Iranian Journal of Polymer Science and Technology
Year:2017 | Volume:30 | Issue:4 |Papers Count:7

In hollow fiber membrane fabrication process, a number of parameters such as dope compositions, flow rate, bore fluid type, flow rate, and air gap affect the structure and characteristics of membrane. Spinneret dimension as the effective parameter on the properties of a polyetherimide (PEI) hollow fiber membrane and its performance in membrane contactor was examined. A polymer solution was used for fabrication of two PEI membranes under the same fabrication conditions, with variable-spinneret dimensions. Through the addition of water as a non-solvent into the polymer solution, the thermodynamic stability of the solution decreased and the phase-inversion process increased, and therefore, the effects of chain reorientation or chain relaxation on the structure of hollow fiber membrane were minimized. The fabricated membranes were characterized by different tests and their performance in membrane contractor and in CO2 absorption test was evaluated in two events: 1-distilled water in lumen side and pure CO2 in shell side and 2-distilled water in shell side and pure CO2 in lumen side. The results showed that smaller dimension of spinneret enhanced the properties of membrane such as 250% increase in mean pore size and 300% increase in gas permeation rate. In addition, the smaller dimension of the spinneret formed more pores in the structure of membrane that could be related to the shorter diffusion distance of the coagulant. Furthermore, the CO2 absorption flux improved by 150%.

Shape memory polymers (SMPs) based on thermoplastic polyurethane/ poly(vinylchloride)/ graphene nanoplatelet (TPU/PVC/GNP) were produced using solution method in tetrahydrofuran (THF) solvent. The blend ratio of all samples was 60/40 (w/w) and the concentrations for both neat and functionalized GNPs were 0. 5, 1 and 2 wt%. Functionalization was accomplished using polycaprolactam in order to obtain better dispersion of GNP particles and inhibit their agglomeration. At first, nanoparticles were treated with nitric acid and in the next step acylation was done using thionyl cholride, and finally polycaprolactam was grafted on the surface of nanoplatelet graphene. The functionaliztion reactions were tracked using Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA) and ultraviolet chromatography. The results of these tests showed that the reaction was successfully carried out and polycaprolactam was grafted on the surface of GNP. The presence of new peaks at 1165 and 1720 cm-1 and 10 and 30 wt% weight losses in the temperature range of 250-500° C for modified nanoparticles revealed the successful modification reactions of functionalized particles. Morphology of the samples was studied using scanning electron microscopy (SEM) and the results depicted a fine dispersion for the samples containing graphene nanoplatelet in comparison to the samples containing unfunctionalized nanoparticles. Shape memory induction and the measurement of shape fixity and shape recovery were done using a thermal-mechanical analyzer (TMA). The results showed that the shape fixity and shape recovery increased from 76. 8 to 83% and from 81. 5 to 86. 7%, respectively, for the samples containing modified GNP resulted from a better dispersion of the nanoparticles.

Synergistic effects of organic montmorillonite (OMMT) and ammonium polyphosphate (APP) on flame retardant enhancement of high density polyethylene/walnut shell powder (HDPE/WSP) biocomposites were investigated using limiting oxygen index (LOI), thermogravimetric analysis (TGA) and cone calorimetry test. The LOI data showed that OMMT had a synergistic flame retardant effect with APP and the LOI value reached 28% for the samples containing 9 phr OMMT and 15 phr APP. The TGA and cone calorimeter data demonstrated that the incorporation of OMMT and APP greatly enhanced the thermal stability of HDPE/WSP/OMMT/APP system. Based on the results of thermogravimetric analysis all samples decomposed in two steps. The addition of OMMT and APP also catalyzed the first stage of decomposition, and produced more char residual. The second decomposition stage occurred at higher temperature. This increase in temperature could be attributed to the presence of OMMT and APP which produced a charred layer and prevented the heat and mass transfer from melting polymer to the surface, leading to improved fire resistance of the composite. The addition of OMMT and APP and subsequent formation of charred layer reduced the HRR and MLR values. Microcellular HDPE/WSP biocomposite foams were prepared with a batch foaming apparatus using nitrogen as blowing agent. In the microcellular biocomposites, the relative density and cell size both were a strong function of the APP and OMMT contents and processing conditions. With increasing the APP content, the cell size increased and the relative density fell first and then increased. The addition of OMMT resulted in smaller cell size and higher relative density. The relative density decreased with increasing the saturation temperature and pressure.

Nowadays, the filtration process is increasingly used in various areas such as water purification, food industries, air dust filtration systems and other separation applications. In this work, HDPE microporous filters were fabricated under different pressures and processing durations using sintering process and then characterized by different techniques. It was expected that the microstructure and mechanical properties of the filters could be controlled by changing the fabrication parameters such as temperature, pressure, processing time and also by changing the properties of resin such as powder shape, particle size and rheological properties. In the first step, using the DSC, MFI, rheological and optical microscopy tests, a most suitable polymer powder was chosen in sintering process. The sintering temperature was fixed in the vicinity of melting temperature of the HDPE powder, based on DSC result. In order to evaluate the mechanical properties and porosity of the samples, the results obtained from the shear punch test, acetone drop permeability, gas permeability, transition optical microscopy and SEM were used, and then the effect of pressure and processing time parameters on the characteristics of the product was studied. Finally, it was concluded that it was possible to make microporous filters with suitable mechanical properties, using sintering process at controlled pressure and temperature conditions. It was observed that, by increasing the time and pressure, on the one hand the mechanical properties of the products increased, and on the other hand, their porosity and the gas permeability of the vents decreased.

