Ahmed Mdarhri

Tensile mechanical characterization was performed on polytetrafluoroethylene (PTFE) to assess how compaction pressure during spark plasma sintering (SPS) influences its properties. Owing to its unique microstructural features, its mechanical behavior exhibits a complex, nonlinear response under external loads. In this study, we employ two phenomenological models—the five‐parameter Mooney–Rivlin and the four‐term Béchir—to replicate the stress–strain curves of PTFE samples sintered at varying compaction pressures during SPS. Although this nonmelting technique overcomes the limitations of conventional methods for densifying highly viscous polymers, it also provides greater control over the microstructure of the sintered material, especially through high heating and cooling rates. Consequently, a significant portion of the amorphous phase can be produced, making the samples nearly incompressible, as confirmed by differential scanning calorimetry measurements (DSC). We evaluate each model's ability to accurately represent the tensile mechanical behavior of the PTFE specimens. We find that there is an inverse correlation between several specific fit parameters of these phenomenological models and the strain hardening obtained from the Haward‐Thackray model in the plastic deformation zone. Our results demonstrate excellent agreement between the experimental data and both phenomenological models, confirming their effectiveness in predicting the nonlinear mechanical behavior of semicrystalline polymers.

We consider the hyperelastic response of semi‐crystalline ethylene–co‐butyl acrylate (EBA) samples filled with carbon black (CB) particles. Such material is structurally complex with its microstructure being characterized by many structural parameters including crosslink density, filler/matrix interfaces, crystallinity, filler network, and chain entanglement which have different degrees of influence on the effective mechanical properties. We evaluate the ability of a number of analytical models to correctly reproduce the non‐linear elastic mechanical response of these samples. We do this by considering either dry samples, or samples which are swollen by a non‐polar solvent (toluene) at equilibrium, and subjected to uniaxial tension at room temperature. As test cases, we focus on six physical models for the purpose of analyzing the stress–strain curves of samples with different cross‐linking densities. Among these frameworks, we show that the Mooney–Rivlin (MR), Ogden, and eight‐chain models accurately describe the stress–strain curves of both dry and swollen CB‐EBA samples. These findings highlight the possibility of attaining a diverse set of mechanical properties of filled polymer samples by tailoring their structural parameters.

The majority of industry using high-speed communication systems is shifting towards higher frequencies, namely the terahertz range, to meet demands of more effective data transfer. Due to the rising number of devices working in terahertz range, effective shielding of electromagnetic interference (EMI) is required, and thus the need for novel shielding materials to reduce the electromagnetic pollution. Here, we show a study on optical and electrical properties of a series of ethylene co-butyl acrylate/carbon black (EBA/CB) composites with various CB loading. We investigate the transmittance, reflectance, shielding efficiency, absorption coefficient, refractive index and complex dielectric permittivity of the fabricated composites. Finally, we report a material that exhibits superior shielding efficiency (SE)—80 dB at 0.9 THz (14.44 vol% CB loading, 1 mm thick)—which is one of the highest SE values among non-metallic composite materials reported in the literature thus far. Importantly, 99% of the incoming radiation is absorbed by the material, significantly increasing its applicability. The absorption coefficient (α) reaches ~100 cm⁻¹ for the samples with highest CB loading. The EBA/CB composites can be used as lightweight and flexible shielding packaging materials for electronics, as passive terahertz absorbers or as radiation shields for stealth applications.

The effect of organic solvents on the transport process and mechanical properties in elastomeric nanocomposite materials is reported. The investigated samples are formed by a semicrystalline ethylene-co-butyl acrylate (EBA) polymer filled with hard spherical carbon black (CB) nanoparticles. The swelling behavior was studied at room temperature by immersion the dried samples in two selected solvents, i.e. toluene and xylene. The transport of the molecules of a given solvent in these filled elastomeric composites is found to follow a Fickian diffusion mechanism. Mechanically speaking, the stress-strain curves of uniaxial tensile tests pre-and post-swelling highlight a remarkably decrease of the Young’s modulus and strength of the swollen samples. This behavior can be attributed to the decrease of the load transfer density between the matrix and the CB in the presence of the solvent. The Mooney-Rivlin model is used to capture the physics of the stress-strain curves in both dry and swollen samples. The results reported in this experimental investigation can be useful for some demanding applications.

Mechanical properties of heterogeneous systems based on carbon black (CB) filled semi‐crystalline ethylene butyl acrylate (EBA) copolymer nanocomposites are characterized using nano‐indentation technique. The size effect and CB content dependence on the deformation behavior at room temperature were investigated. The phenomenology for hardness response (H) indicates a typical enhancement of the H when the indentation depth (h) decreases as for the usual elastomeric materials. All H–h curves, fitted according to the Meyer's empirical power law and Franck elasticity model, highlight the so‐called length‐scale‐dependent deformation. Similar trend is observed for the elastic modulus. Furthermore, it is evidenced that the increases of CB content increases the mechanical properties of composites, that is, hardness and elastic modulus. This behavior can be mainly related, on the one hand, to the change of the meso‐structure, formed by the interconnected network of polymer and the aggregates of CB particles and to the nature of the polymer matrix, on the other hand. The mechanical properties characterized from micro and submicron indentations were compared to that characterized at macroscopic scale to highlight the possible correlations between the two scales. This investigation can interest many applications of polymer composites for rubber technology such as tires industry, soft robotic, and adhesives. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47897.

Tensile and thermo‐mechanical properties of nano‐composites fabricated by mechanically mixing semi‐crystalline ethylene‐co‐butyl acrylate (EBA) and carbon black (CB) nanoparticles are investigated. Stress–strain curves performed on samples over a broad range of CB content evidence the hyperelastic behavior of the EBA matrix. Neo‐Hookean and Mooney‐Rivlin models are used to fit the observed linear and nonlinear mechanical behaviors, respectively. The thermo‐mechanical curves highlight two relaxation phenomena depending on the CB content. Correspondingly, the EBA/CB interface properties are analyzed by correlating the volume fraction of the constrained polymer to the relaxation behavior of the viscoelastic linear regime. POLYM. COMPOS., 40:3005–3011, 2019. © 2018 Society of Plastics Engineers

The temperature effecton the dielectric response of nanocomposite at low frequencies range is reported. The investigated samples are formed by a semi-crystalline ethylene-co-butyl acrylate (EBA) polymer filled with three concentrations of the dispersed conducting carbon black (CB) nanoparticles. The temperature dependence of the complex permittivity has been analyzedabove the glass transition temperature of the neat polymer matrix Tg=-75°C. For all CB concentrations, the dielectric spectra follow a same trend in frequency range 100-106Hz. More interestingly, the stability of the effective complex permittivity ɛ=ɛ' -iɛ'' with the temperature range of 10-70°C is explored. While the imaginary part of the complex permittivity ɛ'' exhibits a slight decreasewith temperature, the real part ɛ' shows a significant reduction especially for high loading samples. The observed dielectric response may be related to the breakup of the three-dimensional structurenetwork formed by the aggregation of CB particles causing change at the interfaceEBA-CB.This interface is estimated bythe volume fraction of constrained polymer chain according to loss tangent data of dynamic mechanical analysis.