Kübra Güneş

Dyes and Pigments: Their Structure and Properties

Dyes and pigments are the most important colorants used to add a color or to change the color of something. They are widely used in the textile, pharmaceutical, food, cosmetics, plastics, paint, ink, photographic and paper industries. Dyes are colored substances which are soluble or go into solution during the application process and impart color by selective absorption of light. Pigments are colored, colorless, or fluorescent particulate organic or inorganic finely divided solids which are usually insoluble in, and essentially chemically unaffected by, the vehicle or medium in which they are incorporated. On the other hand, the color, which is highly dependent on the chemical and physical properties of a matter, is a result of the interaction between light and substance. This chapter is focused on the chemical and structural properties of dyes and pigments, as well as the relationship between light and color.

Colorants in Health and Environmental Aspects

The environmental characteristics of colorants (dyes and pigments) cover the topics pertaining to the impact of such compounds on human health and the environment. Effluent aqueous waste containing dye compounds causes serious problems. Manufacture and use of synthetic dyes for fabric dyeing has therefore become a massive industry today. Consequently, they have become common industrial environmental pollutants during their synthesis and later during fiber dyeing. This is main requirement for the innovations in the related processes as well as the investigation of appropriate and environmentally friendly treatment technologies. Use of synthetic dyes has an adverse effect on all forms of life. Presence of sulphur, naphthol, vat dyes, nitrates, acetic acid, soaps, enzymes chromium compounds and heavy metals like copper, arsenic, lead, cadmium, mercury, nickel, and cobalt and certain auxiliary chemicals all collectively make the textile effluent highly toxic. Dyes have various effects on human health depending on the application area. Skin irritation and contact dermatitis have been reported for some synthetic dyes and the use of azo dyes made from carcinogenic amines has been banned by legislation in many countries. The researches on alternative and innovative wastewater treatment techniques have focused especially on the use of biological materials. Adsorbents such as activated carbon, zeolite and diatomite have been used as efficiently for cleaning by adsorption of colored wastewaters. In this chapter, a wide range of dyes and pigments are discussed in the context of green chemistry with environmental and health aspects by considering their negative results related with their use.

Classification of Dye and Pigments

The global market for pigments and dyes is forecast to reach 9.9 million tons and

Historical Development of Colorants

26.53 billion by the year 2017, driven by the growth in key end-use industries. Before synthetic dyes and pigments were discovered, limited number of natural colorant has been obtained from plants, animals and minerals. The classification of colorants has become mandatory due to huge increase in kind and number of colorants. For this reason, colorants are classified based on their structure, source, color, solubility and application methods. In this chapter, dyes will be investigated in two different groups as accordance with chemical structures and application methods. The basic classification groups were determined as azo, anthraquinone, indigo, phthalocyanine, sulfur, nitro and nitroso dyes by considering their chemical structures. According to application method, they were grouped as reactive, disperse, acid, basic, direct, and vat dyes. However, the classification of pigments as organic and inorganic pigments is also regarded as an appropriate way.

The adsorption-desorption mechanisms on the powdered activated carbon (PAC) of an anionic textile dye (RBY 3GL)

Color is one of the elements of nature that makes the human life more aesthetic and fascinating in the world. Plants, animals, and minerals have been used as primary sources for colorants, dyes or pigments since ancient times. The first fiber dyes known to be used in prehistoric times consisted of fugitive stains from berries, blossoms, barks, and roots. This chapter is devoted to an historical introduction to the colorants, taking into account of the chronological developments in dyeing processes and the origins of dyes used. Even today, the dyeing using natural materials is applied as an adjunct for hand spinning knitting and weaving but it has remained as a living craft in many traditional cultures of North America, Africa, Asia, and the Scottish Highlands. The new discoveries about the science of color have also led to many industrial innovations and a sharp fashion change. Scale insects have long been used to produce crimson-colored dyes. Many plant pigments are used as dyes. Madder has been utilized since times as a red vegetable dye for leather, wool, cotton and silk. Indigo is a natural dye that is structurally related to betalains. Tyrian purple, which is an ancient dye, has been extracted from shellfish of the Murex genus.

Dyeing and Dyeing Technology

Adsorption has many superior properties compared with other techniques for wastewater treatment. Activated carbon has been widely used as a versatile adsorbent with optimal sorption properties for the adsorption of chemical species from their aqueous solutions. One of the main drawbacks of the adsorption process in terms of sustainability is the difficulty of regeneration of treated activated carbon or the production of relatively unstable secondary wastes with waste disposal processes based on adsorption. Moreover, the elucidation of the mechanism of adsorption–desorption is extremely important in terms of regeneration or reuse of adsorbents and designing a sustainable adsorption systems. In this study, it has been aimed the examination of adsorption–desorption behavior of an anionic textile dye (Remazol Brilliant Yellow 3GL) from the aqueous solution on powdered activated carbon using of the corresponding experimental isotherm data together with their mathematical modeling. Experimental isotherms indicate that the adsorption and desorption of the anionic dye on activated carbon took place through the different pathways and exhibited the hysteresis lobes, which are similar to that of gas–solid systems. Also, it was determined that at low equilibrium dye concentrations, the adsorption and desorption pathways overlapped, and the shape of lobes changed with increasing temperature.

A comparative examination of the adsorption mechanism of an anionic textile dye (RBY 3GL) onto the powdered activated carbon (PAC) using various the isotherm models and kinetics equations with linear and non-linear methods

Dyeing is described as the creating of a new and permanent color, by impregnation of especially a dye onto any material namely, textiles, paper or leather. Cochineal, madder, alkanna, henna, brazilwood, red sandalwood, safflower, indigo and logwood were used for the dyeings which can be carried out directly or after mordanting. The goal of dyeing is to provide a uniform coloration for all of fibers forming the material as matched with a pre-specified color. Dyeing is mainly carried out as the continuous or batch processes. Modern dyeing technology consists of several steps determined according to the nature of the fiber and properties of the dyes and pigments for use in fabrics. Other topics which are decisive in terms of the selection of dyeing method or techniques also, cover chemical structure, classification, commercial availability, the fixing properties compatible with the target material, and economic considerations. Many factors can influence the final color. These include fiber characteristics such as the luster, denier, staple length, texture, and cross-section as well as the cloth construction. The dyeing is achieved by the direct application of dye solution onto textiles; whereas, the printing dyeing can be carried out using different specialized techniques. Resist techniques have been in existence in the commercial sector for a long time, with so many different styles and new methods of resist. On the other hand, painting is the practice of application of paint, pigment, color or other medium to a surface and also it is a mode of creative expression. This chapter discuses a wide range of dyeing methods and techniques.