In situ spectroelectrochemistry is utilized as a powerful tool to analyze the development of conductive polymer-based nanocomposite materials. Polymer nanocomposites were obtained based on 2-aminophenol, in separately present nano titanium dioxide and zinc oxide, using gold (Au) and indium tin oxide glass electrodes (ITO). The poly(2-aminophenol) and 2-aminophenol-titanium dioxide and zinc oxide polymer nanocomposite films were characterized by cyclic voltammetry (CV) method, in situ conductivity measurements (resistivity), in situ ultra violet-visible (UV-vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). During polymer growth on the electrode surfaces and with in situ electropolymerization method, the behaviors and different redox electrode potential values were observed for 2-aminophenol-titanium dioxide and 2-aminophenol zinc oxide polymer nanocomposite films in comparison with poly(2-aminophenol). The same treatments were performed on poly(2-aminophenol) and nanocomposite polymers in blank solutions. In situ spectroelectrochemical properties and in situ conductivity of material products were investigated and compared. In situ UV-vis spectroscopy behaviors were observed for polymer nanocomposites under different applied electrode potentials, which were indications of various optical properties. The results of in situ conductivity of poly(2-aminophenol) in sulfuric acid medium and supporting electrolytes in the presence of nanoparticles were indications of improved electrical conductivity. The structures and morphology of nano oxide metals in poly(2-aminophenol) films were confirmed by FTIR spectroscopy, scanning electron microscopy and transmission electron microscopy images. Finally, the presence of nanoparticles in polymer was also confirmed by EDX analysis.

An electroactive polyurethane coating was prepared through ring opening reaction of epoxy-terminated castor oil-based polyurethane prepolymers with an appropriate amount of an amine-terminated aniline trimer oligomer (AT). A non-electroactive polyurethane coating was prepared by replacing AT with 1, 6-hexamethylene diamine (HDA) as a curing agent. The chemical structure of prepared coatings was fully characterized by a conventional spectroscopic method and their physicochemical properties including chemical resistance, hardness and adhesion strength were also evaluated. The electroactivity behavior of the prepared coatings was confirmed by cyclic voltammetry technique. The corrosion protection properties of electroactive and non-electroactive coatings (MS) were both measured by Tafel polarization technique and electrochemical impedance spectroscopy (EIS). According to the Tafel result, a considerable reduction in corrosion current (Icorr) and a more positive shift in corrosion potential (Ecorr) were detected for electroactive polyurethane-coated MS in comparison to those for bare and as well as non-electroactive polyurethane-coated MS. The EIS result indicated higher pore resistance (Rp) and consequently higher corrosion protection for electroactive coating in comparison to non-electroactive polyurethane-coated MS. The higher chemical resistance, hardness, and adhesion strength were recorded for electroactive polyurethane coating. Based on recorded data, it was revealed that the prepared electroactive polyurethane coatings not only could prevent the intrusion of corrosion spices onto the metal surface like a hydrophobic polymer coating, but also could enhance corrosion protection efficiency through redox reactions of their oligoaniline moieties with the metal surface.

Edge-functionalized graphene nanolayers with polystyrene chains were prepared by a "grafting through" approach using reversible addition-fragmentation chain transfer (RAFT) polymerization. For this purpose, a double-bond-containing modifier (MD) was prepared. After edge-functionalization of graphene oxide (GO) using two different amounts of MD and preparation of modified graphenes (LFG and HFG), RAFT polymerization of styrene was applied to achieve functionalized GO with different densities of polystyrene chains. Fourier transform infrared spectroscopy showed that MD and polystyrene chains were grafted at the edge of GO. The gas chromatography results showed that conversion decreased by increasing the modified GO content and grafting density of the MD. The number-average molecular weight and polydispersity index of polystyrene chains were derived from gel permeation chromatography data. A greater content in modified graphene resulted in lower molecular weight of the attached polystyrene chains and an increase in their PDI value. Increase of grafting density of MD resulted in lower molecular weight of polystyrene chains with no considerable variation in PDI value. The thermogravimetric analysis results showed that char residues were about 45. 1 and 46. 8% for LFG and HFG, respectively. The amount of degradation ascribed to polystyrene increased with increase of grafting density of MD and decreased with increase of modified graphene content. The X-ray diffraction results were used for evaluation of interlayer spacing of graphene layers after functionalization process and studying the nanocomposites structure. The results of scanning electron microscopy and transmission electron microscopy analyses showed that graphene layers with high clarity turned opaque with lots of creases by oxidation and attachment of polystyrene chains.