When considering energy consumption and environmental issues, solvent‐resistant nanofiltration (SRNF) based on polymeric materials emerges as a process for substituting conventional separation processes of organic solutions, such as distillation, which consume high amounts of energy. Because SRNF does not involve phase transition, this process can potentially decrease the energy consumption and solvent waste and increase the yield of active components. Such improvements could significantly benefit a number of fields, such as pharmaceutical manufacturing and catalysis recovery, among others. Therefore, SRNF has gained a lot of attention since the recent introduction of solvent‐stable polymeric materials in the manufacture of nanofiltration membranes. The membrane materials and the membrane structures depending on the fabrication methods determine the separation performance of polymeric SRNF membranes. Therefore, this article gives a comprehensive overview of the current state‐of‐art technologies of generating membrane materials and corresponding fabrication methods for SRNF membranes made from polymeric materials expected to provide the most benefit. The transport mechanisms and the corresponding models of SRNF membranes in organic media are also reviewed to better understand the mass transfer process. Various SRNF applications, such as in pharmaceutical and catalyst, among others, are also discussed. Finally, the difficulties and future research directions to overcome the challenges faced by SRNF processes are proposed.
Polyvinyl alcohol (PVA) sponge with a complex interconnecting porous structure indicates suitable mechanical properties at different strain rates. The paper presents the first scientific study to show how different results are given by the various definitions of stress–strain used and to recommend a specific definition when calculating the energy absorption characteristics of the PVA sponge. A series of tensile tests on PVA sponges are carried out. Three stress definitions (second Piola–Kirchhoff stress, engineering stress, and true stress) and four strain definitions (Almansi–Hamel strain, Green–St. Venant strain, engineering strain, and true strain) are used to determine the modulus of resilience and modulus of toughness. The stress–strain curves of PVA sponges show a near constant plateau stress over a long strain range, which is ideal for energy absorption applications. The results reveal that the Green–St. Venant strain definition has the highest modulus of resilience (3000 J/m 3 ) and toughness (56,900 J/m 3 ) at different definitions of stress and may overestimate the modulus of resilience and toughness. The Almansi–Hamel strain definition exhibits the lowest modulus of resilience (1760 J/m 3 ) and toughness (4850 J/m 3 ) at different stress definitions and may underestimate these values. The results also show that the effect of varying the stress definition on the modulus of toughness measurements is significant but not when calculating the modulus of resilience. The true stress–true strain definition favors spongy material mechanics since it gives more accurate measurements of the sponge's response using the instantaneous values.
Properties of natural rubber (NR) filled with various fillers, i.e., furnace black (N330), conductive carbon black (XE2‐B), and carbon nanotube (CNT) were investigated. Both untreated and sonicated carbon nanotubes were used and designated as U‐CNT and S‐CNT, respectively. The filler content was varied from 0 to 8 phr. Regardless of the filler type, the increase in the filler content not only results in increased compound viscosity, reduced cure time, and enhanced cross‐link density but also leads to the increase in the modulus and hardness of the vulcanizates. For N330 and XE2‐B, the tensile strength increases continuously with increasing filler content. However, for both U‐CNT and S‐CNT, the tensile strength tends to increase with increasing filler content up to 2 phr and decreases noticeably afterward. At any given filler content, the CNTs give the vulcanizates with the highest values of electrical and thermal conductivities, storage modulus, and tan δ, followed by XE2‐B and N330, respectively. Results also elucidate that the sonication of CNT without the presence of surfactant prior to mixing could not improve the degree of CNT dispersion, leading to insignificant difference in properties of the U‐CNT‐filled and S‐CNT‐filled vulcanizates.
There is currently a considerable interest in developing bio‐based and green nanocomposites in industrial and technological areas owing to their biodegradability, biocompatibility, and environmental friendliness. In this study, a bio‐based nanosized material, cellulose nanocrystals (CNC), extracted from southern pine pulp was employed as a reinforcing agent in a natural rubber (NR) matrix. NR/CNC nanocomposites were prepared by a solution mixing and casting method. The morphology, thermal, and mechanical properties of the nanocomposites were investigated using scanning electron microscopy, Fourier transform‐infrared spectroscopy, tensile tests, dynamic mechanical analysis, thermal gravimetric analysis, and differential scanning calorimetry. The CNC displayed a gradient dispersion in the nanocomposites, and no microscaled aggregates were observed. Both the tensile strength and modulus of the nanocomposites increased with the addition of CNC, accompanied by a slight decrease in elongation at break. The storage modulus also improved with the addition of CNC, which served as good evidence of the reinforcing tendency of CNC in the NR matrix. The thermal stability of the nanocomposites showed an insignificant decrease in CNC addition. The glass transition temperature of the nanocomposites was not influenced by CNC.
