Iranian Journal of Polymer Science and Technology
Year:2016 | Volume:28 | Issue:5|Papers Count:8

Considering the rapid progress in applications of membrane separation technologies in various industries and the importance of morphologically asymmetrical membranes in governing the separation performance inmembrane systems, control of this parameter in the membrane fabrication process isregarded as a prominent subject in this field. Hence, investigation on the rheologicalproperties of polymer solutions, including viscoelasticity and gelation behaviorand their influence on the membrane formation and morphological structure of them embranes including flat sheet and hollow fiber membranes is a prerequisite to produce asymmetric membranes with desirable characteristics. Phase inversion is the most widely used technique for the preparation of asymmetric membranes. The two major mechanisms of liquid-liquid and solid-liquid demixing in membrane fabricationprocess affect the morphology of the membranes. Therefore, controlling the phaseinversion in the early stage can greatly influence the microstructure of the membrane.The rheological behavior of polymer solutions during the fabrication of membranes as well as other factors that influence the morphological structure of the membranes have been evaluated in the present study. In addition, the principles governing the rheologyof polymer solutions such as viscoelasticity, shear and extensional viscosity play acrucial role in determining the membrane morphology and separation performance.Due to the interaction of the rheology of polymer solutions and phase inversion, the effects of changes in the rheological properties on the phase inversion and the formation of membranes with different structures and morphologies are studied. Furthermore, in addition to the analysis of the relaxation time and gelation mechanisms, discussions are provided on the determination of the final membrane morphology considering the competition between the domains growth and gelation rates.

Zinc oxide (ZnO) nanoparticles were employed as reinforcing agent to improve the antibacterial and mechanical properties of polyvinyl chloride PVC-ZnO nanocomposite was prepared by dispersing ZnO nanoparticles (PVC).into a PVC solution. Taguchi experimental design method was used to determinethe optimal conditions for preparation of nanocomposite. The effects of five factorsincluding ZnO weight percentage, its addition method, type of solvent, film drying temperature and stirring time were investigated on different levels. Optimal conditions were determined by signal/noise (S/N) method. It was found that, type of solvent, the ZnO weight percentage and its addition method are three determining factors at 95%confidence level. Staphylococcus aureus and Escherichi coli, two different types ofbacteria (one gram-positive bacteria and one gram-negative bacteria) were used inMueller-Hinton broth for antimicrobial testing. This test confirmed the antibacterialproperty of the optimal nanocomposite in respect to pure polyvinyl chloride. Ascanning electron microscope (SEM) coupled with an energy dispersive X-ray system (EDX) was used to characterize the composition and structure of the optimalnano composite film.

Olefinic copolymers of ethylene/1-hexene were synthesized by three main types of supported catalysts, including Philips, Ziegler-Natta and metallocene catalysts, and the specific microstructural features delivered by each class of the catalysts were studied. The heterogeneity of comonomer distribution was studied by thermal fractionation using successive self-nucleation annealing (SSA) as a novel method. It was observed that the comonomer incorporation ability decreasedin the order of metallocene>Ziegler-Natta>Philips. The chemical composition distribution (CCD) of the produced copolymers was investigated by differential scanning calorimetry (DSC). Interestingly, we found that the copolymers produced by the directly supported metallocene catalyst displayed heterogeneous distributions of comonomer, similar to the products obtained by Ziegler–Nata and Philips catalysts. The lamellar thickness distributions of the copolymers were calculated by the DSC curvedeconvolution into a number of standard distribution functions. It has been shown thatthe type of supported catalyst does not affect the lamella thickness distribution to adiscernible extent. The range of lamellar thickness was about 2-29 Å for the polymersproduced using directly supported metallocene, Zigler-Natta and Philips catalysts, while the corresponding value for copolymers made by homogeneous metallocenecatalyst was in the range of 2-7 Å. It could be concluded that in-situ supporting of metallocene catalyst increased the comonomer incorporation in a more homogeneous fashion. In addition, comonomer units were distributed more homogeneously at higher1-hexene concentrations as could be realized from the approach of DSC index (DSCI) which showed that the DSC index moved towards unity at higher comonomer levels.

