دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و سوم شماره 4 (پیاپی 168، مهر و آبان 1399)

Hypothesis:

 Nowadays, nanofiltration membranes are used extensively in desalination and water treatment, but some major drawbacks in the desalination such as low flux and rejection should be handled through application of modified nanomaterials. A number of research works have been done in this field but the importance of the subject makes more studies in this field indispensable.

Thin film nanocomposite membranes containing titanium oxide nanotubes and modified titanium oxide nanotubes were evaluated in this study which after synthesis of the nanotubes, their inner surface was modified and after synthesizing the membranes, the membranes’ water permeability and rejection of the monovalent and divalent ions were measured. Furthermore, Fourier transform infrared spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) tests were used to study the neat and modified nanotubes. Field emission scanning electron microscopy (FE-SEM) analysis was used to study the morphology and structure of these thin film membranes.

The performance of polyamide thin film membranes was evaluated by pure water permeation test, contact angle test, permeation flux of the feed and rejection of sodium and copper ions. Due to the hydrophilicity of the nanotubes and formation of small pore on the membrane surface, the maximum pure water flux (26.5 L/m2h) was obtained for the membrane containing 0.05% (wt) unmodified nanotube; an increase of 73.2% compared to its neat membrane. Due to the reduced diameter of the modified nanotubes and providing sufficient energy barrier for the salts to be rejected, the maximum sodium ion rejection (93.11%) was obtained for the membrane containing 0.2% (wt) modified nanotubes.

Hypothesis: 

The present study attempts to develop application of nanofibers containing nanocluster {Mo132} in respiratory masks and absorbent clothing.

Nanofibers polyacrylonitrile-{Mo132} with an average diameter of about 150 nm was produced through electrospinning process which was optimized by experimental design methods such as Taguchi and Central Composite Design (CCD) methods. The morphology and chemical structure of nanofibers were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) techniques. The presence of nanocluster {Mo132} in the nanofiber structure was confirmed by UV-Vis spectroscopy. The nanofiber diameter and number of nodes were determined by image processing software. The final nanofilter was prepared based on the optimized electrospinning conditions and its performance was tested.

The optimized conditions of the elecrospinning process are 10% (wt) concentration, 16 kV voltage, and 10 cm distance. The addition of {Mo132} to the polyacrylonitrile nanofibers improved the properties of nanofibers and their particles' adsorbtion performance. Investigation of nanofiber properties showed that nanoparticles were well distributed with good adhesion on the polymer surface. High adsorption power, fast synthetic method, low cost, biocompatibility and non-toxicity are advantages of our nanofiber structure. The ultimate goal of this research is to design and produce high-performance nanofibers to adsorb suspended particles and chemical pollutants used by police and other members of community. These nanofibers at a flow rate of 5 L/min showed an efficiency of about 93%, a pressure reduction of almost zero and a quality factor of about 4.5, which in the laboratory conditions of the present study is introduced as a particle control medium.

Hypothesis: 

Organogels are hydrophobic macromolecular networks with ability to absorb and retain organic solvents. They have been used in various applications, e.g., production of disinfectant hygienic gels used in medicine and public health. The present paper is a preliminary report on the conversion of common epoxy resin (DGEBA) into a new superabsorbent organogel containing functional groups of furan, carbamate, and triazole.

The organogel was synthesized through a four-step strategy from epoxy resin and furfuryl alcohol. The furfurylated epoxy resin was converted to an isocyanate-terminated compound that then converted into a propargyl-terminated intermediate. The final product was produced by 1,3-dipolar cycloaddition polymerization reaction of a propargylated compound and a diazide compound prepared from epichlorohydrin. The intermediate compounds and the final product were characterized by Fourier transform infrared (FTIR) spectroscopy. The final product was characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Rheological behavior in solvent N-methyl-2-pyrrolidone (NMP) was preliminarily studied and swelling capacity of the organogel was determined in various solvents.

A novel polymeric organogel was synthesized without using a particular crosslinker. Its dried particles were found to have porosity with a pore diameter of ~680 nm. The organogel showed increased swelling capacity with dropping of solvent viscosity and increasing of solvent polarity. The high solvent uptake and storage capacity by this organogel has supported it as a superabsorbent organogelator. Its swelling capacity was determined in the solvents to be in order: ethylene glycol < chloroform < ethanol < acetonitrile < dimethylformamide < dimethylacetamide < dimethylsulfoxide < NMP. For instance, each gram of the organogel can absorb and gelate ~145 g ethanol, or ~1853 g NMP, within ~1 h. The super-swelling behavior of this solvent-retaining network was preliminarily attributed to a combination of limited crosslinkages as well as some polymer-polymer and polymer-solvent supramolecular interactions. The presence of 1,2,3-triazole groups is also expected to induce antibacterial properties in this organogel.

