Iranian Journal of Polymer Science and Technology
Year:2011 | Volume:24 | Issue:2 (ISSUE NO. 112)|Papers Count:11

Nanocomposites based on vinyl ester resin (Derakane 470-300) and nano clay (Cloisite 30B) were prepared. The effect of clay content of 1, 3 and 5% (by weight) on the morphology, mechanical properties and water absorption of vinyl ester resin nanocomposites were studied. The nanocomposites were characterized using small-angle X-ray scattering (SAXS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and mechanical property measurements. SAXS and TEM images revealed a fully exfoliated morphology for clay content of 1 and 3% and an intercalated morphology for clay content 5%. Mechanical tests results showed that the vinyl ester nanocomposites have significantly better mechanical properties than neat vinyl ester resin. It is also found that water absorption drops in all specimens containing nano caly, and it is reduced to half 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 (approximately 43% increase) with by incorporating nanoclay of 1%.

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 studied by differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). To study further, the effect of film thickness on oxidation kinetics was periodically studied by tracing the weight of the samples to make comparison with DSC results at constant temperature of 100oC under atmospheric pressure. Finally, the structural changes of 1, 4-PBD were investigated by carbon-13 nuclear magnetic resonance spectroscopy (13C NMR). The results from 13C NMR from 1, 4-PBD show that 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 bond while, epoxide groups are one of major products of thermal oxidation which can be identified from their 13C NMR peaks.

Poly (styrene-co-butyl acrylate) /clay nanocomposites were synthesized via in situ atom transfer radical polymerization using activators generated by electron transfer in the presence of a montmorillonite ion-exchanged with mixed surfactants of dodecyl trimethyl ammonium bromide and vinyl trimethyl ammonium chloride. The living nature of polymerization is confirmed by occurrence of narrow molecular weight distribution of the nanocomposites in which copolymers with polydispersity index of about 1.13-1.15 were obtained. Partial exfoliation of clay layers in the copolymer matrix was demonstrated by XRD patterns and further studies of TEM images. Thermogravimetric analysis (TGA) results demonstrated a slight increase in the thermal stability of nanocomposites in comparison with the neat copolymer. DSC results indicated a decrease in the glass transition temperature (Tg) of nanocomposites by the addition of clay content which are attributed to low molecular weights of the copolymers and weaker interactions between polymer chains. The chemical structure and composition of copolymers was identified by 1H NMR analysis.

Kevlar is one of the fibers which is used in heavy industrial productions such as, shipping, military and weaving for reinforcement of composites. Initial polymer of Kevlar or poly (para-phenylene terephthalamide) is an oriented liquid crystal polymer. Existence of aromatic group in the main chain leads to formation of 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 of phenylene diamine and terephthaloyl dichloride in n-methyl pyrrolidone and calcium chloride (NMP-CaCl2) solution. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) tests were carried out to characterize chemical bonds and crystalline plates of the polymer, respectively. Concentrated sulfuric acid is a solvent of poly (phenylene terephthalate) therefore, this polymer was dissolved in concentreated sulfuric acid (96%) and the polymer solution was injected into the cylindrical tank contain water. Sulfuric acid was transferred into water and the polymer was solidified. After solidification, tensile force of vortex led to orientation of rigid-rod polymer molecules in direction of water rotation and long fibers were formed from the polymer. The fibers were broken to short fibers by the same force of vortex. The short fibers were dried. SEM images showed the regular particles on the surface of fibers. Results of FTIR and XRD proved that the regular particles are sodium sulphate salt. The effect of sodium sulphate salt as an impurity on the short fibers was studied.

The effect of nanoparticle diamond incorporated in an experimental dental adhesive formulation is evaluated by examining the mechanical properties and shear bond strength of the system. Diamond nanoparticles were incorporated into 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 facilitate the 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 the adhesive system were measured. The adhesive-dentin interface was then observed by scanning electron microscopy. The results were analyzed using one-way ANOVA at a 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 modulus were observed. Microshear bond strength test revealed 70% and 79% improvements of adhesion force in systems containing 0.1% and 0.2% nanoparticles, respectively.Although the neat diamond nanoparticles revealed antibacterial activity, the adhesive containing different percentages of the nano particles did not show any antibacterial activities when tested against, Staphilococcus Aureus, Staphilococcus Streptococcus, Staphilococcus ephidermidis, Saprophyticus, Enterococcus faecalis bacteries.

The residual stresses in composite laminates depend on several factors including the conditions of fabricating process, property of materials, direction and lay-ups of the layers. However the thermo-elastic behavior of composite is one of the most important parameters affecting the magnitude of residual stresses. The elastic properties and residual stresses do not remain constant under cyclic thermal loading and vary in a non-linear manner. The study of these non-linear variations of modulus and strength and their effects on residual stresses in laminates while experiencing thermal load cycles is the main goal of this paper. An experimental device is designed and manufactured conveniently to exert defined thermal load cycles with different 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 before and after experiencing defined number of thermal shocks. The residual stresses in composite laminates are calculated and compared based on the actual behavior of composite and by means of a modified classical laminate theory. The results of this study demonstrate that the non-linear behavior of composites influences the residual stresses significantly. In addition, if the sample becomes more brittle, the residual strains remain constant; while the elasticity modulus and residual stresses decrease.

Kinetics of radical polymerizations of waterborne alkyd/acrylic hybrid resin via batch mini-emulsion technique was studied using redox initiators (TBHP/Fe2+/EDTA/AsAc and TBHP/Fe2+/EDTA/SFS) at relatively low temperatures and thermal initiators (BPO, KPS and AIBN) at higher temperatures to seek 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 low temperature with more efficient control of the reactor temperature. It was found that at 45oC TBHP/Fe2+/EDTA/SFS redox initiator system leads to 98% monomer conversion, a much higher rate than that of systems involved thermal initiators.

Coefficient of friction (COF) for rubber parts is one of the key parameters in their interaction with solid rough surfaces (micrometer to millimeter scales), such as tire-road interactions. COF of rubber depends on viscoelastic properties of rubber, roughness characteristics of the counter-part surface, and process variables such as contact nominal pressure and sliding speed. Due to the need for measuring COF for rubber, a new friction tester, with continuous variation of nominal pressure and sliding speed, was designed and constructed in order to assess the effect of above mentioned parameters. Tire tread compounds, as the most common rubber part in the field of rubber tribology, was used for this purpose. Viscoelastic properties of compounds were varied by changing composition of styrene-butadiene rubber (SBR) and butadiene rubber (BR) in the blend. Effect of surface roughness was evaluated by using silicon-carbide papers with different roughness parameters. By statistical analysis it was shown that the designed friction tester has high accuracy in measuring the coefficient of friction of rubber and differentiating the effective parameters.Increasing the nominal pressure led to reduction of COF and increase in sliding speed forced it through a maximum. In conclusion, the loss factor of the compound and asymmetry in roughness distribution of the counter-surface are considered as the most effective parameters on COF of rubber.