| Abstract: | A study has been made of the diffusion of zinc ions into alkaline solutions of sodium cellulose xanthate (viscose) when these are extruded into acidified salt solutions (spin-bath). Under these conditions, which exist during the manufacture of regenerated cellulose industrial yarns, the zinc ions are diffusing into a continuously coagulating gel structure from which water is exuded as the structure is developed. It has been shown that the presence of certain additives (modifiers) in the viscose can slow down the diffusion of both zinc and hydrogen ions, thus retarding the coagulation and neutralization of the viscose. In the initial stages of coagulation, before the neutralization point is reached, the modifiers reduce the rapid filament shrinkage and pressure rise within the filament which would otherwise be caused by the presence of zinc ions in the spinbath. The mode of action of the modifiers is discussed in the light of current theories. A hypothesis is put forward that the modifiers act by preventing the initial rapid shrinking action of the outer cuticle of the filament. This permits the production of the desired fine structure inside the filament during a slower steady shrinkage which leads to a round cross-sectioned filament of good mechanical properties. |
