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The dyeing, printing and decoration of textiles go back to the earliest times and, historically, have inspired craftspeople to remarkable levels of ingenuity as ways have been sought to exploit the colouring matters to be found in nature. The basis for most of the dyeing methods in use up until the nineteenth century was established by the ancient Egyptians, who developed the application of plant extracts often in association with mordanting (the pre-application of solutions of metal salts such as alum to the textile to give improved washing fastness and, in some cases, a specially desirable shade through the formation of complex compounds). For obvious reasons the plants and other materials used tended to be those indigenous to the region so that, for example, the production of scarlet shades from insects of the kermes family which originated in Persia did not feature in Egyptian dyeing practice. Similarly woad, later to be displaced by indigo, which was one of the most important colouring matters in use in ancient times, did not reach Egypt until about 300 bc. Another important ancient source of dyes was the molluscs used by the Phoenicians to produce the famous Tyrian Purple and related shades. It should not be forgotten that considerable experimentation and chemical expertise were required to make many of the developments which took place.

The role of water in dyeing is discussed from two points of view. Firstly, the use of water as a system for the distribution of dyes and energy in dyeing machines is considered briefly. Secondly, the participation of water in the formation of dye–fibre bonds is examined. Water may act both in assisting dye–fibre bonding and as a competitor. Competition may be allosteric or isosteric and examples are discussed.

The results are presented of an investigation into the instability induced in dye-fibre bonds by peroxide treatments. The nature of the reactions involved are discussed.

Cut segments of wool, as well as whole fibres, have been immersed, under standard conditions, in concentrated aqueous urea. The diameter of each fibre or segment was then determined and compared with that of a control. No swelling occurred with whole fibres, but swelling was observed with the segments, the extent of swelling, in a given time, being inversely proportional to the length of the cut segment. The swelling of cut fibres increased with the time of immersion in concentrated aqueous urea. It is concluded that urea diffused into the cut ends of wool fibres, but that the epicuticle, if intact, is impervious to urea.

The hydrolysis of the bonds formed between a 2,4-difluoro-5-chloropyrimidin-6-yl and a 2,4-dichloro-1,3,5-triazin-6-yl fibre reactive dye and cellulose by treatment in sodium perborate and hydrogen peroxide solutions has been studied. The evidence points to the formation of reactive products between the fixed dye and hydrogen peroxide, with the main part of the hydrolysis promoted by heat rather than light as was believed to be the main factor. Residual leaving groups on the reactive system of the dye provide one of the centres for the formation of reactive products.

Society Centenary Lecture presented at the 13th Congress of the International Federation of Associations of Textile Chemists and Colourists in London on 21 September 1984.

Pretreatments of wool with strong solutions of amines and ammonia have been reported to increase dye adsorption rates in many cases. The effect has been ascribed to the formation of β-aminoalanine residues in the wool with a resultant increase in its electrical potential. The effect of more dilute solutions of ammonia and dimethylamine is reported here. The possibility that the amines act simply as alkaline hydrolysis promoters has been examined by taking into account internal pH effects. The addition of salt to the amine treatment solution has been shown to be very advantageous so that ‘low-temperature-dyeing’ wool may be readily prepared by a simple ammonia-salt pretreatment.

The tracer diffusion of Clr–36 labelled hydrochloric acid and of S–35 labelled C. I. Food Yellow 3 in nylon 6. 6 filaments has been studied. The results have shown that the spun filaments have a surface layer which acts as a barrier to diffusion. Using an analysis, similar to that used by Medley and Andrews [1], the diffusional characteristics of the surface and bulk of the fibres have been determined as a function of draw ratio. Parallel studies, using conventional methods, failed to show the existence of the surface barrier owing to concentration dependence, and diffusion potential effects.

Treatment of wool with dilute ammonia solutions containing salt for short times at low temperatures modifies the wool to make it readily dyeable at 50–70°C. A saline ammonia scouring procedure to produce an easily dyed wool has been developed and has been evaluated both as a scouring procedure with particular preservation of wool quality and as a means of producing wool that can be dyed at 50–70°C. A short-time dyeing cycle for Lanasol (CGY) dyes is considered in detail.

The properties of the surface layer on wool fibres which limits the rate of dye uptake have been examined. The removal of the barrier layer by mechanical means and its degradation by surface reduction using tri–butyl phosphine have been studied using the rate of dyeing as a parameter. The chemical properties of the barrier layer suggest that it is a cystine–rich component of the cuticle layer system, either the exocuticle or its ‘a’ layer sub-system.

Meeting of the Midlands Region, held at the Carpet Trades Ltd Canteen, Kidderminster, on 13 February 1969, Mr D. O. Douglas in the chair The essential features of hank-dyeing machines are discussed in relation to the application of Fick's laws of diffusion to the mass-transfer processes occurring during dyeing. Dispersion equations and a mathematical model of the dyeing process are developed. The determination of dispersion coefficients on model hank systems is described. The results have been applied to the mathematical model using digital- and analogue-computer programs. The predictions of the computer-simulated dyeing process with respect to the distribution of dye within a hank are reasonably accurate in comparison with practical dyeings. The analogue-computer simulation of dyeing processes has general applicability beyond hank dyeing, provided that the appropriate system variables are known.

