Effect of drawing temperature on mesomorphic transitions of oriented poly(ethylene terephthalate) fibers exposed to supercritical CO2

Samples of partially oriented yarn (POY) PET fibers were uniaxially drawn at 23, 68 °C (cold drawing) and 100 °C (hot drawing) and then exposed to the supercritical carbon dioxide (scCO₂) without tension at a temperature of 80 °C and a pressure of 220 bar. The effect of drawing temperature on the evolution of mesomorphic phases and the structural changes under exposure to scCO₂ were investigated by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and wide-angle X-ray diffraction. The orientation factor of the samples was measured using a polarizing microscope. A good correlation was obtained between the results of various analyses. The results illustrate that evolution of structure strongly depends on both process temperature and post-treatment by scCO₂ exposure. The latter process leads to plasticization and reduced glass transition temperature of the samples, thus inducing structural changes in the fibers.     

Effects of Pb-Doping on Phase Structural and Optical Properties of CdZnS Nano-Powders

Cadmium zinc lead sulfide [Cd0.8（Zn1-x7,Pbx）0.2S] nano-powders were prepared by an improved coprecipitation method. The effect of Pb2＋ concentration at 500℃ on the phase and crystalline structure of the Cd0.8（Zn1-x7,Pbx）0.2S powders were investigated by X-ray diffraction （XRD）. According to the transmission electron microscopy （TEM） images, the particles size are in the range of 58 nm to 72 nm. In addition, optical band gap energy and optical constants of nano-powders were determined using the ultraviolet （UV） spectrum, Fournier transform infrared spectroscopy （FTIR）, and Kramers-Kronig analysis, respectively. We calculate the refractive index n, extinction coefficient k, and dielectric function t as a function of the wavenumber. The experiment results demonstrate that the amount of Pb＋2 has been playing an increasingly important role on optical properties of CZPS nanocrystals.     

Bi-objective resource constrained project scheduling problem with makespan and net present value criteria: two meta-heuristic algorithms

Traditionally, the model of a resource-constrained project-scheduling problem (RCPSP) contains a single objective function of either minimizing project makespan or maximizing project net present value (NPV). In order to be more realistic, in this paper, two multi-objective meta-heuristic algorithms of multi-population and two-phase sub-population genetic algorithms are proposed to find Pareto front solutions that minimize the project makespan and maximize the project NPV of a RCPSP, simultaneously. Based on standard test problems constructed by the RanGen project generator, a comprehensive computational experiment is performed, where response surface methodology is employed to tune the parameters of the algorithms. The metaheuristics are computationally compared, the results are analyzed, and conclusions are given at the end.     

Effect of gas diffusion electrode pre-treatment by ultrasonic bath cleaning technique on proton exchange membrane fuel cell performance

Ultrasonic bath cleaning technique was successfully applied for the pre-treatment of the gas diffusion electrode (GDE) before membrane-electrode assembly (MEA). The results show that ultrasonic bath pre-treatment significantly improves MEA performance in all current density regions, especially at the high current density region. This technique also reduces the time of the MEA conditioning, at least 30%. Electrochemical impedance spectroscopy (EIS) results demonstrate that pre-treatment of GDEs by ultrasonic bath technique leads to a decrease in the cell impedance especially in the ohmic resistance, which is very well due to the GDE cleaning process.     

Greener synthesis and medical applications of metal oxide nanoparticles

Over the past decade, the subject of “greener chemistry" and chemical processes has been emphasized. The “greener chemistry” improves environmental efficiency in reducing the consumption of resources and energy and achieving a stable economic development of the environment. Nanotechnology is investigating nanoscale materials that have applications in the area of biotechnology and nanomedicine alongside several other significant applications such as cosmetics, drug delivery, and biosensors. The different shapes and sizes of nanoparticles can be synthesized with physical, chemical, or biological methods. The tendency to produce nanomaterials, especially metal oxides, and use them, is increasing because of their exciting properties in the nanoscale. However, metal oxide nanoparticles produced by chemical methods have significant concerns due to hazardous and toxic chemicals and their environmental damage. The production of metal oxide nanoparticles using the principles of greener chemistry has found a special place in research. Increased awareness of greener chemistry and biological processes has necessitated using environmentally friendly methods for the production of non-toxic nanomaterials. Plants and polymeric materials as renewable and inexpensive sources have received particular attention to prepare nano biomaterials. The use of plants to synthesize metal oxide nanoparticles because of the non-use toxic pollutants is one of the environmentally friendly methods, and that's why this type of synthesis is called greener synthesis. In this review, we exhibit a total sight of greener synthesis methods for producing metal oxide nanoparticles and their medical applications.     

