Measurement of specific surface of colorants in cellulose

Abstract

AbstractA new method is described whereby the specific surface of colorants, i.e. pigments or insoluble or water‐soluble dyes, in cellulose can be measured. The principle of the method is the selective adsorption of p‐nitrophenol (PNP) from water by the colorant particles but not by the cellulose, thus permitting determination of the surface of the particles and the effect thereon of various treatments.Results with organic pigments in spun‐dyed viscose rayon agree with calculations of specific surface from particle‐size analysis of the pigments before incorporation. This shows that the whole surface of the colorants in the cellulose is accessible to PNP and thus measurements can be made with a variety of dyes.Azoic dyes and vat dyes give results that correspond to average particle diameters of ∼ 0.1–0.6 μm and the method detects the increase in their particle size on soaping.A direct cotton dye of low light fastness and a reactive dye give specific surface values much too low for a monolayer and they appear to exist as multilayers in cellulose. A direct cotton dye of high light fastness appears to be present as three‐dimensional aggregates of diameter ∼ 0.08 μm, in agreement with published electron micrograph values for similar dyes.