Iranian Journal of Polymer Science and Technology
Year:2018 | Volume:31 | Issue:2 |Papers Count:7

Hypothesis: The dispersion state of nanoparticles cannot be evaluated accurately by rheological and mechanical testes because their agglomerates break down under applied stress leading to changes in their microstructure. Additionally, the contribution of interparticle interactions to macroscopic properties such as rheological and mechanical properties is still unclear. This is mainly due to the combined effects of interparticle interactions and the particle-polymer interactions. Microscopic measurements which can only provide information on a very small section of a sample are not reliable for this purpose. However, electrical tests as nondestructive methods can be used to assess the microstructure and cluster formation in nanocomposite structures. In addition, it is possible to detect separately the effect of filler-filler interactions using dielectric properties and with a proper choice of materials. Methods: In this study, ZnO/polystyrene (PS) nanocomposites were prepared through conventional mixing, dispersive mixing and surface particle treatment to control the particle dispersion states. The dispersion state of nanoparticles has been analyzed using their optical, electrical and rheological properties. Findings: The results showed that storage modulus increased with increasing filler dispersion, which could be attributed to the increase in interfacial layer and the higher modulus of nanocomposite relative to that of the bulk polymer matrix. The SEM images showed that the dispersive mixing and surface treatment of ZnO nanoparticles with oleic acid improved the dispersion of ZnO particles inside the PS matrix. On the other hand, increase in dispersion decreases the electrical conductivity and dielectric constant due to greater interparticle distance and reduction of dipole-dipole interactions, respectively. Hence, it is possible to detect the particle dispersion state by rheological and electrical properties.

Hypothis: Rubber powder with a very fine particle size, rough surface and very low impurities can be prepared by water jet technology. The use of this powder as a suitable additive in tyre compounds is very important from economic and environmental viewpoints. Methods: Morphology of the water jet powder was investigated using SEM. The rubber powder was added to a SBR/BR-based tyre tread formulation and the curing behavior and mechanical properties of the resultant product were determined. A full factorial experimental design was also conducted to study simultaneously the effects of rubber powder, sulfur and carbon black levels on the curing and mechanical properties of tyre tread formulation. Furthermore, the modification effect of Vestenamer additive and curing agent on the formulation properties was investigated. When using design of experiments, for each property the regression models with linear and binary interaction terms on the basis of three variables were successfully developed and statistically validated. Findings: The rubber powder showed a lowering effect on tensile properties, which was attributed to reduced crosslink density due to the sulfur migration from the rubber matrix to the powder phase. A small, but statistically significant negative effect on the aging, abrasion and resilience properties of rubber compound was also observed, However, the tear resistance and de Mattia crack growth were improved with increasing rubber powder content, that could be attributed to the lesser effect of rubber powder on the compound modulus. It was shown that with some increase in the curing agent, sulfur and accelerator dosage, it was possible to compensate for the tensile properties to some extent and for the abrasion, resilience and aging properties completely, whereas others remained relatively unchanged. It was also shown that except for abrasion, the Vestenamer processing aid had little improving effect in the presence of rubber powder.

Hypothesis: The main objective of this project was the development of a new method for converting natural polymers into hybrid hydrogels. The hybrid hydrogels are usually prepared through grafting of acrylic monomers onto pure polysaccharides, and this study was performed using rice husk to prepare semisynthetic hybrid hydrogels. Methods: Rice husk as a source of polysaccharide was modified with acrylic latexes that were prepared through inverse emulsion polymerization with the use of acrylic monomers such as acrylic acid, acrylamide and 2-acrylamido-2-methyl propane sulfonic acid. This process resulted in the conversion of low-value material into a value added semi-synthetic hydrogel product. Low absorbency under load (AUL) was the main weakness of hybrid hydrogels. The hybrid hydrogels were surface crosslinked through ethylene glycol diglycidyl ether (EGDGE) as surface crosslinker to improve AUL. Findings: The effect of latex type on the swelling capacity of hybrid hydrogels was investigated. The chemical reaction between rice husk and acrylic latex was carried out in modification process of rice husk. The obtained semi-synthetic hydrogel constituted of 51% natural part and 49% synthetic part. Among the microgel latexes with different structures, the poly (NaAA-AA-AM-AMPS) was the most suitable polymer latex for the conversion of rice husk into hydrogel. The swelling of this hybrid hydrogel was 35. 8 and 12. 7g/g in distilled water and saline solution, respectively, whereas the unmodified rice husk showed no water absorption capability. AUL of surface crosslinked hybrid hydrogels was increased up to 27%. The hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM). These hydrogels, which were prepared directly from natural polymers, showed great potentials in agricultural systems applications.