Polyamide 12 (PA12)/high‐density polyethylene (PE)/carbon nanotubes (CNTs) composites were prepared by three melt mixing sequences; premixing the CNT in the PA phase, premixing the CNT in the PE phase, and simultaneous mixing of all components. The interfacial tension and viscosity ratio between the components were altered by modifying the PE minor phase with PE‐ graft ‐maleic anhydride (PE‐g‐MAH) and by using different melt flow rate PE minor phase. Scanning electron microscopy (SEM) and volume resistivity (VR) measurements show that when the matrix's viscosity is greater than that of the dispersed phase, simultaneous mixing and premixing the CNT in the PE phase form a unique microstructure that yields a VR that is 4–6 decades lower than when premixing the CNT in the PA phase. When the viscosity of the dispersed PE phase is greater, kinetic restrictions limit the migration of the CNTs from the PE phase, resulting in high VR values for all mixing procedures. The wetting parameter was used to calculate the thermodynamic drive of the CNTs localization. It was found that the MAH modification reduces the interfacial tension between the CNT and the modified PE phase, which results in selective localization of CNT in there rather than in the PA phase. This observation was confirmed in SEM imaging and also expressed in high VR values of these composites.
This paper addresses the preparation of polyaniline (PAni) and polypyrrole (PPy) nanostructures as humidity sensor elements. The semicrystalline microstructure and chemical structure of synthesized PAni and PPy were studied by X‐ray diffraction and Fourier transform infrared spectroscopy, respectively. The morphology of these polymers was studied by scanning electron microscopy and transmission electron microscopy, indicating fibrillar and tubular nanostructures for PAni and PPy, respectively. The humidity sensing performances of sensors based on the prepared nanostructural PAni and PPy were investigated, and the sensing mechanisms of both systems have been discussed. The interesting reverse behaviors during humidity exposure of PAni‐ and PPy‐based sensors in different water vapor concentrations have been comprehensively justified. The temperature dependency of the electrical conductivity for PAni and PPy samples was investigated. The UV–vis spectroscopy was used to study the effect of moisture on the electronic transport properties of PAni and PPy nanostructures.
The aim of this research work is to investigate adsorption of mercury ions from an aqueous solution on a biocompatible polymeric polypyrrole‐chitosan (PPy/CTN) nanocomposite. The PPy/CTN nanocomposite was prepared in aqueous media by chemical polymerization of pyrrole in the presence of ferric chloride as an oxidant. Langmuir, Freundlich, and Temkin adsorption isotherms were applicable to the adsorption process, and their constants were evaluated. The thermodynamic equilibrium constant and the Gibbs free energy were determined. Results indicated that the Langmuir model gave a better fit to the experimental data than the other two equations. The adsorption capacity ( q max ) of PPy/CTN for Hg(II) ions in terms of monolayer adsorption was 40 mg/g. The negative value of Gibbs free energy (Δ G o ) indicates feasible and spontaneous adsorption of Hg(II) on the PPy/CTN nanocomposite. Also the change in entropy (Δ S o ) and enthalpy (Δ H o ) were estimated to be –0.21 KJ (mol K) −1 and –18.183 kJ mol −1 , respectively.
Polytetrafluoroethylene (PTFE) polymer samples were irradiated by 50 MeV Li 3+ ion beams to the fluences of 1 × 10 10 , 1 × 10 11 , and 1 × 10 12 ions/cm 2 . The structural, optical, and chemical properties were studied by X‐ray diffraction (XRD), UV–visible (UV–vis) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy, respectively. The XRD analyses showed amorphization of the polymer sample at fluences of 1 × 10 10 and 1 × 10 11 ions/cm 2 . Crystallite size (calculated by applying the Scherrer formula) decreased for irradiated samples at fluences of 1 × 10 10 and 1 × 10 11 ions/cm 2 . The other factors like microstrain (ε), dislocation density (δ), and distortion parameters ( g ) showed variations at these fluences. However, there was no change in the interchain separation ( R ) and interplanar distance ( d ) for all irradiated samples. UV–vis showed a shift of the absorption edge of irradiated samples towards the visible region. The band gap energy ( E g ) was calculated using Tauc's relation, and its value decreased with an increase of ion fluence for all irradiated samples. The number of carbon atoms per conjugation length ( N ) increased for the irradiated samples. The FTIR results revealed the liberation of CF 2 groups and the appearance of some new bands after irradiation.
The main aim of this study was to investigate the usability of polyurethane (PU) and polyacrylonitrile (PAN) nanofibers for improving the sound absorption of conventional polyester nonwovens in wide band of frequencies along with weight and thickness reduction. The effect of nanofiber and nonwoven layers number, nanofiber layers surface density, and the type of nanofiber polymer on the sound absorption was studied. To find the optimum conditions for achieving high sound absorption, response surface methodology was used. The results showed that the sound absorption of composite samples is improved when the nanofiber layer number or its surface density increased. The results also showed that the sound absorption of composites is enhanced by using PAN instead of PU. At a constant surface density, the higher resonant peak, without shifting, was achieved with increasing the nanofiber layers number. Optimization process showed that samples containing PAN nanofiber layers with surface density of 4.72 g/m 2 and six nonwoven layers have highest average sound absorption coefficient.
