Synthesis and properties of chelate polymers of VO(II), Mn(II), Zn(II), Fe(III), and Cr(III) with schiff base of 5,5′-methylene bis-salicylaldehyde with aniline

Polychelates of VO(II), Mn(II), Zn(II), Fe(III), and Cr(III) were prepared from Schiff base of 5,5′-methylene bis-salicyladehyde with aniline. All the chelate polymers are amorphous and insoluble in common organic solvents. They have very little solubility in DMF. The first three polychelates are found to be noncharged chelate polymers while the last two polychelates are found to be ionic from their conductivities in DMF. Their probable structures were determined from reflectance electronic spectral and magnetic measurements in conjunction with infrared measurements. The thermal stability, order of reaction and activation energy for all the polychelates were determined from their thermogravimetric analyses.     

Workstation-based logic animation and microarchitecture emulationfor teaching introduction to computer engineering

The authors describe two software tools used for teaching logic design and analysis and basic computer organization in the introductory course on computer engineering at the authors' department. The first computer-aided instruction tool described is a schematic capture, simulation, and logic animation package targeted for teaching combinational and sequential logic concepts. The tool incorporates logic animation capability rather than waveform displays, which allows students to view and control logic values propagating throughout the entire network. The second tool teaches computer organization, including microprogramming concepts, by means of the graphical display of an instructional microprocessor architecture in which users are allowed to view and control internal registers, memory locations, and microcontrol store. Both of the computer-aided instructional tools run on UNIX workstations, with graphics displays, local hard-disk mass storage, and mouse input     

Strength improvements in toughened epoxy composites using surface treated GnPs

Nanographitic materials are gaining enormous interest as a new class of reinforcement for nanocomposites, promising revolutionary electrical, thermal, and mechanical properties. However, the progress has been quite limited especially in terms of mechanical properties. Here we report a significant leap, >2× increases in tensile strength and modulus of an epoxy composite using surface treated graphite nanoplatelets (GnPs). This corroborated by increases in Tgs as well as the presence of oxygen‐functionalized groups verified by XPS, suggest improved distribution and chemical interaction at the filler‐to‐matrix interface. Toughness values also showed increases with concentration, without compromising the strength or failure strain. However, if solvent levels during degassing were not reduced sufficiently, negligible contributions to strength and stiffness were observed with GnP loading. Subsequent elevated temperature treatments increased the strength of the composite due to cure enhancement of the matrix material, yet did not provide mechanical enhancements due to the incorporation of the filler. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40802.     

Vertically aligned carbon nanotube‐based composite: Elaboration and monitoring of the nanotubes alignment

We present the different elaboration steps of a composite formed of carbon nanotubes (CNT) carpet embedded in an epoxy polymer. Detailed characterization at each step of the elaboration process is performed. The good alignment of CNT in as‐grown carpets is kept all along the elaboration process of the composite, as it is measured at both macro and microscopic scales by X‐ray scattering. We also ensured by X‐ray fluorescence measurements that the iron‐based catalyst particles used for the synthesis were removed from the carpet after a high temperature post‐annealing treatment. These measurements give valuable information for further applications involving unidirectional nanotube composites and membranes, where CNT alignment is a key parameter. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39730.     

Synthesis of flame retardant polyester‐urethanes and their applications in nanoclay composites and coatings

This paper describes the synthesis of phosphorus‐containing polyester‐urethanes and their applications in nanoclay composites and coatings. Polyester was prepared by the reaction of bis(bisphenol‐A) monophenyl phosphonate, maleic anhydride and phthalic anhydride. The polyester was reacted with various diols such as ethylene glycol, diethylene glycol and propylene glycol to obtain polyester polyols. Synthesized polyester polyols were characterized by chemical analysis and instrumental analysis and was used further to react with different isocyanates to develop polyester‐urethanes. The synthesized polyester‐urethanes were blended with organo‐modified montmorillonite nanoclay (1 wt%, 3 wt% and 5 wt%) and were cast in a mold and coated on mild steel panels. The thermal stability of neat polyester‐urethane and the nanoclay composites was determined by thermogravimetric analysis. The flame retardant properties of cast films and their composites were determined by the limiting oxygen index and UL‐94 test methods. The physical and mechanical properties of coatings such as pot life, drying properties, scratch hardness, pencil hardness, impact resistance, adhesion and flexibility were investigated. The chemical resistance properties of the coatings were also determined in different reagents. The data reveal that the polyester‐urethane nanoclay composites with 3 wt% clay hold promise for use in effective flame retardant coatings. © 2013 Society of Chemical Industry     

Crystallization kinetics modeling of high density and linear low density polyethylene resins

This paper describes isothermal and nonisothermal crystallization kinetics of a Ziegler‐Natta catalyzed high density polyethylene (HDPE) and linear low density polyethylene (LLDPE) resins. Standard techniques such as differential scanning calorimetry (DSC) and light depolarization microscopy (LDM) techniques were used to measure isothermal kinetics at low supercoolings. DSC was also used to measure nonisothermal crystallization kinetics at low cooling rates. Extrapolation of isothermal crystallization half‐times of Z‐N catalyzed LLDPE resin using the isothermal half‐time analysis led to erroneous predictions, possibly due to Z‐N LLDPE consisting of a mixture of molecules having different amounts of short chain branching (comonomer). However, predicted reciprocal half‐times at high supercoolings, using isothermal half‐time analysis and using nonlinear regression of nonisothermal crystallization kinetics measured at low cooling rates using the differential Nakamura model, of the HDPE were similar to measured reciprocal half times at high supercoolings of a similar HDPE by Patki and Phillips. It is also shown that the differential Nakamura model can be effectively used to model nonisothermal crystallization kinetics of HDPE resins. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improving the dynamic performance of continuous-flow mixing of pseudoplastic fluids possessing yield stress using Maxblend impeller

