Uday Agarwal - Profile on Academia.edu (original) (raw)

Papers by Uday Agarwal

Oriented Crystallization of Random Copolymers

A new model for oriented crystallization of copolymers has been developed. It is based on a combi... more A new model for oriented crystallization of copolymers has been developed. It is based on a combination of (1) the Sanchez-Eby formulation for the free energy of melting of a crystal with an arbitrary level of inclusion of comonomeric defects and (2) the entropy of a polymer melt under an anisotropic stress field obtained through Ziabicki and Jarecki's analysis. The

Recent Developments in Solid State Polymerization of Poly(ethylene terephthalate)

Solid State Polymerization

... C. This process is based on a lambda probe–like measuring unit, which is based on a noble-met... more ... C. This process is based on a lambda probe–like measuring unit, which is based on a noble-metal film such as rhodium or its alloy disposed in the catalyzer. A lambda probe measures quantitatively the purity in the contaminated nitrogen gas stream entering the Page 11. ...

Journal of Applied Polymer Science, 2010

Production of polyester filament involves melt spinning into partially oriented yarn (POY), follo... more Production of polyester filament involves melt spinning into partially oriented yarn (POY), followed by drawing to enhance the bulk and mechanical properties. The industrial demand of increasing productivity is generally met by increasing POY melt spinning speeds, which is limited by increasing polymer chain orientation (and reducing residual drawability) in the POY produced at higher spinning speeds. Modification of the quench geometry during melt spinning is claimed to allow reduction of air drag and polymer chain orientation, permitting an increase in productivity during melt spinning into POY. We present a simple way for modeling the quenching of molten filaments under the modified (axial) air flow. Numerical simulations of the melt spinning are developed to demonstrate the influence of the quench geometry modification as we compare the process with the conventional cross-flow quench and the modified axial quench. We find that increasing quench air flow reduces the polymer chain orientation, in contrast to the well known effect in cross-flow quench.

Endloses polymeres Filamentgarn mit verbesserter Fasergleichm��igkeit und erh��hter Produktivit��t

Journal of Applied Polymer Science, 1998

Experimental data are obtained for the extent of swelling and progress of the step-growth swollen... more Experimental data are obtained for the extent of swelling and progress of the step-growth swollen-state polymerization (SwSP ) of polyethylene terephthalate (PET). The SwSP is carried out in biphenyl and diphenyl ether mixture (26 : 74 w/ w) solvent under appropriate conditions designed to understand the factors responsible for enhanced reaction rates. The kinetics rate constants, evaluated in terms of simple model, are found to be 2.5-5 times higher for SwSP as compared to the solid-state polymerization (SSP). As the diffusional/mass transfer effects are eliminated in our experiments, this increase in rate constants can be attributed to increased mobility of reactive chain ends. Polymerization rate is found to be further enhanced by addition of a polycondensation catalyst (Sb 2 O 3 ) to the solvent during SwSP.

Polymer, 2006

We have investigated the crystallization characteristics of melt compounded nanocomposites of pol... more We have investigated the crystallization characteristics of melt compounded nanocomposites of poly(ethylene terephthalate) (PET) and single walled carbon nanotubes (SWNTs). Differential scanning calorimetry studies showed that SWNTs at weight fractions as low as 0.03 wt% enhance the rate of crystallization in PET, as the cooling nanocomposite melt crystallizes at a temperature 10 °C higher as compared to neat PET. Isothermal crystallization studies also revealed that SWNTs significantly accelerate the crystallization process. WAXD showed oriented crystallization of PET induced by oriented SWNTs in a randomized PET melt, indicating the role of SWNTs as nucleating sites.

Diffusion of rigid rodlike molecules across interfaces: implications in welding of liquid-crystalline polymers

Macromolecules, 1992

Phase equilibria of carbon dioxide with phenol and diphenyl carbonate

The Journal of Supercritical Fluids, 2003

We report the vapor–liquid equilibria (VLE) of the two binary systems (carbon dioxide–phenol) and... more We report the vapor–liquid equilibria (VLE) of the two binary systems (carbon dioxide–phenol) and (carbon dioxide–diphenyl carbonate (DPC)). The bubble points are measured using a Cailletet apparatus in the temperature range 70–180°C and pressures up to 130 bar. The experimental data are adequately represented by the Peng–Robinson equation of state (PR EOS) with quadratic mixing rules. The two binary interaction parameters kij and lij are obtained by fitting, and were found to have a linear dependency with temperature. The data available from literature for the CO2–phenol system could also be predicted very well by the same model and parameter values.

On the stability of grafted polymer molecules in elongational flows

Journal of Non-Newtonian Fluid Mechanics, 1994

ABSTRACT

The Journal of Chemical Physics, 1993

Surface diffusion controlled reactions on a heterogeneous catalyst surface comprising randomly pl... more Surface diffusion controlled reactions on a heterogeneous catalyst surface comprising randomly placed circular reactive sites are considered. The diffusing species adsorbs onto the surface following Langmuir–Hinshelwood kinetics and reacts instantaneously on contact with a reactive site. Approximate theories are formulated to describe the process for high concentrations of the reactive sites, when competition between the sites is significant, following three different approaches: (i) modification of the single sink theory; (ii) using a cell model; and (iii) using an effective medium theory. The predictions of the theories are compared with the results of multiparticle Brownian dynamics simulations for the overall reaction rate, the bulk concentration of the reactive species, and the ensemble averaged concentration profile around a reactive site. The effective medium theory is found to give the best results among the theories considered, and the predictions are in good agreement with...

