فهرست مطالب

  • Volume:21 Issue:12, 2012
  • تاریخ انتشار: 1391/10/02
  • تعداد عناوین: 9
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  • Thermal degradation behavior and kinetic studies of polyacrylamide gel in TiO2 nanoparticles synthesis
    Masoud Rakhshani, Mohammad Mehdi Kamrannejad, Ali Akbar Babaluo, Mostafa Rezaei, Mirkarim Razavi Aghjeh Pages 821-828
    Polyacrylamide gel (PAMG) method is a simple, fast and cheap method used for the synthesis of a wide variety of nanopowders. However, no adequate results have been reported on the thermal degradation behavior of PAMG which can be very effective on the final product properties. In this work, thermal degradation behavior of PAMG in the presence of TiCl4 as a precursor salt for synthesis of TiO2 nanoparticles was examined in comparison with linear polyacrylamide (LPAM) and pure PAMG by thermogravimetry/differential thermal analysis. Their thermal degradation kinetics was investigated, as well. The results showed that thermal degradation of all samples occurred in two stages at different onset temperatures. Despite the high thermal stability of pure PAMG compared to LPAM, the presence of TiCl4 as a mineral material in PAMG structure decreases the thermal degradation onset temperature, considerably. Furthermore for LPAM and PAMG, majority of weight loss occurs in the second stage, but in PAMG with TiCl4 the weight loss occurs mainly at the first stage. For more detailed investigation, residual materials were characterized by Fourier transform infrared spectroscopy and X-ray diffraction (XRD) techniques, attributing this trend to the presence of mineral materials in PAMG structure. XRD and transmission electron microscopy were also applied to confirm anatase crystalline structure and nanoscale distribution of the TiO2 particles synthesized via PAMG method.
  • A superabsorbent hydrogel network based on poly((2-dimethylaminoethyl) methacrylate) and sodium alginate obtained by γ-radiation: synthesis and characterization
    Ghasem R. Bardajee, Zari Hooshyar, Fatemeh Zehtabi, Ali Pourjavadi Pages 829-836
    In this study, the synthesis and characterization of a novel nano-porous superabsorbent hydrogel with high water swelling capacity is described. A nano-porous hydrogel was prepared by employing (2-dimethylaminoethyl) methacrylate (PDMAEMA) as a pH sensitive monomer and sodium alginate (SA) as a water soluble polysaccharide under γ-ray irradiation. The polymerization reaction was performed at room temperature in the absence of chemically toxic crosslinking agent and initiators. The interactive parameters including biopolymer backbone concentration, monomer concentration and γ-irradiation dose were selected as major factors in the synthesis of superabsorbent and three levels for each factor were applied to obtain the highest water swelling according to the central composite design (CCD) method. According to the results of nine different tests which were derived by CCD method, the optimum conditions were determined. The results showed that the hydrogel prepared at concentration of 1.5 g SA, 2.1 mol/L PDMAEMA and at a radiation dose of 5 kGy displayed the highest swelling capacity. In continuation, the effect of salt, pH, and particle size on the swelling behavior of the obtained samples was investigated. We found that the swelling of the optimized sample first increased and then dropped with increases in pH from 2 to 12 and the maximum water absorbency was observed at pH 7. Finally, different techniques such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscope (SEM) were applied for the characterization of optimized nano-porous hydrogel.
  • SiAlON nanoparticles effect on the corrosion and chemical resistance of epoxy coating
    Samire Sabagh, Ahmad Reza Bahramian, Mehrdad Kokabi Pages 837-844
    Effect of incorporating SiAlON nanoparticles at different loading levels (0–12 wt%) on chemical resistance of epoxy coating was investigated by immersion in basic (Na2CO3, pH = 11) and salty (NaCl 3.5 wt%) (environments at 85 °C for 60 days. Epoxy resin chemical resistant coating grade based on bisphenol A was used with polyamine hardener as a curing agent. In these testes, surface morphology changes of the samples were studied and compared owing to initiation and propagation of cracks. Results indicate an enhancement in the epoxy nanocomposite chemical resistance due to the addition of small fraction of SiAlON nanoparticles. Samples containing 3 and 5 wt% of SiAlON nanopowders were considered as optimum samples compared to all the other samples, because they showed more resistances to initiation and propagation of cracks and lower permeability in chemical environment in comparison with neat resin and other samples. Also, epoxy coatings containing SiAlON nanoparticles were successfully coated on steel substrates and corrosion electrochemical behavior of these nanocomposite coatings were characterized by electrochemical impedance spectroscopy (EIS). The electrochemical monitoring of the coated steel over 35 days of immersion in 3.5 wt% NaCl solution at room temperature suggested the positive role of nanoparticles in improving the corrosion resistance of the coated steel.
