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A poor fastness of natural dyes in comparison with synthetic ones is established beyond question. The cause of natural dyes, that, they are not being used for textile goods at commercial scale is due to their poor fastness properties. To face such limitations, the photochemical behavior of natural dye i.e. Turmeric (Curcuma longa L.) and synthetic dyes were investigated. It has been demonstrated that uv-protective effect was strongly dependent on the absorption characteristics of dyes for ultra violet radiations (UVR).Therefore, the improvement of light fastness is sought at the present time. In this respect, various kinds of photo stabilizer (UV-absorbers) were synthesized and applied on to the substrate along with some naturally occurring to prolong the life of coloured species in the natural as well as synthetic dye stuff. At the end, the reactivity of uv-absorbers with the substrate and their properties as auxiliaries increasing UV-protection and dyeing properties were assessed by spectrophotometeric techniques. Significances of uv-absorbers with mordanting agent have been evaluated in different aspects to make the eco-friendly dyes into economical leading commercial dyes.
Dyeing was practiced in ancient times and has undergone many changes in reaching today's development. In the early age, textiles were dyed using plants and animal sources, but with the advent of synthetic dyes, the use of natural dyes in textiles was eliminated since synthetic dyes give variety of shade and colour (Deo and Desai 1999).
Recent studies show that synthetic dyes are non-biodegradable, allergic and some are carcinogenic. Many countries are reluctant to use, import and export the products that are not eco-friendly. Again the world trend is inclined towards natural dyes in textiles as well as in food processing (Sachan and Kapoor 2004).
Good quality dyes must satisfy many requirements in order to be used for colouring of textile materials, one of them is light fastness-an important property determining the fitness of the articles and the durability of their usage (Violeta et al. 1996). Most natural dyes have poor to moderate light fastness, while synthetic dyes represent the full range of light fastness properties from poor to excellent (Daniela and Vilarem 2006). The photochemical behavior of dyes and of the materials which are coloured by them is influenced not only by environmental factors such as light sources and their spectral distribution, temperature, humidity and atmospheric composition, but to a large extent by their chemical structure and the state of the dye in the polymer (Giles et al. 1975).
In last two decades one of the often realized research programmes in the field of textile materials was work on their protective properties against sunlight UV radiation. As it is known radiation of this type emitted by sun in the range between 100 and 400 nm is subdivided into UV-C (100-280 nm), UV-B (280-315 nm) and UV-A (315-400 nm). Higher layers of the atmosphere absorb the radiation of the UV-C range which is most dangerous to living species. Human skin has to be protected against excessive radiation of the UV-B type. It was proved that the excessive radiation of this range is the origin of premature skin ageing, sunburns, allergies and even skin cancer. The UV-A radiation is less dangerous but also its overdose can result in similar effects as described above (Wojciech et al. 2006).
Light fastness of dyed textiles is related to the chemical structure and physical structure of the fiber itself. It is attributed the fading on cellulose to an oxidative process, whereas on protein it have a reductive nature (Cumming et al. 1956). It is stated that indigo is much more light resistant on wool than on cotton (Padfield and Landi et al. 1996). An oxidative pathway is involved in the fading of indigo dyed cotton. As the fading on non-protein substrate is reductive, the indigoid chromophore which is resistant to photoreduction shows high fastness on wool (Roshan et al.1996).
The fabric that was selected for the purpose of dyeing and for the application of UV-absorbers it must have to be suitable for any type of dyeing. It is obvious that UVR protecting property of textile goods are dependent on the absorbance and transmission of UV radiations through the particular fabric. It is understood that these properties depends on some factors like thickness, porosity, chemical composition, and the presence of dyes ,their concentration as well as other textiles auxiliaries like finishers and UV-absorbers (Wojciech et al., 2006). So, pretreatment quality assurance tests of the fabric for dyeing produced results are mentioned in table 4
Different types of absorbers were applied on cotton in "all in" exhaust dyeing method. The results showed that there is significant variation in percentage degree of exhaustion of the dye onto the cotton. Dye uptake increased in all dyes when applied with any type of absorber. Percentage of exhaustion decreases by increasing concentration of the dye. All the absorbers are synergistically increased the exhaustion of the dyes but Benzophenone, J-acid based absorbers are significantly responsible to increase dye uptake. Effect of absorbers on the dye uptake values pf various dyes are shown in figures 6 to 10.
