دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و پنجم شماره 5 (پیاپی 121، آذر و دی 1391)

electrospinning is a known process to produce nanofibers through electrostatic forces. In a typical process, an electrical potential is applied between droplets of polymer solution or melt, held through a syringe needle and a grounded target. In general electrospinning fibers are collected on the grounded target as a random oriented web of nanofiber. Various research projects are attempted to obtain aligned electrospun fibers. This modified electrospinning method can be developed and used in a variety of nanofiber-based applications such as making of nanofibrous scaffolds for tissue engineering. In this study, an effective method has been developed to fabricate aligned nanofibers by manipulation of electrospinning system using two nozzles with opposite charges. Moreover, the effect of some parameters including take-up velocity, applied voltage and polymer solution concentration on alignment of produced nanofibers is investigated. The comparison of fibers alignment was carried out by programming and image processing in MATLAB. It is shown that take-up velocity and polymer solution concentration have significant effect on increasing the fibers alignment. Also, the alignment is increased with applied voltage at first and then, it is decreased. The analytical results and optical microscopic images are clear evidence of showing the maximum alignment of nanofibers obtained at 15% polymer solution concentration with take-up velocity of 600 rpm and 11 kV voltage

Batch emulsion polymerization of butadiene was performed at 70°C in a Buchi reactor equipped with mechanical stirrer (300 rpm) in the presence of potassium persulfate (KPS), and disproportionate rosinate, potassium cation (DPR) as initiator and emulsifier, respectively. t-Dodecyl mercaptane was used as a chain transfer agent in polymerization reactions. Conversion was measured at various time intervals by gravimetry. Polymerization rate was then calculated from the slope of conversion versus time curves. Particle size and its distribution of the polybutadiene latex (PBL) were measured by dynamic light scattering (DLS) and scanning electron microscopy (SEM). Depending on the emulsion polymerization conditions, PBL latices were obtained with average particles’ diameter and particle size distribution in the range of 88.5-189 nm and 35-400 nm, respectively. The number of particles per unit volume of the continuous phase was calculated from the average particle size data, from which polymerization rate per particle or equally its number of growing chains per particle was evaluated. Results showed that by increasing the emulsifier concentration, the average particle size decreases while polymerization rate increases. Moreover, the number of growing chains per particle decreased slightly by increasing the emulsifier concentration. Unlike classic emulsion polymerization, particle size and polymerization rate were observed to be more or less independent of initiator concentration. The results obtained from investigation of the reaction trend showed that kinetics of the emulsion polymerization of butadiene follows case 1(n<<0/5) of the Smith-Ewart kinetics. The observed behaviour was attributed to the lower efficiency of initiator in the particle nucleation and growth processes

the rapidly increasing interest in functional materials with reversibly switchable physico- chemical properties has led to significant work on the development of stimuli responsive membranes. Thermotropic liquid crystals with their exceptional properties have potentials for drug-delivery applications. Thermoresponsive liquid-crystal-embedded membranes were investigated for the purpose of developing the drug delivery systems with thermal stimuli response. Drug release occurs at temperatures above the phase transition temperature of thermotropic liquid crystals. Therefore, they can control drug release in response to small temperature changes. In this work, the biocompatible and thermotropic liquid crystalline polymer cholesteryl-(L-lactic acid)n, CLAn (n=30), was synthesized with accurate control of molecular weight via ring opening polymerization method. Polymerization of L-lactide was carried out in the presence of cholesterol as an initiator and catalytic amount of tin (II) octoate (Sn(Oct)2) at 150°C in 5 h. The number-average degree of polymerization of CLA30 was obtained from 1H NMR spectroscopy. The phase transition behavior of liquid crystalline CLA30 was established by differential scanning calorimetry and polarizing optical microscopy. The resulting liquid crystalline CLA30 was subsequently utilized to prepare CLA30-embedded cellulose nitrate membrane by adsorption method. The CLA30-embedded cellulose nitrate membrane was used byan in-vitro drug penetration studies. Acetaminophen was used as a model drug. The permeation study was carried out at different temperatures around glass transition temperature of polymer CLA30 (37, 45 and 40°C, respectively). The results show that the CLA30-embedded cellulose nitrate membranes exhibit thermo-responsive sensitivity with controlled drug permeation

