Colour gamut produced by applying mixtures of natural dyes on de-inked mechanical pulp

Plants that are available from various regions of Greece were investigated as sources of natural dyes in a paper-dyeing operation. The production of natural dyes was achieved by aquatic extraction of plant materials in order to obtain an environmentally friendly method of producing the dyes. The extracted dyes were applied on de-inked mechanical pulp. A broad variation in shade and colour depth was achieved by applying mixtures of plant extracts in various combinations. The produced colours were found to lie in the first and second quadrant of a two-dimensional chromatic diagram.     

Improving light fastness of natural dyes on cotton yarn

The objectives of this study were to evaluate the light fastness of selected natural dyes (madder, weld and woad) and the effect of some commonly used antioxidants and UV absorbers on the light fastness of these dyes.

The photofading rate curves of madder and weld fixed on cotton correspond to type II fading rate curves described by Giles. These results are in concordance with those of Cox-Crews. The woad presents a type III fading rate curve, similar to the indigo fading rate curve presented by Cox-Crews.

A poor light fastness of the three natural dyes in comparison with synthetic ones is established beyond question. Nevertheless, the use of some additives can improve this default of natural dyes. In all the cases, the use of UV absorbers or antioxidants improved the light fastness of dyed fabrics. The most effectives were the vitamin C and the gallic acid.     

Ink‐jet printing of cotton with natural dyes

Four natural dyes, annatto, cutch, pomegranate fruit rind, and golden dock, were used as colorants for the preparation of water‐based ink‐jet inks for digital textile printing. The physical and rheological properties (pH, conductivity, surface tension, and viscosity) of the inks were measured over a period of 90 days for the evaluation of ink stability and suitability for ink‐jet printing. The inks were found to be suitable and were used for the digital printing of cotton fabrics. The prints were subjected to wash, light, and rub fastness tests and colour measurements. Colour consistency and fastness results, especially after fixation, are comparable with those of synthetic dyes, which paves the way for the production of environmentally friendly ink‐jet inks using natural dyes for the digital printing of cotton through the formulation of suitable printing techniques.     

Colour and fastness of natural dyes: revival of traditional dyeing techniques

Cotton and wool fabrics were dyed with nine natural dyes obtained by aqueous extraction of the original plants/insect in an attempt to reconstruct traditional textile dyeing recipes, to optimise the methodology at all stages, i.e. extraction, mordanting and dyeing, and to standardise it. Cochineal, madder, alkanna, henna, brazilwood, red sandalwood, safflower, indigo and logwood were used for the dyeings, which were carried out directly and after mordanting of the textile material. A variety of mordants, namely, aluminium potassium sulphate, potassium dichromate, copper sulphate, zinc chloride, iron(iii ) chloride, iron(ii ) sulphate and tin chloride, is anticipated to meet both early and recent requirements and options. The dyeings were evaluated through colour measurements and standard wash, light and rub fastness tests. Generally, the mordanting process known for many centuries and connected with the textile dyeing resulted in an improvement in dye absorption and fastness properties mainly for the cotton samples, as is concluded from the tests and measurement assessments.     

Mordant dye application on cotton: optimisation and combination with natural dyes

It is well known that cotton fibres can be dyed through the formation of coordinate bonds involving cellulose chains, mordants such as alum, and natural dyes such as alizarin. Similarly, synthetic dyes known as mordant acid dyes can be used to dye wool fibres. Unlike mordant dyes on wool, the fastnesses of natural dyes on cotton are often low. Although concerns surrounding textile sustainability have sparked renewed interest in the use of natural dyes, extensive replacement of synthetic dyes with natural dyes is neither practical nor fundamentally possible. However, similarities in dyeing methods using mordant and natural dyes raise the possibility of using mordant dyes as alternatives to natural dyes in the dyeing of cotton. Further, the potential for combining suitable dyes from these two classes to expand the colour gamut currently available from natural dyes on cotton seem worthy of exploration. The results of this study indicate that shades comparable with those produced by natural dyes can be obtained on cotton using select mordant dyes following Fe²⁺ and Al³⁺ pretreatments. The best results were obtained using a two‐step/two‐bath process and dyes such as CI Mordant Blue 13 and CI Mordant Orange 6. In evaluations of mordant and natural dye combinations using the two mordant dyes logwood and Osage orange as prototypes, interesting fabric shades were obtained. However, the fastness properties of these dyes must be improved in order to produce commercially viable dyeings.     

