Composite materials containing multi-walled carbon nanotubes (MWNT) in polyolefine (polyethylene and polypropylene) matrix were prepared by coagulation precipitation. The morphology and structure of produced composites was investigated by scanning and transmission electron microscopy. Thermal analysis (oxidation in air) was performed for composites in temperature range 20–500°C. It was shown that the addition of MWNT increases the thermal stability of composites. Electrophysical properties of MWNT/PSt composites were investigated using a four-probe technique. Observed electrical percolation threshold of composite materials is near to 3–3.5wt%. Electromagnetic (EM) response of prepared materials was investigated in broadband region (26–37 GHz and 250–500 GHz). It was found that the EM response of MWNT/polyolefine depends on their electrophysical properties with percolation threshold near 2–3wt%.

Three types of carbon multi-walled nanotubes (MWNT) with different morphology and mean diameter (7.5, 10.5, 22 nm) were used to produce polymethylmetacrylate-based composites (MWNT/PMMA) with variable MWNT loading (0.5–5wt%). The electrophysical properties of produced composites and electromagnetic response in frequency range of 2–12 GHz were investigated. Electrical conductivity of composites depends on the MWNT type increasing with lowering of the nanotube diameter and loading in composite. Reflectance and transmittance coefficients were calculated from dielectric permittivity data and found to correlate with electrical conductivity. The highest level of EM reflection was obtained for 7.5 nm MWNT-based composites and makes the value of 0.65–0.7, whereas 22 nm MWNT/PMMA composites are more transparent for EM radiation with reflection coefficient 0.3–0.4 for the highest MWNT loading. Thus MWNT/PMMA composites demonstrate high EM shielding properties.