Search

In this study, cotton fabric and nylon fabric were dyed with a range of commercial sulphur dyes and the light and wash fastness of the coloured fabrics was investigated. The effect of after‐treating the coloured cotton and nylon fabrics with a tannin‐based commercial product, Bayprotect Cl, in the presence or absence of sodium sulphate in the treatment bath, was found to significantly improve the light fastness of the sulphur‐dyed cotton, and the photoprotective effect was partially stable to ISO 105‐C06 washing. In addition, the tannin‐based after‐treatment also improved the colour stability of the dyed fabrics to the perborate‐based ISO 105‐C06 washing. The possible mechanisms for the improved fastness properties are also discussed. The application of sulphur dyes to nylon is potentially commercially useful but has been limited because of the reported poor light fastness of the dyeings. The photoprotective effect of the tannin‐based after‐treatment was investigated with a view to providing the necessary commercial performance. However, it was established that on this fibre, the light fastness improvement was marginal, and the associated wash fastness to oxidative bleach‐based ISO 105‐C06 washing was limited.

Freshwater is an increasingly scarce resource that is extensively used in textile wet‐processing. In seeking to identify alternative low freshwater‐usage coloration technology, this study examined the potential use of seawater (SEAW) as the dyeing medium for wool coloration using a range of reactive dyes. Initially, the dyeing behaviour of the wool fabric in simulated seawater (SSW) was compared with conventional dyeing from distilled water (DW) using α‐bromoacrylamide‐based Lanasol dyes and sulphatoethyl sulphone‐based Remazol dyes. These preliminary studies demonstrated that comparable coloration could be achieved in the SSW medium based on an assessment of the dye exhaustion, dye fixation, colour yield and levelness. Subsequent dyeing studies of wool using Mauritian seawater with both the Lanasol and Remazol reactive dyes confirmed that, based on the dye exhaustion, dye fixation, colour yield and levelness, comparable coloration could be achieved, highlighting the possibility of substituting freshwater with seawater as the dyeing medium.

Previous studies have established that the application of crosslinking dyes and easy care finishes to cotton can significantly reduce the dissolution of waste cotton in solvents, such as N-Methylmorpholine oxide, and limit the potential recycling of cellulosic materials through the Lyocell fibre regeneration process. In this investigation the surface chemical compositions of three reactive dyed Tencel fabrics were studied using X-ray Photoelectron Spectroscopy (XPS) and the presence of the dye at the fibre surface demonstrated. The effect of the ISO 105 C09 oxidative-bleach fading test on the azo and anthraquinone chromophoric species was established by both surface chemical and colorimetric analyses. At low dye application levels the C. I. Reactive Black 5 and C. I. Reactive Red 228 dyed fabrics (azo chromophore) exhibited obvious colour fade while the anthraquinone-based C. I. Reactive Blue 19 dyed fabric was resistant to colour fade. However it is apparent that although some of the covalently bound dye will be removed during “first life” usage, most of the reactive colorant will remain bound to the cotton and will therefore need to be stripped from the waste garments to produce a white cellulosic feedstock prior to reprocessing through Lyocell fibre regeneration. A sequential acid, alkali and peroxide treatment completely removed the azo-based C. I. Reactive Black 5 and C. I. Reactive Red 228 colorants from the dyed cotton, however, the anthraquinone-based C. I. Reactive Blue 19 was highly resistant to removal and will require alternative chemical processing to remove the colorant.

In earlier papers we have described sulphite-based and secondary amine-based resist printing of cotton using ink-jet procedures. This paper describes the chemical resist printing of polyester fabrics padded with disperse dyes to create a white image on a coloured background. Polyester grounds have been prepared by the pad-dry ‘dyeing’ of polyester fabrics with alkali clearable disperse dyes, such as a Dianix PC (DyStar) or a Dianix SF (DyStar) dye, and subsequently ink-jet printed with sodium carbonate based ink formulations to yield a white image on a solid ground following high temperature steaming and appropriate wash-off procedures. Coloured images have been achieved by a two-step process whereby the coloured ground fabric was initially printed with an alkali based ink and then over-printed in a second step with an illuminating ink formulation containing a alkali stable disperse dye, such as a Dianix AD (DyStar) or Serilene ADS (Yorkshire Chemicals).