The strategic approach of this article is to characterize the continuous-flow mixing of pseudoplastic fluids possessing yield stress in a stirred reactor with the Maxblend impeller. Dynamic experiments were carried out through the frequency-modulated random binary input of a brine solution to determine the extent of non-ideal flows. Mixing quality was determined on the basis of the extent of channeling and fully mixed volume. The effects of important parameters such as impeller speed (25–500 rpm), absence of baffles, fluid rheology (0.5–1.5%), fluid flow rate (3.20–14.17 L min⁻¹), and the locations of inlet/outlet on the dynamic performance of the continuous-flow mixing vessel were explored. The performance of the Maxblend impeller was then compared to the performances of various types of impellers such as close-clearance (an anchor), axial-flow (a Lightnin A320), and radial-flow (a Scaba 6SRGT) impellers. It was found when the channeling approached zero and the fully mixed volume approached the total fluid volume in the vessel, the power drawn by the A320 impeller and the Scaba impeller were about 2.9 and 4.3 times greater than that of the Maxblend impeller. Thus, the Maxblend impeller was able to drastically improve the performance of continuous-flow mixing with huge power savings. The mixing quality was further improved by optimizing the impeller speed, decreasing the fluid flow rate, decreasing the fluid concentration, and using bottom inlet- top outlet configuration. The flow non-ideality of the mixing system increased in the absence of the baffles. Thus, better mixing quality and more energy savings can be achieved by employing the findings of this study.     

Effect of a Hydrophilic PEO–PPO–PEO Copolymer on Cetyltrimethyl Ammonium Tosylate Solutions in Water

Cetyltrimethyl ammonium tosylate (CTAT) in water forms long flexible wormlike micelles at concentrations above 10 mM, leading to highly viscous solutions and viscoelastic stiff gels above 100 mM. In the presence of a nonmicellar hydrophilic PEO–PPO–PEO triblock copolymer F87 (TBC-F87, Total mol.wt. = 7,700, EO = 70%) these wormlike micelles RE transformed into smaller structures, as evident from a sharp decrease in viscosity and increase in specific conductance. These results are quantified by small angle neutron scattering (SANS) measurements. The PPO middle block of TBC-F87 gets inserted in the CTAT micelle, the size and total aggregation number of CTAT/TBC-F87 mixed micelles decreased but the number of TBC-F87 molecules in the mixed micelles increased with an increase in [TBC-F87]. Two break points in the typical specific conductance versus CTAT concentration plot at various [TBC-F87] amounts represent interactions between CTAT and TBC-F87. The penetration of PPO of TBC-F87 inside CTAT micelles decreases hydrophobicity of the core while the presence of PEO end blocks enhances hydrophilicity each favoring smaller micelles.     

Surface modification of low density polyethylene films by homogeneous catalytic ozonation

Low density polyethylene films were treated by ozone to generate peroxides on the surfaces. The peroxides generated are capable of initiating radical graft polymerization of hydrophilic vinyl monomers onto the polymers, resulting in hydrophilic surfaces. Results of ozonation revealed that molecular ozone instead of hydroxyl radicals was the main oxidant for peroxide generation. A novel approach, aqueous ozonation with the addition of a soluble transitional metal salt, FeCl₃, as a homogeneous catalyst, was proposed and proved to be successful in this study. The addition of FeCl₃ could increase peroxide generation by 22.7%, compared to its non-catalyzed counterpart. An optimum catalyst concentration, 0.04 g/L, was determined. Also, the effects of pH, ozonation time and applied ozone dose on peroxide generation were investigated. The loss in tensile strength of the films would be 15% or less if the applied ozone dose was not over 2 wt.%. The functional groups generated on the film surfaces were characterized by FTIR, the contact angle and surface roughness of the film were also examined before and after ozonation.     

Synthesis,characterization, and drug release properties of poly(N-isopropylacrylamide) gels prepared in methanol–water cononsolvent medium

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were simply prepared by free radical polymerization in different methanol–water mixture. A scanning electron microscopy study revealed that the freeze-dried hydrogels were macroporous. The swelling ratios in water at 20°C of the resulting hydrogels followed the order: X_0.43>X_0.21>X_0.76 ≈ X_0.57>X_0.31>X_0.13>X_0.06>X₀, where X_m denotes a gel prepared in a methanol–water mixture with m mole fraction of methanol (x_m). Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with the increase in the temperature. The complete collapse of the PNIPAM chain of all the gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all the PNIPAM gels in the methanol–water mixtures with different x_m values at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X_0.43> X_0.31> X_0.21> X_0.57> X_0.76 ≈ X_0.13> X_0.06> X₀. The reswelling rates of these hydrogels decreased in the following order: X₀> X_0.31> X_0.06 ≈ X_0.13 > X_0.76> X_0.57> X_0.21> X_0.43. The release rates of the Tramadol Hydrochloride drug at 37°C from the drug-loaded hydrogels were almost same for all of the hydrogels. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012