Simulation of Kinetics and Heat and Mass Transfer for the Spinning of Chemical Fibers from Polymer Solutions

Abstract-A mathematical model for the kinetics of nonisothermal wet spinning of chemical fibers from polymer solutions is proposed. The model gives a way to calculate the kinetics of spinning and gelation simultaneously, using the phase diagram with regard to heat and mass transfer, layered two-phase patterns, and movable interfaces. The process is calculated numerically, and a comparison is made between calculated and experimental data. In wet spinning of chemical fibers from polymer solutions, jets of a polymer solution pass through a spinning bath containing an agent that coagulates the polymer. The coagulant finds its way into the solution jets and accumulates there. When enough of the coagulant has been accumulated, the polymer solution is separated into a solid (gel-like) and a liquid phase. The gel-like phase is the primary structure of the fiber and controls its properties in many respects. The new polymer phase (gel) is a very viscous fluid. Its shear viscosity is high compared with the viscosity of the solution. Although separate features of wet spinning of chemical fibers from polymer solutions are thoroughly discussed in [1 -3], a general quantitative theory of this process has not been created as yet. Some technological and physical problems for this process are studied in The gelation model proposed i

GELATION MECHANISMS IN SPINNING OF FIBRES FROM SOLUTIONS OF POLYMERS

In spinning fibres from solutions of polymers, the structure of the fibre is formed through the stage of gelation. Gelation is a complex physicochemical process affected by a large number of factors, and the properties of the gel are very different as a function of the conditions of its preparation. The gel phase, the primary structure of the fibre, determines its properties to a great degree. Investigation of different gelation mechanisms in spinning from solutions of polymers is a pressing problem. The following fundamental factors that affect gelation have been distinguished: diffusion phenomena, heat transfer, and the mechanical stress field. In most studies considering the effect of diffusion on gelation [1-4], this mechanism is assumed to be determining. In the recent concept of "gelation," it is attributed to the effect of heat transfer In industrial spinning of fibres from solutions of polymers, three predominant mechanisms can be distinguished in gelation: -diffusion, based on diffusion of the precipitant into the polymer solution and solvent; -thermotropic, occurring in heat transfer between jet and environment when they are at different temperatures; -mechanotropic, consisting of application of a mechanical field. Gelation is the phase transition of the polymer from liquid phase to gel when such external conditions as the temperature, concentration of precipitant, and mechanical stress chang