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Antonios K. Doufas - One of the best experts on this subject based on the ideXlab platform.

  • Raman spectroscopy for spinline crystallinity measurements. II. Validation of fundamental Fiber‐Spinning models
    Journal of Applied Polymer Science, 2008
    Co-Authors: Rajen M. Patel, Antonios K. Doufas, Rajesh Paradkar
    Abstract:

    The original Doufas-McHugh two-phase microstructural/constitutive model for stress-induced crystallization is expanded to polyolefin systems and validated for its predictive capability of online Raman crystallinity and spinline tension data for two Dow homopolymer polypropylene resins. The material parameters-inputs to the model-are obtained from laboratory-scale material characterization data, that is, oscillatory dynamic shear, rheotens (melt extensional rheology), and differential scanning calorimetry data. The same set of two stress-induced crystallization material/molecular parameters are capable of predicting the crystallinity profiles along the spinline and Fiber tension very well overall for a variety of industrial fabrication conditions. The model is capable of predicting the freeze point, which is shown, for the first time, to correlate very well with the measured stick point (i.e., the point in the spinline at which the Fiber bundle converts from a solid-like state to a liquid-like state and sticks to a solid object such as a glass rod). The model quantitatively captures the effects of the take-up speed, throughput, and melt flow rate on the crystallization rate of polypropylene due to stress-induced crystallization effects. This validated modeling approach has been used to guide Fiber Spinning for rapid product development. The original Doufas-McHugh stress-induced crystallization model is shown to be numerically robust for the simulation of steady polypropylene melt Spinning over a wide range of processing conditions without issues of discontinuities due to the onset of the two-phase constitutive formulation downstream of the die face, at which crystallization more realistically begins. Because of the capturing of the physics of polypropylene Fiber Spinning and the very good model predictive power, the approximations of the original Doufas-McHugh model are asserted to be reasonable.

  • Coupled computational fluid dynamics and multifilament Fiber‐Spinning model
    AIChE Journal, 2006
    Co-Authors: Albert D. Harvey, Antonios K. Doufas
    Abstract:

    A fundamental Fiber-Spinning model (proposed by Doufas and colleagues) is coupled to a three-dimensional Navier–Stokes computational fluid dynamics (CFD) code, where source terms for momentum and energy transfer between the Fibers and the surrounding quench air are treated implicitly. The three-dimensional equations are solved for the airflow using a preconditioning technique in a structured multiblock framework. Scalable parallelism is achieved by assigning an arbitrary number of grid zones to a predetermined number of processors. Individual Fibers are also divided equally among the available processors, allowing for thousands of Fibers to be solved in only a few hours in realistic industrial-scale Spinning processes. Model results are shown to agree with results obtained using Doufas et al.'s stand-alone Fiber-Spinning model in the limit of a small number of Fibers. The coupled model is used to compute the temperature and air flow around individual Fibers on a generic three-dimensional Fiber-Spinning application that contains multiple rows of Fibers. It is found that, for large Fiber bundles (such as 72 Fibers) a significant variation in Fiber cooling and tensile stresses exists across the bundle, which would result in significant variation in Fiber tensile properties within the bundle. It is proposed that the cooling air velocity profiles across a multifilament system that exhibits stress-induced crystallization effects can be extracted from results obtained using the new coupled CFD/Fiber-Spinning model and can then be used in improved calculations (using a stand-alone Fiber model) of the heat-transfer and air-drag coefficients within the Fiber bundle. © 2006 American Institute of Chemical Engineers AIChE J 2007

  • Simulations of Fiber Spinning and film blowing based on a molecular/continuum model for flow-induced crystallization
    Korea-australia Rheology Journal, 2001
    Co-Authors: Anthony J. Mchugh, Antonios K. Doufas
    Abstract:

