The development of a metal-free, tannic acid-based aftertreatment for nylon 6,6 dyed with acid dyes—part 3: different enzymes

Abstract

A single-bath, two-stage aftertreatment for nylon 6,6 dyed with acid dyes has been developed, in which an enzyme is used to complex tannic acid. The effectiveness of four protease enzymes was determined, employing a repeated washing protocol, using five commercial acid dyes on nylon 6,6. It was found that while each of the four enzymes were very effective, when used in conjunction with tannic acid, in improving the fastness of all five acid dyes to repeated washing at 40, 50 and 60 °C, one particular enzyme was, overall, the most effective. While the chemical structures of the four enzymes used are not available, the nature of their interaction with tannic acid is explained in terms of the general interactions that occur between tannic acid and proteins. It is proposed that the enzymes replace the metal salt (potassium antimonyl tartrate) used in the full backtan aftertreatment and that the sequential application of tannic acid and enzyme results in the formation of an insoluble, tannic acid/enzyme complex that is situated at the surface of the dyed substrate and which provides a physical barrier to the diffusion of dye from the dyed fabric during washing. The metal-free, tannic acid/enzyme aftertreatment offers a potentially more environmentally acceptable alternative to the antimony-based and tin-based systems