Hydrophobization and characterization of internally crosslink-reinforced cellulose fibers

Transforming hydrophilic cellulose fibers into hydrophobic, non-hygroscopic fibers could potentially lead to a variety of new products, such as flexible packaging, self-cleaning films and strength-enhancing agents in polymer composites. To achieve this, softwood cellulose pulp was chemically modified with successive chemical treatments. First the C2 and C3 hydroxyl groups of the glucose units were selectively oxidized by periodate oxidation to reactive dialdehyde units on the cellulose chain, followed by a Schiff base reaction with 1,12-diaminododecane to crosslink the microfibrils within the fiber wall. This was done, because introducing high levels of alkylation resulted in fiber disintegration, which could be prevented by crosslinking. After internal crosslinking a second Schiff base reaction was performed with butylamine. This procedure yielded highly hydrophobic and low-hygroscopic cellulosic materials. The modified cellulose fibers were investigated by a variety of techniques, including Fourier transform infrared spectroscopy, nuclear magnetic resonance, field-emission scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, moisture sorption and water contact angle measurements. The water uptake of the fibers after being modified reduced from 4 to around 1 %. Various reaction conditions were studied for optimum performance.     

Structure of swollen carboxylated cellulose fibers

Structural changes in cellulose fibers were elucidated for carboxymethylated fibers and fibers that are oxidized by periodate and chlorite. Non-fibrillated and partially fibrillated softwood, kraft fibers (SKF, m-SKF) were carboxymethylated to investigate the contribution of the S1 layer to the swollen fiber structures. Carboxymethylated non-fibrillated fibers (CMF) form balloon-like structures as they swell heterogeneously. When partially fibrillated SKF is carboxymethylated (m-CMF), the fibers do not exhibit this ballooning phenomenon due to the degradation of the S1 layer. Carboxymethylation disrupts the native cellulose crystalline structure without breaking the fibers apart. Periodate–chlorite oxidized fibers, on the other hand, swell homogeneously without disrupting the native cellulose I crystalline form. Periodate–chlorite oxidation damages all three secondary layers to the extent that any microfibril confinement caused by the swelling is removed. Each chemistry and mechanical treatment affects the cellulose fibers differently to yield various swollen structures.     

Development of Poly(urethane esteramide) Coatings from Pongamia glabra Oil as Anticorrosive Applications

In this study, ethylene glycol polyesteramide (Eg-PEA) was synthesized from N,N-bis (2-hydroxy ethyl) pongamia oil fatty amide and ethylene glycol tetraacetic acid (EGTA) through condensation polymerization. It was further modified by toluene 2,4-diisocynate in different wt.% (20, 25, 30, and 35) to obtain urethane-modified polyesteramide (Eg-UPEA). The synthesized resins were characterized using FT-IR, ¹H NMR, and ¹³C NMR spectroscopic techniques, and molecular weight was determined by gel permeation chromatography (GPC). Physico-chemical and physico-mechanical analyses were carried out by standard laboratory methods. Thermal studies of Eg-UPEA were undertaken by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. To evaluate corrosion prevention performance Eg-UPEA-coated mild steel strips were investigated by potentiodynamic polarization in different corrosive media (5 wt.% NaCl, 3 wt.% HCL, 2.5 wt.% NaOH, and tap water) at room temperature. Thermal analysis revealed that Eg-UPEA30 may find application as an environmentally friendly corrosion protective coating and may be safely used up to 250°C.     

Energy-Conserving Simulation of Incompressible Electro-Osmotic and Pressure-Driven Flow

A numerical model for electro-osmotic flow is described. The advecting velocity field is computed by solving the incompressible Navier–Stokes equation. The method uses a semi-implicit multigrid algorithm to compute the divergence-free velocity at each grid point. The finite differences are second-order accurate and centered in space; however, the traditional second-order compact finite differencing of the Poisson equation for the pressure field is shown not to conserve energy in the inviscid limit. We have designed a non-compact finite differencing for the Laplacian in the pressure equation that allows exact energy conservation and affords second-order accuracy. The model also incorporates a new numerical method for passive scalar advection, called parcel advection, which accurately predicts the evolution of a passively traveling scalar pulse without requiring the addition of any artificial diffusion. The algorithm is used to confirm the experimentally observed asymmetric concentration profile that arises when an external pressure drop is imposed on electro-osmotic flow. Received 25 January 2001 and accepted 10 May 2002 Published online 30 October 2002 Communicated by H.J.S. Fernando     

