Colour gamut of natural dyes on cotton yarns

Cotton fibres were dyed using various natural dyes alone and in combination to yield six basic shades: blue, yellow, red, black, green and fawn. These dyed fibres were then blended in various proportions along with undyed cotton fibres and spun on a rotor-spinning machine to produce 204 coloured yarns. The fastness properties of the six basic shades were determined. The L * a * b * and L * C * h values of the yarns having 50% dyed fibre and 50% undyed cotton fibre was also determined. The values were plotted to obtain the colour gamut of natural dyes on cotton yarns.     

Comparative study of colour yield of cotton knitted fabric made by torque‐free ring‐spun yarns

Torque‐free ring spinning is a new spinning technology that has produced yarns with low twist and balanced torque. In this study, a commercially torque‐free ring‐spun yarn, namely Estex yarn, with three types of cotton fibre, i.e. Pima, upland and organic cotton, were used. Cotton fabric samples were knitted with Estex yarns and conventional ring‐spun yarns. The fabric samples were then dyed with two reactive dyes, Remazol Black B and Remazol Brilliant Blue R Spec., and the fabric dyeability was measured in terms of reflectance and colour yield. Finally, the results were analysed using the statistical software package SPSS and the results revealed that fabric samples manufactured by Estex yarns could achieve a better colour yield than conventional ring‐spun fabric samples. In addition, the Pima cotton gave the best colour yield, followed by upland cotton and organic cotton.     

Assessing colour values of polyester fabrics produced from fibres having different cross-sectional shapes after abrasion

This study assesses the colour, colour difference and colour strength values obtained for eight disperse-dyed polyester fabric samples produced from full and hollow round and trilobal fibres after four sets of abrasion cycle. Each fabric was produced from the same yarns in warp and weft directions. The L *, C *ΔE^*_ab and K/S values of the undyed fabrics and dyed fabrics before and after increasing cycles of abrasion are presented and discussed. Fabrics produced from full and hollow fibres showed great differences regarding colour values in abrasion behaviour. Fabrics produced from hollow fibres were found to be very sensitive to increasing abrasion cycles.     

Determining the dependence of colour values on yarn structure

The colour values of knitted cotton fabrics made from single and plied ring and compact yarns were investigated before and after dyeing. The fabric samples were knitted under the same constructional properties and then dyed with direct and reactive dyes. It was found that fabrics with ring yarns had high lightness and low chroma and colour strength values compared with fabrics with compact yarns. Also colour strength and colour difference values of dyed fabrics were assessed after increasing abrasion cycles (2500, 5000, 7500 and 10 000). The main changes in colour strength values were observed at 2500 abrasion cycles. The effect of abrasion on colour difference values of fabrics having ring yarns was more obvious than fabrics having compact yarns.     

An unsupervised method for dominant colour region segmentation in yarn‐dyed fabrics

This paper presents a novel unsupervised approach to detect dominant colour regions standing out conspicuously in yarn‐dyed fabric images. For a dominant colour region of a yarn‐dyed fabric, measured by an imaging system, its individual yarn has an irregular three‐dimensional shape resulting in significant colour difference among pixels of the yarn. This difference leads to difficulty in segmenting yarns into dominant colour regions. A probabilistic model is proposed in this study to associate the colour of a dominant colour region with the colours of its yarns. Based on this model, the colour histograms of a dominant colour region are first estimated from those of yarns in a yarn‐dyed fabric image. Then, a hierarchical segmentation structure is devised to detect dominant colour regions in the image. Experimental results show that the proposed approach achieves satisfactory performance for dominant colour region segmentation in yarn‐dyed fabric images, with high computational efficiency.     

A novel method for weft and warp yarn segmentation in multicolour yarn‐dyed fabric images

This paper proposes a novel method for segmentation of weft and warp yarns in multicolour yarn‐dyed fabric images. A multicolour yarn‐dyed fabric is cross‐woven by weft and warp yarns with different colours. When a multispectral imaging system is used to measure the colour of a multicolour yarn‐dyed fabric image, its weft and warp yarns need to be detected before analysing their colours. Detection of interstices between weft and warp yarns is firstly conducted. A modified K‐means clustering approach is then utilised to separate weft and warp yarns. The number of clusters is fixed to 2. The metric to measure the distance between a pixel and the mean of a cluster is the CIELAB colour difference. The initial means are determined by the expected values of fitted Gaussian distributions to CIExyY colour histograms. Experimental results show that the proposed method is promising for the segmentation of weft and warp yarns in multicolour yarn‐dyed fabrics, with an improved segmentation accuracy and much faster processing speed than K‐means clustering in CIEXYZ and CIELAB spaces.     

