The effect of various anti-setting systems in wool dyeing. Part 3; Sodium thiocyanate based systems

Wool fabrics undergo setting during dyeing. The degree of set can be controlled by careful selection of dyebath conditions and also by the addition to the dyebath of chemicals termed anti-setting agents. The anti-setting effect of sodium thiocyanate has been evaluated according to its concentration in the dyebath and the dyebath pH. The fabric crease-angle method was adopted to estimate the degree of anti-setting. In the case of wool fabric boiled in the presence of sodium thiocyanate, good anti-setting effects resulted from the pH 3 and pH 5 treatment baths. Chemical changes in the wool were detected using FTIR analysis.     

Minimising the impairment of the physical properties of wool during dyeing by restricting the level of permanent set

If permanent setting of the wool fibre, which occurs during dyeing, can be restricted, the impairment of physical properties is reduced. This can be achieved by adding an oxidising agent, such as potassium bromate or hydrogen peroxide, to the dyebath. Oxidising agents also restrict the extent to which hygral expansion increases as a result of piece dyeing. When used in the presence of dyes, oxidants may cause differences in the colour of the dyed wool.     

The effect of various anti-setting systems in wool dyeing. Part 1: Hydrogen peroxide based systems

Extensive setting of wool fabrics occurs during piece dyeing at the boil and gives rise to adverse changes in dimensional stability such as variable hygral expansion, loss in tensile strength and the appearance of unsightly marks such as 'crow's-feet' on the fabric surface. Anti-setting agents such as stabilised hydrogen peroxide systems have thus been marketed to control this problem. Much has been published regarding the anti-setting and hygral expansion properties achievable but little information regarding the chemical effect of boiling wool with acidic solutions of hydrogen peroxide is available. Fourier transform infrared reflectance spectroscopy has thus been extensively used to quantify the chemical changes occurring on boiling wool in such aqueous solutions of hydrogen peroxide.     

The effect of various anti-setting systems in wool dyeing. Part 2: Sodium maleate based systems

Wool is subject to permanent setting reactions during dyeing at the boil. Sodium maleate additions to the dyebath exert an anti-setting effect, and in the case of wool piece-goods dyeing, the magnitude of anti-setting was evaluated using the crease angle method. To achieve anti-setting, the key reactions are the nucleophilic addition of the activated double bond in sodium maleate with wool thiolate anion groups and with free hydrosulphide anions generated by cysteine thiol decomposition. Optimum antisetting effects were achieved when wool fabric was treated with sodium maleate at pH 3. Fourier transform infrared reflectance spectroscopy was used to monitor chemical changes to the wool fibre. Compared to untreated wool, two new frequencies at 1354 and 865 cm⁻¹ were apparent; the highest intensity values for these bands were obtained for wool treated at pH 3, which indicates that wool, being positively charged in this acidic solution, adsorbed more sodium maleate, thus enhancing the chances for nucleophilic addition reactions.     

Relationship between set and bulk of package–dyed wool yarns

The loss of bulk in hand–knitting yarns as a result of package dyeing has been investigated. Simulated dyeing of packages, prepared with and without axial compression, has revealed a correlation between the bulk of the relaxed dyed yarns and the permanent longitudinal set imparted to the yarns. The strain in the yarn in the wet package, and hence the longitudinal set, is related to the hygral expansion of the yarn and the strain imposed on the yarn during winding of the package. The role of axial compression of the package in determining loss of bulk is also considered. Finally it is shown that by adding reagents to the dyebath that inhibit the setting reaction, the loss of bulk can be markedly decreased, provided also that the yarns are fully relaxed after being dyed.     

Studies on indigo dyeing and diffusion by the film roll method

The influence of reducing agent, indigo concentration and dyebath pH on indigo dyeing and diffusion was studied for the film roll method. An almost linear relationship between the indigo concentrations in the dyed film and in the dyebath was maintained throughout the experiments. Two different calculation methods were used to obtain the diffusion coefficient and the surface indigo concentration in the film. Similar surface indigo concentrations were obtained from the two methods, but a lower diffusion coefficient was obtained by the approximate integral method. It was found that the dyebath pH is the dominant factor influencing the rate of diffusion of indigo and the colour yield of the dyed film. The dyebath pH also had a considerable influence on the reduction of indigo to leuco-indigo, a step that is essential to the dyeing process.     

