Iranian Journal of Polymer Science and Technology
Year:2019 | Volume:32 | Issue:1 |Papers Count:7

Hypothesis: Sensitizing the nanocomposite hydrogel systems to multiple stimuli ensures increasing their efficiency from the viewpoint of the magnitude and rate of response of the system. Adding nanosilver to dual stimuli (pH and temperature) responsive chitosan/poly(vinyl alcohol)/nanoclay nanocomposite hydrogel system increases the sensitivity of the chosen system to the third stimulus, i. e. the electric field, and enhances the overall rate of response of the system. Methods: The reduction of a silver salt to silver nanoparticles was performed by a green synthesis method within the nanocomposite hydrogel system using chitosan as a reducing agent and poly(vinyl alcohol) as a stabilizer. Silver nanoparticle formation was investigated by UV-Vis spectroscopy. SEM was used to study the distribution of silver nanoparticles in the nanocomposite system. The structural characterization of nanocomposite hydrogel was carried out by FTIR. Cyclic voltammetry was employed to evaluate the conductivity of the system. Findings: The peak observed at the wavelength of 410 nm confirmed the synthesis of nanosilver. The SEM micrograph showed the uniform distribution of nanosilver in the system. The results of the sensitivity of the responsive system to multiple stimuli indicated that the nanosilver increased the rate of response of the system in acidic and alkaline solutions. The maximum swelling rate of the system was at pH 2 and the temperature of 55° C, while the minimum rate was at pH 5 and the temperature of 20° C. The presence of nanosilver increased the rate of response of dual stimuli (pH and temperature) responsive system up to three times and its swelling rate to 1. 5 times. By applying an electric field at pH 2, the time of response of system decreased from hours to minutes and its swelling ratio increased up to 1. 7 times.

Hypothesis: Both acrylic and siloxane polymers show good water-repellency when applied on the surface of mineral materials, such as bricks and stones. This property makes them an option to protect the porous surfaces of mineral, such as stone artworks. Another advantage of using these polymers is their waterbased feature and biodegradability. Methods: In this study, substrate was selected from calcium carbonate rocks of the stone artworks of Persepolis. By adding silica nanoparticles to acrylic and siloxane polymers, changes in the properties of coatings, applied on the surface of the mineral substrate, were investigated. For this purpose, the samples were subjected to various experimental tests, such as water absorption at different time intervals, color changes resulted from accelerated aging, hydrophobic behavior study using contact angle measurement, hardness test and TGA. Morphology and surface area of coatings were studied by scanning electron microscopy (SEM). Characterization of these materials was done by various analysis methods. Findings: The effectiveness of acrylic and siloxane polymers alone and also in comparison with each other and after adding nanosilica was evaluated by different tests. This study showed that the addition of silica particles to both polymers improved surface hydrophobic properties. In addition, the silica nanoparticles altered the surface morphology of the coating and increased surface roughness. In addition, silica nanoparticles improved the stability of coatings against accelerated aging conditions, resulting in less color changes after aging. The increase in nanosilica content also increased the average hardness and the thermal resistance of both polymer coatings.

Hypothesis: Due to the unique properties of shape memory polymers (SMPs) including low density, good price, high deformability, reproducibility, molecular tailoring and good processing many applications have found for these materials in different fields. Shape memory properties of the nanocomposite samples based on polyurethane/graphene nanoplatelet (GNp) were investigated. The improvement in performance of SMPs by adding graphene nanoplatelet is the main hypothesis of this study. Methods: At first, two types of polyurethane were synthesized using different formulations (for obtaining the samples with different hard segments) and then nanocomposites samples including GNp were produced through solution method. Two different polyurethanes with hard segment contents of 23. 9% and 24. 4% were synthesized. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), shape fixity and shape recover values of the samples (as indices of shape memory properties) were employed to characterize the synthesis of polyurethane and performance of shape memory behavior of the nanocomposites. Finding: The FTIR spectra showed that the formation of polyurethane was successfully accomplished. The SEM micrographs confirmed the good dispersion of nanoparticles in the matrix and there were no agglomerations and aggregation of particles. No characteristics peaks (crystallization and melting peaks) were observed in DSC thermograms for samples based on toluene di-isocyanate which means the synthesized polyurethane was fully amorphous without crystalline and regular regions. While the samples based on hexamethylene di-isocyanate showed the regular and crystalline regions. Shape fixity and shape recover values of the samples were in the range of 70-90%. These indices were increased by GNp addition.

Hypothesis: Increasing the heat conductivity of rubber compounds is important from viewpoint of properties of uniform distribution in different points of rubber parts and reducing the curing time that affects the quality and the final price of the product. Morphology of alumina powder obtained from spray pyrolysis technology is suitable, so it could be considered as an efficient filler for tyre compounds. Methods: Morphology, composition and crystal size of a novel powder were investigated using SEM and XRD and dispergrader, respectively. The powder was added to a SBR/BR-based tyre tread formulation and the curing and mechanical properties as well as heat conductivity behavior were determined. Heat diffusivity properties were calculated by Abaqus simulation software with the aid of an experimental temperature profile in the center of the rubber part Findings: It was observed that the heat conductivity of the rubber was improved at 3 phr alumina, which was attributed to the improvement of phonon transport phenomena in rubber matrix in the presence of heat conductive filler besides carbon black. A considerable improvement in DeMatia crack growth behavior of the compound was also observed in the presence of the new filler. The other mechanical properties experienced no significant changes, except tear resistance. The rheometry results showed that the curing rate of the compounds decreased in the presence of powder, which was attributed to the surface acidic nature and the presence of surface hydroxide groups. So, it is necessary to do a comprehensive study to investigate the potential of this filler in reducing tyre curing time.