Hypothesis: In controlled polymerization methods, atom transfer radical polymerization (ATRP) is one of the most successful methods for the polymerization of various monomers with the controlled pattern. Effect of some important parameters on kinetics of methyl methacrylate polymerization was investigated using 1H NMR and GPC techniques. Methods: In this work, tridentate ligand bis(2-dodecylsulfanyl-ethyl)-amine (SNS) and the Cu(I)Br catalyst of this ligand were synthesized. The ligand and corresponding catalyst were characterized using 1H NMR, UV-Vis and FTIR techniques. ATRP of methyl methacrylate was investigated in bulk state using the SNS/Cu(I)Br and ethyl-2-bromo-2-methyl propionate as initiator in different conditions. The polymerization kinetic was studied by 1H NMR and gravimetric techniques. The kinetic curves of Ln([M]0/[M]t) versus time were plotted and the kpapp was obtained from the curves. The effect of temperature on the kinetics was studied by on-line 1H NMR spectroscopy (75 and 90° C). The effect of the monomer to initiator ratio (500: 1, 600: 1, 700: 1) was investigated at 90° C. In order to confirm the effect of other variables (temperature, catalyst and monomer concentration) on polymerization kinetics, we employed gravimetric method. Finding: The linear correlation of Ln([M]0/[M]t) versus time and narrow molecular weight distribution (~1. 2) revealed that the polymerization reaction process was according to the controlled/“ living” radical polymerization. With increasing the temperature, the polymerization rate also increased, and the temperature of 90° C was used as the optimum in subsequent studies. The kinetic plots revealed that in bulk state due to the role of monomer as solvent, the polymerization rate decreased with increasing the monomer content, and subsequently reducing the concentration of the initiator. The effect of the ligand to Cu(I)Br ratio (1: 1, 1. 5: 1, 2: 1) on the polymerization kinetic was studied and the results showed increased polymerization rate due to the greater solubility of the catalyst at high ligand concentration.

Hypothesis: Polymer matrix composites (PMCs) have various structural applications. To improve the mechanical properties of PMCs, nanoparticles are usually added to polymer matrix as reinforcements to produce polymer matrix nanocomposites. This research investigates the effects of surface treatment of graphene nanoplatelets (GNPs) on the tensile and impact behavior of basalt fibers\ epoxy composites. Methods: For this purpose, surface treatment of GNPs was performed using (3-aminopropyl) trimethoxysilane. The presence of silicon and nitrogen elements, which are the main components of functionalization group on the surface of treated GNPs, was confirmed by EDX-SEM mapping analysis. The nanocomposites with different weight percentages of treated GNPs (0. 2, 0. 3, 0. 4 and 0. 5) were fabricated by hand lay-up method. Also, two composite samples, one without GNPs and the other with 0. 4 wt% untreated GNPs were fabricated to compare with those reinforced with treated GNPs. Tensile and Charpy impact tests were performed on fully cured samples. Findings: The results showed 21. 1, 3. 6, 35. 1 and 74. 6 percent increase in tensile strength, modulus of elasticity, fracture energy and impact strength, in the order given, for nanocomposites reinforced with 0. 4 wt% treated GNPs were obtained compared to those without GNPs. Also, 52. 1, 37. 5, 57. 9 and 25. 5 percent decrease in properties, in the stated order, were observed for nanocomposites with 0. 4 wt% of untreated GNPs compared to those without GNPs. According to the SEM images, the increase in tensile properties could be related to the improvement in the adhesion between basalt fibers and epoxy resin, and also the toughening mechanism of treated GNPs. The surface treatment increased the interaction between the GNPs and the matrix, and also the presence of treated GNPs promoted crack deflection phenomenon that is one of the major toughening mechanisms of GNPs. The reduction in the mechanical properties of sample containing 0. 4 wt% untreated GNPs was attributed to the uneven dispersion of GNPs in the epoxy matrix and the weak interactions between the graphene nanoplatelets and matrix and fiber.