  • Production of superabsorbents from fungal chitosan
    Akram Zamani, Mohammad J. Taherzadeh Pages 845-853
    Superabsorbent polymers (SAPs) were prepared from fungal chitosan through three steps of carboxymethylation, cross-linking, and freeze drying. The alkali-insoluble material (AIM) of the cell wall of zygomycetes fungus Rhizomucor pusillus was first pretreated with 72 mM sulfuric acid at room temperature to release the phosphates from the cell wall. The phosphate-free AIM was then either subjected directly to carboxymethylation, or treated with 72 mM sulfuric acid at 120 °C to extract and recover the fungal chitosan prior to carboxymethylation. The carboxymethylated derivative of pretreated AIM (CM-P-AIM) and carboxymethyl fungal chitosan (CM-f-CS) exhibited 50 and 100 % water solubility, respectively. Glutaraldehyde was subsequently added to aqueous mixtures of CM-f-CS and CM-P-AIM to cross-link the water-soluble fractions. These mixtures were then frozen at −20 °C and freeze dried. The water-binding capacity (WBC) of the final product obtained from CM-f-CS (30 % of AIM) was 77, 30, 33 and 45 g/g after 10 min of immersion in water, urine, 0.9 % NaCl and artificial blood solutions, respectively. The respective WBCs of the product obtained from CM-P-AIM (90 % of AIM) were 73, 22, 24 and 37 g/g at identical conditions. SEM micrographs indicated that the SAPs prepared from CM-f-CS and CM-P-AIM had porous sheet-like structures.
  • Shrinkage and mechanical properties of unsaturated polyester reinforced with clay and core- shell rubber
    Morteza Ahmadi, Mohammad Reza Moghbeli, Mahmood M. Shokrieh Pages 855-868
    Glassy unsaturated polyester (UP) resin was reinforced using an organically modified montmorillonite (OMMT) and toughened with core–shell rubber (CSR) particles. The nanostructure, morphology, and deformation mechanism of composite specimens were studied by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and reflected optical microscopy (ROM). An intercalated nanostructure with partial exfoliation was observed in the UP reinforced by various amounts of OMMT. Locally clustered but globally good CSR particle dispersion in the UP matrix was evident in UP toughened with 5 and 10 wt% CSR particles. Simultaneous presence of OMMT and CSR particles in UP/OMMT/CSR hybrid composites was found to cause partial phase separation with bigger rubber particle agglomerates and lower clay-intergallery height increase. The effects of OMMT and CSR contents on volume shrinkage, impact fracture energy, fracture toughness, and compressive yield strength of UP were investigated. The introduction of OMMT of up to 3 wt% into the UP matrix lowered volume shrinkage to some extent, while further addition increased the shrinkage slightly. In the hybrid nanocomposites, the volume shrinkage decreased to a minimum level of 5.2 % with increases in OMMT level. The impact fracture energy of UP improved with increasing the OMMT level of up to 3 wt%, whereas its further addition decreased the impact fracture energy slightly due to the clay particle agglomeration. The hybrid composites with OMMT level below 3 wt% showed higher impact fracture energy compared to the reinforced UP specimens with the same OMMT levels. Interestingly, a synergism in the fracture toughness (K IC) was observed in the hybrid composite containing 1 wt% OMMT and 10 wt% CSR particles. The presence of OMMT as reinforcement in the hybrid composites could compensate the lowering of the compressive yield strength caused by low-modulus CSR particles. The clay–rubber particle interaction in the hybrid systems seems to increase the threshold of shear deformation of the UP matrix to some extent.
  • Kinetic study of photodegradation of water soluble polymers
    S. Ghafoori, M. Mehrvar, P. K. Chan Pages 869-876
    The kinetic models of the photo-oxidative degradation of water-soluble polymers, as the main component of water-soluble composite films in aqueous solutions, by ultraviolet radiation and hydrogen peroxide (UV/H2O2) are developed. The rate expressions of the photochemical degradation of soluble polymers are developed based on the mass balance of the main chemical species in water. Continuous-distribution kinetics is applied for the kinetic modeling of the photo-oxidative degradation of polymers in aqueous solutions based on the population balance equations (PBEs). It is assumed that the random chain scission is the mechanism of the chain cleavage. The PBEs are solved by the moment operation which transforms the integro-differential equations into ordinary differential equations that could be readily solved to obtain the rate coefficients of the polymer photodegradation. The model predictions for the number average molecular weight and the number of chain scissions per molecules are in good agreement with the experimental data obtained from the open literature for the photodegradation of poly(ethylene glycol) by the UV/H2O2 process in aqueous solution. The results confirmed the random chain scission assumption. The sequential quadratic programming was used as an optimization technique to find the kinetic parameters that could be used for scaling-up purposes.
