The Basolan AS process: a new concept in wool dyeing

Abstract

The new Basolan AS process for wool dyeing is described. The process restricts the deterioration of wool properties that occurs as a result of dyeing. This is achieved through a reduction in the extent to which wool is permanently set during dyeing. Two options are available to the dyer involving the addition of antisetting chemicals to the wool dyebath. Processing and product benefits can be obtained for wool dyed as loose fibre, top, yarn (package or hank) and woven fabric. Chemical origin Permanent setting of wool takes place through rearrangement of disulphide bonds. This reaction requires the presence of thiolate anions, which are formed by deprotonation of cysteine thiol groups (Schemes 1 and 2). Cysteine thiol occurs naturally in untreated wool, and is also produced as an intermediate in the hydrolytic decomposition of cystine residues [7,8]. Sigruhcant thioldisulphide rearrangement occurs in boiling water after several minutes at pH 4.5 [3]. Permanent setting increases with dyeing pH and temperature (Figure l), and also with dyeing time (Figure 2) [3,9-111. Wool-SH =xr=!~ wool-S-+ H+ Scheme 1 w0ol-Sa-+ wool-s~-sc-wool Scheme 2 MeasurementThe level of permanent set induced by dyeing can be conveniently assessed by the crease-angle method [1,12]. Prior to dyeing, a crease is pressed into a small sample of a woven fabric. This fabric would normally be an undyed, pure wool fabric that has been prepared for piece dyeing. The crease should run along either the warp or weft direction. Following pressing, it is necessary to stitch the fabric to hold the crease in place during dyeing. This is done by inserting one line of stitching approximately 1 mm from, and parallel to, the creased edge, and another approximately 1 cm from the edge.

Wool: Structure, Properties, and Processing

“…(1)). Methods of inhibiting the permanent setting of wool fibers during dyeing have been developed (99). These involve addition to the dyebath of auxiliaries (antisetting agents such as Basolan AS; BASF) that block thiol groups and, thus, prevent thiol/disulfide interchange.…”

“…This can be minimized by including in the dyebath a chemical that reacts with the thiol anions. Minimizing permanent set during dyeing is beneficial in maintaining fiber strength (98) and for maintaining yarn bulk (99).…”

Amineborane: a unique reductive bleaching agent that protects cystine disulphide bonds in keratins

“…Permanent setting generally increases with increasing temperature, pH, reductant concentration and reaction time [1,6–8]. This means that a whiter fibre is usually accompanied by a higher degree of permanent set and deterioration of fibre properties after the reductive treatment.…”

“…It is well known that hydrogen peroxide reacts with cysteine thiol groups in keratin fibres (Scheme 3) resulting in inhibition of thiol–disulphide interchange , providing an anti‐setting effect [6–8].…”

“…As a strong oxidising agent, however, hydrogen peroxide (H 2 O 2 ) is not compatible with these reductive bleaching systems and can only be used to reduce the unwanted setting of wool fibres during dyeing or other high‐temperature treatments, where disulphide bond cleavage occurs in the absence of reducing agents [6–8]. Clearly an innovative approach to this problem is needed.…”