Improvement of the wash fastness of non-metallised acid dyes on conventional and microfibre nylon 6,6

The adsorption of a commercial syntan on to both conventional and microfibre nylon 6,6 was found to increase with decreasing application pH, indicating that ion-ion interaction contributes to syntan-fibre substantivity. Uptake of the syntan on both types of fibre increased with decreasing liquor ratio, possibly as a result of syntan aggregation, and also increased with increasing application temperature, this being attributable to the higher kinetic energy of the syntan molecules and the greater extent of fibre swelling operative at the higher temperatures. I;rom the finding that uptake of the synthetic tanning agent on to undyed conventional and microfibre nylon 6,6 followed a BET mechanism, it was postulated that adsorption involves the formation of multi-layers and that forces other than ion-ion contribute towards syntan-fibre interaction. This postulate gained support from the observation that although the presence of 1% omf dye on the two types of fibre reduced the extent of syntan uptake, the mechanism of syntan adsorption on to both substrates was unaffected The finding that syntan uptake was greater on microfibres than conventional fibres was attributed to the greater surface area of microfibres. Despite the greater uptake of the syntan on to dyed microfibre, the wash fastness of syntanned dyed microfibre was lower than that of its syntanned dyed conventional decitex counterpart. The effectiveness of the syntan in improving the wash fastness of several non-metallised acid dyes on microfibre was enhanced by the subsequent application, to the syntanned dyed substrate, of certain cationic agents. The level of wash fastness achieved using this syntan/cationic agent system was considerably higher than that obtained using an after treatment with either 4% omf syntan or the full backtan.