Diffusion Processes in the Spinning Viscose Filament1

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Abstract
The diffusion processes which take place in viscose model filaments spinning in acid baths were followed by means of a microscopic technique. Three characteristic moving boundaries are present in the spinning filaments, viz. the coagulation, the neutralization, and the acid boundaries. The displacement of these boundaries with time was measured for various spinbath compositions. Special attention was given to the influence of ZnSO4 added to spinbaths containing H2SO 4. In this case the presence of a fourth moving boundary must be assumed, representing the limit of conversion of sodium xanthate into zinc xanthate. At a certain distance from the filament surface this boundary is overtaken by the acid boundary; this results in a visible stationary boundary plane, which is supposed to be identical with the skin-core boundary found in the ready filament. The part of the filament in which transient zinc xanthate formation has taken place during spinning is to become the skin in the final product. By using a standardized staining and washing technique of filament cross sections with Victoria Blue, the relative "skin intensity" in the filament and its variation with the distance from the surface could be estimated. Other factors being equal, the skin intensity decreases with increasing lapse of time between coagulation of the primary gel and its conversion into zinc xanthate, and with decreasing "lifetime" of the latter. The length of this lifetime is mainly governed by the concentration of buffering salts in the viscose.

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