The morphology and gas‐separation performance of membranes comprising multiwalled carbon nanotubes/polysulfone–Kapton

The development of desirable chemical structures and properties in nanocomposite membranes involve steps that need to be carefully designed and controlled. This study investigates the effect of adding multiwalled nanotubes (MWNT) on a Kapton–polysulfone composite membrane on the separation of various gas pairs. Data from Fourier transform infrared spectroscopy and scanning electron microscopy confirm that some studies on the Kapton–polysulfone blends are miscible on the molecular level. In fact, the results indicate that the chemical structure of the blend components, the Kapton–polysulfone blend compositions, and the carbon nanotubes play important roles in the transport properties of the resulting membranes. The results of gas permeability tests for the synthesized membranes specify that using a higher percentage of polysulfone (PSF) in blends resulted in membranes with higher ideal selectivity and permeability. Although the addition of nanotubes can increase the permeability of gases, it decreases gas pair selectivity. Furthermore, these outcomes suggest that Kapton–PSF membranes with higher PSF are special candidates for CO₂/CH₄ separation compared to CO₂/N₂ and O₂/N₂ separation. High CH₄, CO₂, N₂, and O₂ permeabilities of 0.35, 6.2, 0.34, and 1.15 bar, respectively, are obtained for the developed Kapton–PSF membranes (25/75%) with the highest percentage of carbon nanotubes (8%), whose values are the highest among all the resultant membranes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43839.     

Microstructure characterization,mechanical properties,compressibility and sintering behavior of Al-B4C nanocomposite powders

In the present work, Al-xB₄C nanocomposite (x = 0, 1, 2, 3, 4 and 5 in wt%, having the average B₄C size of 50 nm) were prepared using a high-energy ball mill. The milling times up to 16 h were applied. Then, the microstructural evolutions, mechanical properties, compressibility and sintering behavior of nanocomposites were investigated. The changes in powders morphology and microstructure during the milling process were characterized by laser diffraction particle size analyzer (LDA), SEM, XRD, EDS and TEM techniques. Compressibility and sintering behavior of milled powders compacted under different pressures (100–900 MPa) and at different sintering temperatures (500, 550 and 600 °C) were also studied. The pressing behavior of the nanocomposites was analyzed using linear compaction equations developed by Heckel, Panelli-Filho and Ge. The results showed the significant effects of B₄C amounts and sintering temperatures on the compressibility and sintering behavior of nanocomposites. The increase in the B₄C amount led to a decrease in both the compressibility rate and the sinterability of specimens. The maximum compression strength of 265 MPa and Vickers hardness of 165 VHN were obtained for Al-5 wt.% B₄C nanocomposite milled for 16 h followed by sintering at 600 °C.     

Comparison of prolonged antibacterial activity and release profile of propolis‐incorporated PVA nanofibrous mat,microfibrous mat,and film

Propolis as a natural antibacterial agent was incorporated into the poly(vinyl alcohol) (PVA) in different forms of nanofiber, microfiber, and film. The successful fabrication of uniform nanofibers with 85–314 nm diameters and microfibers with 2.02 μm diameter was proved by scanning electron microscopy. Structural analysis by Fourier transform infrared spectroscopy and X‐ray diffraction and swelling properties confirmed the formation PVA hydrogel and its H‐bonding to the propolis. Evaluation and comparison of antimicrobial properties of produced samples against Staphylococcus aureus strains revealed that nanofiber mat with 19 mm inhibition zone has 11.76 and 26.67% higher efficiency against bacteria than microfiber mat and film with 17 and 15 mm inhibition zone, respectively. Nanofibrous mat showed sustained release during 96 h by maintaining full antibacterial activity up to 51 h which is of great importance in burn wounds. These results confirm the advanced performance of natural propolis in the form of nanofiber substrate as wound dressing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45794.     

Modeling and Failure Analysis of a Broken Railway Axle: Effects of Surface Defects and Inclusions

In the present work, the fatigue behavior of an axle was analyzed using modeling and experimental approaches. A failed axle was used for experimental studies. The experimental results were then analyzed in order to model and predict the fatigue life of axle. The three-dimensional finite element analysis was used to simulate the fatigue behavior of axle. The growth of a machining defect, 2 μm initial crack length, was simulated versus applied cycles. The changes in the stress intensity factor as a function of crack length were modeled as well. The model predicted that after about 5 × 10⁸ cycles there was an abrupt increase in the crack length, reaching a critical value of about 65 mm at around N _f = 5 × 10⁹ cycles, indicating that the longer the crack, the higher its growth will be. The experimental results were then compared with the modeling predictions. It is shown that the latter are in a good agreement with the former. The results obtained in this study do give a basis for evaluation of single scratch or notch produced by improper machining.     

Producing Ultrafine Grain Al6061 Alloy by Accumulative Back Extrusion Process

Accumulative back extrusion (ABE) is a kind of severe plastic deformation process to refine the microstructure, resulting in significant improvement in mechanical properties. In the present study, AA6061-T6 alloy was subjected to a newly designed ABE process at room temperature. One cycle of ABE was employed to the workpiece. The microstructural evolution was then characterized using optical microscopy and transmission electron microscopy (TEM) techniques. The results show that after one cycle of ABE, significant grain refinement was achieved. This led to the formation of ultrafine grains of smaller than 1???m. Besides, there was about a two-fold increase in the hardness, increasing from approximately 88 Hv to 155-160 Hv after only one cycle of ABE.