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    Dyes and Pigments

    Due to an increase in the production of green tea, the amount of leaf waste has increased enormously, causing serious environmental problems. With regard to environmental awareness, the possibility of reusing the waste leaves of green tea as a low‐cost and abundantly available source of natural dye for dyeing cotton fibres was investigated. Natural dye powder from the waste leaves of green tea (NDPT) was successfully applied to dye cotton fibres without mordant by batch experiments. NDPT was obtained as a dark brown powder with a yield of 2.7 ± 0.5% w/w from dried waste leaves of green tea. The optimal conditions for dyeing NDPT onto cotton fibres were: pH of dye solution, 3; material to liquor ratio, 100:1; dyeing time, 180 min; concentration of dye solution, 3.0 mg/ml; and dyeing temperature, 100 °C. The colour of cotton fibres dyed with NDPT was observed to be dark brown. The adsorption data of NDPT on cotton fibres was best fitted with a Langmuir adsorption isotherm model with a correlation coefficient (R 2) of 0.997. It is clear that there is a strong possibility of reusing the waste leaves of green tea as a low‐cost and abundantly available source of natural dye for dyeing cotton fibres. [...]
    Mon, Dec 10, 2018
    Source: Coloration Technology Category: DYES PIGMENTS
    Due to an increase in the production of green tea, the amount of leaf waste has increased enormously, causing serious environmental problems. With regard to environmental awareness, the possibility of reusing the waste leaves of green tea as a low‐cost and abundantly available source of natural dye for dyeing cotton fibres was investigated. Natural dye powder from the waste leaves of green tea (NDPT) was successfully applied to dye cotton fibres without mordant by batch experiments. NDPT was obtained as a dark brown powder with a yield of 2.7 ± 0.5% w/w from dried waste leaves of green tea. The optimal conditions for dyeing NDPT onto cotton fibres were: pH of dye solution, 3; material to liquor ratio, 100:1; dyeing time, 180 min; concentration of dye solution, 3.0 mg/ml; and dyeing temperature, 100 °C. The colour of cotton fibres dyed with NDPT was observed to be dark brown. The adsorption data of NDPT on cotton fibres was best fitted with a Langmuir adsorption isotherm model with a correlation coefficient (R 2) of 0.997. It is clear that there is a strong possibility of reusing the waste leaves of green tea as a low‐cost and abundantly available source of natural dye for dyeing cotton fibres. [...]
    Mon, Dec 10, 2018
    Source: Coloration Technology Category: DYES PIGMENTS
    Indigo (CI Vat Blue 1) is a water‐insoluble pigment exhibiting no affinity for fibres and must be chemically reduced in basic solution to form the water‐soluble, alkaline leucoindigo (CI Reduced Vat Blue 1), in order to exhibit substantivity for fibres. Typical vat dyeing processes are time‐ and resource‐intensive, and hazardous by‐products are formed, primarily through the use of reducing agents. We describe a method for synthesising indigo in a flow reactor that allows for application of dye precursors to fibres, milliseconds before the reaction completes. The soluble precursors soak into the cotton fabric just prior to the precipitation of the insoluble indigo, effectively providing in situ coloration, without the need for a traditional redox dyebath. The reaction may be coupled with a propellant, an adaptation that allows for a sprayable form of indigo. In situ coloration with Tyrian purple (6,6′‐dibromoindigo; CI Natural Violet 1) was also demonstrated using the flow chemistry method. This research provides compelling proof of concept, but we acknowledge that the process is in its infancy and needs further development to reach a stage where it can compete commercially with current technology. [...]
    Mon, Dec 10, 2018
    Source: Coloration Technology Category: DYES PIGMENTS
    Indigo (CI Vat Blue 1) is a water‐insoluble pigment exhibiting no affinity for fibres and must be chemically reduced in basic solution to form the water‐soluble, alkaline leucoindigo (CI Reduced Vat Blue 1), in order to exhibit substantivity for fibres. Typical vat dyeing processes are time‐ and resource‐intensive, and hazardous by‐products are formed, primarily through the use of reducing agents. We describe a method for synthesising indigo in a flow reactor that allows for application of dye precursors to fibres, milliseconds before the reaction completes. The soluble precursors soak into the cotton fabric just prior to the precipitation of the insoluble indigo, effectively providing in situ coloration, without the need for a traditional redox dyebath. The reaction may be coupled with a propellant, an adaptation that allows for a sprayable form of indigo. In situ coloration with Tyrian purple (6,6′‐dibromoindigo; CI Natural Violet 1) was also demonstrated using the flow chemistry method. This research provides compelling proof of concept, but we acknowledge that the process is in its infancy and needs further development to reach a stage where it can compete commercially with current technology. [...]
    Mon, Dec 10, 2018
    Source: Coloration Technology Category: DYES PIGMENTS
    This paper reports on the colorimetric properties of natural dyes from madder and weld plants. For both crops, a comparison is made among several individual dye compounds and the total plant extracts. Dyeing properties, colour properties and colour stability have been studied. Insight has been gained into the role of the major dye compounds present in the plant. For madder as well as for weld, the use of the total plant extract is considered to be advantageous over the use of individual dye compounds in terms of solubility, colour tone and stability towards light, and non‐coloured components present in the plant extract are considered to be responsible for increasing the solubility and the stability of the dye compounds. [...]
    Wed, Dec 05, 2018
    Source: Coloration Technology Category: DYES PIGMENTS
    This paper reports on the colorimetric properties of natural dyes from madder and weld plants. For both crops, a comparison is made among several individual dye compounds and the total plant extracts. Dyeing properties, colour properties and colour stability have been studied. Insight has been gained into the role of the major dye compounds present in the plant. For madder as well as for weld, the use of the total plant extract is considered to be advantageous over the use of individual dye compounds in terms of solubility, colour tone and stability towards light, and non‐coloured components present in the plant extract are considered to be responsible for increasing the solubility and the stability of the dye compounds. [...]
