Simultaneous Determination of the Main Constituents of Viscose Spinning Solutions by Visible near Infrared Spectroscopy

The production of cellulose fibres by wet fibres spinning requires a careful monitoring of the spinning bath and especially the spinning solution in terms of product control and for quality assurance purposes. The chemical composition as well as the ripening of the spinning solution are of major importance for maintaining a constant product quality. The conventional determination of the quality parameters of the viscose spinning solution are rather time- and labour-intensive due to the fact that several independent analytical procedures are involved which score low in time efficiency themselves. Briefly, the complete characterisation of the spinning solution requires an iodometric titration of the cellulose xanthogenate (γ-number), an acidimetric titration of the sodium hydroxide (NaOH) content, a UV-VIS spectroscopic determination of the trithiocarbonate (TTC) content and a time-consuming gravimetric cellulose content determination. Sometimes, also, a colloid chemical determination of the degree of ripening (Hottenroth number) is performed in the plant control laboratory. With this work, an approach will be demonstrated, which enables the substitution of these numerous analytical procedures by a single and time-efficient method—a VIS-NIR spectroscopic technique. Therefore, it is possible to determine the parameters: NaOH, TTC, cellulose xanthogenate content and the cellulose content of the viscose spinning solution simultaneously with a reasonable precision within a few minutes.