The elastomeric composites using styrene butadiene rubber (SBR) as the polymeric matrix with two types of carbon nanofi llers, carbon black and carbon nanotubes, are prepared by melt mixing with the aim to use them as sensors of organic gases for monitoring industrial environments. The prepared composites contain various amounts of conducting nanofi llers and are cross-linked before examination for gas sensing. The electrical conductivity of the prepared composites is measured and the percolation threshold is calculated for both types of composites. The fi rst aim is to determine compositions slightly above the percolation threshold for later testing of the sensing properties. Swelling/deswelling experiments have also been performed. The dispersion of conducting fi llers in SBR matrix is studied by scanning and transmission electron microscopy techniques, and the mechanical properties of the pure matrix and all prepared composites are determined by tensile testing. Three organic gases, toluene, tetrahydrofuran, and n -hexane, in various mixtures with air are used to examine the ability of the prepared composites to react in their presence by changing the electrical properties. Cyclability of the sensing performance of the composites is also examined. Sensing results reveal the suitability of the prepared SBR-based materials as sensors for harmful solvents and gases widely used in industry.
Polymeric composites of the linear triblock copolymer poly(styrene-co-ethylene/butylene-co-styrene) grafted with maleic anhydride units (SEBS-MA) or MA modified by hydrophilic polyethylene glycol (PEG) and containing various amounts of multiwall carbon nanotubes (MWCNTs) as conducting filler-were prepared by solvent casting. The MWCNT surface was modified by a non-covalent approach with a pyrene-based surfactant to achieve a homogeneous dispersion of the conducting filler within the polymeric matrix. The dispersion of the unmodified and surfactant-modified MWCNTs within the elastomeric SEBS-MA and SEBS-MA-PEG matrices was characterized by studying the morphology by TEM and SAXS. Dynamical mechanical analysis was used to evaluate the interaction between the MWCNTs and copolymer matrix. The electrical conductivity of the prepared composites was measured by dielectric relaxation spectroscopy, and the percolation threshold was calculated. The prepared elastomeric composites were characterized and studied as humidity sensor. Our results demonstrated that at MWCNTs concentration slightly above the percolation threshold could result in large signal changes. In our system, good results were obtained for MWCNT loading of 2 wt% and an ∼0.1 mm thin composite film. The thickness of the tested elastomeric composites and the source current appear to be very important factors that influence the sensing performance.
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