(698h) Modeling of Wet Spinning

Wet spinning is an important processing operation used in the production of fibers from systems such as polyacrylonitrile and the cellulosic and vinyl-based polymers, as well as in the fabrication of hollow fibers for membrane separation and drug delivery applications.  In wet spinning, an initially homogeneous solution is extruded directly into a liquid bath where mass, momentum, and heat transfer processes take place, resulting in liquid demixing and gelation to form a solid, structured fiber. Modeling involves coupling the simultaneous transport and phase separation processes with constitutive models that account for viscoelastic effects. Important effects that should be captured include predictions of the locking-in of fiber diameter, stresses, and internal structure along the spin line, since these, to a large extent, fix the as-spun fiber properties. The text by Ziabicki (1) reviews wet spin modeling up to about 1976; however, since then, there have been relatively few new studies reported.  The most complete recent studies we are aware of are those of Kalabin et al. (2) that combine Newtonian constitutive modeling with a two-phase binary diffusion model that incorporates thermally-induced phase separation/gelation along the spinline. Our recent studies follow a different approach built on our successful dry spinning modeling (3) that incorporates a two-component constitutive model based on parallel combination of Newtonian and Giesekus equations. This is coupled with a 2-d pseudo-ternary diffusion formalism that utilizes separate diffusion equations for the fiber gel and solution phases.  These are combined with mass transfer boundary conditions at the fiber-bath interface and incorporation of the ternary phase diagram based on Flory-Huggins theory to quantify the gelation dynamics along the spinline.  Model results illustrating predictions of the spinline fiber profiles and structuring for a variety of systems and processing conditions will be discussed along with comparisons of literature data for the wet spinning of PAN fibers.

1. A. Ziabicki, Fundamentals of Fiber Formation, John Wiley and Sons, NY, 1976.
2.  A.L. Kalabin, Fibre Chemistry, 37, 141 (2005).
3. Z. Gou and A.J. McHugh, J. Non-Newt. Fl. Mech. 118, 121 (2004).