دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و یکم شماره 6 (پیاپی 98، بهمن و اسفند 1387)

Two steps synthetic method for the preparation of a novel emulsion stabilizer called poly(ricineoleic acid-b-ethyleneglycol-b-ricineoleic acid) with average mass molecular weight of 7000 Daltons is investigated. In the first step, oligoricineoleic acid with average mass molecular weight of 1800 Daltons is synthesized (yield 70%). In the second step, the desired copolymer is synthesized from the reaction of two moles of oligomer with one mole of polyethylene glycol and its stabilizing effect on an water/oil emulsion is investigated. For the formulation of the emulsion, the synthesized copolymer is first dissolved at 45oC in diesel oil while stirring, and then this solution is added dropwise to the solution of saline water (1M). Then the mixture is stressed under ultrasonic waves for 5 s to afford smaller drops, after which the emulsion shows good stability. A thin layer film of emulsion- produced from injection of emulsion (0.1 μL) is studied by light microscope equipment. In this study the number of oil droplets and the average diameter of droplets are determined. Also the mole fractions (φ = 0.32) are calculated. This copolymer can be used as a stabilizer in invert emulsion muds, which are used in perforating industry and as a thickener in food and cosmetic industries.

Polymer application for the improvement and modification of the bitumen used in roads surfaces has expanded in recent decades. The roads engineers and constructors, therefore, have used the modified bitumen in asphalts helping in this way to increase roads and pavements service life and improving the durability of the roads and asphalts. The bitumen used in asphalt mixture constitutes only a low percentage of the weight of this mixture (between 4% and 6%), but even this small amount has a significant effect on asphalt performance. The polymers that are mostly used in promoting the bitumen specifications are polymer modifiers including: styrenebutadiene- styrene (SBS), as well as similar polymers such as styrene-butadiene-rubber (SBR), ethylene-vinylacetate (EVA) and polyethylene (PE). Polymers as the most important family of bitumen modifiers are added to bitumen to improve bitumen performance and to increase its effectiveness. Among the existing polymers, SBS is considered as the best bitumen modifier. In this research, SBS as one of the elastomer-thermoplast modifiers was added in different weights (2%-5%) to bitumen 60/70 in Isfahan Refinery and its effect on asphalt properties were investigated. Adding this polymer to bitumen improves the Marshall stability of sample asphalt, flow, module of rupture and asphalt content voids. However, it has a minor effect on asphalt special weight. Adding SBS would also lead to asphalt fatigue life.

In this work, a thermoplastic polyurethane elastomer (TPUE) model based on polytetramethylene glycol, toluene diisocyanate and 1,4-butanediol was selected and synthesized. According to this model two types of polyurethane nanocomposites were prepared by in situ polymerization and melt intercalation procedures. The organo-modified nanoclay was used in nanocomposites samples in 0.4 weight percent level. The prepared nanocomposites were studied by WAXD, tensile and thermal analysis. Thermal properties of the nanocomposites were higher than those of pure polyurethane elastomers. Nanocomposites prepared via melt intercalation method showed a lower tensile strength and hardness than those prepared through in situ polymerization method.

Applications of thermoplastic composites have developed extensively. The thermoplastic composites in comparison with the thermoset composites have many advantages. Thermoplastic composites can be melted and remolded many times. The duration of manufacturing process of these composites is short, producing very tough material, and the welding ability and multiple recyclings are their further advantages. The lack of knowledge in this group of composites is the main obstacle in their development. In this review the research works in the field of residual stresses in thermoplastic composites is presented. First, a literature survey on the available research on residual stresses on thermoplastics and thermoplastic composites reinforced with short fibers is compiled. Moreover a review on the available research on residual stresses on thermoplastic composites reinforced with long fibers is presented as well. The effects of the residual stresses on these composites are discussed. Experimental techniques for the measurement of residual stresses in thermoplastic composites and the methods for reducing the existing residual stresses are studied.

In this study, porous scaffolds from poly(D,L-lactic acid) have been prepared via liquid- liquid phase separation method in ternary system of polymer-1,4-dioxane-water. Polymer dissolved in dioxane in 1.5, 2.5 and 5 % wt/v and the solvent/non-solvent ratios were 13/87, 15/85 and 17/83. Cloud point curves prepared by visual turbidometry. In order to obtain porous scaffolds with inter-connected pores structure, each system cooled below its cloud point temperature to achieve phase separation then promptly freezed. Furthermore, sublimation in freeze-dryer took place. Scanning electron microscopy have been used to study the morphologies of the scaffold and average pore sizes from 10 to 37 μm were obtained with variation in systems concentrations. Porosity density and of the scaffolds were measured by volumetric method and 85.5% was achieved. The results show that variation in concentration of ternary system has great effect on morphology, pore size and porosity density of the scaffolds.

In current work a comprehensive mechanism based on intermediate radical termination theory is assumed for RAFT polymerization of styrene over cumyl dithiobenzoate as RAFT agent. Rate constants for addition (ka) and fragmentation reactions (kf) are set to 6×106 and 5×104 respectively, which lead to an equilibrium constant value of K = ka/kf = 1.2 x 102. Moment equations method was used to model this mechanism and the results were compared to experimental data to verify modeling. The effects of changing RAFT agent concentration on conversion, molecular weight and polydispersity index of the final product were investigated through the modeling. According to the results, the likelihood of living polymerization increases with raising RAFT agent concentration which leads to linearity of conversion and molecular weight curves and therefore lowering the polydispersity index and narrowing the molecular weight distribution.

Ethylene was polymerized in slurry phase over a TiCl4/Mg(OC2H5)2 catalyst activated by Al(C2H5)3. It was shown experimentally that mass transfer resistance has no effect on polymerization kinetics. After estimation of the active site concentration by inhibition method with carbon monoxide, the effects of polymerization temperature, monomer and cocatalyst oncentrations and hydrogen were investigated. By determination of the average rate of polymerization at 13 min and 50 min of reaction times it was observed that the polymerization rate was first order with respect to the monomer concentration and the dependence of the polymerization rate on the concentration of Al(C2H5)3 could be described by the Langmuir-Hinshelwood mechanism. The polymerization rate decreased with the increase of hydrogen partial pressure. Polymerization rate as a function of polymerization temperature showed a maximum point.

The preparation and characterization of the vinyltriethoxysilane-modified silica nanoparticles were investigated. Also the surface tension of polystyrene, native (hydrophilic) silica and silane-modified (hydrophobic) silica were determined. Two kinds of polystyrene/silica (treated and non-treated) nanocomposites were prepared with different filler loadings by solution method. Their viscoelastic properties were studied by dynamic stress controlled rotary shear rheometer. Solid-like response of polystyrene / native silica nanocomposites were observed in the terminal zone. Solid inclusions increase the storage modulus more than the loss modulus, hence decrease the material damping. By increasing filler volume fraction, the particles tend to agglomerate and build clusters. The presence of clusters increases the viscosity, the moduli and the viscoelastic non-linearity of the composites.Treating the filler surface reduces its tendency to agglomerate as well as the adhesion between the particles and the polystyrene, leading to lower viscosity and interfacial slippage. Also the loss modulus peak is affected significantly by the particle surface area and its surface property in silica-filled polystyrene, which corresponds to its glass transition.