فهرست مطالب

علوم و تکنولوژی پلیمر - سال بیست و چهارم شماره 2 (پیاپی 112، خرداد، تیر 1390)

دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و چهارم شماره 2 (پیاپی 112، خرداد، تیر 1390)

  • تاریخ انتشار: 1390/05/01
  • تعداد عناوین: 8
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  • E. Jowdar, M.H. Beheshty, M. Atai Page 83
    Nanocomposites based on vinyl ester resin (Derakane 470-300) and nanoclay (Cloisite 30B) were prepared. The effect of clay content of 1, 3 and5% (by weight) on the morphology, mechanical properties and water absorptionof vinyl ester resin nanocomposites were studied. The nanocomposites werecharacterized using small-angle X-ray scattering (SAXS), field emission scanningelectron microscopy (FE-SEM), transmission electron microscopy (TEM) and mechanicalproperty measurements. SAXS and TEM images revealed a fully exfoliatedmorphology for clay content of 1 and 3% and an intercalated morphology for claycontent 5%. Mechanical tests results showed that the vinyl ester nanocomposites havesignificantly better mechanical properties than neat vinyl ester resin. It is also foundthat water absorption drops in all specimens containing nano caly, and it is reduced tohalf its value with respect to the neat resin when the Cloisite 30B content is only 1%.The hardness of vinyl ester samples increased from 40 to 57 Barcol (approximately43% increase) with by incorporating nanoclay of 1%.
  • F. Ziaee, A. Shoushtari-Zade Page 93
    The thermo-oxidative degradation of two viscous liquid resins of 1,2- polybutadiene(1,2-PBD) and 1,4- polybutadiene (1,4-PBD) have been studiedby differential scanning calorimetry (DSC) and thermogravimetry analysis(TGA). To study further, the effect of film thickness on oxidation kinetics wasperiodically studied by tracing the weight of the samples to make comparison withDSC results at constant temperature of 100°C under atmospheric pressure. Finally,the structural changes of 1,4-PBD were investigated by carbon-13 nuclear magneticresonance spectroscopy (13C NMR). The results from 13C NMR from 1,4-PBD showthat after heat treatment new carbon peaks are obtained for an epoxide carbon at 58.6 ppm, an adjacent methylene carbon of epoxide group at 24.0 ppm and a peroxide methine carbon group at 86.7 ppm. The results from TGA and DSC studies conclude that 1,2- PBD do not age due to its structure. The results from NMR spectroscopy indicate that besides structural changes, increase in mass is due to radical addition to double bondwhile, epoxide groups are one of major products of thermal oxidation which can beidentified from their 13C NMR peaks.
  • L. Ahmadian-Alam, V. Haddadi-Asl, H. Roghani-Mamaqani, L. Hatami, M. Salami-Kalajahi Page 101
    Poly(styrene-co-butyl acrylate)/clay nanocomposites were synthesized via insitu atom transfer radical polymerization using activators generated by electrontransfer in the presence of a montmorillonite ion-exchanged with mixedsurfactants of dodecyl trimethyl ammonium bromide and vinyl trimethyl ammoniumchloride. The living nature of polymerization is confirmed by occurrence of narrowmolecular weight distribution of the nanocomposites in which copolymers with polydispersityindex of about 1.13-1.15 were obtained. Partial exfoliation of clay layers inthe copolymer matrix was demonstrated by XRD patterns and further studies of TEMimages. Thermogravimetric analysis (TGA) results demonstrated a slight increase inthe thermal stability of nanocomposites in comparison with the neat copolymer. DSCresults indicated a decrease in the glass transition temperature (Tg) of nanocompositesby the addition of clay content which are attributed to low molecular weights of thecopolymers and weaker interactions between polymer chains. The chemical structureand composition of copolymers was identified by 1H NMR analysis.
  • M. A. Semsarzadeh, A. Dadkhah Page 113
    Kevlar is one of the fibers which is used in heavy industrial productions suchas, shipping, military and weaving for reinforcement of composites. Initialpolymer of Kevlar or poly(para-phenylene terephthalamide) is an orientedliquid crystal polymer. Existence of aromatic group in the main chain leads to formationof rigid-rod molecules in the polymer, high strength and high modulus in it is fibers.Impurities in the polymer lead to decrease in fibers performance. In this research,poly(para - phenylene terephthalamide) was synthesized from polycondensation ofphenylene diamine and terephthaloyl dichloride in n-methyl pyrrolidone and calciumchloride (NMP-CaCl2) solution. Fourier transform infrared spectroscopy (FTIR) andX-ray diffraction (XRD) tests were carried out to characterize chemical bonds andcrystalline plates of the polymer, respectively. Concentrated sulfuric acid is a solventof poly(phenylene terephthalate) therefore, this polymer was dissolved in concentreatedsulfuric acid (96%) and the polymer solution was injected into the cylindricaltank contain water. Sulfuric acid was transferred into water and the polymer wassolidified. After solidification, tensile force of vortex led to orientation of rigid-rodpolymer molecules in direction of water rotation and long fibers were formed fromthe polymer. The fibers were broken to short fibers by the same force of vortex. Theshort fibers were dried. SEM images showed the regular particles on the surface offibers. Results of FTIR and XRD proved that the regular particles are sodium sulphatesalt. The effect of sodium sulphate salt as an impurity on the short fibers was studied.
  • Z. Ebadi, M. Atai, M. Ebrahimi Page 121