    This paper describes the application of our recently developed two-phase model for flow-induced crystallization (FIC) to the simulation of Fiber Spinning and film blowing. 1-D and 2-D simulations of Fiber Spinning include the combined effects of (FIC), viscoelasticity, filament cooling, air drag, inertia, surface tension and gravity and the process dynamics are modeled from the spinneret to the take-up roll device (below the freeze point). 1-D model fits and predictions are in very good quantitative agreement with high- and low-speed spinline data for both nylon and PET systems. Necking and the associated extensional softening are also predicted. Consistent with experimental observations, the 2-D model also predicts a skin-core structure at low and intermediate spin speeds, with the stress, chain extension and crystallinity being highest at the surface. Film blowing is simulated using a "quasi-cylindrical" approximation for the momentum equations, and simulations include the combined effects of flow-induced crystallization, viscoelasticity, and bubble cooling. The effects of inflation pressure, melt extrusion temperature and take-up ratio on the bubble shape are predicted to be in agreement with experimental observations, and the location of the frost line is predicted naturally as a consequence of flow-induced crystallization. An important feature of our FIC model is the ability to predict stresses at the freeze point in Fiber Spinning and the frost line in film blowing, both of which are related to the physical and mechanical properties of the final product.l product.

  • Modeling flow-induced crystallization in Fiber Spinning
    Composites Part A: Applied Science and Manufacturing, 2001
    Co-Authors: Anthony J. Mchugh, Antonios K. Doufas
    Abstract:

    A brief review is given of the microstructural/constitutive model for flow-induced crystallization (FIC), developed by the authors that couples polymer microstructure (molecular orientation and crystallinity) with the macroscopic velocity/stress and temperature fields. Application of the model to melt Spinning of nylons and poly(ethylene terphthalate) (PET) under both low- and high-speed spinline conditions is described. The Fiber Spinning model includes the combined effects of FIC, viscoelasticity, filament cooling, air drag, inertia, surface tension and gravity, and simulates melt Spinning from the spinneret down to the take-up roll device (below the freeze point). For both nylons and PET, model fits and predictions are shown to be in very good quantitative agreement with spinline data for the Fiber velocity, diameter and temperature fields at both low- and high-speed conditions, and, with flow birefringence data available for high speeds. The model captures the necking phenomenon for nylon and PET quantitatively and the associated extensional softening at high-speed conditions and the occurrence of the freeze point naturally at both low- and high-speed conditions.

Keiji Numata - One of the best experts on this subject based on the ideXlab platform.

  • Combination of Amorphous Silk Fiber Spinning and PostSpinning Crystallization for Tough Regenerated Silk Fibers
    Biomacromolecules, 2018
    Co-Authors: Kenjiro Yazawa, Ali D. Malay, Nao Ifuku, Takaoki Ishii, Hiroyasu Masunaga, Takaaki Hikima, Keiji Numata
    Abstract:

    An artificial Spinning system using regenerated silk fibroin solutions is adopted to produce high-performance silk Fibers. In previous studies, alcohol-based agents, such as methanol or ethanol, were used to coagulate silk dope solutions, producing silk Fiber with poor mechanical properties compared with those of native silk Fibers. The alcohol-based coagulation agents induce rapid β-sheet crystallization of the silk molecules, which inhibits subsequent alignment of the β-sheet crystals. Here, we induce gradual β-sheet formation to afford adequate β-sheet alignment similar to that of native silk Fiber. To this aim, we developed an amorphous silk Fiber Spinning process that prevents fast β-sheet formation in silk molecules by using tetrahydrofuran (THF) as a coagulation solvent. In addition, we apply postdrawing to the predominantly amorphous silk Fibers to induce β-sheet formation and orientation. The resultant silk Fibers showed a 2.5-fold higher extensibility, resulting in 1.5-fold tougher silk Fibers compared with native Bombyx mori silk Fiber. The amorphous silk Fiber Spinning process developed here will pave the way to the production of silk Fibers with desired mechanical properties.

Thomas Hagen - One of the best experts on this subject based on the ideXlab platform.