Investigation of the clean patterning possibilities on cotton socks through laser technology

The aim of this research is to reveal the effect of laser treatment at different resolutions (10, 20 and 30 dpi) and pixel times (80, 100 and 120 μs) on reactive dye uptake of cotton fabrics and the fastness values obtained. Yellowness index, Fourier Transform–infrared analysis, scanning electron microscopy analysis and bursting strength tests were applied to samples. The samples treated with laser were dyed in lighter shades than the untreated ones, with all three of the reactive dyes used in the experiments. In general, colour yield values decreased when the resolution and pixel time increased. However, no significant change was observed in washing, rubbing, light and perspiration fastness values. The possibilities of obtaining various patterns on cotton socks dyed with reactive dyes by laser treatment at different resolutions and pixel times were also investigated. According to the results, it was determined that if laser treatment was not applied to some parts of reactive dyed cotton socks, and 10 dpi 100 μs and 20 dpi 100 μs laser was applied to other parts of those socks, then it was possible to obtain patterns with different shades of the same colour on the socks. On the other hand, laser application after dyeing does not have a negative effect on fastness values. After determining the optimum conditions for the laser process, non-see-through tights were produced with cotton yarn on the front and polyester/elastane yarn on the back, and patterns were obtained by applying laser treatment before or after dyeing via sample scale industrial production.     

A multispectral imaging approach to colour measurement and colour matching of single yarns without winding

This paper investigates a multispectral imaging approach to colour measurement and colour matching of single yarns. The small size of a single yarn makes it impossible for spectrophotometers directly to acquire its spectral reflectance. Multispectral imaging systems, on the other hand, have the potential to measure the reflectance of single yarns as they can record both the spectral and the spatial information of a sample. A multispectral imaging system, namely imaging colour measurement, has been developed to conduct colour measurement of single yarns. A single yarn is first detected from backgrounds by a modified K‐means clustering method. The reflectance of the single yarn is then specified by an averaging method. Comparative experiments based on 100 pairs of single yarns and corresponding yarn windings show that the reflectance magnitude of a single yarn acquired by imaging colour measurement is smaller than that of corresponding yarn winding measured by a Datacolor 650 spectrophotometer. Experiments on 16 single yarns show that the repeatability and spatial reproducibility of the imaging colour measurement system in measuring a single yarn colour are 0.1185 and 0.2827 CMC(2:1) units. A colour matching comparison experiment (pass or fail), using 24 pairs of single yarns and corresponding pairs of solid‐colour yarn dyed fabrics, shows that single yarns measured by imaging colour measurement can achieve similar colour matching results to solid‐colour yarn dyed fabrics measured by the Datacolor 650 spectrophotometer, with degrees of similarity of 87.5 and 83.3% when the CMC(2:1) and CIE2000(2:1:1) colour difference formulas are employed.     

Prediction of depth of shade of a dyed polyester fabric based on fibre fineness and fabric structure

A colour prediction model containing four parameters of dye concentration, fibre fineness, fabric roughness and dye parameter is developed. The model can predict the shade depth of a dyed polyester fabric. The relationship among these factors and shade depths of dyed polyester fabrics was investigated to elucidate the role of fibre fineness and fabric structure on surface reflectance and colour efficiency. The shades of several additional dyed samples were measured and compared against the predicated values to validate the accuracy and performance of the model. The results showed that the predicated depths of shade matched the experimental data to a good extent.     

Application of the nondestructive second derivative spectrophotometry to eliminate the effect of substrate in identification of madder used in Persian carpets

The handmade Persian carpet is famous worldwide not only for its elegant design and artistic structure, but also for its brilliant color harmony and incomparable raw materials. Various natural dyes accompanied by different mordants are used on various woolen yarns to obtain a wide range of unrepeatable shades for carpet. In this article, as a first step, the diversity of the undyed woolen yarns used in Persian carpets was statistically investigated by implementation of the Principle Component Analysis. Then the second derivative of Kubelka‐Munk function of samples dyed with madder was considered to reach a pattern for identifying madder. The results show that, although the spectral reflectance of different selected woolen yarns has at least 3 dimensions, all derivative curves are qualitatively very similar with the same minimum and maximum peaks at 510 and 605 nm, respectively. The findings are confirmed when various types of madder were used in the dyeing process. As a result, it is shown that the nondestructive derivative spectrophotometry is able to identify madder on alum mordanted woolen yarns used in Persian carpets and to eliminate the effect of substrate. It is a useful technique for preservation, conservation, and dissemination of the Persian carpet.     