    The effect of nanoparticle diamond incorporated in an experimental dentaladhesive formulation is evaluated by examining the mechanical propertiesand shear bond strength of the system. Diamond nanoparticles were incorporatedinto the dentin adhesive system in different concentrations of 0, 0.05, 0.1,0.2, 0.5, and 1.0 weight percentages. The suspensions were ultrasonicated to facilitatethe nano-particle dispersion in an adhesive solution containing ethanol, bis-GMA,UDMA, TMPTMA, HEMA and photo-initiator system. Diametral tensile strength,flexural strength, flexural modulus, depth of cure and microshear bond strength of theadhesive system were measured. The adhesive-dentin interface was then observed byscanning electron microscopy. The results were analyzed using one-way ANOVA ata significant level of P>0.05. No significant difference was observed between the diametral tensile strength of the adhesive. At nanoparticle content level of 0.1% (by wt),however, 85% increase in flexural strength and 13% enhancement in flexural moduluswere observed. Microshear bond strength test revealed 70% and 79% improvementsof adhesion force in systems containing 0.1% and 0.2% nanoparticles, respectively.Although the neat diamond nanoparticles revealed antibacterial activity, the adhesivecontaining different percentages of the nano particles did not show any antibacterialactivities when tested against, Staphilococcus Aureus, Staphilococcus Streptococcus,Staphilococcus ephidermidis, Saprophyticus, Enterococcus faecalis bacteries

  • A.R. Ghasemi, R. Baghersad, M.R. Vaziri Sereshk Page 133
    The residual stresses in composite laminates depend on several factors includingthe conditions of fabricating process, property of materials, direction andlay-ups of the layers. However the thermo-elastic behavior of composite isone of the most important parameters affecting the magnitude of residual stresses. Theelastic properties and residual stresses do not remain constant under cyclic thermalloading and vary in a non-linear manner. The study of these non-linear variations ofmodulus and strength and their effects on residual stresses in laminates while experiencingthermal load cycles is the main goal of this paper. An experimental deviceis designed and manufactured conveniently to exert defined thermal load cycles withdifferent temperatures and cycle time on composite laminates. Then orthotropic glassepoxy composite laminates made by hand lay-up are tested under cyclic thermal loading.The elastic modulus and fracture strength of the samples are measured beforeand after experiencing defined number of thermal shocks. The residual stresses incomposite laminates are calculated and compared based on the actual behavior ofcomposite and by means of a modified classical laminate theory. The results of thisstudy demonstrate that the non-linear behavior of composites influences the residualstresses significantly. In addition, if the sample becomes more brittle, the residualstrains remain constant; while the elasticity modulus and residual stresses decrease
  • Sh. Madadi, A.A. Yousefi, E. Keshmirizadeh Page 141
    Kinetics of radical polymerizations of waterborne alkyd/acrylic hybrid resinvia batch mini-emulsion technique was studied using redox initiators(TBHP/Fe2+/EDTA/AsAc and TBHP/Fe2+/EDTA/SFS) at relatively lowtemperatures and thermal initiators (BPO, KPS and AIBN) at higher temperatures toseek the most suitable initiator system. At the end of all reactions the unreacted monomer content was reduced using post-polymerization technique; consequently, leading to increased monomer conversion and film formation with improved properties. The kinetics of mini-emulsion polymerization showed that in all redox initiator systems(Fe2+ catalyst + EDTA chelating agent), the radials are produced at relatively lowtemperature with more efficient control of the reactor temperature. It was found thatat 45°C TBHP/Fe2+/EDTA/SFS redox initiator system leads to 98% monomer conversion,a much higher rate than that of systems involved thermal initiators.
  • M. Razzaghi Kashani, R. Esmaeely Nisiany Page 153
    Coefficient of friction (COF) for rubber parts is one of the key parametersin their interaction with solid rough surfaces (micrometer to millimeterscales), such as tire-road interactions. COF of rubber depends on viscoelasticproperties of rubber, roughness characteristics of the counter-part surface, andprocess variables such as contact nominal pressure and sliding speed. Due to the needfor measuring COF for rubber, a new friction tester, with continuous variation ofnominal pressure and sliding speed, was designed and constructed in order to assessthe effect of above mentioned parameters. Tire tread compounds, as the most commonrubber part in the field of rubber tribology, was used for this purpose. Viscoelasticproperties of compounds were varied by changing composition of styrene-butadienerubber (SBR) and butadiene rubber (BR) in the blend. Effect of surface roughness wasevaluated by using silicon-carbide papers with different roughness parameters. Bystatistical analysis it was shown that the designed friction tester has high accuracy inmeasuring the coefficient of friction of rubber and differentiating the effective parameters.Increasing the nominal pressure led to reduction of COF and increase in slidingspeed forced it through a maximum. In conclusion, the loss factor of the compoundand asymmetry in roughness distribution of the counter-surface are considered as themost effective parameters on COF of rubber.