THE AFFINITIES OF ACID DYES FOR SILK

Abstract

The adsorption of acid azo dyes by silk was investigated. The amount of saturated adsorption and the standard affinity of acid dyes were estimated by Gilbert-Rideal theory.The results obtained were as follows:(1) The amounts of saturated adsorption of dye acids were estimated by the extrapolation of the relation between and For five levelling dyes, the mean of saturation values was 19.4×10-5 eq/g, which was almost equivalent to that of hydrochloric acid. This indicates that not only mono-anionic dyes, but also poly-anionic ones are sorbed stoichiometrically. Therefore, it was reasonably considered that adsorption of levelling dyes is mainly due to ionic linkage between dye anion and cationic sites in silk.On the other hand, the amounts of saturated adsorption of Acid Blue 92 and Acid Red 85 which belong to grade III and IV, respectively in SDC Migration Test, were by about 18% larger than those of levelling dyes.These results suggest the increase of non-polar van der Waals force contribution in the adsorption.(2) The standard affinities were hardly dependent on adsorpted amounts over the concentration range studied and reasonable agreed as revealed in Table 2-6. It was found that the standard affinities increase with the molecular weight of dyes and also are somewhat affected by the nature and position of the substituents. Moreover, the standard affinities of dye anions decreased by 2.38 kcal/mol when an additional sulphonic acid group was introduced into the dye molecules.(3) From the difference of the standard affinities of Acid Orange 7 and Acid Yellow 36 between silk and wool, it was considered that the role of hydrogen ion for silk is more important than that for wool in dyeing by levelling dyes.(4) In the range 40 to 80°C, the standard heats of levelling dye in adsorption were calculated as -4.5_??_-6.5 kcal/mol. These values are slightly smaller than those for wool. The standard entropy was positive as found for hydrochloric acid.