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Multiple-walled carbon nanotube (CNT)-and carbon black (CB)-polymer composites have been fabricated by mechanical mixing with different loadings, the polymeric matrix being identical between the two series of samples. The main focus of this work is to report measurements of physical properties of these mixtures in ambient conditions and to discuss the origin of similarities and differences among them according the kind of carbonaceous filler. The uniform dispersion of the carbonaceous phase in the dielectric matrix was probed by high-resolution transmission electron microscopy. The good dispersibility of the filler particle is also reflected in the much lower conduction threshold observed for CNT-containing samples than in the CB composites. This is likely due to the high aspect ratio of the CNTs. Mechanical properties show that the storage modulus of the two kinds of samples is close to the modulus value of the neat styrene-butadiene rubber (SBR), independent of filler content over a wide range of compositions ([lowercase_phi_synonym]<0.1) encompassing the percolation threshold. Microwave measurements show that the real part of the effective permittivity exhibits a flat frequency response, with the exception of the sample containing 30 vol % CB for which an inverse-power law is observed revealing a behavior that has been seen for many random heterogeneous soft materials. No resonant dielectric absorption is evidenced within the frequency range explored and for the filler concentrations investigated. The results were also compared with analytical effective (mean-field) models. The symmetric Bruggeman model is in very good agreement with the microwave effective permittivity once account is taken of the depolarization factor which is close to the value found for a three-dimensional (3D) random dispersion of monodisperse spherical conductive inclusions within a dielectric matrix. By combining microwave frequency-domain spectroscopy with uniaxial tension, we obtain the effective permittivity as a function of the elongation ratio. Our results indicate that the effective permittivity spectrum of the CNT-polymer samples and their CB-based counterparts is not very sensitive to the applied stress in the range of elongation ratios explored. For the sample containing 30 vol % CB, the relative variation in the effective permittivity as a function of the elongation ratio is well described by the Gaussian molecular network model. The experimentally determined mechanical and microwave properties of these nanocomposites is related to the change in the mesostructure, formed by the heterogeneous 3D interconnected network of polymer and of aggregates (or agglomerates) of filler particles, as the composite is stretched. The results of this study provide another insight and opportunities to the comprehension of multifunctional materials, including novel nanoelectronic components, and carbon-based systems. [ABSTRACT FROM AUTHOR]

An experiment was carried out to investigate the effect of zinc sulfate on the qualitative and production characteristics of two varieties of Summer Squashplanted underplastichouses. The study was included two factors: the first factor was two varieties of Summer Squash(V1 Carisma) and (V2 Alexandria) and the second factor was represented by five concentrations of zinc sulfate (0, 25, 50, 75, 100 mg). The experiment was of Randomized Complete Block Design RCBD design with three replicates as a factorial experiment (2 x 5). The experiment included 10 treatments and 30 units, each unit includes 8 plants. The obtained results were analyzed by SAS program and the averages were compared by the Duncan Multipliers test at a probability level of 5%. The present results showed that the varieties varied in most productivity and quality traits. Alexandria was significantly higher in the number of male and female flowers, number of fruits, weight of fruit, plant yield, total yield and carbohydrates with mean values of 16.13 flower/Plant-1, 35.19 flower/Plant-1, 14.28 fruit/Plant-1, 172.08 g/Plant-1, 2.40 kg/plant-1, 4.03 ton/B-1 and 17.38% respectively. Spraying with zinc sulfate at concentration of 75 mg/L-1resulted in a significant increase in the number of male flowers, the fruit weight, plant yield and the total yieldwith means of 18.00 flower/plant-1, 179.17 g/plant-1, 2.51 kg/plant-1 and 4.22 tons/ B-1 respectively. Additionally, the interaction between Alexandria and sprayingwith a concentration of 75 mg/L-1of zinc sulfate was significantly higher in the number of male and female flowers, number of fruits, fruit weight, plant yield, total yield and carbohydrates. The highest sex ratio (2.57) was noted in the treatment of the interaction between Carisma and spraying with a concentration of 75 mg/L-1 of zinc sulfate which was superioron the other interaction treatments. [ABSTRACT FROM AUTHOR]

Layered montmorillonite was synthesized by hydrothermal method, progressively modified by an alkylammonium and thoroughly characterized by elemental, thermal, and X-ray diffraction (XRD) analysis. Pristine and modified clays were introduced in maleic anhydride-modified ethylene-co-propylene-co-diene monomer matrix. XRD and transmission electron microscopy investigations showed microcomposite as well as intercalated or exfoliated nanocomposites morphologies depending on the organic content of the clay. The inhibitor character of the pristine clay on peroxides as crosslinking agent for rubbers was then demonstrated and overcome by using electron beam irradiation for specimens containing unmodified clay. Dynamic mechanical analyses and swelling measurements showed that it is possible to obtain the same degree of crosslinking of the polymer matrix by electron beam irradiation of the composites based on pristine clay specimens and conventional peroxide curing of modified-clay-based ones. Finally, flame-retardant properties of different clays-based composites showed a direct dependence on the degree of exfoliation. It was observed that the better the exfoliation, the higher is the flame retardancy. POLYM. COMPOS., 38:966-973, 2017. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

This study focuses on the relations between the microstructure and the viscoelastic behavior of an industrial solid propellant belonging to the class of highly filled elastomers. Precisely, the study aims at determining the impact on the viscoelastic behavior of the presence of the sol fraction inside the polymer network. The sol fraction is the part of the binder that a good solvent can extract. The solid propellant is swollen to various extents by solutions of plasticizer and polymer molecules. This swelling leads to a hydrostatic deformation of the polymer network, corresponding to an extension or contraction loading for each specimen. Prestrained dynamic mechanical analysis tests, superimposing a small oscillating strain on a prestrain, characterize the viscoelastic behavior. The degree of swelling of the network and the effective filler fraction drive the viscoelastic response. In addition, the mechanical behavior does not depend on the chemical nature of the introduced sol fraction. Moreover, a nonlinear behavior, i.e., an increase in both storage and loss moduli with increasing prestrain, is initiated at low prestrain. This nonlinearity depends on the contraction or extension of the network and could result from particles aligning with prestrain, which is expected in such highly filled materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Presents a letter to the editor about preparation of EPDM/synthetic montmorillonite nanocomposites.