Coaxial poly(ε‐caprolactone) (PCL)/gelatin nanofibers were successfully fabricated by electrospinning, using 2,2,2‐trifluoroethanol (TFE) as a solvent. The morphology of the PCL/gelatin coaxial fibers was evaluated using attenuated total reflectance Fourier transform infrared (FTIR) spectroscope, scanning electron microscope, and transmission electron microscope. The disappearance of gelatin absorption bands in FTIR spectrum after the mat washing step suggested that coaxial nanofibers were obtained. The coaxial morphology was confirmed by transmission electron microscopy. The influences of PCL concentration, applied voltage, and feed rate on the characteristics of the PCL core were analyzed in correlation with the structure of the nanofibers. The morphology of the coaxial fibers was observed to be mainly affected by the PCL solution concentration. Extraction of the PCL core using dichloromethane allowed the preparation of hollow gelatin nanofibers. The replacement of TFE by a formic acid–acetic acid (1:1) system as a less toxic solvent also successfully resulted in the preparation of coaxial PCL–gelatin nanofibers.
The aim of this study is design and prepare medical grade polyurethane (PU) film based on castor oil without any additives. Acrylic acid (AAc) was grafted onto the surface of PU films using a two‐step oxygen plasma treatment. The first step of this method includes oxygen plasma pretreatment of the PU films, immersion in AAc monomeric solution, removal from the solution, and drying. The second step was carried out by plasma polymerization of preadsorbed reactive monomers on the surfaces of dried pretreated films. The effects of pretreatment time length and monomer concentration were studied on AAc graft amount. The surface of the modified PU films were characterized using attenuated total reflection Fourier transform infrared (ATR‐FTIR) spectroscopy, scanning electron microscopy (SEM), and water drop contact angle measurements. The ATR‐FTIR results proved that the carbonyl (CO) and hydroxyl groups (OH) of AAc give rise to an absorption peak at 1698 cm –1 , which was observed in the spectra of the modified PU. The SEM micrographs showed that poly(acrylic Acid) (PAAc)–grafted PU films have a different pattern compared with nonmodified PU films. Moreover, it was found that a decrease in contact angle indicated to a higher grafting amount of polymer. Finally, L929 fibroblast cell culture was done onto the PAAc–PU films. It was observed that cells are spherical and not uniformly distributed on the modified polymer surface.
In this study, it is aimed to investigate the physical properties of poly(lactic acid)/thermoplastic starch (PLA/TPS) blends as a function of number of recycling (NOR) for different blend compositions. The flexural and impact properties, dynamic mechanical behavior, thermal transitions, thermal stability, phase, and fracture morphology are presented. Thermogravimetric analysis shows that the thermal stability of blends diminished by the increasing amount of TPS. It is revealed from differential scanning calorimetry results that the glass transition temperature ( T g ) and melting temperature ( T m ) are negatively affected by the NOR. Flexural and impact tests show that the mechanical properties are deteriorated by NOR. The TPS phase size becomes coarser with NOR as observed from scanning electron microscopy. It is concluded that the properties of PLA/TPS blends are very sensitive to NOR and the PLA/TPS concentration as well.
Core‐shell magnetic nanoparticles have received significant attention recently and are actively investigated owing to their large potential for a variety of applications. In this study, the synthesis and characterization properties of magnetite @ polyrhodanine (Fe 3 O 4 @ PRh) core–shell nanoparticles have been investigated. To monitor the morphology, size, structure, thermal stability, and magnetic properties of nanoparticles, scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, thermogravimetic analysis, and vibrating sample magnetometer were carried out. The results indicate that a thin film of polyrhodanine was coated on the surface of Fe 3 O 4 nanoparticles. The coated shell of polyrhodanine can protect the Fe 3 O 4 cores from being oxidized. Also, the results presented the crystalline, small size, and high magnetization value for the core–shell structure.
The forward bias current conduction mechanisms of Au/PVC + TCNQ/p-Si structures have been investigated in a wide temperature range of 120-420K for various applied bias voltage. The analysis of the main electrical parameters such as zero-bias barrier height (BH) (phi(Bo)), ideality factor (n), and interface states (N-ss) was found strongly dependent on temperature and voltage. The obtained results show that, while phi(Bo) increases, n decreases with increasing temperature. The plot of phi(app) versus q/2kT was drawn to show a Gaussian distribution (GD) of the BHs, and this plot shows two distinct linear regions. The phi(Bo) and standard deviation (sigma(s)) values were found from the slope and intercept of these plots for two regions as 1.16 eV and 0.161V for the first region and 0.71 eV and 0.093V for the second region, respectively. Such behavior is typical of a double GD (DGD) of the BHs due to the BH inhomogeneities at the metal-semiconductor interface. The slope and intercept of the modified (ln(I-0/T-2) - q(2)sigma(2)(0)/2k(2)T(2)) versus q/kT plot gives the and phi(Bo) and effective Richardson constant (A*) as 1.16 and 0.76 eV and 36.7 and 83.8 A/cm(2)K(2), respectively. The value of the A* (36.7 A/cm(2) K-2) is very close to the theoretical value of 32 A/cm(2) K-2 for p-Si. In addition, to interrupt the voltage-dependent activation energy, the ln(I-s/T-2) versus q/kT plot was drawn in the voltage range of 0-0.3V in 0.05V steps. All of experimental results confirmed that the BH or E-a values depend on the temperature as well as bias voltages.