Effects of temperature dependent fluid properties and variable Prandtl number on the transient convective flow due to a porous rotating disk

In this paper we have studied the effects of temperature dependent fluid properties such as density, viscosity and thermal conductivity and variable Prandtl number on unsteady convective heat transfer flow over a porous rotating disk. Using similarity transformations we reduce the governing nonlinear partial differential equations for flow and heat transfer into a system of ordinary differential equations which are then solved numerically by applying Nachtsheim–Swigert shooting iteration technique along with sixth-order Runge–Kutta integration scheme. Comparison with previously published work for steady case of the problem were performed and found to be in very good agreement. The obtained numerical results show that the rate of heat transfer in a fluid of constant properties is higher than in a fluid of variable properties. The results further show that consideration of Prandtl number as constant within the boundary layer for variable fluid properties lead unrealistic results. Therefore, modeling thermal boundary layers with temperature dependent fluid properties Prandtl number must treated as variable inside the boundary layer.     

Optical binary logic gate-based modified signed-digit arithmetic

A new design approach for a three-step modified signed-digit (MSD) adder is presented that can be optically implemented using binary logic gates. The proposed scheme depends on encoding each MSD digits into a pair of binary digits using a two-state and multi-position encoding scheme. The proposed design algorithm depends on constructing the addition truth table of binary-coded MSD numbers and then using Karnaugh map to achieve output minimization. The optical binary logic gates are obtained by simply programming the decoding masks of a shadow-casting-based optical logic gate system. The proposed scheme results in a simple, compact, and efficient optical binary gate-based parallel addition system.     

Fully automated chip‐based negative mode nanoelectrospray mass spectrometry of fructooligosaccharides produced by heterologously expressed levansucrase from Pseudomonassyringae pv. tomato DC3000

Pseudomonas syringae pathovars possess multiple levansucrases with still unclear specific roles for bacteria. We have cloned and expressed three levansucrase genes, lsc1, lsc2 and lsc3, from P. syringae DC3000 in Escherichia coli. Levansucrases synthesize a high molecular weight fructan polymer, levan, from sucrose and in the case of some levansucrases, fructooligosaccharides (FOS) with potential prebiotic effects are also produced. The ability of purified Lsc3 protein of DC3000 to synthesize FOS was tested using prolonged incubation time and varied concentrations of sugar substrates. Thin‐layer chromatography (TLC) analysis of reaction products disclosed formation of FOS from both sucrose and raffinose, revealing a new catalytic property for P. syringae levansucrases. In order to analyze Lsc3‐produced FOS in underivatized form, we optimized a novel method recently introduced in carbohydrate research, based on fully automated chip‐based nanoelectrospray ionization (nanoESI) high‐capacity ion trap mass spectrometry (HCT‐MS). Uding chip‐based nanoESI MS in negative ion mode, FOS, with degrees of polymerization up to five, were detected in reaction mixtures of Lsc3 with sucrose and raffinose. For confirmation, further structural analysis by tandem mass spectrometry (MS/MS) employing collision‐induced dissociation at low energies was performed. To validate the method, commercial inulin‐derived FOS preparations Orafti®P95 and Orafti®Synergy1, which are currently used as prebiotics, were used as controls. By chip‐based nanoESI HCT‐MS, similar FOS distribution was observed in these reference mixtures. Thereby, the obtained data allowed us to postulate that FOS produced by the Lsc3 protein of P. syringae DC3000 may be prebiotic as well. Copyright © 2009 John Wiley & Sons, Ltd.     

Semileptonic (Λ b → Λcev) decay in a field theoretic quark model

The semileptonic decay width of heavy baryons such as (Λ _b → Λcev) has been estimated in the framework of a nonrelativistic field theoretic quark model where four component quark field operators along with a harmonic oscillator wave function are used to describe translationally invariant hadronic states. The present estimation does not make an explicit use of heavy quark symmetry and has a reasonable agreement with the experimentally measured decay width, polarisation ratio and form factors with the harmonic oscillator radii and quark momentum distribution inside the hadron as free parameters.     

Low mass dileptons from Pb + Au collisions at 158 A.GeV

The medium modification of vector meson properties in hot/dense hadronic matter and its role in explaining the CERES/NA45 dilepton data at different centralities are discussed.