Indigo carmine can be used as a source of blue dye for wool and hair dyeing. The option to use indigo carmine in combination with other natural dyes in a one-bath procedure as a hybrid dyeing concept ...is of interest both for natural dyeing and for coloration of hair. The present study shows that indigo carmine dyeing on wool exhibits the substantial sorption in the range of pH 4–5 and temperature between 40 and 60
°C. Experiments with human hair samples indicate that the experiments on wool can serve as a model that can be applied for hair dyeing. Comparisons of the energy, water and chemical consumption between two-bath dyeing with indigo and natural dyes separately and a one-bath dyeing using indigo carmine together with other natural dyes demonstrates the advantages of the one-bath hybrid dyeing concept.
Indigo carmine can be used as model for a blue natural colorant for wool and hair dyeing in a one-bath procedure. The sorption and dyeing properties of indigo carmine on wool are studied as a ...prerequisite for the successful application in combination with natural dye. To evaluate the suitable conditions for the dyeing process, different pH, dye concentrations and temperatures were studied. The dyeing and sorption characteristics on wool were determined on the basis of spectrophotometry and color measurement. Both high dye sorption and color strength were obtained when dyeing at elevated temperature, e.g. 80°C, and lower pH, e.g. pH 3. However, there is significant potential to apply the dyestuff also at temperatures in the range of 40—60°C and pH values of 4—5. Depending on the dyebath pH the sorption isotherms follow the Langmuir- or Freundlich-type isotherm. At pH 3 and 4 Langmuir isotherms are observed, while at pH 5, 6 and 7 sorption on wool follows the Freundlich isotherm behavior. From the dyeing isotherms the standard affinity (Δµ) of the dyeing step was determined. At pH 3 the heat of dyeing (ΔH) and entropy of dyeing (ΔS) were calculated as 40.22 kJ mol -1 and 0.19 kJ mol-1 K -1, respectively.
Zn-Mg alloys containing up to 5.28 wt.%Mg were prepared by gravity casting. Light and scanning electron microscopy with energy-dispersive X-ray spectrometry were used to characterize their as-cast ...microstructure as compared to that of pure zinc. The alloy with 3.60 wt.%Mg was found to be eutectic. Phase identification by X-ray diffractometry suggested that the eutectic Mg-rich phase wasMg2Zn11 with two types of intermetallic compounds, including Mg2Zn11 and MgZn2, present in the alloy with 5.28 wt.%Mg. The microhardness increased with increasing Mg content from 41 HV for pure zinc to 266 HV for the alloy with 5.28 wt.%Mg. The electrochemical behavior of the alloys was studied by potentiodynamic polarization test at room temperature using 8.5 M KOH solution as electrolyte. Hydrogen evolution was generally postponed for the cases of Zn-Mg alloys as compared to pure zinc. The corrosion potential (Ecorr) was not significantly affected by Mg addition into Zn, while the corrosion current density (icorr) was significantly increased, especially for the case of the alloy with 3.60 wt.%Mg, as compared to that of pure zinc. It can be proposed that, due to its relatively higher hydrogen overpotential and uniform corrosion in KOH solution, the eutectic alloy with 3.60 wt.%Mg can be an alternative to pure zinc for use as anode in applications related to alkaline electrolyte.
The dyeing characteristics of lawsone–indigo mixtures on wool and their electrochemical properties were studied as a model for natural dyeing. To determine the optimum conditions for dyeing, ...experiments with different levels of pH in the oxidising and reducing states were performed. The dyeing characteristics on wool were studied using basic colour measurement. The colour depth of the dyeings was strongly dependent on the pH of the solution. Dyeing of lawsone in oxidising and reducing states at pH 4–6 showed the highest colour depth. For lawsone–indigo mixtures, the pH of the maximum colour strength shifted to pH 6–7. The dyeing properties of henna showed similar behaviour to the lawsone dyeing. The electrochemical properties of the lawsone–indigo mixtures were studied using cyclic voltammetry. The cathodic peak current increased with the increasing lawsone concentration. Furthermore, the cathodic peak current of the lawsone–indigo mixtures, which was less than the cathodic peak current of pure lawsone, indicates the sorption of lawsone molecules on the surface of dispersed indigo.
The indirect cathodic reduction of the vat dye indigo (C.I. Vat Blue 1) by cathodically reduced Lawsone (2-hydroxy-1,4-naphthoquinone; C.I. Natural Orange 6) was studied in aq. solution at different ...pH values. Cyclic voltammetry and spectroelectrochemistry were used to investigate the electrochemical behavior of 2-hydroxy-1,4-naphthoquinone at a hanging mercury drop electrode. The cathodic peak potential (
E
p)
d measured at 0.1 mM lawsone solution at a scan rate of 50 mV s
−1
changed from −425 mV at pH 7, to −730 mV at pH 11.5 and −750 mV at pH 13 (vs. Ag/AgCl, 3 M KCl). Particularly at pH values of 8–9 and 11.5–13 voltammograms indicated successful, indirect cathodic reduction of the dye in which the cathodically reduced 2-hydroxy-1,4-naphthoquinone acted as soluble mediator. The linear relationship obtained for (
I
p)
d vs.
v
1/2 is indicative of a diffusion-controlled electrode reaction mechanism. In the presence of dispersed indigo, the overall cathode reaction is similar to the
E
cat process with continuous regeneration of the electroactive species. Spectrochemical experiments were used to prove the indirect cathodic reaction of dispersed vat dyes by 2-hydroxy-1,4-naphthoquinone.
