-MWNTs. Thus, epoxy composites with BPEI-g-MWNTs can be further explored as self-healing materials.
RESUMO
Blends of polystyrene (PS) and poly(methyl methacrylate) (PMMA) with different surface-functionalized multiwall carbon nanotubes (MWNTs) were prepared by solution blending to design materials with tunable EMI (electromagnetic interference) shielding. Different MWNTs like pristine, amine (â¼NH2), and carboxyl acid (â¼COOH) functionalized were incorporated in the polymer by solution blending. The specific interaction driven localization of MWNTs in the blend during annealing was monitored using contact mode AFM (atomic force microscopy) on thin films. Surface composition of the phase separated blends was further evaluated using X-ray photoelectron spectroscopy (XPS). The localization of MWNTs in a given phase in the bulk was further supported by selective dissolution experiments. Solution-casted PS/PMMA (50/50, wt/wt) blend exhibited a cocontinuous morphology on annealing for 30 min, whereas on longer annealing times it coarsened into matrix-droplet type of morphology. Interestingly, both pristine MWNTs and NH2-MWNTs resulted in interconnected structures of PMMA in PS matrix upon annealing, whereas COOH-MWNTs were localized in the PMMA droplets. Room-temperature electrical conductivity and electromagnetic shielding effectiveness (SE) were measured in a broad range of frequency. It was observed that both electrical conductivity and SE were strongly contingent on the type of surface functional groups on the MWNTs. The thermal conductivity of the blends was measured with laser flash technique at different temperatures. Interestingly, the SE for blends with pristine and NH2-MWNTs was >-24 dB at room temperature, which is commercially important, and with very marginal variation in thermal conductivity in the temperature range of 303-343 K. The gelation of MWNTs in the blends resulted in a higher SE than those obtained using the composites.