sandwich structures are widely used in aerospace, high speed trains and marine applications because of lightweight and high in-plane and flexural stiffness. Sandwich structures consist of two thin face sheets and a core. Face sheets usually are made from highly stiff and highly strong materials; In general, the face sheets may be of different metal or composite layers. Both metal and composite face sheets have advantages and disadvantages, and searching for new materials with better properties is in progress. In this paper flexural behavior of a new generation sandwich beams with fiber metal laminate (FML) face sheets were investigated experimentally. Three groups of specimens with different layer arrangements of face sheets consist of (Al/GE (0-90)/GE(90-0)/Al), (Al/GE(0-90)/Al/GE(90-0)) and (GE(0-90-0-90-90-0- 90-0)) and 40 kg/m3 polyurethane foam core were made and tested. The results show that sandwich beams with FML face sheets have better resistance against local loads, while composite faces are weak against intense loads. Also, FML faces are lighter than metal face sheets and have better connection to foam core. Also, a simple classical theory was used to predict the force-deflection behaviour of sandwich beams in elastic region. Good agreement between the experimental results and analytical prediction were obtained. Sandwich beams with FML face sheets have larger elastic region than beams with composite face sheets therefore agreement between the analytical andexperimental results in these specimens are in larger area

This study focused on the properties of alkaline pulp obtained from the soda pulping of pre-extracted bagasse and the effects of dry strength polymers on mechanical properties of paper in comparison to a paper obtained from nonextracted bagasse. Hot-water pre-extraction was carried out at 135°C for 30 min. Consequently, soda pulping and ECF bleaching were performed on pre-extracted and un-extracted bagasse, under similar conditions. It was found that pre-extraction of about 50% of hemicelloluse of the bagasse decreased total pulping yield, kappa number and increased bleachability of pulps and resulted in a significant loss in tensile and burst strengths of hand-sheets. Then, reinforcing effect of the pulps with chitosan and cationic starch applied in the wet-end were investigated. The results obtained with suitable amounts of chitosan and cationic starch were encouraging, because comparable strengths were obtained from pre-extracted and un-extracted bleached soda bagasse pulps with 1% chitosan and 1.5% cationic starch. According to the results, drop in paper strength due to hemicellulose pre-extraction of the bagasse could be compensated using suitable dry strength polymers

nucleating agents are commonly used for controlling cell nucleation in the production of high-quality foam products. The surface properties of nanoparticles include geometrical characteristics, such as the particle shape, size, and size distribution and in this respect there are few reports on the effects of geometry of particles on foaming efficiency. This study is an effort to control polymeric foam structure with addition of silica nanoparticles in a batch process. In this research polystyrene (GPPS 1540) was used as a matrix, nanosilica as nucleating agent and supercritical carbon dioxide (CO2) as blowing agent. For better dispersionof nanoparticles in the matrix, a combination of solution and melt method was employed. In continuation, the effect of surface treatment of nanoparticle on polymer foam is investigated. First, silica nanoparticles were modified by reaction with vinyltriethoxysilane followed by characterization of the results. Then, the surface tension of polystyrene, silica and modified silica were determined by contact angle test in order to predict the dispersion of nanoparticles in polystyrene. Then, two kinds of polystyrene/silica (treated and non-treated) nanocomposites were prepared with different filler loadings by a combination of solution and melting methods. A high pressure/high-temperature vessel capable of instantaneous pressure release and controlled stabilization was used to prepare polystyrene-nanosilica nanocomposites foam. The effect of surface treatment of nanosilica particles on microcellular foaming was investigated by characterizing the cell density and cell size of the foamed productusing SEM. The results showed that surface-treated nanosilica has considerable effect on decreasing cell size and increasing the cell density.

polyacrylamides are water soluble macromolecules. These polymers are widely used for flocculation, separation and treatment of solid-liquid phase materials. In this research, organic-inorganic hybrid of polyacrylamide/silica nanoparticle is prepared via radical polymerization. First, the silica nanoparticle surfaces were modified by 3-methacryloxypropyltrimethoxysilane as coupling agent using a sol-gel technique in aqueous media in acidic condition. Afterwards, the modified nanoparticles are copolymerized by acrylamide monomer in presence of a peroxide initiator during a free radical polymerization. The chemical structure of the prepared modified nano-silica as well as polyacrylamide nanocomposite was studied and confirmed by FTIR spectroscopy technique. The morphology of nanocomposite was investigated by scanning electron microscopy. The SEM micrograph showed that the surface of the composite did not display any phase separation. Nanoparticles distribution was investigated by SEM-EDX technique. The results showed a uniform distribution of particles throughout the polymer bulk. TEM analysis showed the presence of silica nanoparticles in bulk of polymer which is an indicative of suitable dispersion of nanoparticles. The thermal stability of hybrid nanocomposite with that of polyacrylamide was compared by TGA technique. The higher thermal stability of hybrid nanocomposite with respect to homopolymer is indicative of a reaction between the modified nanoparticles and polyacrylamide chain. The presence of silicaparticles in copolymer was also confirmed with EDX analysis in ash content of hybrid nanocomposite.