Carbon-based nanoparticles have recently generated a great attention, as they could create polymer nanocomposites with enhanced transport properties, overcoming some limitations of electrically-conductive polymers for high demanding sectors. Particular importance has been given to the protection of electronic components from electromagnetic radiation emitted by other devices. This review considers the recent advances in carbon-based polymer nanocomposites for electromagnetic interference (EMI) shielding. After a revision of the types of carbon-based nanoparticles and respective polymer nanocomposites and preparation methods, the review considers the theoretical models for predicting the EMI shielding, divided in those based on electrical conductivity, models based on the EMI shielding efficiency, on the so-called parallel resistor-capacitor model and those based on multiscale hybrids. Recent advances in the EMI shielding of carbon-based polymer nanocomposites are presented and related to structure and processing, focusing on the effects of nanoparticle's aspect ratio and possible functionalization, dispersion and alignment during processing, as well as the *Manuscript 2 use of nanohybrids and 3D reinforcements. Examples of these effects are presented for nanocomposites with carbon nanotubes/nanofibres and graphene-based materials. A final section is dedicated to cellular nanocomposites, focusing on how the resulting morphology and cellular structures may generate lightweight multifunctional nanocomposites with enhanced absorption-based EMI shielding properties.

Abstract. The present work considers the preparation of medium-density polyetherimide foams reinforced with variable amounts of graphene nanoplatelets (1-10 wt%) by means of water vapor-induced phase separation (WVIPS) and their characterization . A homogeneous closed-cell structure with cell sizes around 10 µm was obtained, with foams exhibiting zero crystallinity according to X-ray diffraction (XRD). Thermogravimetric analysis under nitrogen showed a two-step thermal decomposition behaviour for both unfilled and graphene-reinforced foams, with foams containing graphene presenting thermal stability improvements, related to a physical barrier effect promoted by the nanoplatelets. Thermo-mechanical analysis indicated that the specific storage modulus of the nanocomposite foams significantly increased owing to the high stiffness of graphene and finer cellular morphology of the foams. Although foamed nanocomposites displayed no further sign of graphene nanoplatelets exfoliation, the electrical conductivity of these foams was significant even for low graphene contents, with a tunnel-like model fitting well to the evolution of the electrical conductivity with the amount of graphene.

Foams based on polyetherimide (PEI) with carbon nanotubes (CNT) and PEI with graphene nanoplatelets (GnP) combined with CNT were prepared by water vapor induced phase separation. Prior to foaming, variable amounts of only CNT (0.1–2.0 wt %) or a combination of GnP (0.0–2.0 wt %) and CNT (0.0–2.0 wt %) for a total amount of CNT-GnP of 2.0 wt %, were dispersed in a solvent using high power sonication, added to the PEI solution, and intensively mixed. While the addition of increasingly higher amounts of only CNT led to foams with more heterogeneous cellular structures, the incorporation of GnP resulted in foams with finer and more homogeneous cellular structures. GnP in combination with CNT effectively enhanced the thermal stability of foams by delaying thermal decomposition and mechanically-reinforced PEI. The addition of 1.0 wt % GnP in combination with 1.0 wt % CNT resulted in foams with extremely high electrical conductivity, which was related to the formation of an optimum conductive network by physical contact between GnP layers and CNT, enabling their use in electrostatic discharge (ESD) and electromagnetic interference (EMI) shielding applications. The experimental electrical conductivity values of foams containing only CNT fitted well to a percolative conduction model, with a percolation threshold of 0.06 vol % (0.1 wt %) CNT.

Significant improvement in electrical conductivity of graphene nanoplatelets‐filled polyetherimide (PEI) foams was achieved by simultaneously increasing the porosity and graphene nanoplatelets dispersion. Foams were prepared by means of water vapor‐induced phase separation using a concentration of graphene nanoplatelets (GnP) between 1 and 10 wt%. To obtain two sets of foams having different density and porosity, PEI's concentration in N‐methyl pyrrolidone (NMP) solvent prior to foaming was set at 15 and 25–30 wt%, respectively. High‐power sonication was applied to GnP‐NMP suspension before PEI's addition for the foam series with higher porosity (15 wt% PEI). All foams were later characterized in terms of cellular structure, thermal stability, dynamic‐mechanical properties, and electrical conductivity. A notable enhancement in electrical conductivity was observed with foaming, especially when increasing the porosity and applying sonication, with foams reaching values as high as 1.7 × 10−1 S/m while maintaining the thermal stability and mechanical performance. POLYM. COMPOS., 40:E1416–E1425, 2019. © 2018 Society of Plastics Engineers

Polyetherimide (PEI) foams with graphene nanoplatelets (GnP) were prepared by supercritical carbon dioxide (scCO2) dissolution. Foam precursors were prepared by melt-mixing PEI with variable amounts of ultrasonicated GnP (0.1–2.0 wt %) and foamed by one-step scCO2 foaming. While the addition of GnP did not significantly modify the cellular structure of the foams, melt-mixing and foaming induced a better dispersion of GnP throughout the foams. There were minor changes in the degradation behaviour of the foams with adding GnP. Although the residue resulting from burning increased with augmenting the amount of GnP, foams showed a slight acceleration in their primary stages of degradation with increasing GnP content. A clear increasing trend was observed for the normalized storage modulus of the foams with incrementing density. The electrical conductivity of the foams significantly improved by approximately six orders of magnitude with only adding 1.5 wt % of GnP, related to an improved dispersion of GnP through a combination of ultrasonication, melt-mixing and one-step foaming, leading to the formation of a more effective GnP conductive network. As a result of their final combined properties, PEI-GnP foams could find use in applications such as electrostatic discharge (ESD) or electromagnetic interference (EMI) shielding.

Polysulfone (PSU) foams containing 0-10 wt% graphene nanoplatelets (GnP) were prepared using two foaming methods. Alongside the analysis of the cellular structure, their thermal conductivity was measured and analyzed. The results showed that the presence of GnP can affect the cellular structure of the foams prepared by both water vapor induced phase separation (WVIPS) and supercritical CO 2 (scCO 2 ) dissolution; however, the impact is greater in the case of foams prepared by WVIPS. In terms of thermal conductivity, the analysis showed an increasing trend by incrementing the amount of GnP and increasing relative density, with the tortuosity of the cellular structure, dependent on the used foaming method, relative density, and amount of GnP, playing a key role in the final value of thermal conductivity. The combination of all these factors showed the possibility of preparing PSU-GnP foams with enhanced thermal conductivity at lower GnP amount by carefully controlling the cellular structure and relative density, opening up their use in lightweight heat dissipators.

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