A tannic acid/ferrous sulfate aftertreatment for dyed nylon 6,6

Both a single-stage and a two-stage aftertreatment using tannic acid in conjunction with ferrous sulfate improved the fastness to repeated washing at 60 °C of two acid dyes on nylon 6,6 most likely via the formation of a low solubility, large molecular size, iron tannate complex within the periphery of the dyed fibre. The iron tannate complex imparted a slight greyish-brown colour to dyeings, although this did not affect the λmax of the dyeings and also increased the colour strength of the dyeings. Neither the single-stage nor the two-stage aftertreatment affected the light fastness of dyeings but both aftertreatments reduced rub fastness.