Abstract

The previous study of the interaction between chrome-tanned hide powder and C.I. Acid Orange 7 has been extended to seven other simple acid dyes in the form of their specially purified dye acids. Good reciprocal plots were obtained at 45 and 60°C, leading to saturation capacities greater than 2 meq/g dry hide substance, except for the dye acids bearing sulphonic groups peri to the azo link. The affinities obtained are lower than those for untanned hide powder and this must be viewed as a consequence of the much greater saturation capacity, which leads to the production of a lower activity in the fibre by a given amount of dye. The affinity of a dye acid for chrome-tanned hide powder increases with the insertion of a methyl group or a fused-on benzene ring, but movement of a sulphonic group to a position peri to the azo link reduces it. Overall, the standard heats and entropies of dyeing chrome-tanned hide powder are of the same sign and order of magnitude as those for the untanned substrate. The thermodynamics of dyeing chrome-tanned hide powder thus do not appear to differ fundamentally from those of dyeing untanned hide powder.