Hypothesis The morphological attributes of polymer blends have a significant influence on the final properties of the blend. Many attempts have been made to simulate morphological changes of a blend in various equipments، using several mathematical models and numerical simulations. In this study، mixing of non-Newtonian fluids was simulated using a power-law rheological model in a typical twin screw extruder in three dimensions. Modified marker and cell (MAC) method was used for simulation. In modified MAC، for simulation of polymeric fluids flow، power law rheological model was used to generalize velocity equations to non-Newtonian fluids. Interfacial tension and viscosity ratios were used to introduce the effect of miscibility parameter. Methods In this method، momentum equations were solved and discredited using finite volume method. The linear algebraic equations were solved using three diagonal matrix and the coefficients of network’ s points were obtained. Then، velocity values were obtained for any control volume in three dimensions by introducing typical rheological and interfacial tension parameters for a pair of polymers. The under relaxation factors (URFs) were used for velocities in three dimensions and pressure for faster convergence. Then، new spatial peculiarities of particles of two phases were traced by taking appropriate time intervals. The geometry of screws in twin screw extruder was achieved using hypothesis of imaginary domain of screws tips. Findings A twin screw extruder with glass barrel was designed and constructed for intuitive investigation of mixing development. Mixing of polymer pairs of different miscibility was performed in equal time intervals. The experimental pictures were compared with the simulation results. A very good agreement was observed between the results of numerical simulation and experimental images in both miscible and immiscible fluids. The determined separation areas for theoretical and experimental images also confirmed the accuracy of the simulation. Therefore، modified marker and cell (MAC) method could be used to simulate the mixing of polymer blends in twin screw extruder، as the most common blending equipment.

Hypothesis: Reduction of rolling resistance in tyres plays a crucial role in reducing global warming and CO2 emissions. Consequently, the prediction of energy dissipation in tyre tread compounds has received increasing interest from tyre manufacturers to design low dissipative compounds. In the present work, a triple model based on the Ogden hyperelastic equation, Bergstrom-Boyce nonlinear viscoelastic relationship in conjunction with a stress softening equation was proposed for the prediction of the force-displacement behavior of tread compounds. Methods: Two series of rubber blends compounds based on SBR/BR solution and SBR/BR emulation reinforced by two carbon black (CB) grades and a surface-modified silica were prepared. Each series was comprised of three blends with different filler contents. The total part of filler in each compound was kept constant as 80 phr. The first compound contained 80 phr of CB without any silica, while the second and third compounds were prepared using 20 and 40 phr silica as replacement. The mechanical behavior of the cured compounds was determined using a tensile test carried out on a ribbon type sample with 2X11 cm dimension and ATM D412 C test specimens. An optimization loop was designed in Isight code using three Abaqus, data matching and optimization components. The developed algorithm was used for the determination of the parameters of the mentioned model. Findings: It is shown that the proposed material model and the developed numerical algorithm can predict the mechanical behavior of the compounds during a loading/ unloading cycle. The trends of the variations of the predicted parameters are in reasonable agreement with macro-and micro-structure of the SBR and filler type (CB or silica). It is also found that the addition of silica to rubber compound has 25-35% decreasing effect on energy dissipation. Moreover, solution SBR has approximately 50% more reduction effect on energy dissipation compared to emulsion SBR at equal filler type and content.

Hypothesis: The purpose of this study was to investigate the effect of bending load on the electrical conductivity of carbon-epoxy composites containing various nanoparticles. The developed samples, while having sufficient flexural strength, must have the electrical conductivity proposed by the U. S Energy Institute to be used in the manufacturing of electrodes. Methods: For this purpose, carbon black nanoparticles, carbon nanotubes and expanded graphite with unidirectional carbon fabrics and epoxy resin were used to make the samples. Carbon black particles, carbon nanotube and expanded graphite with optimum weight percentages (25, 10 and 15%) were added to carbon/epoxy composite and the electrical conductivity threshold of the samples was measured according to the four-point strength method. The average electrical conductivity permeability threshold for composites containing carbon black, expanded graphite and carbon nanotubes was 23. 2, 27. 3 and 24. 7%, respectively. The samples were then subjected to bending load and for the 0. 5, 1, 1. 5, 2 and 2. 5 mm transverse displacement, the electrical conductivity value was measured during loading and unloading. Findings: The results showed that the value of electrical conductivity loss in carbon/ epoxy samples containing carbon nanotubes caused by bending was at lowest and in the carbon/epoxy containing carbon black samples displayed the highest value. Then, the flexural strength of the specimens was measured using a three-point bending test method. The pattern of nanoparticle distribution in the samples was studied on images acquired by scanning electron microscope images. The result of this research could be used in manufacturing of composite electrodes which are subjected to flexural loading (electrostatic desalting crude oil tanks) in services.