فصلنامه مواد پیشرفته و پوشش های نوین
پیاپی 31 (زمستان 1398)

Polyacrylonitrile (PAN) Nanofibers and Multi-walled carbon nanotubes (MWCNTs) were fabricated by using the needleless and conventional electrospinning. CNT-Activated carbon nanofibers prepared by stabilization, carbonization, and activation processes and evaluated by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) and BET method. SEM analysis showed that by increasing the concentration of MWCNT the average nanofibers diameter changed for pure and activated nanofibers and electrical conductivity and viscosity of nanofibers were increased. DSC plots showed different enthalpy and cyclization degree of embedding of MWCNTs in PAN nanofibers. Also, the generated nanofibers from disk shape nozzles were finer with a narrower distribution than produced by the cylinder type. The nanofibers produced by needleless method provided larger diameter nanofibers with less uniformity and higher production rate comparing to the conventional method. FTIR Spectroscopy and XRD studies showed that PAN-MWCNT nanofibers exhibited higher crystallinity compared to PAN nanofibers and the crystallite size was decreased. The XRD analysis revealed that different diffraction angles (2θ) in stabilized and carbonized PAN-MWCNT nanofibers that shifted to the smaller one by increasing of carbon nanotubes contents. The BET results indicated the improvement of porosity in MWCNT-ACNF nanofibers comparing to ACNF nanofibers and diameter of pore was decreased.

In order to enhance the water flux and rejection of polyethersulfone (PES) membranes for membrane distillation process (MDP), we have developed a new PES membrane using a oleic acid as a hydrophobic agent. The synthesis membranes are fabricated via the phase inversion procedure and we examined the effects of oleic acid on hydrophobicity, porosity, surface roughness, morphology and MDP performance. For the membrane characterization, the produced membranes were characterized by contact angle, FTIR spectroscopy, field emission scanning electron microscopy, atomic force microscopy and porosity measurements. The outcomes demonstrated that the presence of the small amount of oleic acid in the membrane has led to an increment in the membrane hydrophobicity and porosity, and also improves the water flux and rejection of the MDP. The increment amount of oleic acid not only have no positive efficacy on the membrane performance, but can also reduce the MDP efficiency. In some areas, the excess concentration of oleic acid prevents the crossing of vapors evaporation through the cavities, so it will diminish the MDP flux.

In this research, micro- and nanocapsules of melamine-formaldehyde-pentaerythritol tetrakis successfully synthesized. These micro/nanocapsules are pH-sensitive, the capsule wall degrades in the alkaline environment and releases its core content. The purpose of this paper is to investigate the two parameters, the surface tension of the capsule core material and the effect of shear stress on the encapsulation process as parameters affecting the size of the capsules. The size, morphology, and behavior of the capsules were investigated by scanning electron microscopy (SEM). By using Measurement software, the size of the capsules was obtained. Then the distribution and histogram were plotted with using SPSS software. The size of the microcapsules was 5.5 μm and the nanocapsules in three different synthetic conditions were: 225, 312, 250 nm. Thermogravimetric analysis was also used to evaluate and compare the core to shell ratio of the micro- and nanocapsules. The results determined that by changing the size of the capsules, the core to shell ratio, the optimum conditions to achieve smooth morphology and release behavior changed.

In this study, due to the poor corrosion resistance of Mg alloys in aquatic environments, TiO2 ceramic coating applied by the magnetron sputtering technique to enhance the corrosion resistance and biocompatibility of AZ91D alloy. The Microstructural studies by field emission scanning electron microscopy (FESEM) and X-Ray diffraction (XRD) analysis showed that the coating formed uniformly with semi spherical morphology containing TiO2, Mg2TiO4 and MgTi2O5 spinels, so that above of the substrate was Ti diffiusion affected. The polarization corrosion test in simulated body fluid (SBF) solution showed that applying the coating by reducing the corrosion current by about 100 times improves the corrosion resistance of the magnesium substrate so that MTT results show that density and number of cells on the coated sample is higher than substrate without coating due to cell joint stronger. The viability of MG67 cells on the samples increased from 77% in the substrate to 89% in the coated sample.

In this study, Co-P-nanoAl2O3 composite coating was deposited onto AISI 430 substrate using direct current electric deposition technique. The microstructure and corrosion behavior of the fabricated coatings at different current densities (10 mA/cm2, 15 mA/cm2, 20 mA/cm2, 25 mA/cm2) were studied. In order to investigate the morphology of the composite coating and the analysis of the coated samples, scanning electron microscope (SEM) and EDS were used, respectively. The results showed, the composite coating formed at the current density of 15 mA/cm2, is completely uniform and continuous. In order to investigate the corrosion resistance, potentiodynamic polarization experiment was applied in aqueous solution of 3.5% NaCl on coated and uncoated AISI 430 samples. The results of Tafel and electrochemical polarization tests were also correlated with microscopic images and showed that the coated specimen at the current density of 15 mA/cm2 had the maximum corrosion resistance.

Non-isothermal crystallization kinetics of Polypropylene (PP) melt as a continuous phase of thermoplastic elastomers (TPEs) based on polypropylene / polybutadiene rubber (TPE1: PBR/PP) and polybutadiene rubber / acrylated-polybutadiene compatibizer / polypropylene (TPE2: PBR/ Ac-PBR /PP) as well as their the corresponding thermoplastic vulcanizate(TPV) samples (TPV1 and TPV2) were investigated using Ozawa's kinetic model. The results of the DSC data and the Ozawa model show that the Ac-PBR compatibilizer, increases the onset and the final temperature of crystallization and make the crystallization region narrower. Dynamic vulcanization also results in shifting the onset and the final crystallization temperatures to lower values. The temperature (Tc) and the half-time for crystallization (t_(1/2)) of all blends decrease with increasing cooling rate. The crystallization rate constant and the ozawa model exponent (m) for four different temperatures (110, 115, 120 and 130 C °) were obtained by linear regression method. The exponent of ozawa model changes with increasing degree of molten/crystal conversion. While the “m” value for the pure PP varies from (1.4 at 110℃) to (3 at 120 ℃), these values for TPE1 range from (1.7 at 110℃) to (3.3 at 120℃) and for TPE2 are higher and varies from (1.1 at 110℃) to (4 at 125℃). The maximum value of the crystallization rate constant (KC ) for all blends occurs at approximately 50% relative crystallinity; the highest crystallization rate constants obtains for TPE2.

In this study, the combination of chemical, biological and membrane processes was investigated for landfill leachate treatment. In order to reduce the contamination level, the chemical coagulation process was used by coagulants such as aluminum sulfate and poly aluminum chloride. Also, the optimum pH range and concentration of the coagulant were determine following by the biological process of activated sludge. Finally, the leachate separation of the aerobic bioreactor was carried out by FO-MBR membrane process and the effect of powder activated carbon adsorbent was studied on this process. The results showed that the amount of COD in leachate decreased by 48% after pretreatment using coagulants (optimum concentration of 1 g / l and pH = 8). Then, the COD removal rate reached to 24% by using the aerobic activated sludge process under optimum aeration conditions, F / M = 0.312 COD / MLSS.d ratio and 24h hydraulic retention time. In the last section, the usage of synthesized cellulose membrane in form of the frame and plate modules immersed in the aerobic bioreactor of the FO-MBR process, was examined. Furthermore, 2 g / l powder activated carbon adsorbent was used to improve the performance of this process and the reduction of membrane fouling, which improved the performance of the landfill leachate wastewater treatment system by increasing the COD removal rate from 74% to 92% as well as the changes in MLSS concentration during the 4-day FO-MBR process increased by 24% compared to the absence of adsorbent.