The dyeing and colour characteristics of alkali–treated polyester fibres dyed with disperse dyes

Alkali–treated and untreated polyester fabrics were dyed for up to 6 h at 100°C with a series of six disperse dyes of different chemical structures. The alkali–treated polyester samples adsorbed more dye and were dyed to deeper depths of shade and slightly different shades than was the untreated polyester. The greatest differences were observed for the alkali–treated polyester with the most outer surface or skin removed. Dye structure and molecular size also affected the amount of dye adsorbed on the fibres, but did not delineate the nature of differences between skin and core morphology. This study shows that significant differences exist between the molecular structure of the skin and core of melt–spun polyester fibres.     

Effect of the ozonation process on the dyeability of mohair fibres

This work has focused on the use of ozonation in order to improve the dyeability of mohair fibres. The study was carried out using a known concentration of ozone and involved process parameters such as wet pick‐up, level of pH and treatment time. The effect of fibre ozonation was assessed in terms of colour, and test samples were also evaluated using scanning electron microscopy and Fourier transform–infrared spectroscopy. The optimum conditions of the ozonation process were determined as 60% wet pick‐up, pH 7 and 30 min. According to the experimental results, it can be concluded that ozonated mohair fibres can be dyed both at 90 and 80 °C with all dye classes without causing any decrease in colour yield. Dyeing kinetics and thermodynamics were also studied and it was demonstrated that the rate constant and the standard affinity of the ozonated sample increased.     

Effects of alkali and ultraviolet treatment on colour strength and mechanical properties of jute yarn

In this study, jute yarns were treated with an aqueous alkali solution and ultraviolet light to improve dyeability. Ultraviolet light treatments were carried out at an air pressure of 1 atm, under water and vacuum, and all the samples were dyed with reactive dyes. Virgin samples and treated jute yarns were analysed by Fourier Transform–infrared spectroscopy. K/S values were determined by a reflective spectrophotometer and used to establish the fixation values and colour strength of the dyed samples. The tensile mechanical properties of the samples were also measured by a tensile testing apparatus and were compared with the virgin samples. Alkali treatment resulted in a reduction in carbonyl group concentration. However, atmospheric ultraviolet light treatment increased carbonyl group concentration. Dyeability and dye fixation values for atmospheric and underwater ultraviolet light‐treated samples increased. Furthermore, the loss of tensile strength for alkali‐treated samples was much greater than others (up to 50%) in comparison with ultraviolet light‐treated samples.     

Colour of flax fibres in regard to different pretreatment and dyeing processes

The main objective of this work was to compare the colour of different pretreated (alkaline, acidic and enzymatic) and dyed (conventional and ultrasonic-assisted) flax fibres, to establish the impact of various parameters on dyeing kinetics. Flax fibres were dyed using two direct dyes of different chemical structures and molecular mass. Diffusion profiles were established by the application of Fick's Law and dyeing behaviour was studied by means of online spectrophotometry. Finally, the dyed samples were colorimetrically evaluated and colour differences and colour strengths were subsequently calculated. The results provided evidence that a dye molecule's size has a greater influence on the exhaustion degree, migration and diffusion than individual pretreatment processes. The determined diffusion coefficients indicated superior dye mobility and faster diffusion into the fibres when ultrasonic power was used in comparison with conventional process. Nevertheless, the colour depth obtained was found to be low after ultrasonic dyeing using a larger dye molecule, implying part degradation of CI Direct Red 80 (and total degradation of small-size dyestuff, CI Direct Red 81).     

Determining the effect of enzymatic pretreatment on the low temperature dyeability of polyamide fabrics

In this study, by pretreating polyamide 6/elastane knitted fabrics with serine-type protease enzyme, the aim was to reduce dyeing temperatures. It is known that the elasticity of elastane fibres is damaged in dyeing at high temperatures. On the other hand, to enable efficient dyeing, it is necessary to use boiling temperatures in synthetic fibres such as polyamide, or even mild high temperature conditions, to support more uniform dyeing. Protease enzymes are enzymes that hydrolyse amide bonds, and consequently, new amine and carboxyl groups are released in fibre macromolecules, resulting in an increase in the functional group content to which anionic dyes can bind. In this study, to compensate for the loss of colour yield caused by lowering the dyeing temperature, an increase in the functional groups was provided by enzymatic pretreatment. For this purpose, the fabrics were pretreated with a commercial serine-type protease enzyme then dyed with 1:2 metal complex dyes at different temperatures. The effects of enzymatic pretreatment on colour, fastness, fibre surface characteristics and fabric strength were investigated.     