In an earlier paper we have described sulphite-based resist printing using ink-jet procedures. This paper describes an alternative approach to sulphite inactivation of vinylsulphone dyes by using secondary amines to inactivate fluoro-s-triazine dyes while maintaining the reactivity of the vinylsulphone dyes. Monofluoro-s-triazine reactive dyes are padded onto cotton fabrics and then deactivated by ink-jet printing with a suitable secondary amine formulation to produce a white image on a solid ground colour after appropriate fixation and soap-off procedures have been undertaken. A coloured image can be achieved by overprinting the resist-printed areas with a coloured ink formulation containing a β-sulphatoethylsulphone-type reactive dye; such dyes form a β-bis-alkylaminoethylsulphone dye via reaction with the secondary amine. This latter dye ‘unblocks’ during a mildly acidic steaming process to form the reactive vinylsulphone dye, and so, unlike the monofluoro-s-triazine dye, is not deactivated towards subsequent covalent reaction with the cotton substrate.

Discharge printing provides a method of producing either a white or coloured image on a solid ground fabric; unfortunately, the shade range from this process is limited. An alternative approach to discharge printing is resist printing, which provides prints that are almost indistinguishable from those achieved by the discharge printing process and has the advantage of offering a wider shade range. In resist printing, the resist agent prevents fixation of the background colour by chemical (resist agent inhibits dye fixation) or physical (resist agent inhibits dye absorption) processes and so yields a white print. Printing is carried out on grounds that have been pad-dry ‘dyed’ with selected reactive dyes; the dyes must not fix during this process otherwise white grounds are not achievable – subsequently fixation is achieved by steaming after digitally printing the resist agent. In this paper, the resist agent studied is sodium sulphite, which selectively blocks reactive groups in reactive dyes – the ground shade reactive dye must be deactivated in this reaction to produce the resist effect. A coloured print may be achieved by incorporating a suitable reactive dye, of a different class to that used in the ground shade, which is not deactivated by the resist agent, in the resist ink.

A polyfunctional reactive dye containing two dichloro-s-triazine residues linked through aliphatic amino groups via a third triazine system to the chromophoric residue has been prepared. The dye was synthesised stepwise from a specially synthesised 2,4-dichloro-s-triazine dyes. The first step is the reaction of both carbon–chlorine sites in the ‘parent’ dye with 2 mol ethylenediamine under selected conditions of pH and temperature; these conditions ensure that only one of the amino groups in the ethylenediamine will react to give the bis-2,4-aminoethyleneaminotriazine dye. The second step is the condensation of 2 mol cyanuric chloride with the two pendant primary amino groups. The alkylamino-linked dichloro-s-triazine dyes show very different dyeing properties when compared with those shown by the parent dichloro-s-triazine dye, which has the reactive group linked directly into the aromatic chromophore; in particular, the new dyes have high fixation efficiencies when dyed on cotton at 50 °C and the dye–fibre bond stability to boiling acidic conditions is very good.

A series of water-soluble fibre-reactive arylating agents were synthesised and evaluated from the stand-point of improving fibre coloration with disperse dyes. In particular, the compound, sodio-2,4-dianilino-6-[4′-β-sulphatoethylsulphonylanilino]-s-triazine (FAA 200) was found to be promising; this compound could be applied in the same bath as a disperse dye at pH 5–6. Under the latter conditions this compound showed high substantivity to wool and at the boil readily underwent β-elimination of the sulphate ester residue to give the vinyl sulphone reactive group which adds on to nucleophilic sites in the fibre to form a covalent bond. Coapplication with commercially available disperse dyes gave bright, level dyeings that exhibited promising wet fastness. FAA 200 was used as an auxiliary to dye disperse dyes on both fibre components of a wool–polyester blend fabric; it was found that addition of hydrogen peroxide or sodium thiocyanate was necessary to obviate reduction of certain disperse dyes when dyeing at 120 °C.

The modification of cotton cellulose through a nucleophilic substitution reaction with sodium benzoylthioglycollate (BTG) is described. BTG has been applied to cotton fabric by pad-thermosol processes and the resulting benzoylated fabrics assessed for disperse dyeability.

The extensive amount of work which has been carried out to increase disperse dye substantivity for cellulosic fibres is critically assessed. From the viewpoint of the practical colourist it is important that such systems should be operable in aqueous media. A water soluble acylating agent, sodium benzoylthioglycollate, (BTG) was therefore synthesised and characterised. The stability of BTG to hydrolysis in aqueous media was determined, together with its reactivity towards other nucleophiles.