دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و هشتم شماره 4 (پیاپی 138، مهر و آبان 1394)

Mechanical properties of epoxy and glass/epoxy filled with 0. 25، 0. 5 and 1 vol% of TiO2 nanoparticles have been studied using tensile and three-point bending tests. For the TiO2/epoxy nanocomposites، the results showed that the strength and stiffness were improved، though the strain at ultimate strength point and breaking strain decreased. Moreover، the hybrid nanocomposites composed of 4 layers of woven E-glass fabric and TiO2/epoxy matrix were fabricated and cut onaxis and 45° off-axis by water jet. The results of tensile and three-point bending tests indicated a remarkable improvement in the strength and stiffness that could not be related to the mechanical improvement of the matrix. The samples containing 1 vol% nano TiO2 were improved relative to samples without the nanoparticles. The tensile strength of the on-axis and off-axis samples containing 1 vol% TiO2 increased by about 25. 9% and 17. 9%، in the order given، compared to that of the glass/epoxy specimens. In three-point bending test، the strength of the on-axis and off-axis specimens was improved 26% and 23. 2%، respectively. In addition، the tensile stiffness of the onaxis and off-axis samples containing 1 vol% TiO2 increased، respectively، by about 14. 4% and 17. 5% compared to that of the glass/epoxy specimens. Also for the same on-axis and off-axis samples the three-point bending stiffness increased about 19. 8% and 14. 6%، respectively. The whole investigation on the microstructure of the hybrid nanocomposites illustrated that stronger interfaces between the fiber and TiO2/epoxy matrix were formed and improvement was noticed on mechanical properties of ternary composite compared to those of the fiber/epoxy composites. The analysis of damage zones of hybrid nanocomposites showed that the surface area of the damaged zone declined considerably due to the brittle behavior of TiO2-filled specimens but the area below the stress-strain curve، showing energy absorption during the test، increased.

The influence of hydrophilic spherical nanoparticles on the kinetics of spinodal decomposition (SD) in PS/PVME (polystyrene/polyvinyl methyl ether) blend was studied. For the PS/PVME 30/70 blend at 110oC a highly interconnected structure was developed in the early stages of phase separation as a characteristic of spinodal decomposition. Due to the presence of highly curved interface between the phases in a co-continuous morphology، a considerable free energy was stored at the interface. Thus، interconnected structure was not in thermodynamic equilibrium and broke up into droplet-matrix morphology. At later stages، droplets grew dramatically and a broad size distribution of droplets was observed. Phase contrast optical microscopy (OM) and scanning electron microscopy (SEM) were employed to investigate the morphological evolution of PS/PVME blends during the phase separation. In order to investigate the kinetics of phase separation in the presence of nanoparticles، OM observations and rheological analysis were employed. Nanosilica particles were strongly driven by the thermodynamic forces into the bulk of PVME-rich phase to reduce the free energy of the system during the phase separation، as verified by TEM micrographs and thermodynamic equation. Nanoparticles considerably slowed down phase separation kinetics of SD at a low volume fraction of 0. 5% which was intensified as the volume fraction was increased to 1%. Surprisingly، at 2% nanoparticle loading phase separation was arrested and a stable co-continuous structure induced by SD was formed. TEM images indicated that double percolated structure was induced in the presence of 2% A200 nanoparticles: a network of nanoparticles was induced in the network of PVME-rich phase.

Due to the characteristics such as flexibility، adhesion، hydrophobicity and low price، bitumen is used in different construction and insulation industries. The major problem with the bitumen material is its restricted physico-mechanical properties، mainly high temperature rutting and low temperature cracking. The aim of this work was to modify bitumen، produced in Tabriz Pasargad Oil Company، and evaluation of its different properties to make it suitable for the weather conditions of North West of Iran. The physico-mechanical، morphological and rheological characteristics of EVA/Cloisite 15A modified bitumen were studied. Two different feeding instructions were used in the mixing of bitumen with modifiers. In the first method، EVA and Cloisite 15A nanoclay were simultaneously added into the molten bitumen and in the second method، EVA and Cloisite 15A were premixed in an internal mixer before adding the polymer/nanoclay nanocomposite into the molten bitumen. The results showed that addition of nanoclay and polymer into the bitumen، led increased softening point and a decrease in the penetration of base bitumen، in which the extent of changes، was higher for the samples prepared by masterbatch method. The rheological properties of the pre-mixed samples exhibited more improvement and these samples showed more elastic behavior. The results of optical microscopy showed that the pre-mixing of polymer and nanoclay led to a more uniform distribution of the swollen polymer phase at the base bitumen. These samples also showed higher morphology stability than those samples prepared in single step. These effects were related to the probable localization of nanoclay at the interface of the two phases.

Polyvinylidene fluoride (PVDF) membranes are widely used in microfiltration and ultrafiltration processes for their excellent mechanical and chemical resistance and thermal stability in comparison with other polymeric membranes. Non-solvent induced phase separation (NIPS) is the most important method by which the PVDF membranes are prepared. The structure of the membranes prepared by NIPS method depends on different parameters including the concentration of the polymer solution، polymer molecular weight، the composition and temperature of coagulation bath، type of solvent and the presence of additives in the initial solution. In the present work، the effects of coagulation bath temperature and LiCl content of the dope solution were studied with respect to the structure and performance of PVDF membranes. N-Methyl-2-pyrrolidone and water were used as solvent and coagulation bath، respectively. A set of analytical techniques including: scanning electron microscopy، mechanical test، pure water permeability and mean pore radius of pores was used to characterize the membranes. Moreover، the separation of humic acid، a main biological contaminant in surface water resources، was studied to determine membranes performance. The results show that at constant coagulation bath temperature، presence of LiCl in the dope solution increased the number as well as the mean pore radius of the pores at the surface of membranes and consequently، pure water permeability of the membranes was increased، whereas، the mechanical strength and humic acid rejection of the membranes were dropped. Moreover، at a constant content of LiCl، increasing the coagulation bath temperature decreased the size of macrovoids so that the mechanical strength as well as humic acid rejection of the membranes was increased.

