1wileyonlinelibrary.com an extremely high graphene loading is required. For example, the fi rst graphene based EMI shielding composite exhibited an EMI SE of ≈21 dB with a graphene loading of 15 wt%. [ 5 ] Ling et al. reduced the graphene loading of a polyetherimide/ graphene composite to 10 wt%, while keeping EMI SE at 20.0 dB. [ 6 ] On the other hand, an improved EMI SE, 29.3 dB, of graphene/polystyrene (PS) composite was obtained at the cost of extremely high graphene loading of 30 wt%. [ 7 ] Graphene or reduced graphene oxide (rGO) composites based on poly (methyl methacrylate), [ 8 ] water-borne polyurethane, [ 9 ] phenolic [ 10 ] were also reported in published papers, nevertheless, satisfactory EMI SE always requires abundant nanofi llers due to the homogenous dispersion structure of these composites. High nanofi ller concentrations result in high production costs and poor composite processability. Preparing CPC materials with superior EMI SE at low nanofi ller loading remains a challenge.The formation of segregated architectures can reduce the electrical percolation threshold, and improve electrical conductivity. [11][12][13][14][15] In such architectures, electrical nanofi llers are distributed only at the interfaces of polymer granules not homogeneously distributed in the whole volume of the polymer matrix. Graphene was fi rst utilized to construct segregated conductive networks in ultrahigh molecular weight polyethylene (UHMWPE) matrix, exhibiting an electrical conductivity of 0.04 S m −1 at a rather low content of 0.6 vol%. 12] A comparative study of segregated and homogeneous graphene/polycarbonate composites showed that the percolation threshold of the former composite was one third of that for the latter, and electrical conductivity was also higher by 220% at the same graphene loading of 4 wt%. [ 13 ] Segregated architectures also provide enhanced EMI SE, for example, when Cu nanowires were used as an electrical nanofi ller in PS, the segregated composites exhibited EMI SE levels of 26 and 42 dB at 10 and 13 wt% Cu loading, respectively. [ 15 ] Very recently, our group reported an in situ thermally reduced graphene/ultrahigh molecular weight polyethylene composite with a segregated structure, revealing the EMI SE of 28.3-32.4 dB at an ultralow graphene loading. [ 16 ] Although the formation of such segregated architectures could improve electrical and EMI shielding performance, one major issue of segregated architectures is that the existence of nanofi ller agglomerates at polymer granule interfaces restricts molecular diffusion between granules, leading to poor Ding-Xiang Yan , Huan Pang , Bo Li , Robert Vajtai , Ling Xu , Peng-Gang Ren , Jian-Hua Wang , and Zhong-Ming Li * A high-performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via highpressure solid-phase compression molding. Superior shielding effectiveness of 45.1 dB, the highest value among rGO based polymer composite, is achieved with only 3.47 vol% rGO lo...

Graphene oxide (GO) was successfully prepared by a modified Hummer's method. The reduction effect and mechanism of the as-prepared GO reduced with hydrazine hydrate at different temperatures and time were characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), x-ray diffractions (XRD), Raman spectroscopy and thermo-gravimetric analysis (TGA). The results showed that the reduction effect of GO mainly depended on treatment temperature instead of treatment time. Desirable reduction of GO can only be obtained at high treatment temperature. Reduced at 95 °C for 3 h, the C/O atomic ratio of GO increased from 3.1 to 15.1, which was impossible to obtain at low temperatures, such as 80, 60 or 15 °C, even for longer reduction time. XPS, 13C NMR and FTIR results show that most of the epoxide groups bonded to graphite during the oxidation were removed from GO and form the sp(2) structure after being reduced by hydrazine hydrate at high temperature (>60 °C), leading to the electric conductivity of GO increasing from 1.5 × 10(-6) to 5 S cm(-1), while the hydroxyls on the surface of GO were not removed by hydrazine hydrate even at high temperature. Additionally, the FTIR, XRD and Raman spectrum indicate that the GO reduced by hydrazine hydrate can not be entirely restored to the pristine graphite structures. XPS and FTIR data also suggest that carbonyl and carboxyl groups can be reduced by hydrazine hydrate and possibly form hydrazone, but not a C = C structure.

A combination of high-pressure compression molding plus saltleaching was first proposed to prepare porous graphene/polystyrene composites. The specific shielding effectiveness of the lightweight composite was as high as 64.4 dB cm 3 g À1 , the highest value ever reported for polymer based EMI shielding materials at such a low thickness (2.5 mm).

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