Technological evaluation of reactive cyclodextrin in cotton printing with reactive and natural dyes

The chemical modification of cotton fabric with reactive cyclodextrin (R‐CD) at different concentrations was carried out to enhance the printability of cotton fabric. The extent of the modification reaction was expressed as %N. Reactive and natural dyes were used to print cotton fabric before and after modification. Printing pastes were applied immediately after preparation or after 24 h of storage. Printing fixation was performed through either steaming or thermal treatment. The effect of the incorporation of R‐CD in the printing paste of unmodified cotton was also studied. The results reveal that the extent of the modification reaction increased with increasing R‐CD concentration and so did the color strength (K/S) of the printed sample regardless of the dye used. The results also revealed that K/S of the R‐CD modified cottons were higher than that of the corresponding unmodified samples regardless of the method of fixation or the time elapsed before printing. On the other hand, the incorporation of R‐CD in the printing pastes of reactive dyes, namely, Cibacron Brown 6R‐P or Remazol Brilliant Red GG, had adverse effects, most probability due to the (a) increasing viscosity of the paste and/or (b) interaction of the reactive dye with R‐CD hydroxyls. The opposite held true when a natural dye was used. Further, the incorporation of R‐CD in the printing pastes had no effect on the rheological type of the pastes or the on overall fastness properties of the prints. Nevertheless, such an incorporation of R‐CD was accompanied by a remarkable increase in the magnitude of the apparent viscosity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 338–347, 2006     

Colour constancy of vat prints on cotton fabrics

Colour constancy of prints with vat dyes on cotton fabrics was investigated by computing the CMCCON02 colour inconstancy index with the key element CAT02 for chromatic adaptation transform. The results show that the highest changes in colour appearance can be expected when the average daylight is replaced with fluorescent light. If D65 daylight is replaced with some other type of daylight, such as D50 or D55, only minor colour deviations occur which do not substantially change the colour appearance of the prints. The analysis of the influence of the lightness and chromaticity of prints shows that the chromaticity of the samples significantly affects their colour constancy. The change of appearance of the prints with lower chroma because of changed illumination conditions is less probable. The influence of a dye blend composition was also investigated. On average, multi‐coloured dye blends have proved to be more colour constant.     

The effect of electrolytes on direct dyes for cotton

Electrolytes generally promote dyebath exhaustion when direct dyes are used for cellulosic fibers, but the extent with which they do so usually varies from one electrolyte to another. Two direct dyes with varying numbers of sulfonic acid groups were investigated. Cotton cellulose was dyed with these dyes using different electrolytes and a phosphate buffer system. The relationship between strength loss with increase in number of sulfonic acid groups was an obvious observation. Wash fastness results had indicated that the most important consideration is the molecular weight and the overall molecular architecture of the dye.     

Neutral-fixing reactive dyes for cotton.

Research into a new type of reactive dye based on the monochlorotriazine group is described. Reactive dyes of the 3-carboxypyridino-1,3,5-triazine type have been investigated, with a nicotinic acid leaving group, having high stability and fixation efficiency. Dyes of this type react with cellulose in a neutral bath, so widening the scope of reactive dyeing. A classification scheme for reactive dyes is outlined.     

Tensile properties of chemically modified ring- and rotor-spun cotton yarns

The effects of chemical treatments and modifications on the tensile properties of ring-and rotor-spun cotton yarns is discussed. The rotor-spun yarns treated with zinc chloride show a higher tenacity at low stretch levels compared to sodium hydroxide, whereas with sodium hydroxide, the rotor-spun yarns show higher tenacity at higher stretch levels compared with zinc chloride. The aqueous-treated rotor-spun yarns show a higher change in tenacity compared to ring-spun yarns. Sodium hydroxide-treated yarns before resin treatment show a higher retained tenacity compared to zinc chloride-treated yarns. The substitution treatment after swelling and stretching to 100% shows a higher tenacity than that of the slack substituted yarns. © 1995 John Wiley & Sons, Inc.     

Printing of cationised cotton with reactive dyes

The printing properties of cationised cotton that had been pretreated with 2,3-epoxypropyltrimethylammonium chloride were examined. Fixation (steaming) time, colour yields, colorimetric properties, fastness properties, staining of the white grounds and penetration behaviour were evaluated for a number of reactive dyes with cationised cotton fabrics. The cationisation of cotton was found to be very effective in reducing steaming times and washing off processes, and in increasing colour yield. Fastness and other properties of the printings are also discussed.     

