Modeling of the Wet Spinning Process for Hollow Fiber Membrane Formation

C.-H. Shih, C.C. Gryte (USA), and L.-P. Cheng (Taiwan)

Keywords

Modeling, hollow fiber, phase inversion

Abstract

Theory A quantitative analysis is presented, which describes the ternary diffusion process encountered in the formation of polymeric hollow-fiber membranes by the isothermal wet spinning process. Coordinate transformations were employed to derive the mass transfer equations both for the bath and hollow fiber membrane. The calculated diffusion trajectories and concentration profiles in the nascent membrane were found to agree with the membrane morphologies observed by electron microscopy. 1. Ternary diffusion equations for the hollow fiber region The geometry for the spinning model is shown in Figure 1. A hollow fiber dope solution (called fiber solution, hereinafter) of thickness M0 is surrounded by a reservoir of coagulation bath liquid (called outer bath, hereinafter) and a coagulation inner liquid (called inner bath, hereinafter) flowing through the center region of the system. Polymer is restricted to the fiber solution while solvent and non-solvent components in the baths and the fiber solution are free to migrate. Assuming that the partial molar volume of each component is constant, the equation of continuity for the membrane solution is given by8 ,

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