دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و هفتم شماره 4 (پیاپی 132، مهر و آبان 1393)

Pure polyacrylonitrile (PAN) nanofibers and functionalized-single walled carbon nanotube (FSWNT)، reinforced by PAN nanofibers with variable FSWNT content (up to 1 wt%)، were fabricated by electrospinning process. The chemical structure، morphology and microstructure of the electrospun nanofibers have been characterized using Fourier transform infrared (FTIR)، scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM analysis of the nanofibers revealed that the deformation of the nanofibers increased with increasing FSWNT concentration. Very smooth surfaces of the composite electrospun nanofibers even for nanofibers with concentration of 1 wt% FSWNT have been successfully prepared because of the high stability dispersion of FSWNTs. Moreover، with increasing the concentration of FSWNT in the PAN solution from 0 to 1 wt%، the average nanofibers diameter increased from 405 ± 54 nm to 488 ± 50 nm. The recorded spectra from FTIR were close to PAN nanofibers with peaks at 2243 cm-1 (CN stretch)، 2932 cm-1 (CH2 stretch)، 1450 cm-1 (CH bend) and 1730 cm-1 (C=O stretch) wavenumbers. FTIR Spectroscopy and XRD studies showed that PAN/FSWNT nanofibers exhibited higher crystallinity compared to PAN nanofibers without FSWNT. The analysis of the microstructural properties of the composite nanofibers with 1wt% FSWNT revealed that they exhibit an enhanced crystallinity from 44% to 48%، and the crystallite size was decreased from 25. 0 nm to 19. 9 nm، as compared to pure PAN nanofibers. The results indicated that the embedded FSWNTs in the PAN nanofibers nucleated the growth of crystals.

A semiconducting nanoparticle indium tin oxide (ITO) was modified with silane groups and for this purpose trimethoxysilane (TMOS) precursor was used under specific experimental conditions for surface modification of ITO nanoparticles. It is found that the modification of ITO nanoparticles increases the interactions between the filler and the matrix and subsequently improves the distibution of indium tin oxide nanoparticles in the polymer matrix. The epoxisilica polymer matrix was produced using trimethoxysilane and 3-glycidyloxypropyl trimethoxysilane precursors and ethylenediamine (EDA) as curing agent at low temperature by sol-gel process. The sol-gel process was very useful due to its easily controllable process، solution concentration and homogeneity without using expensive and complicated equipments in comparison with other methods. Then، Fourier transform infrared (FTIR) spectroscopy was employed to study the formation of Si-O-Si and Si-OH groups on ITO nanoparticles. X-Ray diffraction (XRD) technique and thermal gravimetric analysis (TGA) were employed to investigate the modification and weight loss of the modified ITO، respectively، as an indication of the presence of organic groups on these nanoparticles. The separation analyzer tests were performed to check the stability of the nanoparticles suspension and it revealed that due to better interaction of nanoparticles with the polymer matrix the stability of modified ITO suspention is higher than the unmodified sample. The morphology and particle distribution were determined by scanning electron microscopy (SEM). It was found that the distibution of modified indium tin oxide in epoxy-silica polymer matrix was improved in comparison with pure ITO.

Many studies have been conducted on production of biodegradable polymers such as polyhydroxyalkanoates (PHAs) in overcoming the environmental problems due to the accumulation of synthetic plastics as waste materials and excessive activated sludge produced in municipal waste water treatment plants. In this study; the effect of magnetic field intensity of 5، 10، 15، 20، 25 and 50 milliTesla (mT) was investigated on the type and amount of monomers produced in the copolymer and PHA production in activated sludge and the results were compared simultaneously with the results of PHA production without the magnetic field (0 mT). The experimental procedure included the transfer of the activated sludge into the batch reactor، addition of sodium acetate، magnetic field generation by magnets، aeration for 30 h، sampling at definite timing، measurement of PHA by gas chromatography. In summary، this research indicated that، the maximum PHA content was produced at 20 mT which was equal to 0. 75 g/L، whereas the lowest PHA content was observed at 50 mT (0. 55 g/L). In addition، the magnetic field was influenced by the type and amount of monomer produced in PHA. The highest amount of valerate was observed at 50 mT، while this magnetic field decreased the amount of PHA (8. 33%) compared to the control sample. Also، the maximum amount of butyrate monomer in the copolymer was observed at 5 and 20 mT، which were equal to 81% and 74 %. According to the results obtained، the mass percentage of valerate in the control sample and those exposed to magnetic field with negative effects was more than the mass percentage of butyrate; an indication of better copolymers on the basis of their mechanical properties.

