Iranian Journal of Polymer Science and Technology
Year:2016 | Volume:28 | Issue:6|Papers Count:7

Magnetic nanocomposites were prepared by incorporation of pure Fe3O4 and surface-modified Fe3O4 nanoparticles (dipodal silane-modified Fe3O4) into a polyurethane elastomer matrix by in situ polymerization method. In preparation of these magnetic nanocomposites, polycaprolactone (PCL) was used as a polyester polyol. Because of dipole-dipole interactions between nanoparticles and a large surface area to volume ratio, the magnetic iron oxide nanoparticles tended to agglomerate. Furthermore, the most important challenge was to coat the surface of magnetic Fe3O4 nanoparticles in order to prepare well dispersed and stabilized Fe3O4 magnetic nanoparticles. It was observed that surface modification of Fe3O4 nanoparticles enhanced the dispersion of the nanoparticles in polyurethane matrices and allowed magnetic nanocomposites to be prepared with better properties. Surface modification of Fe3O4 was performed by dipodal silane synthesized based on 3-aminopropyltriethoxysilane (APTS) and γ-glycidoxypropyl trimethoxysilane (GPTS). Dipodal silane-coated magnetic nanoparticles (DScMNPs) were synthesized and incorporated into the polyurethane elastomer matrix as reinforcing agents. The formation of dipodal silane was investigated by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR) and transmission electron microscopy (TEM). Characterization and study on the magnetic polyurethane elastomer nanocomposites were performed by FTIR, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and dynamic mechanical thermal analysis (DMTA). The VSM results showed that the synthesized polyurethane elastomer nanocomposites had a superparamagnetic behavior. The TGA results showed that the thermal stability of dipodal silane-modified Fe3O4/PU nanocomposite was higher than that of Fe3O4/PU nanocomposite. This could be attributed to better dispersion and compatibility of dipodal silane-modified Fe3O4 nanoparticles in the polyurethane matrix compared to pure Fe3O4 nanoparticles.

Iodine transfer radical polymerization as an easy, efficient and robust method of controlled radical polymerization has been applied for a wide range of monomers. This polymerization technique is used in both homogeneous and heterogeneous processes. Iodine transfer radical bulk polymerization of the vinyl acetate (VAc) monomer was carried out in the presence of 2, 2' -azobis (isobutyronitrile) (AIBN) as an initiator and ω-iodine-terminated poly (dimethyl siloxane) (PDMS-I) as a macrotransfer agent at 80oC. PDMS-I with a number average molecular weight of 5029 g/mol and a polydispersity index of 1.23 was synthesized by bromination followed via iodination of the w-hydroxyl-terminated poly (dimethyl siloxane) (PDMS-OH). The product was used as a macrotransfer agent in the iodine transfer radical polymerization of VAc. Formation of the poly (vinyl acetate) -b-poly (dimethyl siloxane) diblock copolymer with a number average molecular weight of 19620 g/mol and a polydispersity index of 1.53 was proved by proton-nuclear magnetic resonance spectroscopy and gel permeation chromatography. A good agreement between the theoretical and experimental molecular weight calculated by proton-nuclear magnetic resonance spectroscopy and gel permeation chromatography was achieved, indicating that the PDMS-I macrotransfer agent was completely consumed and the PDMS impurities did not participate in the polymerization reaction. The analysis of the chain-ends was performed by using proton-nuclear magnetic resonance spectroscopy technique. It was found that a considerable number of inverse chain-ends were present at the end of the polymerization. Moreover, formation of several other side products due to degradation of the functional chain-ends was confirmed.

an acrylic pressure-sensitive adhesive was prepared by free radical polymerization of 2-ethyl hexyl acrylate in ethyl acetate and in the presence of an oil soluble initiator such as AIBN. In order to adjust the appropriate properties for the synthesized acrylic pressure-sensitive adhesive, two comonomers; vinyl acetate and hydroxyl ethyl acrylate were introduced into the structure of the acrylic adhesive. The prepared acrylic pressure-sensitive adhesive was characterized by analytical instruments such as FTIR (Fourier transform infrared), NMR (nuclear magnetic resonance), GPC (gel permeation chromatography) and HPLC (high performance liquid chromatography). Reaction conditions such as comonomer type and concentration, reaction time and initiator could affect the final properties of the synthesized acrylic pressure-sensitive adhesive. Therefore, the effect of parameters, especially time of the reaction, initiator concentration and that of each comonomer and degree of cross-linking was studied with respect to the final properties of the acrylic pressure-sensitive adhesive such as tack, peel strength and shear strength. Shear strength of the adhesive was increased by increases in the amount of HEA and VAc and reducing the amount of the initiator. Tack of the polymer was improved by the higher amounts of initiator and VAc monomer. Moreover, the peel strength of polymer was decreased by increasing the amount of VAc and raised by increasing the amount of HEA. It was found that cross-linking significantly raised shear strength of the adhesive. The optimum time of reaction was obtained by 10 h and the optimum amounts of initiator, vinyl acetate and hydroxyl ethyl acrylate were 0.5, 22 and 6 wt%, respectively.

