دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و یکم شماره 5 (پیاپی 157، آذر و دی 1397)

Epoxy resins are widely used in composites, aerospace, construction, electronic, adhesive and coatings industries due to their high physical and mechanical, thermal resistance, electrical and chemical properties. For curing epoxy resins, a chemical material, called curing agent or hardener, must be used. Curing agents have strong effect on the processing conditions and final properties of the cured resins. In general, epoxy curing agents can be classified in two groups of normal (room or high temperature) and latent curing agents. Normal curing agents increase the resin viscosity at room temperature due to crosslinking or curing reactions and the resin is gelled and finally cured. The rate of viscosity increment would be different and depends on the kind of curing agent. On the other hand, latent curing agents cannot react with epoxy resin at room temperature and do not increase the resin viscosity. Therefore, they are being used for preparing one-part epoxy resins. Latent curing agents are not active at room temperature, but they will react with epoxy resin by the application of an external force like heat or light. Thermally-latent curing agents are well-known and they are widely used. They include substances with active hydrogen, and are catalyzed and protected by chemical groups and microcapsules. Selection of a latent curing system for an application is an important issue which affects the processing conditions and final properties of the cured resins. In this paper, the latest achievements in this area are reviewed.

Nowadays, the use of scaffolds in tissue engineering to repair and regenerate human lesions, including nervous injuries has been widely considered. Also, nanofibrous scaffolds due to their structural similarity with the extracellular matrix (ECM) in the body are found to be suitable substrates for cell growth. Therefore, the main focus of the present work is on the production of conductive nanofibrous scaffolds for neural cell culture and their electrical stimulation performance. Two biocompatible polymers including polycaprolactone (PCL) and poly(lactic-co-glycolicacid) (PLGA) were used as main materials, and polyaniline (PANI) was applied as a conductive polymer to create conductivity in the substrates. After determination and optimization of the electrospinning process factors, 4 types of nanofibrous scaffolds with 4 levels of conductive polymer (0%, 1%, 10% and 18%) were prepared. To investigate the effect of scaffolds' conductivity and electrical stimulation on the nerve cells behavior, a plate with steel electrodes was designed to apply electrical field to the scaffolds during cell culture experiments. SEM, Dino-Lite digital microscopy, Potentiostat-Galvanostat and 3-(4,5-dimethylthiazed-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay were used to study the properties of scaffolds including hydrophilicity, conductivity, fiber diameter and the results of cell culture. By investigation of the physical properties of the scaffolds it was shown that increasing the amount of PANI in scaffolds causes significant drop in the fiber diameter and hydrophilicity. In cell culture experiment, shape and proliferation of nerve cells were studied. MTT assay and SEM images showed that electrical stimulation, proportional to the amount of polyaniline, enhanced neurite outgrowth compared to the scaffolds that were not subjected to electrical stimulation. Furthermore, proliferation of cells on conductive scaffolds (by 10% v/w of PANI) increased and subsequently the cell proliferation decreased with increasing conductive polymer content due to its toxicity.

The surface modification of polyvinylchloride-based heterogeneous cation exchange membranes was carried out using chitosan-co-polyaniline/graphene oxide nanocomposite layer for the application in electrodialysis process. The PANI/GO nanocomposites were prepared by in situ chemical oxidative polymerization of aniline in the presence of graphene oxide nanoplates. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), water content, flux and permeability, areal ionic resistance, water softening ability and fouling measurements were used to characterize the membrane. The FTIR analysis results and SEM images demonstrated successful formation of polyaniline on the graphene oxide nanoplates. The scanning electron microscope images of membranes also exhibited a uniform layer of chitosan-co-PANI/graphene oxide nanoplates on the membrane surface. The water content of modified membranes was higher than that of pristine membrane. The sodium flux and sodium permeability were improved about 20% by 0.1 %wt PANI/graphene oxide nanocomposite. The areal ionic resistance of modified membranes also showed a decreasing trend by utilizing composite nanoplates in the membrane matrix. The prepared membranes showed good ability for Ca and Mg removal from water. The removal efficiency of Ca and Mg by membrane containing 0.5 %wt PANI/graphene oxide composite nanoplates was, respectively, 61 and 79% during 15 min. Moreover, the pollutant and foulant formed on the membrane surface were totally removed by sonication technique. The modified membranes showed suitable electrochemical characteristics compared to membranes reported by other researchers and made by industries.