Various samples of poly (vinyl alcohol) have been prepared under different conditions. Temperature and time in the presence of catalyst were assumed as important parameters affecting the properties of poly (vinyl alcohol). The degree of hydrolysis and molecular weight، as dependent parameters، were determined. First the temperature was kept at 45°C and hydrolysis reactions were conducted at different times. To investigate the effect of temperature on hydrolysis process the time was kept constant at 40 min and the reaction was carried out at various temperatures. By considering the various uses of poly (vinyl alcohol) and the properties of its various grades such as solubility، surface tension، resistance in tension، viscosity، the crystallinity properties of various prepared samples were investigated using differential scanning calorimetry. Increasing the time and temperature of the reaction led to higher degree of hydrolysis and lower molecular weight. Molecular weight، thermal treatment، degree of hydrolysis and the type of configuration of the molecules were the most important parameters affecting the crystallinity. Increasing the degree of hydrolysis increased the crystallinity and reduction in molecular weight and in this respect the effect of degree of hydrolysis on crystallinity was more evident than the molecular weight. In order to have similar molecular configuration for raw material the same polyvinyl acetate was used in all the tests. FTIR results showed that syndiotactic structure was dominant and favored the crystallinity. By considering the variation in three parameters during reaction the individual and associated effects of degree of hydrolysis، molecular weight and configuration was investigated on the crystallinity and melting point.

Preparation of appropriate powder-binder mixtures is the crucial step of powder injection molding process. Hence، the rheological properties of powder-binder mixture are important factors in production of sound parts using powder injection molding. Nowadays، the use of nanoparticles in powder injection molding is increasing due to the improved properties and dimensional precision of the final parts. On the other hand، nanoparticles can initiate problems such as agglomeration and loss of rheological properties and homogeneity. In the present study، the rheological behavior of aluminum mixtures containing nanoalumina particles was investigated. Two powder loadings of aluminum powder (54 vol% and 60 vol%)، in which 0، 3، 6 and 9 wt% of aluminum was replaced with nanoalumina، were used. The powder systems were blended with the molten binder system in a banbury internal mixer and the rheological properties of the resulting mixtures were evaluated. All feedstocks showed pseudo-plastic behavior. The presence of nanoparticles increased the viscosity of feedstocks. Due to overwhelming particles cohesion by hydrodynamic forces، the viscosity of the mixtures decreased at high shear rates. Tap density results confirmed an improvement in packing compressibility of the mentioned powders. Shear rate sensitivity decreased with incorporation of nanoparticles into the mixtures. This phenomenon improved the injection capability through further reduction in viscosity.

This research work is devoted to the simulation of a steel-belted radial tire under different static loads. The nonlinear finite element calculations were performed using the MSC. MARC code، installed on a computer system equipped with a parallel processing technology. Hybrid elements in conjunction with two hyperelastic models، namely Marlow and Yeoh، and rebar layer implemented in surface elements were used for the modeling of rubbery and reinforcing parts، respectively. Linear elastic material models were also used for the modeling of the reinforcing elements including steel cord in belts، polyester cord in carcass and nylon cord in cap ply section. Two-dimensional axisymmetric elements were used for the modeling of rim-mounting and inflation and three-dimensional models were developed for the application of the radial، tangential، lateral and torsional loads. Different finite element models were developed، in which both linear and quadratic elements were used in conjunction with different mesh densities in order to find the optimum finite element model. Based on the results of the load deflection (displacement) data، the tire stiffness under radial، tangential، lateral and torsional loads were calculated and compared with their corresponding experimentally measured values. The comparison was verified by the accuracy of the measured radial stiffness. However، due to the neglecting of the stiffness in shear and bending modes in cord-rubber composites، modeled with rebar layer methodology، the difference between computed values and real data are not small enough so that a more robust material models and element formulation are required to be developed.

The effect of Materials Institute Lavoisier-53 (MIL-53) particles on gas transport properties of polymethylpentyne (PMP) was investigated. MIL-53 was added to the polymer matrix with different loadings of 10، 20 and 30 wt%. The properties of MIL-53 and prepared membranes were analyzed through FTIR، SEM and TGA methods. The adsorption of CO2 and CH4 was conducted and analyzed accurately through Langmuir equation to investigate the gas transport properties of membranes. The results from TGA showed that degradation temperature (Td) increases significantly with increasing MIL-53 loading. SEM images demonstrated that MIL-53 particles dispersed well in polymer matrix with no considerable agglomeration and no non-selective void formation at polymer/filler interface. In addition، CO2 and CH4 permeability measurement along with calculation of CO2/CH4 selectivity were performed. The results showed that the permeability of gases (especially for CO2) increased significantly by increasing the MIL-53 loading. Additionally، CO2/CH4 selectivity showed an increasing trend with increasing the MIL-53 weight percent. Unlike CH4، the CO2 solubility coefficient increased with increasing the MIL-53 loading because of high free volume of membrane and selective adsorption of CO2 with MIL-53. Despite CO2 solubility enhancement its diffusivity coefficient remained more or less unchanged. The enhancement in CH4 permeability has been mainly attributed to its slight incremental diffusivity due to the membrane''s increasingly higher free volume. Finally، a comparison between membranes performance and CO2/CH4 Robeson upper bound showed that، the performance of membranes improved due to the presence of MIL-53 which was very close to the Robeson bound.