Hypothesis: Removal of toxic dyes from wastewater has attracted considerable attention in recent years. Conventional methods are not usually effective for the removal of dyes. Much effort has been expended on the development of nanocomposite hydrogels with more efficient adsorption properties. In this research, a nanomagnetic hydrogel was synthesized useing carboxymethyl cellulose (CMC), diatomaceous earth (celite), and acrylamide (AAm). The hydrogel was used for adsorption of crystal violet from aqueous solutions. Methods: Initially, the hydrogels were synthesized using CMC, celite, and AAm in the presence of ammonium persulfate (APS) as initiator and methylene bisacrylamide (MBA) as a crosslinker. The nanomagnetic hydrogel was prepared by loading Fe(II) and Fe(III) ions into the hydrogel and subsequent co-precipitation of Fe(II) and Fe(III) ions in an alkaline solution. The hydrogel and nanomagnetic hydrogel were characterized by Fourier transmission infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and a vibrating-sample magnetometer (VSM). Findings: The results of SEM showed that the magnetic nanoparticles were well dispersed throughout the hydrogel. The TEM images indicated that the size of the magnetic nanoparticles was about 5-15 nm. The effects of various factors such as temperature, contact time, pH, and initial dye concentration on the dye adsorption behavior of the hydrogels were determined. The maximum adsorption at pH 7 in a 10 ppm of dye concentration reached 96% after 60 min at room temperature. The nanomagnetic hydrogel could be used as an effective adsorbent for the removal of cationic crystal violet dye from aqueous solutions and could be easily removed by an external magnetic field and reused. The adsorption behavior was modeled accurately using the Temkin model. The kinetics of adsorption followed a pseudo-second-order kinetic model.

Hypothesis: Water pollution has been emphasized as one of the major threats to environment and human health. In this regard, various adsorbents with high adsorption capacities and rapid sorption rates have been synthesized. In the present study, we report the synthesis, structure characterization and methylene blue adsorption of a novel hydrogel nanocomposite based on sodium alginate and silver nanoparticles. Methods: The hydrogel nanocomposite was prepared using grafting of acrylic monomers onto sodium alginate by using ammonium persulfate (APS) as free radical initiator and methylene bisacrylamide (MBA) as crosslinker in the presence of Ag nanoparticles synthesized by an in situ chemical reduction method. The structure of hydrogel nanocomposite was then characterized by FTIR, SEM, TEM, EDX, XRD, and TGA techniques. Findings: The adsorption behavior of methylene blue dye on the synthesized hydrogel nanocomposites was studied. In order to obtain the maximum adsorption capacity, the effects of various parameters were optimized with respect to dye adsorption capacity of hydrogel nanocomposites in detail. The thermodynamic parameters also demonstrated that the dye adsorption process was spontaneous and exothermic in nature. Moreover, the hydrogel nanocomposite adsorbents showed a high selectivity for the adsorption of cationic dyes with a high adsorption capacity of 168 mg/g. The antibacterial activity of the nanocomposites was examined against E. coli using disk diffusion method. In general, the results indicated that the synthesized hydrogel nanocomposite with antibacterial and dye adsorption properties is a potential material for medical applications as well as wastewater treatment.