The accessibility of cotton to anionic dyes

Adsorption isotherms have been obtained for two direct dyes on unmercerised cotton and viscose yarns at the boil in the presence of sodium chloride. Both dyes, CI Direct Red 81 and CI Direct Green 26, show evidence of monomolecular layer adsorption. Controlled acid hydrolysis of cotton was carried out in order to remove non-crystalline cellulose, and dye sorption values were obtained for the residues. Accessible surface areas have been calculated from the saturation values obtained from the reciprocal plots of the adsorption data. The results are interpreted in terms of a crystalline fibril model of the cotton fibre.     

Viscoelastic modeling of natural and synthetic textile yarns

Viscoelastic models were employed to analyze the stress–strain behavior of cotton, acrylic, and polyester yarns. The potential model and the modified Maxwell model gave the best fits as regards the stress–strain behavior of these yarns. The results of the potential model resembled those of the modified Maxwell model with an infinite relaxation time. The potential model is suitable for explaining the rearrangement undergone by the yarns when no slippage between fibers under strain occurs. When slippage occurs, Maxwell models are able to explain the stress–strain behavior of the yarns. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2062–2067, 2000     

Dyeing of cationised cotton with acid dyes

The production of cationised cotton fabrics, via Sandene 8425, 1, 1-dimethyl-3-hydroxy azetidinium chloride and 1, 1-diethyl-3-hydroxy azetidinium chloride, greatly enhances the exhaustion and fixation of acid dyes. This paper shows that these dyes can be used in the absence of salt in a neutral medium. Wash fastness, light fastness and other properties were studied.     

Subjective evaluation of natural high‐saturated images on a wide gamut display

In previous studies of image evaluation using wide color gamut displays, it is unclear to what degree people prefer the chroma‐varying images, especially the images that are more saturated than the most preferred image. Here, we present a study using a wide color gamut display, which measured viewers' most preferred level of image chroma (experiment 1) and their subjective evaluation of images that were less or more saturated than the previously most preferred one (experiment 2). The results showed that (a) the subjects' preferences for the original or for more saturated images depended on the images' original chroma and (b) the subjective evaluation of the images, that is, Valence and Arousal, did not deteriorate when the chroma of images increased more than the most preferred level. Such results indicate that the increase of the image chroma in wider color gamut displays can have a substantial influence on the impression images have on viewers.     

Dyeing method and properties of polymaleic acid dyes on cotton

A polymaleic acid dye based on poly(maleic anhydride) was synthesised and evaluated in the dyeing of cotton. A series of dyeing auxiliaries were examined, and results showed that a composite auxiliary agent consisting of 20 g/l of zinc nitrate and 30 g/l of dicyandiamide was the most effective when a conventional pad‐dry‐cure dyeing process was used. The fixation could reach 99% and the wash and dry rub fastness could reach grade 4 and grade 4–5 respectively. The decrease in tearing strength of the dyed cotton was between 17.8 and 32.1%.     

Continuous dyeing of cationised cotton with reactive dyes

Cotton fabrics pretreated with cationic starch have been dyed with reactive dyes by a continuous dyeing method and the pretreatment conditions influencing dyeability of the treated cotton investigated. Cationised cotton has been found to give level dyeing without the presence of salt and dye fixation is improved compared with untreated cotton. The dyeings show good wash and rub fastness.     

Colour constancy based on texture similarity for natural images

Colour constancy is a classical problem in computer vision. Although there are a number of colour constancy algorithms based on different assumptions, none of them can be considered as universal. How to select or combine these available methods for different natural image characteristics is an important problem. Recent studies have shown that the texture feature is an important factor to consider when selecting the best colour constancy algorithm for a certain image. In this paper, Weibull parameterisation is used to identify the texture characteristics of colour images. According to the texture similarity, the best colour constancy method (or best combination of methods) is selected out for a specific image. The experiments were carried out on a large data set and the results show that this new approach outperforms current state‐of‐the‐art single algorithms, as well as some combined algorithms.     

Diffusion of dyes in natural fibres

This review provides a summary of research on the penetration of dyes into natural fibres. Emphasis is placed on the relationship between diffusion and the structural morphology of the fibres. The types of commonly dyed natural fibres, the methods of measurement of diffusion and the data that have been collected by the use of each method are reviewed. The applicability of general theories of dyeing to natural fibres is also examined. Recent developments that have led to the direct observation of penetration pathways in wool fibres are described, together with the insights obtained into diffusion phenomena. Areas for future work are briefly indicated.     

Revival of natural dyes in Asia

Increasing environmental awareness has persuaded some of the major Asian countries to reassess the feasibility of natural colorants. As one of the most agriculturally rich regions of the world, the emphasis has been on finding new colour sources which have the potential to yield high quality dyes. Syed Ishrat Ali argues that a detailed programme of R & D into the capabilities of natural dyes is of vital importance.