Effect of Phase Diagram on Spinning of Chemical Fibers from Solution

The spinning of polyacrylonitrile fiber from dimethylformamide solution is analyzed on the basis of a previously developed model of the spinning of fibers from solutions of polymers. It was shown that the phase diagram of the system and its variation as a result of change in the concentration of the precipitant in the solution, the temperature, and the mechanical field have an effect on the gelling process and on its kinetics in spinning of the fiber. A proposal is made about the conditions for the attainment of a more uniform structure in the fiber. It is shown that if the phase diagram in the working region of precipitant concentration is changed by 3.5% the time for complete gelling changes from 1.1 to 1.8 s. The dependence of the thickness of the gel on time Rg(t) does not change in qualitative respects. The dependence of the thickness of the gel Rg(t) and of the gelling rate dRg(t)/dt on time differs in form for diffusion and thermotropic gelation. The total gelation times and gelling rates for the diffusion and thermotropic processes differ by almost an order of magnitude: tc/tt ~ 10. The regime for minimal diffusion, at which the gelling rate is almost constant while the dependence of the thickness of the gel on time Rg(t) is close to linear, was determined. Such a regime can give the fiber a uniform structure.