Different types of absorbers were applied on cotton in "all in" exhaust dyeing process. Dye fixation increased in all dyes when applied with any type of absorber. Percentage of dye fixed on to the fabric decreases by increasing concentration of the dye. So from the results it can be observed that high percentage of dye shade producing low level of exhaustion as well as fixation. All the absorbers are synergistically increased the fixation of the dyes but Benzophenone, J-acid based absorbers are significantly responsible to increase dye uptake. Effect of absorbers on the dye uptake values pf various dyes are summarized in figures. In case of reactive dye 1 all the absorbers increased the percentage of dye fixation except gallic acid (G) which showed low level of fixation of dye when applied in 5% dye shade. All the other additives catalytically increase dye fixation especially when dye was applied in lower concentration, summarized in figures.
When dye 1 is applied on to the fabric, the wet crock fastness not showed appreciable results in lower concentration shade (1%) as compared to non treated dye with absorbers. Fading of the dye is reduced and staining of the washed dye onto the adjacent fabric is not altered by the addition of absorbers in low concentration of the dye. As a result dark shades show high level of light fastness but when the same dyes are applied on fabric in light shades these are faded away easily by the action of UV radiations. The results showed the addition of UV absorbers in the dye bath including light shades enhanced the light fastness of the dyed article.
The results obtained after the application of dye 3 on to the fabric, revealed that the wet crock fastness not showed appreciable results in lower concentration shade (1%) as compared to non treated samples. The crock (rubbing) fastness remains unchanged in most cases of addition of additives in dyeing bath for both the studied shades
The fastness of a mordant dye depends on the mordant and the mordanting method. As different dye metal complexes are formed which may cause difference in their stability to light and also because the metal have a positive or negative catalytical effect on the photochemical degradation of the dye (Gupta, 1999). For better fastness to light radiations and washing fastness the use of mordant is essential for most of natural dyes. The effect of mordant is to assist the adsorption of the dye molecule and also to promote good bonding of coloring component with fiber as a bridge which helps to bond the dye and fiber at molecular level (Feng et al., 2007). The improvement in washing fastness of the mordanted samples is due to decrease in dye solubility (Tsatsaroni and Eleftheriadis 1994). Its yellow color is faded away after exposure to UV radiations. (Shinyong and Yiqi 2005). Some of inherent fluorescent properties in Curcumin the active life period of these molecules is longer and chances of collision with oxygen in air and radiations that make them more feasible to photochemical oxidation.
Recent studies show that synthetic dyes are non-biodegradable, allergic and some are carcinogenic. Many countries are reluctant to use, import and export the products that are not eco-friendly. On the other hand natural dyes don't have excellent fastness properties at all; especially turmeric a natural yellow colour produces poor washing and light fastness rating. Such problems resist using natural dyes as economical source at industrial level. Not even natural dyes but most of the reactive dyes have moderate to good fastness properties. To overcome such limitations of industrial dyes some additives were synthesized and applied along with some naturally occurring. These additives applied on the white fabric and also along with natural and synthetic dyes especially to protect the textile articles from solar ultraviolet radiations. In this regard, the induced UV absorbers and their reducing effect of photo degradation of color was subject of interest. Along with improvement in light fastness, some other physico-chemical properties like crock and washing fastness were also studied. The whole study project concluded that the applied UV absorbers significantly increased the light and wash fastness properties of all the natural and synthetic dyes but these are unable to enhance the crock (rubbing) fastness at appreciable extent. During study it was the keen result that synthetic as well as natural absorbers improve the exhaustion and fixation of all the dyes synergistically during dyeing. The significances of these UV absorbers are helpful to increase the fastness properties of industrially used dyes including reactive, direct and natural curcumin dyes.
So the result showed that the application of UV absorbers is very helpful to increase exhaustion, fixation and fastness properties of treated fabric with UV absorbers. Protection against the UVR is very helpful to avoid the skin and dyed article from damaging ultraviolet radiations, which is economically and hygienically handy in textiles.