Co-precipitation method was employed for the intercalation of carboxymethyl cellulose (CMC) into layered double hydroxide (LDHs) sheets and preparation of CMC-LDH nanocomposites. CMC-LDH nanocomposites were synthesized by a reaction of basic solution of CMC with the mixed aqueous metallic salt solutions of M2+ (M2+ = Mg and Ni) /Al3+ ratio of 2. The structure and morphology of the synthesized CMC-LDH nanocomposites were characterized using Fourier transform infrared spectroscopy (FTIR)، X-ray diffraction (XRD)، transition electron microscope (TEM) and thermal gravimetric analysis (TGA). Furthermore، the swelling behavior of the nanocomposites was studied in aqueous solutions of various pH. The intercalation of carboxymethyl cellulose polymeric chains into the LDH sheets was confirmed by FTIR spectroscopy and XRD analysis. The interlayer distance of Mg-Al-CMC-LDH and Ni-Al-CMC-LDH nanocomposites was found to be 1. 73 and 2. 23 nm، respectively. The XRD patterns confirmed a multilayer arrangement of CMC polymeric chains between the LDH sheets. TEM analysis revealed a highly intercalated morphology for the nanocomposites، which was agreed with XRD data. Thermal gravimetric analysis showed a better thermal resistance of carboxymethyl cellulose in the presence of LDH sheets، especially for Mg-Al-CMC-LDH. Thermal stability of CMC in the nanocomposites increased for about 50°C and 133°C for Ni-Al-CMC-LDH and Mg-Al-CMC-LDH، respectively. The obtained nanocomposites revealed a pH-dependent swelling behavior. The swelling of the prepared nanocomposites increased slowly with increasing the pH from 2 to 10. However، their swelling ratio increased sharply in pH values above 10.

In addition to properties such as biocompatibility and biodegradability، cellulosic natural fibers have a higher strength property than the synthetic polymers and glass fibers. So they are suitable alternatives to synthetic and glass fibers. However، cellulose is highly hydrophilic and has low reactivity. Therefore، its industrial applications are limited. To overcome such drawbacks، the chemical modification of the cellulose structure is necessary. Graft copolymerization، a commonly used method for the modification of polymer surfaces، can be applied as an important tool for modifying the physical or chemical properties of polymers. By grafting hydrophobic polymer chains onto the cellulose fiber surface، the hydrophilicity of the cellulose can be altered. In this project، polyacrylonitrile was grafted onto cellulose surface by atom transfer radical polymerization (ATRP) technique. In the first step، the reaction of OH cellulosic groups with acryloyl chloride in the LiBr/N،N-dimethyl acetamide mixture was carried out to form pendant double bonds and yield water soluble cellulose acrylate. Then، 4-chloromethyl styrene in the presence of toluene was grafted onto the unsaturated group via free radical polymerization and using azobisisobutyronitrile as the initiator. Finally، the synthesized cellulose-graft-polychloromethyl styrene having a transferable atom (Cl) for the polymerization of acrylonitrile in THF and in the presence of copper (I) chloride /2،2’-bipyridine as a catalyst system was used as an ATRP macroinitiator to prepare the cellulose-graft-polychloromethylstyrene-graftpolyacrylonitrile terpolymer. The products were characterized by scanning electron microscopy، X-ray diffraction and FTIR spectroscopy and their thermal stability was investigated by the thermogravimetric analysis and differential scanning calorimetry.

Biocompatible nanoparticles are widely used in biomedical engineering. In this study، chitosan nanoparticles were prepared using ionic gelation method in view of two determining factors namely method of adding chitosan into the tripolyphosphate (TPP) solution and thermal shock application. With regard to the concentration of chitosan and TPP solutions as two variables، the mean particle size of chitosan nanoparticles and their preparation yield were optimized using response surface method. According to previous studies and some preliminary experiments، the chitosan and TPP solution concentration ranges were determined to be 0. 5-2. 5 mg/mL and 0. 25-1. 25 mg/mL، respectively. The optimum values of 1. 25 mg/mL and 0. 6 mg/mL were obtained for chitosan and TPP solution concentrations in the order given. The optimized response value for the chitosan nanoparticles size was found to be 54 nm and preparation yield was 62%. The Zeta potential of resulting spherical nanoparticles was around 31 mV. Chitosan-fluorescein isothiocyanate (FITC) polymer was prepared based on the reaction between isothiocyanate functional group of FITC and primary amine functional group of chitosan. FTIR analysis was performed to demonstrate the presence of new bond formation. Labeled chitosan nanoparticles were prepared in the optimized condition using chitosan-FITC polymer. The release behavior of the labeled chitosan nanoparticles from transdermal patches was evaluated. The mean size of chitosan-FITC nanoparticles was determined to be 70 nm. Finally، it was shown that the chitosan nanoparticles were not able to release from acrylic adhesive film without using a method to speed up their diffusion.