Fabrication of an efficient microfiltration polymeric membrane with low fouling characteristics and high permeation flux is an essential task for conducting membrane-related research and its development toward its industrial applications. Surface skin layer which decreases the membrane permeation and accelerates the membrane fouling in purification and separation of protein solution is usually observed for all membranes fabricated via thermally induced phase separation (TIPS) method. In this work, the impact of coagulation bath temperature on the skinlayer thickness and performance of fabricated membranes was investigated. Collagenprotein purification tests were carried out to investigate the impact of skin layer on the performance and fouling mechanisms of the membranes. The obtained results showed that when coagulation bath temperature increases, the thickness of skin layer decreases.In membranes with lower surface porosity, the decline in protein permeation is mainly due to the standard blocking fouling mechanism which is a kind of the irreversible fouling phenomenon. In membranes with higher surface porosity, however, decline inprotein permeation is mainly due to the intermediate blocking fouling mechanism which is a kind of reversible fouling phenomenon. The obtained results from permeation flux and spectrophotometric analyses of the inlet feed and retentate streams within 800 min showed that the collagen recovery ratio for modified membrane was 5.6% and that of an unmodified membrane was less than 1%. It is worth to mention that for membrane with lower surface porosity the collagen filtration process was stopped within 400 mindue to the membrane fouling. For membrane with higher surface porosity, however there was no halting in filtration process within 800 min.

A comparative study has been carried out on thermal properties, flammability and mechanical properties of three different kinds of unsaturated polyester resins, ortho, iso and vinyl ester and an epoxy resin based on diglycidyl etherof bisphenol-A. Because of the wide application of these resins in the composite industryit is vital to understand their properties. For this purpose, viscosity, burning rate, limitingoxygen index (LOI) and flexural properties were measured. Fourier transform infrared (FTIR) spectroscopy and thermal gravimetric analysis were also performed. Theviscosity of unsaturated polyester resins which was in the range of 300 to 450 cP showedan advantage compared to the viscosity of epoxy resin which was in the range of 600to 1000 cP. The low viscosity which usually appears in unsaturated polyester resins isvery important from the processing point of view, which in turn helps to ensure a simpleprocessing. The ortho resin showed the highest conversion and conversion rate amongthe three unsaturated polyester resins. The vinyl ester resin showed a higher conversionthan the iso resin. The results showed that the vinyl ester resin had the highest thermalresistance, flammability and mechanical properties among the unsaturated polyesterresins used in this work. On the other hand, although the epoxy resin showed the highestburning rate but it had the highest carbon residue or char yield (12.4%) and LOI (20.2%), and consequently the highest thermal resistance. The results of flexural test have shownthat the epoxy resin has displayed the highest flexural strength (116 MPa) and modulus (4.1 GPa) and the lowest deflection-at-break (2.8%) and toughness in comparison withthe unsaturated polyester resins used in this work.

Phase inversion is a common method for preparation of polymeric membranes. It is noticeable that most of the membranes prepared by this method have an asymmetrical structure. In this type of membranes, separation of particles occurs only by top dense layer in a high operating pressure. On the other hand, these paration process using symmetric membranes containing surface pores occurs on the top surface and in the depth of the membrane at lower operating pressure. In thisresearch, preparation of polyethersulfone-based membranes was performed throughthe phase inversion method by dimethylacetamide as a solvent and water as the nonsolvent. Changing the coagulation conditions by applying one pause stage in anenvironment with the precise control of temperature and humidity, along with usingpolyvinylpyrrolidone as a hydrophilic additive, were attempted in order to controlthe porosity and structural changes of the membrane. Scanning electron microscopy) SEM (images, bubble point test, porosity, and mean pore radius measurementswere used to study the structure of the prepared membranes. The performance of themembranes was evaluated by pure water permeation test and elimination of bacteriafrom cell culture medium. The results obtained illustrate that the implemented methodis capable of preparation of membranes with symmetrical structure and pore diameterless than 0.4 μm featuring acceptable pure water flux and bacteria removalability. Itwas also observed that increase in the concentration of polyvinylpyrrolidone additiveleads to an increase in porosity, permeation and pore size of the membrane samples.On the other hand, the tensile strength and elongation-at-break of the membranesamples were reduced upon increasing in polyvinylpyrrolidone concentration.