Fiber spinning modeling

R.M. Patel, A.K. Doufas and R.R Raradkar, Raman spectroscopy for spinline crystallinity measurements. II. Validation of fundamental fiber-spinning models, J. Appl. Polym. Sci., 109, 3398-3412 (2008). 

Application of Raman spectroscopy to obtain crystallinity data, on-line, during fiber spininning of polypropylene polymers is described. These data were obtained to develop validated fundamental fiber spinning models. These validated fiber spinning models will be used to guide fiber spinning for rapid product development. 

Fiber crystallinity data for fibers spun from two polypropylene resins was obtained, on a commercial fiber line, using on-line Raman spectroscopy. The experimental data presented here will be used to validate fundamental fiber spinning models. Results from the model validation/refinement will be are presented in a separate paper. The validated models and experimental observations can be used to guide fiber spinning of hPP polymers for rapid product development. Some key results obtained from the online Raman measurements can be summarized as follows... 

Crystallinity Development during spinning of Polypropylene Part II Fiber spinning model... 

Fiber spinning, 11 174, 175, 170-171 carbon-nanotube, 13 385-386 methods of, 16 8 models of, 11 171-172 of polyester fibers, 20 12-15 Fiber structure, of aromatic polyamides, 19 727... 

The process of fiber spinning, described in Chapter 3 and schematically represented in Fig. 6.18, will be modeled in this section using first a Newtonian model followed by a shear thinning model. To simplify the analysis, it is customary to set the origin of the coordinate system at the location of largest diameter of the extrudate. Since the distance from the spinnerette to the point of largest swell is very small, only a few die diameters, this simplification will not introduce large problems in the solution. 

The derivation of the fiber spinning equations for a non-Newtonian shear thinning viscosity using a power law model are also derived. For a total stress, axx, in a power law fluid, we write the constitutive relation... 

It is appropriate at this time to introduce viscoelastic flow analysis. Fiber spinning is one of the few processes that can be analyzed using analytical viscoelastic models. Here, we follow the approach developed by Denn and Fisher [4], Neglecting inertia, we can start with the momentum balance by modifying eqn. (6.79) as,... 

Figure 6.20 Comparison between experimental and computed velocity profiles during fiber spinning using Denn and Fisher s viscoelastic model [4].

The polystyrene simulation followed the experiments of Bell and Edie (12) with good agreement. Figure 14.8 shows the simulation results for fiber spinning nylon-6.6 with a draw ratio of 40. The figure demonstrates the wealth of information provided by the model. It shows the velocity, temperature, axial normal stress, and crystallinity fields along the threadline. We see the characteristic exponential-like drop in diameter with locally (radially) constant but accelerating velocity. However, results map out the temperature, stress, and crystallinity fields, which show marked variation radially and axially. 

Fiber spinning Finite element modeling — MD modeling... 

Fig. 14.11 Schematic representation of fiber spinning process simulation scheme showing the multiple scale simulation analysis down to the molecular level. This is the goal of the Clemson University-MIT NSF Engineering Research Center for Advanced Engineering Fibers and Films (CAEFF) collaboration. CAEFF researchers are addressing fiber and film forming and structuring by creating a multiscale model that can be used to predict optimal combinations of materials and manufacturing conditions, for these and other processes.

Middleman S. 1977. Fundamentals of Polymer Processing. McGraw-Hill Book Co., New York. Chapter 6 on Extrusion, Chapter 8 on Coating, Chapter 9 on Fiber Spinning, Chapter 14 on Elastic Phenomena, and Chapter 15 on Stability of Flows, cover fragments of the subject as it was understood in the mid-1970s, and show how simple models can sometimes be useful (but not how such models can be misleading - and they sometimes are). 

Figure 4.9 Acrylic fiber structural model showing effect of stretching and relaxation. Source. Reprinted with permission from Capone GJ, Wet-Spinning Technology, Masson JC ed., Acrylic Fiber Technology and Applications, Marcel Dekker, New York, p. 96 and 99, 1995. Copyright 1995, CRC Press, Boca Raton, Florida.

Keywords die swell, extrudate swell, blow molding, modelling of die swell, rheology, finite element modelling (FEM), creep fiber spinning. 

Modeling of the blown film process illustrates characteristics that are very different from those of fiber spinning, even with primitive representations of the heat transfer (37). These differences are a consequence of the hoop stress in the bubble. Multiple steady states are computed for fixed operating conditions, for example, and steady axisymmetric bubbles can vanish suddenly following small changes in operating parameters both phenomena are seen in practice. The... 

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