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The detailed understanding of the interaction between dyes and additives in the practical service condition is required to develop an inkjet ink for textiles. In the present study, the interaction between three acid dyes (C. I. Acid Red 88, 13, and 27) and a water-soluble polymer, poly(vinylpyrrolidone) (PVP), with different molecular weight was investigated. The binding constants of the dyes with PVP, Kbind, were determined by means of the visible absorption spectrum measurements. The Kbind values decreased with an increase in the number of sulfonate groups in the acid dyes (an increase in the solubility of the dyes in water). This suggests that the affinity to PVP decreases with increasing water solubility. Furthermore, the binding constants were diminished by increasing molecular weight of PVP. It is presumably due to the conformation change of PVP with molecular weight. For further discussion, the thermodynamic parameters for the binding, viz. the enthalpy change, ΔHbind, and the entropy change, ΔSbind, were determined from the temperature dependence of Kbind. The ΔHbind values for all the dyes were negative, showing that the binding processes are exothermic. The absolute values of ΔHbind decreased with the increase in the number of sulfonate groups in the dye molecules. On the other hand, the increase of PVP molecular weight made the thermodynamic process to be less enthalpic and more entropic. Thus, the nature of the interaction should be affected by PVP molecular weight, because the polymer conformation is strongly influenced by the molecular weight.

Effects of Polymer Molecular Weight on the Interaction between Acid Dyes and Poly(vinylpyrrolidone) in Inkjet Ink for Textiles