Preparation and characterization of conductive and antibacterial polyacrylonitrile terpolymer yarns produced by one-step organic coating

In this research work, electrically conductive PAN yarns were produced by coating with copper sulfide and, afterward, evaluated. PAN yarns were treated in a bath containing divalent copper ions, a reducing agent, which is capable of reducing the divalent copper ions to monovalent copper ions and a sulfur-containing compound for sulfidation of copper ions attached to the samples. A pH controlling agent (an organic acid) may be used to enhance the quality of copper sulfide adsorbed by the yarns which, in turn, improves the electrical conductivity of the samples. Using the results obtained from this study, we had to develop appropriate suitable formulation for application and optimization of copper sulfide coating of PAN-based materials. The copper coating of PAN yarns resulted in a reduction of electrical resistivity to 1 × 10¹⁰ that of an almost infinite resistance for the untreated yarns. The influence of linear density of the samples on the electrical conductivity and the mechanical properties of the copper-coated PAN yarns were evaluated. Copper-coated PAN yarns displayed very high light fastness and a washing fastness property to multiple washes in terms of electrical conductivity changes. The coating of PAN yarns with copper sulfide confers good antibacterial performance and the antibacterial activity of coated yarns against S. aureus after eight home laundering cycles was not significantly reduced. Results showed that coating PAN samples with copper sulfide can produce samples with good antistatic and antibacterial properties while, at the same time, retaining touch, washability, and other physical properties of the starting samples.     

The occurrence,fate, and distribution of natural and synthetic hormones in different types of wastewater treatment plants in Iran

Over the past few years, the presence of steroid estrogens in the environment has become a major concern. In this study, the concentrations of estrone(E1), 17β-estradiol(E2), and 17α-ethinyl estradiol(EE2) were measured in some wastewater treatment plants(WWTPs) in Iran. These samples were collected from the municipal, rural,livestock, commercial, and hospital WWTPs, extracted by dispersive liquid–liquid micro extraction(DLLME)technique, derivatized, and detected by GC/MS. In these treatment plants, various processes including conventional activated sludge(CAS), aerated lagoon(AL), moving bed biofilm reactor(MBBR), and activated sludge with wetland(AS + WL) are used. The highest concentration of hormones was observed in the influents and effluents of livestock, municipal, commercial, and hospital WWTPs, respectively. The maximum elimination rate was obtained in MBBR followed by AS + WL, CAS and AL. The biodegradation and adsorption rates along with adsorption coefficients of lg kdand lg kocwere measured for all target compounds.     

Development and thermal performance of wood-HPDE- PCM nanocapsule floor for passive cooling in building

Cooling demand in the building sector is growing rapidly; thermal energy storage systems using phase change materials (PCM) can be a very useful way to improve the building thermal performance. This work shows the benefits of PCM when incorporated in wood fiber-polymer composite as floor cooling system using nano-encapsulated PCMs. The wood-plastic-NPCM composites were produced using compression molding process and its mechanical and thermal properties were investigated. Two dynamic simulators were employed to investigate synthesized composites thermal performance. Increasing NPCM content in WPC showed that the fluctuations of the simulator temperature was decreased while the heat fluxes through the floor was increased. The variations of ambient maximum temperature have little effect on the air temperature of the simulator with 40% PCM which indicates that the amount of PCM was enough for studied environmental condition. Field experiments were performed using two medium-scale test houses located on Tehran-Iran. It can be concluded that using NPCM helps to reduce heating and cooling demand. Moreover, the natural night ventilation by opening windows reduced the number of hours that the temperature is above 23°C from 499 h/year in case1 (without opening) to 255 h/year in case 2(with opening). This means that natural night ventilation could help reduce the overheating period to about 50% with the use of NPCM.