Hypothesis: 

The effects of four accelerators 2,4,6-tris(dimethyl aminomethyl) phenol (DMP30), 2-methylimidazole (2MI), 2-phenylimidazole (2PhI) and carbonyldiimidazole (CDI) at 0.6 and 1 phr contents on the curing behavior of a diglycidyl ether of bisphenol A epoxy resin and dicyandiamide (dicy), a  solid curing agent, was investigated. Obviously, by changing the type and amount of accelerator, the reactivity and curing behavior of the epoxy/daisy system can be controlled.

Measuring the viscosity build-up versus time, gelation time measurement at 110, 120 and 130°C, tack, non-isothermal differential scanning calorimetry (DSC) and glass transition temperature characterization were used to study the reactivity and curing behavior of epoxy/dicy system.

The CDI accelerator at 0.6 phr content showed the highest pot-life. The pot-life of formulations decreased by increasing the amount of accelerator particularly when CDI was used. This difference in pot-life was lower for 2PhI and was not changed for 2MI. Gel-time data showed that the reactivity of different accelerators at high temperature was in order: 2MI > DMP30 > CDI > 2PhI. DSC test results showed that by increasing the amount of accelerator the heat of reaction increased, curing profile became sharp and glass transition temperature remarkably decreased. The broadest curing profile of 14°C also was seen for CDI. The DSC results showed that the reactivity of different accelerators was in order: 2MI > CDI > DMP30 > 2PhI. In other words, 2PhI showed the lowest activity and the sharpest curing profile and 2MI showed the highest activity with the wide curing behavior. It seems that the CDI accelerator at 0.6 phr content would be the best accelerator regarding the highest pot-life at room temperature, high curing rate and maximum Tg.

Hypothesis:

 A three-component material model based on the combination of three hyper-viscoelastic equations,eight-chain constitutive equation, Bergstrom-Boyce relation and Ogden-Roxburgh stress softening model (Mullins effect)  was selected to study the mechanical behavior of various SBR/CB (carbon black) filled rubber compounds.

Three rubber compounds based on E-SBR were prepared using different carbon black contents (20, 40 and 60 phr) and cured into rubber sheets. The rubber test specimens (ASTM D412 C) were then cut and underwent cyclic tensile tests at two extension rates of 500 and 100 mm/min. In order to show the stress softening behavior, three cycles were selected in a way that the maximum stretch at each cycle was increased consecutively. The volumetric tests were also carried out to determine the bulk modulus of the samples. The stress-strain data were calibrated using MCalibration software in which three different optimization algorithms were utilized to compute the parameters of the models.  

Very good agreements were found between experimentally measured and predicted stress-strain data for low and medium CB filled compounds. However, for highly filled compounds there were some discrepancies at higher extensions, which may be due to the formation of a strong filler network and percolation threshold. This indicates that we may need another modeling component to be incorporated into main model for the description of the mechanical behavior of the filler-filler network itself. Moreover, it is found that there is good correlation between variation of the model parameters and filler content.

Hypothesis: 

Fiber metal laminates (FMLs) are made up of fibrous composites layers and metal sheets that are stacked alternatively and joined together with polymeric resin. The purpose of this study is to investigate the flexural properties of environmental friendly and cost-effective fiber metal laminates. In recent decades, natural fiber composites have become popular due to their recyclability, renewability and low cost, and their applications in various industries are growing. Combining natural composites with aluminum layers and manufacturing fiber metal laminates led to improved mechanical properties and increased resistance to environmental factors such as moisture, heat and sunlight.

Jute fiber-based fiber metal laminates and composites containing jute fibers were made using epoxy and vinyl ester resins by hand lay-up method. The flexural properties of composites and fiber metal laminates were investigated using a three-point bending test. After performing mechanical tests, scanning electron microscopy images were prepared to check the fracture surface. For comparison, similar samples were made and tested using glass fibers.

The results of the tests showed that the use of aluminum layers along with composites containing jute fibers increases the flexural modulus and the ultimate strength of the samples. Samples made with vinyl ester resin had better bending properties than epoxy matrix composites due to proper bonding between jute fibers and vinyl ester. The vinyl ester resin could penetrate into the void space inside the jute fibers. In addition, scanning electron microscopy images showed that due to the rough surface and special form of jute fibers, better adhesion was created between the jute fibers with vinyl ester resin and epoxy in comparison with glass fibers.