Hydrodynamic shielding induced stability of zipping macromolecules in elongational flows

The Journal of Chemical Physics, 1994

Enhanced shear stability of associating polymers during drag reduction observed recently has been... more Enhanced shear stability of associating polymers during drag reduction observed recently has been attributed to the breakage of reversible associations (e.g., hydrogen bonds) in preference to covalent bonds in the polymer backbone. A simple mechanistic analysis of a perfectly ‘‘zipped’’ assembly of fully extended bead rod chain model of two macromolecules in steady elongational flow is presented. It explains the enhanced stability as a result of (i) distribution (near the vulnerable chain center) of the drag tension into the two parallel ‘‘zipped’’ chains, and (ii) reduction of the drag force due to the enhanced hydrodynamic shielding. Some guidelines for optimum design of shear stable and effective drag reducing macromolecules have been deduced.

The Journal of Chemical Physics, 1998

We use Brownian dynamics simulation to study coil–stretch transition of macromolecules in solutio... more We use Brownian dynamics simulation to study coil–stretch transition of macromolecules in solution. Into a simple elongational flow field, we introduce freely jointed bead-rod chain model molecules in their coiled and stretched states, and follow the conformational changes. We find good agreement of our simulation results with the available theoretical predictions for low and high strain rates (ε̇). At the intermediate elongation rates (near the onset of coil–stretch transition) of the flow field, we find that the residence time required for stretching of an initially coiled chain can be extremely large as compared to predicted (1+ln(√N))ε̇−1, especially for the non-free-draining case. Hence, the chain conformation is dependent on the initial state of the chain molecule for residence time as long as 100ε̇−1. Thus, hysteresis is predicted when chain residence time in such an elongational flow field is limited, as in practical situations. Further, at such intermediate ε̇, the chain mo...

The Journal of Chemical Physics, 1992

A theoretical investigation of rates of diffusion-limited polymerization between rigid rodlike mo... more A theoretical investigation of rates of diffusion-limited polymerization between rigid rodlike molecules in dilute solutions is presented, incorporating both translational and rotational diffusion of the molecules. Simplified criteria for reaction are proposed according to which molecules must approach within a specified reaction radius, and have a relative orientation angle in a specified range to react. The translational diffusion of the molecules is assumed to be isotropic. The results of the exact analytical solution, finite element computations, as well as approximate solutions for low rotational diffusivity, are presented. The match between the solutions is satisfactory in the appropriate limits, although the exact solution is found to be computationally intensive for low rotational diffusivities and rapid intrinsic kinetics. The reaction rate is found to decrease to a limiting value with decreasing rotational diffusivity, and the magnitude of the decrease in rate increases wi...

Extraction of CdS pigment from waste polyethylene

Journal of Applied Polymer Science, 2006

... How to Cite. Wanrooij, PHP, Agarwal, US, Meuldijk, J., Kasteren, JMN v. and Lemstra, PJ (2006... more ... How to Cite. Wanrooij, PHP, Agarwal, US, Meuldijk, J., Kasteren, JMN v. and Lemstra, PJ (2006), Extraction of CdS pigment from waste polyethylene. Journal of Applied Polymer Science, 100: 10241031. ... Copyright © 1999-2010 John Wiley & Sons, Inc. All Rights Reserved.

Journal of Applied Polymer Science, 2007

Migration of macromolecules under flow: the physical origin and engineering implications

Chemical Engineering Science, 1994

... Dill (1979) and Dill and Zimm (1979), who observed radially inwards migration of DNA molecule... more ... Dill (1979) and Dill and Zimm (1979), who observed radially inwards migration of DNA molecules during ... shearing flow stretches the spnngs, caus ing a component F of the stretching tension F0 to ... migration in such flows, the polymer molecular weight must be higher than 106. ...

Modeling viscoelastic resistance of deposited polymer during olefin polymerization

Chemical Engineering Science, 2001

As olefin polymerization proceeds on a heterogeneous catalyst, the polymer so formed gets deposit... more As olefin polymerization proceeds on a heterogeneous catalyst, the polymer so formed gets deposited on the catalyst fragment. This presents diffusional resistance to further monomer transport to the catalyst fragment. In the recent past, we considered that this deposited polymer brings in additional viscous deformational resistance to the otherwise Fickian diffusion, thereby limiting the polymerization rate. In the present work we account for the rheological behavior of polymers being not just viscous, but viscoelastic. We find that the elastic deformation may largely facilitate the overall polymer deformation in situations where monomer transport would have been predicted to suffer severe limitations if only viscous deformation were considered.