  • Analysis of Fiber Spinning for the upper-convected Maxwell fluid
    Nonlinear Analysis: Real World Applications, 2012
    Co-Authors: Thomas Hagen, Dias Kurmashev
    Abstract:

    Abstract The Fiber Spinning process of a viscoelastic liquid modeled by the constitutive theory of the Maxwell fluid is analyzed. The governing equations are given by one-dimensional mass, momentum and constitutive equations, which arise in the slender body approximation by cross-sectional averaging of the two-dimensional axisymmetric Stokes equations with free boundary. Existence, uniqueness and regularity results are proved by means of fixed point arguments, energy estimates and weak/weak ∗ convergence methods. The difficulty in this problem lies with the constitutive model of the Maxwell fluid: when both the outflow velocity at the spinneret and the pulling velocity at take up are prescribed, a boundary condition can be imposed for only one of the two elastic stress components at the inlet. The absence of the second stress boundary condition makes the mathematical analysis of the problem hard.

  • The effect of shear in Fiber Spinning
    ZAMM, 2009
    Co-Authors: Shaun Ceci, Thomas Hagen, Catherine Frost, Dias Kurmashev
    Abstract:

    We study the equations of isothermal Fiber Spinning under the assumption that viscous friction in the Fiber is balanced by shear stresses. Our discussion gives a rather complete picture of the existence and nonexistence of stationary solutions. The linearization about steady state of the governing equations is analyzed by semigroup methods and shown to have the spectrally determined growth property. Both linear and nonlinear stability of stationary solutions is investigated numerically.

  • On the effects of spinline cooling and surface tension in Fiber Spinning
    ZAMM, 2002
    Co-Authors: Thomas Hagen
    Abstract:

    In contrast to isothermal Fiber Spinning, nonisothermal Fiber Spinning is a remarkably stable process. In this note, we shall study the effects of continuous spinline cooling and surface tension on the stability of stationary nonisothermal Fiber Spinning flow. We systematically derive an appropriate extension of the one-dimensional Matovich-Pearson thin filament equations of viscous liquids. This model will account for the physical chemistry of the Fiber surface and the temperature dependence of the material parameters. We employ semigroup theory to discuss the linear stability of stationary solutions. To this end, we prove the spectral determinacy of the associated semigroup. This approach is made viable by a reformulation of the governing equations to avoid a moving flow domain. Finally, we shall give some computational results to study the onset of surface tension instabilities and their suppression by cooling.

  • On the Equations of Fiber Spinning in Nonisothermal Viscous Flow
    Topics in Nonlinear Analysis, 1999
    Co-Authors: Thomas Hagen, Michael Renardy
    Abstract:

    We discuss the equations of nonisothermal Fiber Spinning for viscous fluids. Existence, uniqueness and regularity of solutions will be established. Our solution strategy employs weak* compactness arguments together with the Contraction Mapping Principle in suitable Banach spaces. Energy estimates of the solutions for certain boundary-initial value problems for the first-order hyperbolic equation form the basis of our results.

Alexander Josef Antonites - One of the best experts on this subject based on the ideXlab platform.

  • Fiber Spinning During the Mapungubwe Period of Southern Africa: Regional Specialism in the Hinterland
    African Archaeological Review, 2019
    Co-Authors: Alexander Josef Antonites
    Abstract:

    The Middle Iron Age (MIA) of southern Africa is a period characterized by increased social complexity centered on the polity of Mapungubwe. This article considers the role that Fiber Spinning played in the regional political economy of the period. At Mutamba and other sites in the southern hinterland of Mapungubwe, Spinning was a significant economic activity. Evidence from 187 spindle whorls from the site suggests that intensive Spinning of cotton was practiced by households. This enabled hinterland communities to actively participate in regional trade networks and acquire trade goods, including objects that were often restricted in the Mapungubwe heartland. This casts hinterland communities as active participants, rather than passive bystanders, in the regional economy. L'âge du Fer Moyen en Afrique du sud est une période caractérisée par une complexité sociale accrue centrée sur la politique de Mapungubwe. Cet article examine le rôle joué par la filature de fibres dans l'économie politique régionale de cette période. À Mutamba et dans d’autres sites de l’arrière-pays méridional de Mapungubwe, la filature était une activité économique importante. Des preuves provenant de 187 volants de fuseaux du site suggèrent que le filage intensif du coton était pratiqué par les ménages. Cela a permis aux communautés de l'arrière-pays de participer activement aux réseaux commerciaux régionaux et d'acquérir des biens commerciaux, notamment des objets souvent restreints dans le centre de Mapungubwe. Cela fait des communautés de l'arrière-pays des participants actifs aux économies régionales plutôt que des passants passifs.