Full Text [PDF 900KB] Incorporation of inorganic nanoparticles into polymer matrices is a method to increase the hydrophilicity and to reduce fouling in polymer membranes. Among different types of inorganic nanoparticles employed in mixed matrix membranes, TiO2 and ZnO play significant role in their unique physical and chemical properties. In the present work, the effect of TiO2 and ZnO nanoparticles on the structure and fouling behavior of polyethylene membranes was studied. High density polyethylene (HDPE) was used as polymer and TiO2 and ZnO were of nanoparticle size. Thermally induced phase separation method was used to prepare membranes and different characterization methods including (field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microcopy (AFM), contact angle, pure water flux and mean pore radius measurements were acquired to evaluate the structure and surface of the membranes. Moreover, the performance and fouling of the membranes were studied by separating 1 wt% collagen protein solution. The results of FESEM images showed that all the membranes had leafy structure, indicating solid-liquid phase separation during membrane preparation. The results of TEM and EDX confirmed the presence of nanoparticles in the membranes. Based on the Wenzel model, contact angle of the membranes was not reduced by increasing the content of hydrophilic nanoparticle due to increased surface roughness. However, pure water flux of the membranes increased as the content of nanoparticles increased. Finally, it was shown that the incorporation of nanoparticles increased reversible fouling, flux recovery and fouling resistance of the membranes in separation of collagen protein solution due to the antifouling properties of TiO2 and ZnO nanoparticles.

Electrospinning as a simple method was used to produce cellulose acetate porous fibers. Motivation for production of fibers with small diameter in the submicron and nano scales was to achieve the material with a large surface area with porosity formation in the structure of electrospun fibers. In this study, porous cellulose acetate (CA) fibers were produced by electrospinning process from solution of CA/acetone/water. The porosity of the fiber was controlled by adjustment of the temperature and humidity of electrospinning chamber. Scanning electron microscopy (SEM) and densitometry were employed to evaluate the morphology and porosity of the samples. The results showed that the morphology and porosity of cellulose acetate fibers depend on the polymer solution concentration and relative humidity of electrospinning atmosphere. Cellulose acetate fibers were electrospun best at the concentrations of 12 to 18 wt% and relative humidity range of 40 to 80%. The highest porosity was obtained at the relative humidity of 80% and concentration of 15 wt%. In addition, by increasing the relative humidity of electrospinning environment and polymer concentration, the average diameter of the fibers was increased. With increasing the polymer concentration, there was less likelihood in thermodynamic instability and phase separation. In contrast, increases in relative humidity led to diffusion of more water into the electrospinning jet, giving rise to phase separation. Our observations revealed that the skin of fibers was formed at the earlier stage of the process and prevented the stretch in electrospinning jet.

Microcellular thermoplastic foams can be usually produced in a one-step batch system using a physical foaming agent which is dissolved in a polymer system under specific pressure and temperature, higher than the critical condition of solvent and the glass transition temperature of polymer and solvent mixture. By application of a sudden pressure drop the foam structure is formed through stages of nucleation, growth and coalescence. After pressure drop, if the foam temperature is reduced below the glass transition of the gas-polymer mixture, the cells stop growing which results in a foam with stabilized morphology. This stabilization stage has not been thoroughly focused in previous studies. In this work, polystyrene as a polymer system and supercritical carbon dioxide as a solvent were used at 18.5 MPa pressure and different temperatures. The stabilization process took place within milliseconds and helped to a better understanding of cellular structure in thermoplastic foams. In this mechanism, the nucleation takes place in the phase transition of solvent molecules at supercritical state to the gas state and the formation of very small nuclei containing gas molecules between polymer chains. The energy originated from the nuclei growth is in competition with the elastic energy of polymer chains, and the predominance of one type of energy over another determines the final cell size. The results showed that the effect of stabilization process on the structure of the foam depended on the foaming temperature. Stabilization at 110°C resulted in a 50% cell size reduction and a 60% cell density promotion, while at lower temperatures, the stabilization led to greater cell size and reduced cell density.

Novel hydrogel nanocomposites, based on κ-carrageenan polysaccharide, were prepared by graft copolymerization of acrylamide (AAM) and maleic anhydride (MAH) as comonomers in the presence of multiwall carbon nanotubes (MWCNT), using methylene bisacrylamide (MBA) and ammonium persulfate (APS), former as a crosslinking agent and the latter as an initiator. The hydrogel Nano composites structure was characterized by FTIR spectroscopy, scanning electron microscopy (SEM) and XRD patterns, and their thermal stability was investigated by TGA thermal analysis. The hydrogel Nano composites were evaluated using gel content measurements and swelling rate in distilled water and in saline solutions. The carbon nanotube content was examined in relation to its effect on the properties of nanocomposites. The results showed that with increasing carbon nanotube content, the rate of water absorbency and equilibrium swelling in distilled water decreased whereas the water absorbency in the saline solutions increased. Water retention capacity was also studied and the results indicated that the inclusion of carbon nanotube increased water retention under heating condition. Furthermore, the experimental conditions of adsorption kinetics and dynamics for the removal of cationic dye, Brilliant Green (BG), were studied in the range of 6-8 for pH, 10-60 min for time (t), and 10-300 mg/L for initial concentration (C0) of the dye. The optimum conditions obtained for adsorption of Brilliant Green dye were pH 7, t=50 min and C0=10 mg/L. Also, the results indicated that more than 98% of the maximum adsorption capacity toward Brilliant Green dye was achieved within the initial 10 min. The experimental tests showed that the hydrogels could be used as fast–responsive and high capacity sorbents in Brilliant Green removal processes from industrial waste water.