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    Dyes and Pigments

    Synthesis of a di‐(p‐sulphophenoxy)‐s‐triazine reactive dye and its application in wool fabric ink‐jet printing

    Reactive dyes based on p‐sulphophenoxy‐s‐triazines were synthesised, characterised and applied to wool fabric by ink‐jet printing. The extent of dye‐fibre covalent bonding (% fixation) was measured on prints produced using different development methods. The most promising method to obtain high dye‐fibre fixation values was to interleave the printed wool with a pre‐wetted cotton fabric and store for 3 h. Steam fixation was also investigated but gave lower fixation values. The degree of dye hydrolysis vs time in the ink formulation was evaluated because ink stability is critical in commercial operation; a reformulated ink based on a phosphate buffer was found to improve ink stability.

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    Source:: Coloration Technology

          

    A comparative study of ultrasonic degumming of silk sericin using citric acid, sodium carbonate and papain

    The utilisation of ultrasonics has been shown to enable efficient and environmentally friendly textile wet processing. This study conducted a comparative investigation of silk degumming by using a conventional heating bath and ultrasonic irradiation at a range of ultrasonic frequencies. Citric acid, sodium carbonate and papain were used as degumming agents. Sericin degumming rate, fibre whiteness, fibre surface morphology, fibre structure characteristics and fibre tensile properties were measured and analysed. Results showed that ultrasonics at a lower frequency produced a greater degumming rate than at a higher frequency. Ultrasonics is a more effective way than the conventional heating bath of improving degumming efficiency, especially at a lowered temperature of 60 °C. When sodium carbonate was applied at 90 °C, a conventional heating bath was found to be more effective than ultrasonics. Papain was found to be more effective in sericin removal than citric acid and sodium carbonate, with a degumming rate of 22% achieved at 60 °C under ultrasonic irradiation at 40 kHz. The use of papain can, however, cause a possible overreaction to silk under certain severe conditions, resulting in a loss of fibre whiteness. Negligible changes in fibre structure characteristics were measured by Fourier Transform–infrared spectroscopy and X‐ray diffraction after ultrasonic degumming with papain. Slightly reduced fibre strength and increased fibre extensibility were observed in ultrasonically degummed silk samples compared with un‐degummed and conventionally degummed silk samples.

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    Source:: Coloration Technology

          

    Effects of the side chain density of polycarboxylate dispersants on dye dispersion properties

    Comb‐like polycarboxylates were synthesised by copolymerisation of methacrylic acid and nonylphenol polyethylene glycol methacrylate ester, and can be used as dye dispersants. In order to achieve good dispersive ability, three polycarboxylates were synthesised, each having a different side chain density. The side chain density of polymers was controlled by different ratios of monomers in the copolymerisation process. Acidic polymers were neutralised using sodium hydroxide. These polymers exhibit good dispersing performance, such that carboxylate groups are adsorbed onto the dye particle surface and the side chains enable the formation of a thick layer, thus providing the steric hindrance effect. Improvement of dye dissolution in the presence of polycarboxylates was studied. Polymers with a lower side chain density demonstrated a higher dye dissolution in water, which could be as a result of more effective adsorption of dispersant on the dye surface (CI Disperse Blue 79). The dyeing performance of the prepared dye dispersions on polyester was investigated. Spectrophotometric analysis of dyed fabrics using synthesised polycarboxylates demonstrates that there should be an optimum side chain density of polymer in order to control both dye solubility and dispersive ability. The result of turbidimetry and particle size analysis have proven this phenomenon. A comb‐like polycarboxylate with optimum side chain density was a better dye dispersant compared with a commercial sodium naphthalene sulphonate compound, as a result of its better heat stability.

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    Source:: Coloration Technology

          

    Polydopamine‐coated silk yarn for improving the light fastness of natural dyes

    One of the problems occasionally associated with the use of natural dyes in the dyeing of silk is the susceptibility of the dyed yarn to fading in light. While a number of approaches have been used to address this problem, the use of polydopamine (PDA), a known agent with photo‐protective properties, has not been assessed previously. In this study, silk was pretreated with nano‐particulate PDA formed in situ by oxidation of a dopamine solution, then dyed with lac dye or annatto dye as model natural dyes. Photofading rates were significantly reduced in the case of annatto‐dyed, PDA‐coated silk relative to uncoated silk, while wash fastness was unaffected and remained only moderately good. In contrast, no significant change was seen in photofading rates with treated or untreated lac‐dyed silk, and wash fastness was also unaffected. The PDA did not adversely affect resultant colour values if the concentration of the dopamine precursor was kept low. When this was done, acceptable colours were obtained in the dyed silk. Further investigation is warranted of PDA as a photofading protectant and mordant with other natural dyes on silk and other fibres.