  • Fiber Spinning during the mapungubwe period of southern africa regional specialism in the hinterland
    African Archaeological Review, 2019
    Co-Authors: Alexander Josef Antonites
    Abstract:

    The Middle Iron Age (MIA) of southern Africa is a period characterized by increased social complexity centered on the polity of Mapungubwe. This article considers the role that Fiber Spinning played in the regional political economy of the period. At Mutamba and other sites in the southern hinterland of Mapungubwe, Spinning was a significant economic activity. Evidence from 187 spindle whorls from the site suggests that intensive Spinning of cotton was practiced by households. This enabled hinterland communities to actively participate in regional trade networks and acquire trade goods, including objects that were often restricted in the Mapungubwe heartland. This casts hinterland communities as active participants, rather than passive bystanders, in the regional economy.

Anthony J. Mchugh - One of the best experts on this subject based on the ideXlab platform.

  • Prediction of the influence of flow‐enhanced crystallization on the dynamics of Fiber Spinning
    Polymer Engineering & Science, 2007
    Co-Authors: William H. Kohler, Anthony J. Mchugh
    Abstract:

    A linearized sensitivity and stability analysis of Fiber Spinning of semi-crystalline polymers has been carried out for both low- and high-speed Spinning conditions to investigate the relative roles of flow-enhanced crystallization (FEC) and thermal-induced crystallization (TIC) on the process dynamics. The analysis is based on an earlier-developed two-phase constitutive model for FEC that utilizes either the Giesekus or the Extended Pom-Pom constitutive equations for the amorphous phase and a rigid-rod model for the semi-crystalline phase, combined with the transport balances for the 1-D Fiber Spinning model. Model parameters from fits of the steady-state low- and high-speed Spinning of Nylon and L-polylactic acid are used to illustrate the effects of changes in various process variables (principally air cooling rate and temperature) on the system sensitivity. Results show that higher crystallization, whether from TIC or FEC, generally equates to lower spinline sensitivity. However, factors such as high-speed necking induced by FEC, viscoelastic stresses, and thermal transport properties are also shown to impact trends in the sensitivity. Because of the specific nature of the FEC model and lack of a general theory for determining model parameters from first principles, calculations and conclusions are necessarily system specific. POLYM. ENG. SCI., 48:88–96, 2008. © 2007 Society of Plastics Engineers

  • 2D Modeling of high-speed Fiber Spinning with flow-enhanced crystallization
    Journal of Rheology, 2007
    Co-Authors: William H. Kohler, Anthony J. Mchugh
    Abstract:

    A two-dimensional (2D) analysis of Fiber Spinning is presented based on a modified version of the two-phase model [Shrikhande et al., J. Appl. Polym. Sci. 100, 3240–3254 (2006); Kohler et al., J. Macromol. Sci. Phys. 44, 185–202 (2005)] that accounts for flow-enhanced crystallization (FEC). The modified model employs the extended pom-pom (XPP) constitutive equation for the amorphous phase and the rigid rod equation for the semicrystalline phase. Calculations are carried out for the high-speed Spinning of nylons, polyethylene terephthalate (PET), and pure poly(L-lactic acid) (PLLA), as well as racemic mixtures of the latter (rPLA). Radial variations in temperature and degree of crystalline transformation and microstructure for the PLLA, rPLA, and higher speed PET examples show significant patterns in the skin and core regions of the Fiber that reflect the interplay between FEC and thermal-induced crystallization (TIC). Insight is gained into the relationship of TIC and FEC in determining radial birefringen...

