Dyeing of Papermaking Fibers with Dyes of Various Structural Types as a Means for Fiber Surface Characterization

Birch kraft fibers of various composition with respect to lignin, hemicelluloses and cellulose and cotton were stained with cationic dyes belonging to different structural classes: Methylene Blue (MB), Crystal Violet (CV), 4-phenylazo- N,N,N-trimethylanilinium nitrate (TMY), Astra Blue (AB) and Alcian Blue pyridine variant (ABP). Adsorption isotherms measured at pH 8 were found to be in good agreement with Langmuir model. Methylene Blue and Crystal Violet exhibit adsorption proportional to the amount of anionic groups on fibers. A binding of a related cationic dye, 4- phenylazo-N,N,N-trimethylanilinium nitrate, is much lower. The behavior of cationic phthalocyanine dyes is more complex; besides their dependence on the quantity of anionic groups, these dyes exhibit marked affinity to fibers with low content of lignin. For phthalocyanines a different binding mechanism is apparent.