It is demonstrated that silica and carbon black have inhibiting effect by the former and accelerating effect by the latter in the kinetics of sulfur vulcanization of rubber. It seems that in sulfur vulcanization reaction of rubber some kinetic phenomena are not systematically investigated. In this regard, due to the autocatalytic mechanism of vulcanization and the diffusional effect of its chains, it seems that immobilization of rubber chains as a result of the presence of reinforcing fillers has an essential role in changing the kinetics of sulfur vulcanization of rubber. This concept has not been explored in other researches. Kinetics measurements were performed by means of an oscillating disc rheometer. The extent of filler/filler interactions was monitored by means of dynamic-mechanical and electrical conductivity tests for silica and carbon black filled compounds, respectively. It was shown that the autocatalytic nature of the vulcanization remains unchanged regardless of the type and concentration of fillers. It was demonstrated that the vulcanization rate goes through a maximum as the loading of fillers rises, regardless of the type and surface chemistry of the fillers. Consequently, silica can also accelerate the vulcanization rate at low loading and decelerate it above a critical loading. Such critical loading exists for both silica and carbon-black, and it is related to the percolation threshold for filler network formation. Therefore, it is discussed that not only the filler surface chemistry, but also the physical phenomena originating from the filler/filler interactions can alter the vulcanization kinetics of rubbers. Such physical effect is attributed to the immobilization and lack of kinetic energy in the entrapped rubber chains which reduce the probability of reaction between the macro-radicals. Therefore, a single mechanism is introduced here to explain the effect of reinforcing fillers on the vulcanization kinetics of the filled rubber.

Carbon dioxide (CO2) separation from flue gases as a green-house gas produced from the combustion of fossil fuels is one of the main concerns in controlling the green-house gas emissions. Among the various technologies employed for gas separation, membrane technology due to its many advantages has attracted more attentions. A new blend membranes were prepared by solution casting/solvent evaporation method from poly(ether-b-amide) (Pebax) – as a backbone structure – and glycerol as an additive in the membrane matrix. CO2 and N2 permeability rates were measured at pressures of 2-10 bar and temperature of 25 °C. Afterwards, the CO2/N2 gas permeation properties were determined. Moreover, the effect of different glycerol loadings (0-25 wt%) in the membrane matrix and also the effect of feed pressure on CO2 permeability and CO2/N2 selectivity were investigated. Morphological characteristics of the prepared membranes were determined by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) analyses. The achieved results showed that by addition of glycerol to Pebax matrix, CO2 permeability was decreased somewhat but the CO2/N2 selectivity was considerably increased. At pressure of 10 bar, CO2/N2 selectivity of the blend membrane with 15 wt% glycerol was 172% higher than that of pure Pebax, while the CO2 permeability declined only by about 23%. Therefore, the blend membrane containing 15 wt% glycerol with a good CO2 permeability and a high CO2/N2 selectivity was selected as the optimum membrane. The FE-SEM observations revealed the compatibility and homogeneity of glycerol in the Pebax matrix. The XRD analysis determined that the addition of glycerol decreases the membrane crystallinity and the d-spacing between the polymer chains. The DSC results revealed that the insertion of glycerol in the membrane structure decreased the glass transition temperature. The FTIR spectra showed no new absorption band except for those for the constituent species, which suggests a physical interaction between Pebax and glycerol.

Surface and structural modification of membranes in order to improve their filtration properties have been one of the vast research areas in the field of membranes in recent years. Nanomaterials are most widely used for modifying the surface and structure of the membranes. In this study, carboxylic acid and sulfate carboxylic groups were deposited on the surface of zirconia nanoparticles in order to improve their arrangement within the membrane matrix. Then, the structure and behavior of the nanocomposite membrane was compared with those of raw membrane. ZrO2, Zr-COOH and Zr-SO4 nanoparticles were added to the polysulfone (PSf) membrane substrate, and the effect of the surface, structural and filtration properties of raw and nanocomposite membranes were compared in relation to their textile wastewater treatment performance. For this purpose, PZC, EDX, SEM, AFM, CA and porosity analysis as well as viscosity, flux recovery and dye rejection measurement were performed. The results of analyses showed that the presence of Zr-COOH nanoparticles led to greater finger pores, smaller size of the nanoparticles, and the presence of Zr-SO4 nanoparticles led to fewer finger pores, less porosity and larger nanoparticle size. The presence of the functional groups increased the number of nanoparticles in the skin layer of the membrane and improved the membrane surface properties. Analysis of variance obtained using RSM method for porosity and contact angle data showed that the most effective factor on porosity and contact angle is nanoparticles concentration. By increasing the concentration of ZrO2, Zr-COOH and Zr-SO4 nanoparticles from 0 to 2 wt%, the flux recovery was increased by 15, 25 and 45%.