Acid modified multiwalled carbon nanotubes (a-MWCNT) reinforced polyurethane (PU) composite films have been fabricated using a solvent casting technique with 0-10 wt% of a-MWCNTs. A nanoindentation study has been carried out on these films in order to investigate the mechanical properties. Incorporation of a-MWCNTs in a PU matrix led to a drastic increase in the hardness and elastic modulus. The maximum nanoindentation hardness of 217.5 MPa for 10 wt% a-MWCNT loading was observed as compared to 58.5 MPa for pure PU (an overall improvement of 271%). The nanoindentation elastic modulus for a 10 wt% a-MWCNT loaded sample was 1504.2 MPa as compared to 385.7 MPa for pure PU (an overall improvement of 290%). In addition to hardness and elastic modulus, other mechanical properties i.e. plastic index parameter, elastic recovery, ratio of residual displacement after load removal and displacement at the maximum load and plastic deformation energy have also been investigated. The enhancement in the mechanical properties was correlated with spectroscopic and microscopic investigations using Raman spectroscopy, SEM and TEM. Dispersion of a-MWCNTs in the PU matrix was studied using Raman mapping. Besides the improvement in mechanical properties, the electromagnetic interference shielding properties were also investigated in the 8.2-12.4 GHz (X-band) frequency range. A value of $29 dB for the 10 wt% MWCNT loaded sample having a thickness of 1.5 mm was obtained.Therefore, these polyurethane composite films shall not only be useful for hard and scratchless coatings but also for protection from electromagnetic radiation in making electromagnetic shielding bags for packaging of electronic circuits and for scratchless tape for laminating circuit boards.

The multiphase approach was adapted to enhance the electromagnetic interference (EMI) shielding effectiveness (SE) of polyaniline (PANI) based nanocomposites. The natural graphite flakes (NGF) incorporated modified PANI was used for the development of multi-walled carbon nanotubes (MWCNTs) based nanocomposites. In PANINGF-MWCNTs composites, multilayer graphene was synthesized in situ by ball milling. The resultant PANINGF-MWCNTs nanocomposites were characterized by different techniques. It was revealed from the transmission electron microscope (TEM) observation that in situ derived multilayer graphene acts as a bridge between PANI and MWCNTs, and plays a significant role for improving the properties of multiphase nanocomposites. It was observed that EMI-SE increases with increasing the MWCNTs content from 1 to 10 wt% in the multiphase nanocomposites. The maximum value of total EMI-SE was À98 dB of nanocomposite with 10 wt% of MWCNTs content. The high value of EMI-SE is dominated by the absorption phenomenon which is due to the collective effect of increase in space charge polarization and decrease in carrier mobility. The decrease in carrier mobility has a positive effect on the shore hardness value due to the strong interaction between the reinforcing constituent in multiphase nanocomposites. As a consequence, shore hardness increases from 56 to 91 at 10 wt% of MWCNTs.

Microwave shielding properties of chemically synthesized MnO 2 decorated graphene nanoribbons (GNRs) are reported for the first time. The nature of MnO 2 decoration on the GNRs has been investigated using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy. The electromagnetic interference (EMI) shielding effectiveness of this material was investigated in the microwave region . The presence of MnO 2 on GNR enhances the interfacial polarization, multiple scattering, natural resonances and the effective anisotropy energy, which leads to absorption dominated high shielding effectiveness of À57 dB (blocking >99.9999% radiation) by a 3 mm thick sample. Dielectric attributes (3 0 and 3 00 ) were evaluated to understand the mechanism of the excellent shielding effectiveness. The material will be an excellent choice for radar absorbing applications.

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The electromagnetic interference (EMI) shielding of reduced graphene oxide (MRG), B-doped MRG (B-MRG), N-doped MRG (N-MRG), and B-N co-doped MRG (B-N-MRG) have been studied in the Ku-band frequency range (12.8-18 GHz). We have developed a green, fast, and cost-effective microwave assisted route for synthesis of doped MRG. B-N-MRG shows high electrical conductivity in comparison to MRG, B-MRG and N-MRG, which results better electromagnetic interference (EMI) shielding ability. The co-doping of B and N significantly enhances the electrical conductivity of MRG from 21.4 to 124.4 Sm(-1) because N introduces electrons and B provides holes in the system and may form a nanojunction inside the material. Their temperature-dependent electrical conductivity follows 2D-variable range hopping (2D-VRH) and Efros-Shklovskii-VRH (ES-VRH) conduction model in a low temperature range (T<50 K). The spatial configuration of MRG after doping of B and N enhances the space charge polarization, natural resonance, dielectric polarization, and trapping of EM waves by internal reflection leading to a high EMI shielding of -42 dB (∼99.99% attenuation) compared to undoped MRG (-28 dB) at a critical thickness of 1.2 mm. Results suggest that the B-N-MRG has great potential as a candidate for a new type of EMI shielding material useful in aircraft, defense industries, communication systems, and stealth technology.

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