Swelling of the jet during the formation of chemical fi bers by the wet method is studied. The swelling of a jet is investigated in the shear regime during extrusion of the spinning solution through a capillary with free effl ux and with stretching of a freshly formed jet in the spinning bath. It is shown that the magnitude of the swelling is determined by the viscoelastic properties of the polymer system (equilibrium relaxation time and power-law exponent) and by the conditions of extrusion of the polymer system through a capillary. Relations for determining the magnitude of the swelling and the equilibrium relaxation time are presented.The initial results of research on the formation of fi bers through spinnerets with multiple openings have been published in [11]. As a result of the differences in the geometric dimensions of individual openings (within the tolerance limits) and the conditions of precipitation during formation through such spinnerets the indices of elementary fi bers differ from one another, as a result of which the measured forces that remove a fi lament from the spinneret are averages, which obscures certain features of the manifestation of the deformation properties of freshly formed fi bers. For this reason, to investigate the formation process single capillaries of different diameter and length were also investigated. In the fi rst place, this made it possible to obtain more accurate experimental data and determine certain particulars of the extrusion of the spinning solution through a capillary and subsequent precipitation of the fi ber-jet which have not been noted in the literature. In the second place, the capillaries made it possible to use for analyzing the formation process the theory of deformation of viscoelastic polymer systems in the shear regime [2] and extend it to formation through commercial spinnerets.An important feature of the formation process is the capability of polymer systems in fl ow through a capillary (spinneret) for the jet to swell at the exit from the capillary, which greatly affects the condition of stretching and precipitation of the fi ber-jet in the precipitation medium and complicates the analysis of the formation process. For this reason, we shall start the study of the formation process by analyzing the swelling of a fi ber-jet. Ordinarily, the swelling of a jet is evaluated by the swelling coeffi cient B, equal to the ratio of the jet diameter d j to the capillary diameter d o , i.e., B = d j /d o . On the basis of the established opinion that the swelling of a jet is due to the relaxation of the elastic (high-elastic) deformation stored by the polymer system as it fl ows through a capillary, a number of relations were proposed; the main ones are presented in [3,4]. In these relations the swelling is related to the "high-elastic" deformation that is determined by Weissenberg's relation. Ignoring the defi ciencies of these relations we note that the analysis is greatly simplifi ed if the previously examined [2] deformation characteristics are used --the e...
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