فهرست مطالب

دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و چهارم شماره 5 (پیاپی 115، آذر و دی 1390)

  • تاریخ انتشار: 1390/09/22
  • تعداد عناوین: 7
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  • Laleh Basiri, Gholam Reza Bakhshandeh, Ghasem Naderi, Shirin Shokoohi Page 343
    Nanocomposite samples based on elastomer blends of butyl rubber (IIR) and ethylene propylene diene monomer (EPDM) were prepared using a laboratory scale two-roll mill in order to study the effect of Cloisite 15A organoclay content (i.e., 1, 3, 5 and 7 wt%) on the mechanical and morphological properties of IIR/EPDM/Cloisite 15A nanocomposites compared to the unflled EPDM/IIR blends. Rheometer (RPA), X-ray diffraction (XRD) and scanning electron microscope (SEM) were utilized for relevant characterization of cure behavior and microstructural properties of the prepared samples. Cure characteristics of the prepared compounds including optimum cure time (t90) and scorch time (t5), depicted a decrease in these two parameters with increasing nanoclay content; where the cure time was prolonged with EPDM increasing content. In fact, nanoclay not only acts as a reinforcing agent in nanocomposites but also accelerates the cure process of IIR/EPDM elastomer compounds. Intercalation of elastomer chains into the organoclay silicate layers was determined by d-spacing values calculated according to the results of X-ray diffraction patterns. XRD results of all the nanocomposites samples prepared here showed a leftward shift towards lower diffraction angles in the organoclay characteristic peak, indicating an increase in the d-spacing values compared to the pure organoclay which emphasizes the intercalation of elastomer chains into the clay galleries. This phenomenon was also confrmed according to the direct observation of the cryogenically fracture surfaces of the samples by SEM micrographs depicting a combination of intercalated and exfoliated microstructures. However, there appeared incrementally slowed down rate in higher clay contents. With addition of nanoclay, mechanical properties of the nanocomposite samples including hardness, fatigue strength, tensile modulus and tensile strength were observed to be improved. Elongation-at-break and resilience of the nanocomposites were decreased as expected.
  • Mamhmood M. Shokrieh, Majid Safarabadi Page 355
    The effects of physical, thermal and mechanical parameters on curing micro-thermal residual stresses are studied, based on the energy method, to present a theoretical solution for prediction of residual stress felds. A fnite element analysis is developed to compare the theoretical and numerical results together. There is found to be a good agreement between the results of the two methods. However, due to the edge effect, the fnite element method is not able to satisfy the boundary conditions at the composite ends. An increase in the fber length leads to a signifcant increase in axial and shear stresses. In addition, for long fber composites the axial and shear residual stresses distribution become more uniform along the fber length and suddenly decrease to zero at the composite edge. The results of the two methods demonstrate that besides the physical characteristics of composites, the order of mismatch in thermal and mechanical properties of the fber and matrix has a considerable infuence on the axial and shear residual stress felds. It must be noted that the radial stress distribution is approximately independent of these parameters and only its maximum value is changed at fber end. The presented analytical solution not only satisfes all governing boundary conditions, but also yields the residual stress felds according to longitudinal and radial coordinates. A shear stress concentration occurs at vicinity of composite edge that signifcantly intensifes due to increasing the mismatch in thermal and elastic properties of the fber and matrix. High mismatch in coeffcient of the thermal expansion and Young’s modulus of the fber and matrix causes a substantial increase in the axial and shear stresses, while the difference between the Poisson’s ratios of the composite constituents has not any signifcant effect on the residual stress feld.
  • Mir Hamid Reza Ghoreishy Page 369
    This research work is devoted to experimental and theoretical evaluations of a hybrid constitutive model which was designed to simulate the mechanical behavior of a tread rubber compound. The model is a combination of Yeoh hyperelastic model with a strain-rate hysteresis model developed by Bergstrom and Boyce. The parameters of the Yeoh model were calibrated from experimental data of the ASTM D-412 stress-strain test. Three rubber strip specimens with 11 cm length and 1, 2 and 3 cm widths were selected and simulated under tension using ABAQUS/Standard code. Comparison of the results with those obtained by experiments on the samples revealed that ignoring the viscoelasticity led to a signifcant error in prediction of the force-elongation behavior. Consequently, the simulations were repeated by using a hybrid model and the results showed that there were very good agreement between the experimental and simulated results. The model is also capable of calculating the dissipated energy which can be used for the prediction of temperature rise in rubber articles with dynamic loading.
  • Pouyan Ghabezi, Mohammad Golzar Page 379
    An aircraft wing needs to display different mechanical behavior in different directions. 1- stiffness in the spanwise (transverse to the corrugation) direction which enables the aerodynamic and inertial loads to be carried. 2- compliance in the chordwise (corrugation) direction which would allow shape changes and increases in surface area; whereas a corrugated sheet due to their special geometry has potential to use in morphing applications. Therefore, in this paper the mechanical behaviour of quasi-sinusoidal corrugated composites is studied by commercial FEM software ABAQUS and a simple analytical model which is used for the initial stiffness of the quasi-sinusoidal corrugated composites (Yokozeki model). The elongation and effective stiffness in longitudinal and transverse directions of quasi-sinusoidal corrugated skins and fat composites are calculated and compared together. Using frst and second Castigliano’s theorem and Bernoulli-Euler beam theorem can be used to calculate the defection and rotational angle of a beam (sheet). In this research, different dimensions of quasi-sinusoidal element for unidirectional and woven composites of E-glass/epoxy are investigated. FEM results and analytical model are compared together. Then, the analytical model is validated by experimental results of plain woven E-glass/epoxy composites. The results of FEM, experimental and analytical simulations show that how a corrugated composite can afford with certainty larger deformation than the fat composite in using this analytical model to predict the mechanical behavior of quasi-sinusoidal corrugated composites. It was found that the corrugated composites display extremely high anisotropic behavior and have high tensile and fexural stiffness in transverse direction while exhibiting low stiffness in longitudinal direction of corrugation.
  • Nooshin Noushirvani, Babak Ghanbarzadeh, Ali Akbar Entezami Page 391

