AbstractA large amount of work has been reported in the literature on the influence of insoluble materials on the viscose process. Detrimental effects of insolubles on filtration has been the subject of the majority of the research in the past, but some efforts have included studies of the effect of insolubles on yarn strength. A wide range of physicochemical techniques have been applied to the problem with varying degrees of success. Counting of the insoluble particles has been mainly done by microscopic methods or equipment utilizing the breaking of a light beam and photoelectric detection. In the work reported herein, a commercially available particle counter (Coulter counter) which operates on electronic principles has been applied with considerable success to cellulosic solutions. The instrument permits determination of cellulosic particle sizes and size distributions in the size range of real interest to cellulose workers (4–50 μ) and over an even wider range with other accessories. Viscose solutions, diluted 1:10 with dissolving caustic, have been counted before and after filtration. The number of counts varies considerably with species, pulp type, processing conditions, and the presence or absence of surfactant. Filtration through a medium similar to that used in commercial viscose preparation causes a fairly sharp drop in the number of particles greater than 8 μ. The counts below 8 μ are not changed appreciably by filtration. The filter cutoff of cellulose acetate solutions (diluted to similar concentrations) is much less sharply defined. Acetate counting is done in aqueous acetone solution with sulfuric acid as electrolyte. Coulter counts parallel microscopic values, but are far less laborious, and more information about the size distributions is obtained. The instrument has also been used to evaluate filter media for both viscose and cellulose acetate filtra
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