  • A modified model and algorithm for flow-enhanced crystallization—Application to Fiber Spinning
    Journal of Applied Polymer Science, 2006
    Co-Authors: Prashant Shrikhande, William H. Kohler, Anthony J. Mchugh
    Abstract:

    A modified version of the two-phase flow-induced crystallization model of Doufas et al. (J Non-Newtonian Fluid Mech 2000, 92, 27) for melt Spinning of polymeric Fibers is presented to address three issues: (1) discontinuities generated due to the imposition of continuation conditions at the crystallization onset at Tmo; (2) excessive strength of the flow enhancement component coupling the total extra stress tensor invariant to the crystallization kinetics; and (3) Avrami isotherms used. The modified model provides seamless, two-phase predictions for all-state variables in the Fiber-Spinning process and significantly reduces discontinuities. Moreover, a new component for the flow-induced crystallization rate and Avrami crystallization rate isotherms increase the predictive capability of the model. Quantitative prediction of the velocity, stress, temperature, density (or crystallinity), and birefringence profiles are demonstrated for Nylon 66 and PET melts for a variety of process conditions, including predictions of quenched-sample density profiles and the take-up speed dependence of as-spun Fiber density. The new algorithm, assisted by the coupling model, provides a more efficient and robust convergence of steady-state calculations and has been tested to predict Spinning phenomena up to spin speeds of 9000 m/min. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3240–3254, 2006

  • Simulations of Fiber Spinning and film blowing based on a molecular/continuum model for flow-induced crystallization
    Korea-australia Rheology Journal, 2001
    Co-Authors: Anthony J. Mchugh, Antonios K. Doufas
    Abstract:

    This paper describes the application of our recently developed two-phase model for flow-induced crystallization (FIC) to the simulation of Fiber Spinning and film blowing. 1-D and 2-D simulations of Fiber Spinning include the combined effects of (FIC), viscoelasticity, filament cooling, air drag, inertia, surface tension and gravity and the process dynamics are modeled from the spinneret to the take-up roll device (below the freeze point). 1-D model fits and predictions are in very good quantitative agreement with high- and low-speed spinline data for both nylon and PET systems. Necking and the associated extensional softening are also predicted. Consistent with experimental observations, the 2-D model also predicts a skin-core structure at low and intermediate spin speeds, with the stress, chain extension and crystallinity being highest at the surface. Film blowing is simulated using a "quasi-cylindrical" approximation for the momentum equations, and simulations include the combined effects of flow-induced crystallization, viscoelasticity, and bubble cooling. The effects of inflation pressure, melt extrusion temperature and take-up ratio on the bubble shape are predicted to be in agreement with experimental observations, and the location of the frost line is predicted naturally as a consequence of flow-induced crystallization. An important feature of our FIC model is the ability to predict stresses at the freeze point in Fiber Spinning and the frost line in film blowing, both of which are related to the physical and mechanical properties of the final product.l product.

  • Modeling flow-induced crystallization in Fiber Spinning
    Composites Part A: Applied Science and Manufacturing, 2001
    Co-Authors: Anthony J. Mchugh, Antonios K. Doufas
    Abstract:

    A brief review is given of the microstructural/constitutive model for flow-induced crystallization (FIC), developed by the authors that couples polymer microstructure (molecular orientation and crystallinity) with the macroscopic velocity/stress and temperature fields. Application of the model to melt Spinning of nylons and poly(ethylene terphthalate) (PET) under both low- and high-speed spinline conditions is described. The Fiber Spinning model includes the combined effects of FIC, viscoelasticity, filament cooling, air drag, inertia, surface tension and gravity, and simulates melt Spinning from the spinneret down to the take-up roll device (below the freeze point). For both nylons and PET, model fits and predictions are shown to be in very good quantitative agreement with spinline data for the Fiber velocity, diameter and temperature fields at both low- and high-speed conditions, and, with flow birefringence data available for high speeds. The model captures the necking phenomenon for nylon and PET quantitatively and the associated extensional softening at high-speed conditions and the occurrence of the freeze point naturally at both low- and high-speed conditions.