  • Statistical analysis of experimental parameters in characterization of ultraviolet-resistant polyester fiber using a TOPSIS-Taguchi method
    Gui-Bing Hong, Te-Li Su Pages 877-885
    Cells may be damaged under long-term exposure to ultraviolet (UV) rays; hence, titanium dioxide has been used to produce polyester (PET)/titanium dioxide (TiO2) UV-resistant fibers using the melt-spinning method. This study employed the Taguchi method and the technique for order preference by similarity to the ideal solution (TOPSIS) to plan the melt-spinning process parameters in to save experimental costs and time. Both the Taguchi method and TOPSIS could effectively obtain the mechanical characterization of PET/TiO2 UV-resistant fiber and replace the original 19,683 groups of experiments with 27 groups. The analysis of variance and response surface methodology found that the key factors for the quality attributes of PET/TiO2 UV-resistant fiber are the die temperature and the winding speed. By controlling these factors, the mechanical characterization of PET/TiO2 UV-resistant fiber could be effectively enhanced. The optimal conditions and quality characteristics obtained by the proposed method are in the 95 % confidence interval, proving the reliability of this study. The PET/TiO2 UV-resistant fiber, obtained under the best conditions, could effectively absorb both UVA and UVB radiations, and thus be applied in sports leisure clothing, umbrellas, work uniforms, hats, tents, curtains and other products. The results also proved that the method could save experimental costs and time, which meets the world trends of energy saving and carbon reduction.
  • Multi-walled carbon nanotube-filled polypropylene nanocomposites: high velocity impact response and mechanical properties
    Mahdieh M. Zamani, Abdolhossein Fereidoon, Alireza Sabet Pages 887-894
    Polymer nanocomposites containing 0.75, 1.0 and 1.5 wt% of multi-walled carbon nanotubes (MWNTs) in a polypropylene (PP) matrix were studied in relation to their low and high velocity impact performances. PP nanocomposites reinforced MWNTs were prepared via melt compounding in an internal mixer followed by injection molding. Transmission electron microscopy analysis confirmed well dispersed 1 wt% MWNT in the polymer nanocomposites. The same analysis showed agglomeration and cluster formation in 1.5 wt% MWNT specimens. Results showed increase in Izod impact strength in nanocomposites containing 1 wt% MWNT, which attained the highest value (with 33.4 % increment). A single stage gas gun was used to carry out high velocity impact test in velocity range of 20–150 m/s using hard steel hemispherical tip projectile of 11.34 g weight and 8.1 mm diameter. Results showed better ballistic limit velocity (the average of highest impact velocity causing perforation but unable to go through and lowest impact velocities with no residual velocity recording) and energy absorption for specimens, each containing 1 wt% MWNT, showing the highest value (with 100 % increment), compared with neat PP. Considerable increases were observed in tensile and flexural strengths and modulus for the MWNT-containing specimens as compared with neat PP.
  • Synthesis, characterization and protein separation efficiency of N-isopropylacrylamide-co-N-tertiary butylacrylamide-co-acrylamide-based hydrogels
    Suman Shekhar, M. Mukherjee, Akhil Kumar Sen Pages 895-905
    In the present study, hydrogels were prepared by free radical polymerization in water–dioxane mixture with fixed molar ratio (25 mol%) of N-isopropylacrylamide (NIPAM) and varying remaining molar concentrations of N-tert-butylacrylamide (NTBA) and acrylamide (AAm). The structure of the resultant hydrogels was studied by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques. The thermal properties of the hydrogels were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) methods. DSC thermograms were used for the quantitative determination of free, interfacial and bound water contents. The result showed that the free and interfacial water contents increased with increase in the hydrophilic AAm content, and the bound water content increased with hydrophobic NTBA content in the hydrogels. Swelling behavior of the hydrogels was evaluated at different temperatures. The percentage swelling and diffusion kinetic parameters (network structure constant, type of diffusion and diffusion constant) were calculated for all samples. The diffusion was found to be Fickian type for copolymer having equimolar concentrations of NTBA and AAm and non-Fickian type for others. Diffusion coefficients of the hydrogels were found to be increased with increasing temperature. In addition, poly(NIPAM-co-NTBA-co-AAm) hydrogels were used in concentration separation process for BSA solution. The result showed that the copolymer with equimolar NTBA and AAm contents has high separation efficiency with good thermoresponsive behavior among all copolymers.