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    Dyes and Pigments

    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. [...]
    Sun, Mar 03, 2019
    Source: Coloration Technology Category: DYES PIGMENTS
    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. [...]
    Thu, Feb 28, 2019
    Source: Coloration Technology Category: DYES PIGMENTS
    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. [...]
    Sun, Feb 17, 2019
    Source: Coloration Technology Category: DYES PIGMENTS
    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. [...]
    Mon, Feb 11, 2019
    Source: Coloration Technology Category: DYES PIGMENTS
    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. [...]
    Mon, Feb 11, 2019
    Source: Coloration Technology Category: DYES PIGMENTS
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