    Wed, Dec 05, 2018
    Source: Coloration Technology Category: DYES PIGMENTS
    Mahī, a unique herbal ink used in medieval Assam in India for writing and illustrating manuscripts, is known for its intense colour and durability for centuries, and its non‐corrosive nature. Mahī is distinctly different from the other contemporary inks used elsewhere in the world, including other parts of India. The interesting features of Mahī are due to its special recipe involving several herbal ingredients in addition to iron sourced from fish blood or the rust of iron tools, with cow urine as an extractant and solvent. The objective of the current study is an in‐depth understanding of the traditional method of the preparation of Mahī, and its characterisation through analysis of the physicochemical properties using spectroscopic and imaging techniques as well as biochemical analysis. A series of model Mahī samples are prepared following the traditional method with varying ingredients, and their compositions and physicochemical properties are evaluated with respect to the ingredients using standard methods and analytical tools including atomic absorption spectroscopy, tensiometry, ultraviolet ( UV )‐visible, Fourier Transform‐infrared ( FT‐IR), Raman, steady‐state fluorescence, UV fluorescence and emission microscopy. The colour of the ink has been attributed to various polyphenols, gallic acid, epigallocatechin gallate, epicatechin, quercetin, kaempferol and tannic acid, and their iron complexes. UV fluorescence and emission microscopy confirmed an autofluorescence indicative of the presence of phenolic and chlorophyll pigments. Solubilisation by glycosidic biosurfactant contributes to stabilisation of Mahī. The non‐corrosive nature of Mahī has been attributed to its neutral pH and absence of free iron and copper ions. [...]
    Thu, Nov 29, 2018
    Source: Coloration Technology Category: DYES PIGMENTS
    Mahī, a unique herbal ink used in medieval Assam in India for writing and illustrating manuscripts, is known for its intense colour and durability for centuries, and its non‐corrosive nature. Mahī is distinctly different from the other contemporary inks used elsewhere in the world, including other parts of India. The interesting features of Mahī are due to its special recipe involving several herbal ingredients in addition to iron sourced from fish blood or the rust of iron tools, with cow urine as an extractant and solvent. The objective of the current study is an in‐depth understanding of the traditional method of the preparation of Mahī, and its characterisation through analysis of the physicochemical properties using spectroscopic and imaging techniques as well as biochemical analysis. A series of model Mahī samples are prepared following the traditional method with varying ingredients, and their compositions and physicochemical properties are evaluated with respect to the ingredients using standard methods and analytical tools including atomic absorption spectroscopy, tensiometry, ultraviolet ( UV )‐visible, Fourier Transform‐infrared ( FT‐IR), Raman, steady‐state fluorescence, UV fluorescence and emission microscopy. The colour of the ink has been attributed to various polyphenols, gallic acid, epigallocatechin gallate, epicatechin, quercetin, kaempferol and tannic acid, and their iron complexes. UV fluorescence and emission microscopy confirmed an autofluorescence indicative of the presence of phenolic and chlorophyll pigments. Solubilisation by glycosidic biosurfactant contributes to stabilisation of Mahī. The non‐corrosive nature of Mahī has been attributed to its neutral pH and absence of free iron and copper ions. [...]
    Thu, Nov 29, 2018
    Source: Coloration Technology Category: DYES PIGMENTS
    As part of an approach to enhancing the efficiency of reactive dye adsorption on cellulosic fibres at low electrolyte levels, commercially available dyes were dimerised using hexamethylenediamine (HMDA) as a linking group. A key component of this work involved using high‐resolution mass spectrometry (HRMS) to characterise a group of polysulphonated heterobifunctional monochlorotriazine/vinyl sulphone reactive dyes (CI Reactive Yellow 176, CI Reactive Red 239, CI Reactive Blue 221, CI Reactive Red 194 and CI Reactive Blue 222) and their dimeric analogs. In this respect, dimeric dye ions of differently charged states were observed using HRMS‐negative electrospray ionisation in combination with quadrupole time‐of‐flight mass spectrometry. For example, HRMS showed that the HMDA‐linked reaction products were mixtures of the target (unhydrolysed) dimers, hydrolysed dimers, monoreacted products and hydrolysed unreacted dyes, with CI Reactive Yellow 176 and CI Reactive Red 194 producing the desired unhydrolysed dimers. [...]
    Thu, Nov 29, 2018
    Source: Coloration Technology Category: DYES PIGMENTS
    As part of an approach to enhancing the efficiency of reactive dye adsorption on cellulosic fibres at low electrolyte levels, commercially available dyes were dimerised using hexamethylenediamine (HMDA) as a linking group. A key component of this work involved using high‐resolution mass spectrometry (HRMS) to characterise a group of polysulphonated heterobifunctional monochlorotriazine/vinyl sulphone reactive dyes (CI Reactive Yellow 176, CI Reactive Red 239, CI Reactive Blue 221, CI Reactive Red 194 and CI Reactive Blue 222) and their dimeric analogs. In this respect, dimeric dye ions of differently charged states were observed using HRMS‐negative electrospray ionisation in combination with quadrupole time‐of‐flight mass spectrometry. For example, HRMS showed that the HMDA‐linked reaction products were mixtures of the target (unhydrolysed) dimers, hydrolysed dimers, monoreacted products and hydrolysed unreacted dyes, with CI Reactive Yellow 176 and CI Reactive Red 194 producing the desired unhydrolysed dimers. [...]
    Thu, Nov 29, 2018
    Source: Coloration Technology Category: DYES PIGMENTS
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