Colour Yield and Appearance of Cellulosic Fibres Dyed with Reactive Dyes

The factors affecting the colour yield and appearance of cellulosic fibres dyed with reactive dyes have been investigated. Colour yields obtained with trichloropyrimidyl and fluorochloropyrimidyl dyes are compared. Using Danckwerts' equation, the parameter – depth of penetration of reactive dyes – is defined. The appearance of cellulosic substrates dyed with reactive dyes is quantified in terms of the diffusion and reaction properties of the dyes.     

Dyeing of cotton and jute with tea as a natural dye

Cotton and jute fabrics were dyed with an aqueous extract of tea, containing tannins as the main colorant species. The dyeing was carried out with and without metal salts as mordants, using three different dyeing methods: pre-mordanting, meta-mordanting and post-mordanting. The resulting wash and light fastnesses of the dyed fabrics were good to excellent. The colour of the fabrics was investigated on computer colour matching system in terms of K/S , and CIELAB colour-difference values. Deep shades ( K/S = 3.9) were obtained for jute in acidic media, while cotton fabrics could be dyed in medium depths ( K/S = 2.0) under identical conditions of dyeing.     

Dye distribution in the dyeing of mixed denier polyester fabrics

Microfibre polyester is sometimes blended with higher denier fibres to achieve good aesthetic effects at lower cost. Two polyester yarns of 1.4 and 0.7 denier were dyed singly and together with a range of depths of CI Disperse Blue 79, and the dye distribution over the course of the dyeings was examined. The uptake is initially greater on the microfibre, but as dyeing is continued the distribution becomes more even, and eventually the same concentration of dye is present on both fibres. Based on the common observation that a given concentration of dye produces a lighter shade on a microfibre, the redistribution of dye during the process causes a continuing shade change even though the bath exhaustion is constant. A mixture of three dyes produced a stable hue on a fabric of 1.0 denier polyester after 20 min at a fixed dyeing temperature, but when dyed on a fabric of 1.0 and 0.5 denier yarns, a change in hue continued for more than 60 min.     

Influence of Eri silk fibre on the physical characteristics and dyeing properties of Eri silk/cotton blended yarn

Different blending ratios of Eri silk and cotton fibres were prepared. The optimum bleaching condition chosen for the blends containing 0–25% silk content was the oxidative bleaching method, whereas the blends at 50–100% should be bleached using the two‐stage bleaching method (oxidative bleaching followed by reductive bleaching). These conditions did affect the force–displacement characteristics of the fibres with no yield point. X‐Ray diffraction results showed that the percentage of crystallinity of the cotton yarn tended to increase after bleaching, whereas the percentage of crystallinity of the Eri yarn decreased marginally. Dyeing properties of the blended yarns were investigated using warm‐dyeing reactive dyes. Percentage exhaustion and the colour yield of the blends tended to decrease with the increasing silk content. Shade variation was observed on the yarns at different blend ratios. This was expected to be caused by the different physical nature of Eri silk and cotton fibres. Consequently, the dye uptake and visual shade of each dye on the two fibres were different.     

Topping of naturally dyed wool fabrics with different natural dye sources

Wool fabrics can be dyed with synthetic dyes and even with natural dyes. To present a different aspect to the coloration of wool, the current study was focused on a topping process (ie, the dyeing of wool that was already dyed) with different natural dye sources. For this purpose, the fabrics that were already dyed with a natural dye source were once again dyed with two different natural dyes. In bottom dyeing (bottoming), fabrics were dyed with hops (Humulus lupulus L.) in the presence of different mordanting agents. Then the dyed, washed and dried samples were once again dyed (topping) with two different natural dye sources. For topping, powdered madder and acorn were tested in direct dyeing of wool samples. Finally, the colour changes were analysed with the use of a spectrophotometer. The study demonstrates that such a process (ie, bottoming with hops in the presence of different mordanting agents and then topping with madder or acorn) can be a way of obtaining different shades and colours with sufficient/good fastness values by natural dyeing.