دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و پنجم شماره 6 (پیاپی 122، بهمن و اسفند 1391)

The polyaniline-glucose oxidase (PANI-GOD) electrode has been investigated in the present work. Polyaniline (PANI) film via cyclic voltammetric method was synthesized at room temperature, in a standard three-electrode cell. Aniline films were deposited from 1 M acidic (H2SO4) aqueous media containing 0.2 M aniline by voltammetric sweep between −0.1 V and 1 V, Ag/AgCl, at 50 mV/s. The sweep was stopped after 30 cycles at −0.1 V Ag/AgCl and the working electrode was deposited by polyaniline. Platinum plate (0.4cm×0.4cm), platinum rod and Ag/AgCl electrodes were used as working, counter and reference electrodes, respectively. The synthesized PANI films were characterized by electrochemical technique, electrical conductivity, UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS). A simple technique was used for fabrication of a glucose sensor. In this method glucose oxidase as an enzyme was immobilized by glutaraldehyde 0.1% as cross-linking agent and kept pH around 7 using 0.1 M phosphate over polyaniline thin films, glucose oxidase was deposited on a platinum plate in phosphate or acetate buffer. The results of EIS indicated the successful immobilization of enzyme over polymer films. Effects of some experimental variables such as cross-linking agent volume content, pH, applied potential, and temperature on the amperometric response of the sensor were investigated. It was obsereved that the activity of modified electrodes changed with various amounts of cross-linking agent volume percent. The activation energy for polyaniline-modified electrode in acetate and phosphate buffer were obtained as 41 and 37 kJ/mol, respectively. A maximum current response was resulted at pH 7 and potential 0.65 V (versus Ag/AgCl).

The biopolymer-based nanocomplexes are a group of nanocapsules that are used for encapsulation and control delivery of nutraceuticals. They are formed by binding of proteins and polysaccharides. In this study, complex formation between pectin and sodium caseinate was taken place by addition of pectin solutions (0.2, 0.45 and 0.7 % w/v) into the caseinate solutions (0.5, 1 and 1.5 % w/v) and adjusted their pH below isoelecteric point of sodium caseinate. The effect of various factors such as biopolymer concentration, salt concentration, temperature and time of ultrasound on the properties of pectin-casein nanocomplexes was investigated. Differential scanning calorimetry (DSC) and particle size analyzer were used for study of complex formation and particle size determination, respectively. The results of DSC and turbidimetry showed complex formation between the pectin and casein at pH below 5 and the results of particle size showed formation of stable dispersion with a minimum size of 86 nm at pH 4.1, caseinate of 1 % w/v and pectin 0.45 % w/v concentration. The ultrasound for more than 1 min reduced particle size and addition of salt at high and low concentrations had different effects on the stability of the colloidal system. The lowering of temperature from 21 to 4°C resulted in smaller particle size of nanocomplexes. The oscillatory rheological results showed that with increasing pectin concentration, viscoelastic moduli were increased and loss moduli were higher than storage modulus.

Thermal insulation of rocket motor chamber is one of the most important functions of elastomeric ablative material. Combustion of solid rocket motor propellant produces turbulent media containing gases with a velocity more than 1000 m/s, temperature and pressure more than 3000°C and 10 MPa, respectively,which destroys all metallic alloys. Elastomeric nanocomposite heat insulators are more attractive subjects in comparison to their non-elastomeric counterparts, due to their excellent thermal stresses and larger deformation bearing capacity. Nitrile rubber with high thermal properties is a proper candidate in such applications. Development in ablation performance of these heat shields is considered as an important challenge nowadays. A few works have been recently carried out using organoclay to enhancethe ablation and mechanical properties of heat insulators. In this work, an elastomeric heat insulator with superior ablative and mechanical properties was presented using nanotechnology. The results showed that an elastomeric nanocomposite heat insulator containing 15 wt% organoclay exhibits superior characteristics compared to its composite counterpart such as: 46% more tensile strength, 60% more elongationat-break, 1.7 times higher modulus (at 100% strain), 62% higher “insulating index number” and 36% lower mass ablation and erosion rates under a standard test with a heat flux of 2500 kW/m2 for 15 s.