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    Source:: Coloration Technology

          

    A semi‐aza‐crown‐based chemosensor for colorimetric detection of iron(III) and iron(II) in aqueous media with large bathochromic shift

    A colorimetric chemosensor, EDDAN (1,1′‐((1E,11E)‐5,8‐dioxa‐2,11‐diazadodeca‐1,11‐diene‐1,12‐diyl)bis(naphthalen‐2‐ol)), based on a semi‐aza‐crown structure, was designed and synthesised to sense iron(III) and iron(II). EDDAN showed a unique colour change in the presence of either iron(III) or iron(II), turning from pale yellow to deep purple with large bathochromic shifts. The detection limits of iron(III) and iron(II) were 2.70 and 3.43 μm, respectively. EDDAN displayed a high selectivity for iron ions in the presence of other metal cations except copper(II). In addition, EDDAN showed excellent reversibility by using ethylenediaminetetraacetic acid. Moreover, EDDAN was applied to test strips as well. Based on ultraviolet‐visible titrations, Job plots, electron paramagnetic resonance study and electrospray ionisation mass spectrometry analyses, a mechanism for the sensing of iron(III) and iron(II) was also proposed.

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    Source:: Coloration Technology

          

    Extraction of anthocyanins from Aronia melanocarpa skin waste as a sustainable source of natural colorants

    Aronia melanocarpa (Michx.) Elliott (black chokeberry) skin wastes from the production of Aronia fruit juice were extracted using a batch extraction method and a novel integrated extraction‐adsorption process. Optimum conditions for batch extraction were as follows: 60 °C, 3 h, acid (0.1% v/v hydrochloric acid), biomass‐to‐solvent ratio of 1:16, and biomass‐to‐solid phase extraction resin ratio of 1:1. The integrated extraction‐adsorption process gave improved anthocyanin yields of higher quality when the process was performed for 3 h without cooling of the circulating liquid, and with a flow rate of 1.3 ml s−1. Overall, the new method showed better anthocyanin yield and purity compared with the batch method, increasing the extraction yield by ca. 20% (5.25→6.34 mg g−1 dry weight of pomace) and increasing anthocyanin content by ca. 40% (19.9%→28.4% w/w dry weight of extract). This method also simplified the process as three steps were eliminated saving time and energy. Furthermore, the integrated extraction‐adsorption method is industrially scalable to produce large quantities of anthocyanins. In the batch method, anthocyanins present in A. melanocarpa skins were identified as cyanidin‐3‐O‐galactoside (38.8%), cyanidin‐3‐O‐arabinoside (6.4%), cyanidin‐3‐O‐glucoside (3.6%), cyanidin‐3‐O‐xyloside (0.5%), and the cyanidin aglycon (50.7%); in the continuous method, anthocyanin content was cyanidin‐3‐O‐galactoside (45.7%), cyanidin‐3‐O‐arabinoside (16%), cyanidin‐3‐O‐glucoside (3.6%), cyanidin‐3‐O‐xyloside (2.7%), and the cyanidin aglycon (32%). The integrated extraction‐adsorption method was shown to be substantially less susceptible to acid‐catalysed anthocyanin decomposition processes. All anthocyanins were derived from only one anthocyanidin parent structure (cyanidin), and only monosaccharide glycosides were identified, which is unusual when compared with other berries that typically have more anthocyanidins and/or greater glycosylation diversity.

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    Source:: Coloration Technology

          

    Colour and gloss properties of pigment‐printed synthetic leather using an ultraviolet‐curable water‐borne polyurethane acrylate binder and two photoinitiators at different ratios

    This study reports on the colour and gloss properties of pigment‐printed polyurethane‐based synthetic leather using an ultraviolet (UV)‐curable water‐borne polyurethane acrylate binder and two types of photoinitiators (Omnirad 819 DW and Omnirad 500) at different ratios. The UV curing of printed synthetic leather samples was conducted with gallium and mercury lamps, either singly or in combination, at three different power levels. Chemical changes in the cured films because of the polymerisation of the UV‐curing process were analysed by Fourier Transform‐infrared spectroscopy, which showed that the polymerisation reaction occurred after UV curing in both the clear and in the pigmented films. The Omnirad 500 photoinitiator is more effective in surface curing and the Omnirad 819 DW photoinitiator is more effective in deep curing. The Omnirad 500 photoinitiator caused the gloss values to drop significantly, especially in the formulation including both photoinitiators, Omnirad 819 DW and Omnirad 500, at a 1:2 ratio, respectively. In the formulation including a higher ratio of the Omnirad 819 DW photoinitiator, higher gloss values were obtained compared with the formulation including a higher ratio of the Omnirad 500 photoinitiator. Considering all the results, the highest gloss value of 20.96 was obtained with samples printed with the formulation of the two photoinitiators at an equal ratio (1:1) cured under a gallium/mercury lamp combination at a power level of 90 W/cm. Moreover, the highest K/S value of 10.86 was obtained with samples printed with the formulation of the two photoinitiators at an equal ratio cured under the gallium lamp at 90 W/cm.

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    Source:: Coloration Technology

          

    Dyeing of cotton with the natural dye extracted from waste leaves of green tea (Camellia sinensis var. assamica)

    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.

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    Source:: Coloration Technology

          

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