Thermotropic gelation in wet spinning of fibres from polymer solutions

Abstract

More than one-third of the chemical fibres manufactured in the world --cellulose, polyacrylonitrile, aramid, polyvinyl chloride, etc. --are now manufactured by wet spinning fi'om polymer solutions. All of these technologies have a common mechanism of fibre formation. Beginning with S. E Papkov's studies [ 1 ], the gelation process in spinning has been considered with respect to the phase state of the polymer solutions. The kinetics of fibre formation (gelation) was investigated experimentally in [2], and there are also studies on modeling this process [2-6] based on its diffusion nature.The growth rate of the gel coating in time and the duration of total gelation in a small jet of spinning solution are very important features in wet spinning technology. Our previously proposed [7] model for describing gelation in "'wet" spinning of chemical fibres from polymer solutions differs from the existing models [2-6] due to the possibility of calculating the gelation kinetics using the phase diagram.The phase transition in polymer systems can be caused by not only a change in the composition of the solvent (addition of a precipitator) but also by a change in the temperature or application of a mechanical field. The kinetics of attaining the condition of phase equilibrium to a significant degree determines the structure and physicomechanical properties of the gel. The gel phase, in turn, is the primary structure of the fibre which greatly determines its properties. The further investigation of gelation from polymer solution is pressing. The formation of a gel in thermotropic conditions [8], where fibre formation takes place due to heat exchange alone without diffusion, is described in recent publications on gelation.Thermotropic gelation is examined in the present study. The current gel layer thickness can be determined from the transcendental equation in [7] C[R(r),t] = Cc,[r(r,t)],where C[~;t] is the concentration of precipitator in the polymer solution jet (r is a coordinate along the radius of the jet; t is the time); C is the concentration of precipitator at the time of the phase transition at temperature T; the value of Cis found from the Cr phase diagram of the polymer--solvent--precipitator system. Equation (1) is solved relative to R -R(t) --the coordinates of the gelation front. The current gel layer thickness R(t) is determined as the difference between the radius of the fibreR 0 and the coordinate of the gelation front Rg(t) =R 0 -R(t). "(his relation and Eq. (1) can be used to find the gel layer thickness as a function of time R(t).The calculation ofR(t) for a nonlinear model ofgelation is reported in [7]. An approximate linear model of the process, expressed in algebraic equa'tions, will be examined tbr the analysis of the change in the size of the gelation zone in time R(t) and for the estimations. It is hypothesized that the qualitative shape of Rg(t) will be preserved when the nonlinear model is

Electrospinning based on benign solvents: current definitions, implications and strategies

“…This phenomenon is called "mechanotropic spinning". 77 Kotomin et al showed that the mechanotropic process has to be taken into account even for ES from polymer solutions. 76 Above all, mechanotropic spinning may be more reasonable for polymer solutions in solvents having low vapor pressures and high boiling points, like DMSO.…”