The yellowing of wool is a complex phenomenon which is induced by a variety of agencies such as light, heat and aqueous chemical reactions. Yellowing of wool by light depends critically on the wavelength distribution of the light (u. v. region), humidity and the type of prebleach given to the wool; if fluorescent whitening agents (FWAs) are employed in the bleaching process then the sensitivity to photo‐yellowing is drastically increased. The copious amount of work carried out to overcome this complex situation will be summarised and the important role of the aromatic indole amino acid, tryptophan, will be detailed. In contrast to photoyellowing, exposure of wool to visible blue light (maximal effect 420–450 nm) promotes photobleaching of the yellow pigments, giving rise to complaints of colour change, especially in wool products dyed to pastel colours. To remove natural yellowness, chemical bleaching of wool is usually carried out by using hydrogen peroxide, the usage of which should be carefully controlled because of its fibre damaging characteristics. Optimisation of wool peroxide bleaching procedures has therefore been the subject of much work and these studies will be reviewed. Bleaching of wool with reducing agents is often practised either as an alternative to peroxide bleaching or more usually as an aftertreatment of peroxide‐bleached wool to improve the whiteness and stability to light. Trade practice in the field of wool bleaching has recently been critically reviewed; the results and recommendations of this assessment will be given. More recently, significant progress has been made in the field of selective dark fibre bleaching and in the bleaching of heavily pigmented wools (e.g. karakul) using methods based on ferrous ion mordanting.
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.
The new pyrethroid, permethrin, previously shown to have high activity against textile pests, was successfully applied to wool from a conventional dye bath. The stability of permethrin to boiling aqueous conditions and to some textile testing regimes was shown to be satisfactory, although some loss on prolonged boiling did occur. Industrial trials made on both wool and wool/nylon blends are described.
2,3-Dihydro-I H-I ,4-diazepines are normally brominated at the 6-position. Phenyl substituents are usually unaffected, although with 2.3-dihydro-I .4-diphenyl-5,7-dimethyl-1H-l,4-diazepinium salts, the benzene rings are also brominated. 2.3-Dihydro-I ,7-dimethyl-5-phenyl-1 H -I ,4-diazepine is brominated at the 7-methyl group. N-Chlorosuccinimide and N-iodosuccinimide also substitute dihydrodiazepines at the 6-position. Under appropriate conditions 6.6-dihalogenodihydro-6H-diazepines have been isolated, but they revert to monohalogenocompounds in dilute hydrobromic acid. 6-Bromodihydro-I H-diazepinium salts are debrominated by strong acid in the presence of bromide ion.With nucleophiles, 6-bromodihydro-I H-diazepines either undergo normal nucleophilic substitution or suffer replacement of the bromine by hydrogen.THE most characteristic feature of the chemistry of the 2,3-dihydro-lH-1,4-diazepinium cations is the readiness with which they undergo electrophilic substitution at the fi-position, with retention of the initial mesomeric ~y s t e m . ~, ~ Because of this behaviour they have been described as quasi-aromatic corn pound^.^*^ A study
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.