The relation between industrial and academic research is discussed, and a distinction is drawn between discovery– the revelation of what exists in our environment and the study of the laws that govern it– and invention– the utilisation of the results of discovery to change that environment. Problems arising from difficulties in communication, especially in large industrial complexes, are discussed and illustrated. Finally, the role of the universities in the training of graduates for participation in applied scientific activities is examined.

The interaction of the acid dye Biebrich Scarlet (C.I. Acid Red 66) with α-, β-, and γ-keratoses obtained from wool fiber by performic acid oxidation was studied. The extrapolated saturation values of dye bound to protein and the association constants for the interactions were obtained. Maximum dye uptake was found for α-keratose, followed by γ- and β-keratoses, in that order. Incorporation of varying amounts of m-cresol in the dye solutions showed no significant effect. There was no indication of an interaction between m-cresol and the keratoses from direct studies.

A study has been carried out of the relationship between polymer orientation and dyeing behavior using a specially prepared range of nylon 66 samples varying only in orientation and five dyes normally showing varying degrees of sensitivity to physical variations in nylon. Integral diffusion coefficients have been calculated using Crank's finite dyebath equation from appropriate rate of dyeing data. Evidence has been produced which suggests that except with dyes of low molecular weight, i.e., dyes insensitive to physical variations in the nylon, a diffusional interaction between diffusing dye molecules exists which leads to a variation in the concentration dependence of the diffusion coefficient with fiber orientation. The length of the diffusing dye ion has been shown to be of decisive importance in this interaction.

The introduction of reactive dyes has significantly affected the established economic relationship between batch and continuous processing. Reactive dyes have properties which are suited to high-speed continuous dyeing without the need for specialised equipment. On the other hand, conventional dyes, e.g. direct and vat dyes, are designed primarily for batch-dyeing methods. It is found that the direct production costs for the continuous dyeing of reactive dyes are comparable with those for dyeing direct dyes on the jig or winch. This fact, coupled with the high wet-fastness properties of reactive dyes, is likely to accelerate the growth of more productive dyeing processes throughout the world.

Improved experimental methods have shown that the conclusions drawn in earlier work [1, 2] are only partially correct. The kinetics of hydrolysis of Type 3 dye-fibre bonds have been shown to be complex and not first-order as believed. The reason lies in the variation of the internal pH of the fibre as dye is removed. Redetermined bimolecular hydrolysis constants for H-acid derivatives show that the more ready hydrolysis of Type 3 dyeings from red H-acid dyes is associated with the formation of a highly active species in the internal pH region 3-3.5. The problems these findings pose for the establishment of a ‘bleaching’ test are raised.

The introduction of reactive dyes has made possible the development of methods for linking the dyeing and finishing processes. This step offers considerable economy in operating costs because of the simplicity of the operations and the streamlining of production, and at the same time dye consumption is markedly reduced as a result of the very high degree of fixation obtained. Two processes are described: the Procion–Resin process for cotton fabrics, which permits simultaneous dyeing and finishing, and the two-stage Procion–Resin process for viscose rayon fabrics, which links the two processes. Excellent fastness properties and high-quality finishes can be obtained by the two processes.

The kinetics of the acid hydrolysis of Type 3 dyeings produced by the reaction of dichlorotriazinyl aminoazo dyes with cellulose have been studied at 40°C. A marked effect has been observed owing to what are believed to be localised pH effects, i.e. a non-uniform distribution of hydrogen ions within the fibre phase owing to the localised charges on the dye molecules attached to the fibre. Variation of the ionic strength in the reaction medium does not affect the bimolecular rate constants for the hydrolysis, but brings about changes that can also be ascribed to pH effects in the fibre phase. There is evidence for two kinds of Type 3 dye-fibre bonding, giving a very rapidly hydrolysed species, present in relatively low concentration, and a more stable species.

The kinetics of the hydrolysis of dichlorotriazinyl reactive dyes have been studied over a range of temperatures and pH values. The results have been examined in accordance with the generally accepted reaction scheme, and methods of calculating the separate rate constants are described. The activation energy of hydrolysis varies with temperature and this variation is thought to be due to changes in the activity coefficient or probability factor with temperature. The equilibrium between two forms of the dye does not have the characteristics of a simple acid-base equilibrium with respect to temperature, indicating that it may not arise from the ionisation of the imino bridging group, as has been generally supposed.

The development of reactive dyes for cellulosic fibres is considered, together with their organic and physical chemistry. The relation between the theoretical aspects of the chemistry of reactive dyes and their application and development problems is discussed.