A Method for Stabilising Wool Carpet Yarns to Withstand Piece Dyeing

The twist in wool carpet yarns can be stabilised throughout piece dyeing by setting the twist by a traditional method, e.g. by steaming the yarn in hank form in the presence of a reducing agent, and then dyeing the finished carpet in a dyebath containing formaldehyde.     

细旦腈纶染色工艺研究

介绍了腈纶的上色性能,研究了细旦腈纶染浴pH值和染浴温度对细旦腈纶染色的影响。结果表明:适当降低起染温度,控制好升温速度和保温时间,调整合适的染浴pH值,可有效提高细旦腈纶的染色效果。     

The reduction of vat dyes by indirect electrolysis

The reduction of vat dyes by an indirect electrolytic process is described. The dyeing procedure and the relevant dyeing parameters for this new reduction technique are discussed. The dyeing results are comparable with those obtained by standard experiments using sodium dithionite. After removal by filtration techniques of the remaining dye from the exhausted dyebath, regeneration of the reducing agent by cathodic reduction is possible. The results demonstrate the applicability of this reduction method for larger-scale vat dyeing procedures.     

Diffusion of disperse dyes into super-microfibres

The disperse dyeing process for polyester fibres is complex. It is characterised by the diffusion-controlled sorption of dyes and depends on dye concentration, dyebath temperature, dye liquor flow rate and fibre count. Moreover, the dyeing properties of super-microfibres are also quite different from those of microfibres or conventional polyester fibres. In this paper the influence of dyebath temperature, initial dye concentration and fibre count on the diffusion coefficient and the sorption isotherms has been studied. The analysis of kinetic properties has been restricted to infinite dyebath conditions. All experimental results have been compared terms of fibre count and dyebath temperature.     

Constant-temperature Dyeing Process for Nylon Fibres I—A Study of the Mechanisms

The various interactions that can occur in a dyebath containing nylon, an anionic dye, an anionic agent (Lissapol D) and a mildly cationic agent (Dispersol CWL) are described and discussed. A mechanism by which these agents influence the dyeing of nylon is postulated. The importance of considering the individual behaviour of anionic dyes in such a dyeing system is emphasised, since it is demonstrated that the strengths of the complexes formed between dye and cationic agent vary from dye to dye, in some instances being more stable and in others less stable than that between the anionic and the cationic agents.     

偶氮染料的光还原脱色及其染色废水的回用研究

用还原脱色剂对水溶性偶氮染料进行光还原脱色降解,重点考察了还原脱色剂、辐射光以及染料浓度等对还原脱色反应的影响,并将脱色后的染色废水回用于棉织物染色中.结果表明,以适当比例的引发剂和促进剂组成的还原脱色剂具有较强的脱色降解能力,辐射光对染料的还原脱色反应具有明显的促进作用,染料浓度的提高不利于染料的脱色降解反应.脱色废水可以回用于棉织物的活性染料染色中,通过降低染色过程中氯化钠和碳酸钠的添加量,可使染色试样与自来水染色试样的总色差(DE*)＜1.0.     

Colour variation in the dyeing of denim yarn with indigo

In this paper, various parameters of warp yarn dyeing using indigo dyes are investigated. These parameters include dye concentration, number of dips in the dyeing process, dyebath pH, amount of reducing agent, immersion time, oxidation (skying) temperature, effects of a wetting agent and soaping temperature. This study revealed that these parameters have varying degrees of influence on the resultant colour of the samples dyed. The degrees of variation in colour were expressed using the CIE L* a* b* system as well as the shade depth (Integ).     

Reuse of spent dyebath following decolorisation with ozone

Spent reactive dyebaths were decolorised by treatment with ozone and reused in the bleaching, whitening and dyeing of two textile substrates. The study shows that the reuse of a spent dyebath is possible with little modification to the standard processes for dyeing cotton with reactive dyes, provided that the pH of the treated dyebath is adjusted. Moreover, the cycle of decolorisation and reuse was successfully repeated. Renovated reactive dyebaths were also reused for bleaching cotton fabric with hydrogen peroxide, whitening with optical brightener and dyeing polyester fabric with disperse dyes. The whiteness index of bleached and whitened cotton was comparable to that of the same fabric given a control treatment with fresh baths. Likewise, there was a negligible colour difference between polyester dyed using liquor from a spent reactive dyebath and the same fabric dyed in a new bath.     