A route for the synthesis of an associative thickener (AT), composed of polyethylene oxide, end-capped with nonadecylamide groups, has been devised. The molecular weight of PEO was 20,000 Daltons. PEO, with such molecular weight, was converted to a hydrophobically end-capped copolymer (hydrophobically associating nonadecanamide polyethylene oxide copolymer, POER), by three chemical reactions on its end-groups. In the first step, tosyl polyethylene oxide (Ts-PEO) was obtained from the reaction of polyethylene oxide (PEO) with tosylchloride by 95% yield. In the second step, the Ts-PEO was convertedto polyethylene oxide diamine (PEOA) by inserting ammonia gas in the solution of Ts-PEO at 0°C (90% yield). Finally, in the third step the desired associative thickener (POER) was obtained from the reaction of PEOA with nonadecanoyl chloride (90%yield). Because of chain degradation probability the reaction was carried out at the temperature lower than 45°C. Therefore, there was no chain degradation during eachreaction step. The successful conversion of hydroxyl groups was shown by viscosity behavior. This was proved by measuring the polydispersity of the reactant PEO and the product PEOR, by gel permission chromatography and comparing the viscosity of PEO with the product of the second step, polyethylene oxide diamine (POEA). The results show that through the synthetic preparation the molecular weight of thebackbone remains unchanged (~20000 D). The flow curve of a 10% aqueous solution of POER-AT shows that the solution is non-Newtonian, but the flow curve of a 10% aqueous solution of POE is a Newtonian fluid. Also the variation in viscosity of a 10% aqueous solution of POER shows that this solution is thixotropic. The effects of synthesized AT was investigated on the thickening of one formulated latex paint and it is shown an increase in the shearing strength of the formulation.

Hollow microspheres or microballoons are gas-filled spherical particles with diameters between 1 to 1000 micrometers. The wall material may be made from glass, ceramic oxides, polymers or even metals. The typical thickness of the wall is in the range of 1 to 10% of the outer diameter of the sphere. Hollowmicrospheres have low density and high specific surface. They are widely used as toners, immobilization carriers, chromatographic packings, and sound dampening or adsorption materials. Thermally expandable microspheres are hollow balloons that consist of a thermoplastic shell with a liquid blowing agent as the core. These microspheres are expanded by applying temperatures higher than the glass transition temperature of the thermoplastic shell. The particles expand due to the evaporation of the encapsulated solvent which causes an internal pressure. In this study the primary expandable particles were synthesized via suspension polymerization of methacrylate monomers in the presence of pentane as a blowing agent and benzoyl peroxide as a thermal initiator. In the second step, the particles consisting of PMMA shell and pentane core were expanded at elevated temperature to obtain microballoons with a very low density. Morphology of the particles was studied using scanning electron microscopy. The results showed that the process successfully resulted in formation of spherical microballoons. The mean diameter of unexpanded particles was about 30 μm and thickness of the shell was about 2 μm while, their mean diameter after expansion was about 90 μm and the thickness of the shell decreased to 400 nm. The diameter to wall thickness ratio of expanded particles was about 1:200 which provided particles with a very low density of 0.05 g/cm3.

Developing new methods and technologies for CO2 removal with a variety of applications, such as purification of synthesis gas, natural gas sweetening, and greenhouse gas sequestration are nowadays carried out in research works involving polymeric membranes. By employing suitable reactive carriers into the membrane matrix, the solubility and absorption rate of the reactive gas (i.e., CO2) are enhanced. In facilitated transport membrane, the selective transport through the membrane occurs owing to a reversible reaction between the reactive carriers and the target gas, while in contrast the solution-diffusion is the dominant mechanism for permeation of inert gases such as CH4, N2 and H2. In this work, the cross-linking of diethanolamine (DEA)-impregnated polyvinyl alcohol (PVA) by glutaraldehyde (GA) with different blend compositions (GA/PVA: 0.5, 1, 3, 5, 7 ratio%) were performed in the absence of an acid catalyst and organic solvents in order to avoid any interference in CO2 facilitation reaction with DEA. The fabricated membranes were characterized by differential scanning calorimetry, Fourier transform infrared (FTIR) and scanning electron microscopy. Furthermore, the effects of cross-linking agent content and feed pressure on CO2/CH4 transport properties were investigated in pure gas experiments. Finally, the cross-linked membranes showed reasonable CO2/CH4 permselectivity indexes in comparison to uncross-linked membranes. The best-yield in CO2-selective membranes (DEA-PVA/GA (1 wt%)/PTFE) represented the best CO2/CH4 selectivity of 91.13 for pure gas experiments.

Natural rubber and styrene butadiene rubber (NR/SBR) reinforced with short nylon fibers along with nanoclay (Cloisite 15A) hybrid composites were prepared in an internal and a two roll-mill mixer by a three-step mixing process. The effects of fiber content at a constant loading of 3 wt% nanoclay were studied on the microstructure, mechanical and morphological properties of the prepared nanocomposites. The adhesion between the fiber and the rubber was enhanced by the addition of a dry bonding system consisting of resorcinol, hexamethylene tetramine and hydrated silica (HRH). The curing characteristics of the composites were determined and subsequently vulcanized at 150°C using a hot press. It was observed that the cure time and swelling index of the composites decreased while maximum torque, and cure rate increased with increasing of short fiber and nanoclay contents. The structure and fracture surface morphology of the nanocomposites were characterized using X-ray diffraction, scanning electron microscopy. X-ray diffraction results of nanocomposites indicated that the interlayer distance of silicate layers increased. The mechanical properties (tensile, tear strength, elongation-at-break and hardness) ofnanocomposites containing virgin and waste fibers in the longitudinal direction are compared.