Commencing with a simple but realistic mathemati cal model of dispersion, absorption, and desorp tion of dye within a cylindrical packed bed of fibers, a finite difference scheme of equations was developed capable of analog solution. By varying the main kinetic and mass-transfer pa rameters, the dynamic response of the system was determined and preferred changes of operating values were indicated. We suggest that these methods could be widely ap plied in the study of systems involving mass trans fer and reaction; to determine the individual effect of descriptive physical parameters on a pro cess without recourse to complex mathematical procedures.

Meeting of the Midlands Region, held at the Carpet Trades Ltd Canteen, Kidderminster, on 13 February 1969, Mr D. O. Douglas in the chair Simulation of dyeing processes on an analogue computer, using techniques described in Part I of this paper (p. 187), has been employed to establish the minimum flow requirements for practical machines using dyes differing in dyeing behaviour. A limiting rate of flow requires to be achieved to eliminate differences in colour between hanks in practical machines. The failure to meet this condition is responsible for much of the problem of achieving level dyeings.

The effect of adding urea to the dyebath on the rate of absorption of reactive and acid dyes by wool, and of acid dyes by other protein bres, has been studied. Possible modesof action of aqueous solutions of urea on wool are discussed. The observed increase in the ite of dyeing in the presence of urea is due to disaggregation of the dye in solution and reduction in dye-protein hydrophobic interactions. The action of urea in promoting fibre swelling is also likely to be a contributory factor.

The exhaustion of three selected prechromed dyes at different dyebath pH values has been measured, and the results show marked differences from those obtained with level–dyeing acid dyes under similar conditions. It is shown that the levelling properties of this type of dye increase with decrease in the dyebath pH. The boiling–off properties of the dyes examined have been shown to be better in the presence of sulphuric acid than hydrochloric acid at the same final dyebath pH.

The tracer diffusion coefficients of three S-35-labeled dyes in nylon 6 film have been determined. The diffusion coefficients show marked concentration dependence, but this takes a form different from that shown by chloride ions in a related study. It is not possible to explain the data on the basis of electrostatic factors as in earlier work in which diffusion was accompanied by a free-energy change. A diffusional interaction between dye molecules is postulated which takes the form of a free-volume saturation effect leading to an upper limiting diffusion coefficient at adsorption levels which depend upon the polymer order and the characteristics of the diffusing ion.

Tracer diffusion coefficients of chloride ions in nylon 6 film have been determined by standard techniques combined with liquid scintillation counting. The tracer diffusion coefficients depend markedly on the amount of chloride ion sorbed by the nylon. The observed diffusional flux is a function of two diffusional interaction coefficients relating to the interaction of the diffusing ion with ‘unoccupied’ charge centres in the polymer and with the absorbed water. The interplay of these two interactions may be important in connection with the problem of dyeing barre nylon.

The fixation of some Procion T phosphonated reactive dyes on cotton in the presence of dicyandiamide in different conditions of dyeing is reported, in order to clarify the role of the carbodiimide in the fixation process. Paper chromatographic studies on Procion Red T-2B show that the reaction mechanism between the phosphonic dye and cellulose in the presence of dicyandiamide is an initial condensation of the phosphonic dye with dicyandiamide to produce a phosphonic acid anhydride, followed by subsequent reaction with cellulose to give a dye covalently bonded to the cellulose. The phosphonic acid anhydride, isolated by means of column chromatography, shows the characteristic adsorption bands of the P—O—P linkage.

Pigments AN Introduction to their Physical Chemistry. Edited by David Patterson. Pp. xii + 210. (Amsterdam, London and New York: Elsevier Publishing Company, Ltd., 1967.) 65s.

An experimental application of electrical conductivity is described. The causes and method of elimination of some anomalous results are given. Suggestions are made for the further successful application of electrical conductivity measurements as a simple and convenient method of tracer detection in fluid flow systems, suitable for semi-technical plant investigations.

The causes of anomalous results obtained in the measurement of the swelling of wool fibres by different methods have been investigated. The British Standard method (BS 2043) and the fixed-point method were examined. When urea solutions are used as the swelling media, the results obtained by the two methods differ considerably. The short lengths of fibre used in the BS 2043 method are well within the fibre dimensions for swelling to occur by end penetration and hence give results that can be misleading when related to the swelling of undamaged fibres during processing. When the swelling agent itself can penetrate the fibre wall, either method will give reliable results. When, however, the agent can show colligative osmotic properties typical of many non-volatile salts, discrepancies may arise between the two methods.

With a view to explaining the effect of m-cresol on the kinetics of dye uptake by wool and other proteins, a study has been made of the interaction of Biebrich Scarlet (C.I. Acid Red 66) with α-chymotrypsin in the presence and absence of m-cresol. It has been found that a 1:1 dye-protein complex is formed in the absence of m-cresol and that m-cresol displaces the dye from the complex through allosteric competition.