Sorption of nonionic auxiliary products by wool and its influence on dyeing with acid dyes

Pretreatment of wool fibres with nonionic auxiliary products recommended for low-temperature dyeing resulted in an increase in dyebath exhaustion and a faster rate of dyeing. This indicated that the auxiliary product was absorbed to a certain extent by the wool. This absorption occurred rapidly and produced an increase in dyebath exhaustion and improved the levelness of the resultant dyeings     

Dyeing machine control using in-line colour measurement Part 2: On-line control of dye exhaustion rate

Part 1 of this paper reported a novel method of dyebath analysis, based on an in-line analysis cell with links to a computer-based match prediction system that included compensation for changes in dyebath temperature. We now describe the cell's use in feedback control of the rate of uptake of dye from the dyebath by controlling the dyebath temperature in conventional (all-in) and continuous-addition dyeing. For all-in dyeing, a high level of control was achieved, allowing experimental verification of the theoretical result that a quadratic exhaustion profile gives the best levelness. When dye was added continuously, a linear exhaustion profile proved to be the most robust and gave the best levelness with either linear or exponential addition of dye.     

Acid dyeing isotherms of cotton fabrics pretreated with mixtures of reactive cationic agents

Reactive cationic agents, phenylmonochlorotriazinyl and epoxypropyl, are used for cotton pretreatment using a pad–dry–curing technique. The dyeability of cationised cotton fabrics using CI Acid Red 1, determined spectrophotometrically for the residual dyebath, has been dependent on the cationic agent concentration and the appropriate mixture used. Comparative sorption isotherms, rate of dyeing at different temperatures, standard affinity, entropy and heat of dyeing for three different pretreated fabrics have been calculated and discussed. The equilibrium data obtained were fitted by the Langmuir isotherm model, allowing the corresponding sorption parameters to be determined.     

Fuzzy control of dyebath pH in exhaust dyeing

In textile exhaust dyeing, the control of dyebath pH is a critical factor in order to achieve optimum colour yield and levelness. Conventional controllers have not proved entirely successful in controlling dyebath pH since it is difficult to develop an exact mathematical model for the dyeing process. One method is to apply fuzzy control to the dyeing process. For the fuzzy controller to operate successfully, it is important to understand how the dyeing system responds to given reference pH/time profiles. A dynamic model for the dyeing process has been developed and this allows the fuzzy controller to be fine-tuned by computer simulation. Results of the control system simulation showed very satisfactory tracking performances of the pH profiles. This provides a starting point for further fine-tuning of the system under practical dyeing conditions.     

The Use of Permethrin in New Insect Proofing Agents for Wool

The development and properties of the photostable pyre–throids are reviewed with reference to the use of permethrin for the protection of wool. An emulsifiable concentrate formulation (of this insecticide) – Perigen * – has been developed for use as an industrial mothproofer. The compound shows excellent fastness on wool and good biological activity against the major textile pests. The influence of dyebath pH, dyeing auxiliaries and duration of boiling in the dyebath on the application of the insecticide, is discussed. The low residue levels in effluent from dyebaths following application of Perigen are unlikely to pose any hazard during disposal. Application rates are given for Perigen as an insect–proofing agent for yarn destined for carpets and other products.     

Statistical investigation of the cotton dyeing kinetics of CI Reactive Black 5 dye

In this study, the dyeing kinetics of CI Reactive Black 5 dye was statistically investigated. Cotton fabrics were dyed with this dye under different conditions by the exhaustion technique. Dye samples were taken from the dyebath from the start to the end of the process at 10 min intervals in order to determine the percentage dye exhaustion. The transmittance of the coloured dyebath samples was measured using a UV‐vis spectrophotometer. The results were investigated by statistical methods using analysis of variance and regression curves. The dye exhaustion of the cotton fabrics was found to change as a function of the dyeing parameters. Times of half‐dyeing were determined from the regression curves.