    The objective of this research was to compare the tensile, permeability, solu- bility and color properties of plasticized starch-polyvinyl alcohol-Montmo- rillonite (PS-PVA-MMT) and plasticized starch-polyvinyl alcohol-cellulose nanocrystal (PS-PVA-NCC) bionanocomposite flms. The results showed that adding MMT (7%), increased the ultimate tensile strenght from 4.2 MPa to 4.61 MPa, however, NCC (7%) did not show signifcant (p < 0.5) effect on the ultimate tensile strength. Addition of MMT decreased while NCC increased the strain-to-break of the flms. The solubility in water decreased from 23.56% to 18.77% and 11.75% for the flms containing NCC and MMT, respectively. Similarly, water vapor permeability value of 7.41 ×10-7 g/m.h.Pa was dropped to 7.05×10-7 g/m.h.Pa and 6.19×10-7 g/m.h.Pa in flms containing NCC and MMT, respectively. The results showed that the effects of MMT on tensile and permeability were higher than NCC, which can be attributed to differences in the structure and hydrophilicity of two nanoparticles.

  • Farshid Ziaee Page 403
    The unsaturation content of various polybutadiene (PBD) types of 1,4- cis, 1,4-trans and 1,2-vinyl isomers with different molecular weights was investigated. An important parameter for unsaturation content of polybutadiene would be the determination of olefnic and aliphatic contents for three types of isomers. For this purpose, proton and carbon nuclear magnetic resonance spectroscopy methods were employed for determination of 1,4-cis, 1,4-trans and 1,2-vinyl contents. A change of adjustable parameter of NMR software was made for accurate integrals giving better results. The accuracy in calculation of low molecular weight PBD, surface area of chain end group decreased in aliphatic region. Furthermore, the changing of unsaturation content versus time was considered for 1,2-PBD and 1,4-PBD in thermal degradation conditions at 250°C. NMR results showed that during heating, the unsaturation content decreased for 1,2-PBD and was not changed for 1,4-PBD. In fact, the basic factor responsible for changing of unsaturation content in thermal degradation of PBD may be due to the presence of 1,2-vinyl isomer. Finally, changing in unsaturation content versus time was observed for 1,2-PBD and 1,4-PBD in thermo-oxidative degradation conditions at 100°C. The NMR results showed that at extended time, the unsaturation content decreased for 1,4-PBD and was not changed for 1,2-PBD. Moreover, the basic factor for changes in unsaturation content in thermo-oxidative degradation of PBD is due to the presence of 1,4-cis and 1,4-trans isomers.
  • Gholam Bagheri Marandi, Lila Mahmoodpoor Sharbian Page 413
    Hydrogel nanocomposites based on alginate polysaccharide were prepared by graft copolymerization of acrylamide and itaconic acid in the presence of carbon nanotube, using methylene bisacrylamide and ammonium persulfate as crosslinker and initiator, respectively. The synthesized samples were characterized by infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. The effect of carbon nanotube content on some properties of the nanocomposites was investigated. The results showed that with increasing carbon nanotube content, the rate of water absorbency and equilibrium swelling in distilled water decreased whereas in saline solutions the water absorbency increased. Water retention capacity was also studied and the results indicated that the inclusion of carbon nanotube causes an increase in water retention under heating and loud. Furthermore, the possibilities of Cd (II) ion adsorption of samples have been investigated. It was found that incorporation of nanotubes into the hydrogel structure increased the Cd (II) metal ion adsorption capacity of the nanocomposites compared to a free-carbon nanotube sample. It is concluded that the hydrogels can be used as fast-responsive and high capacity sorbents in Cd (II) ion removing processes.