Progress in Color, Colorants and Coatings
Volume:8 Issue: 2, Spring 2015

The large number of publications in the field of extraction, purification, modification, and process optimization of natural dyes and their application on textiles demonstrates the revival of natural dyes on textile coloration. The use of natural dyes is growing in popularity because of the quality of the natural dyestuff obtained, the environmental compatibility of the dyes and the substantial minimization of processing costs. Natural dyes are extracted from different parts of the plants such as bark, leaf, root, fruit, seed, and flower that contain coloring materials like tannin, flavonoids, quinonoids, etc. In this paper, it has been tried to give the latest scientific overview on extraction and application of natural colorants on textiles processing. The benefits and limitations of application on textiles along with the different methods of extraction of natural colorants have been discussed. Moreover, the examples of early applications of natural dyes on textile processing have been reviewed.

Styrene-acrylate copolymer was synthesized in presence of carbon black through heterogeneous polymerization. The percentage of monomer conversion was measured by gravimetric method, also PSA, SEM, DSC and GPC were used for studying the particle size and particle size distribution, morphology, thermal properties and molecular weight, respectively. As well as color properties were characterized by spectrophotometry method. The results showed that the copolymer was appropriate for applying as printing toner. In this study to improve the monomer conversion, a redox initiator system was applied, so the conversion increased from 20 to 75. Other properties such as particle size, particle size distribution, morphology, thermal behavior, molecular weight and color properties were affected by this change but they were in the acceptable range.

In this study, the oxidation of dye from colored wastewater by H2O2/ MWCNT’s multi walls carbon nano tubes solution assisted with UV radiation was investigated. Disperse Blue 56 DB 56 was used as a model dye. Adsorption behavior of DB56 from aqueous solution onto MWCNT’s was investigated under various conditions such as initial pH value, dye concentration, H2O2 and MWCNT’s dosage. Maximum adsorption capacity for DB 56, at pH 7.0, 5.0 and 3.0 was found to be 0.53, 0.56 and 0.97 mmol/g, respectively. Obtained result of isotherm displayed that the linear correlation coefficients and standard deviations of Nernest and Freundlich isotherms were specified and the results revealed that Freundlich isotherm fitted the experimental results better than Nernest. The adsorption kinetics was more precisely denoted by a pseudo second-order model revealed by regression grades. Furthermore, results displayed that the UV/H2O2/MWCNTs process could be used as eco-friendly method to degrade dyes from colored wastewater.

In this paper, the spectral dimensions of two sets of samples including 457 black and 84 white fabrics are compared. White fabrics are treated with variety of fluorescent whitening agents and the blacks are fabrics that dyed with different combinations of suitable dyes and pigments. In this way, the reflectance spectra of blacks as well as the total radiance factors of whites are compressed in one to five compressed spaces using the principal component analyzing technique. The reduced data are then reconstructed and the averages of the percentile relative root mean square errors between the actual and the recovered spectra of each dataset are calculated to show the spectral dimensionality of both groups through the analyzing of spectral errors. Besides, the colorimetric errors between the actual and the compressed-reconstructed spectra are represented by the mean values of ΔE00 color difference values under D65 illuminant and 1964 standard observer. Results show that the total radiance factors of white samples are smoother than the reflectance spectra of blacks and could be adequately described in a 2 dimensional space, while blacks need to be characterized in higher dimensions i.e., 4, to approximately provide same cumulative energy content as well as spectral and colorimetric errors.

In the present study, nine bis-azo dyes based on 5-arylidene-2,4-thiazolidinone were obtained in two steps, using Knoevenagel condensation and azo coupling reactions. The structure of the dyes was confirmed on the basis of spectral data. Analysis of spectroscopic data shows that there is equilibrium between the azo and hydrazone tautomers for all dyes in solutions. Investigation of antioxidant activity of compounds was carried out by 2,2-dipheny l-1-picrylhydrazyl DPPH and ferric reducing antioxidant power FRAP methods. The antibacterial activity towards three Gram negative and two Gram positive bacteria was also investigated. The activity data show that the synthesized dyes 3a-i have promising antibacterial activity, comparable with their precursor 1.

Two different natural dyes containing anthocyanin extracted from black carrot and bramble from Iran. Spectrophotometric evaluations of the natural dyes in solution and on a TiO2 substrate were carried out in order to assess changes in the status of the natural dyes. The results show that the natural dyes indicate buthochromic shift on the TiO2 substrates. The chemical adsorption of natural dyes present at the surface of TiO2 substrate that their chemical binding can be increased by the chelating effect to the TiIV ions. Finally, dye sensitized solar cells were fabricated in order to determine the photovoltaic behaviour and conversion efficiencies of each dyes and mixture of extracts. Such evaluations demonstrate conversion efficiencies of 0.33, 0.69 and 0.47 for black carrot, bramble and mixed extract, respectively. Natural dyes are suitable alternative photosensitizers for dye-sensitized solar cells due to simple preparation method, low cost, environmentally friendly and widely available.

Thermochromic printing inks could be security inks which respond to the color change when are being exposed to different temperatures. These inks with unusual chemical and physical specific characteristics are mostly produced for flexographic, screen and rotogravure printing systems under the supervision of skilled technical experts and with precise security controls. Since flexographic thermochromic inks can be used easily for smart packaging including different substrates, in this study a thermochromic ink was prepared with an activation temperature of 31 °C for flexographic printing. The dynamic colorimetric properties were studied during the range of 28-45 °C temperature. TC contrast and yellowness of TC sample were calculated during heating and cooling.