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Introduction to Advancement in Textile Dyes and Pigments

Pintu Pandit1*, Kunal Singha1 and Subhankar Maity2

1Department of Textile Design, National Institute of Fashion Technology, Patna, Bihar, India

2Uttar Pradesh Textile Technology Institute, Kanpur, Uttar Pradesh, India

Abstract

Dyes differ from pigments because they do not bind chemically to textile material. Both dyeing and pigmenting processes of textile colouration are chemical intensive, low energy efficient, requiring huge water and discharging huge wastewater. Therefore, there is need to develop advanced technologies to mitigate them. Application using advanced technology, such as ultrasonic cavitation speeds up the dyeing process, chemical reducing agents are replaced by electrons from the electric current in electrochemical dyeing, plasma technology is regarded as an exciting future-oriented process, and supercritical CO2 dyeing is still in its infancy. The methods are cost-effective and reduce the environmental impact of the chemical textile industry because they do not produce wastewater or chemical effluents. This chapter deals with detailed studies on the classification of textile dyes and advanced technology for wet textile processing.

Keywords: Natural dyes, synthetic dyes, pigments, wet processing

1.1 Introduction

The dyes are usually involved in an aqueous solution. Still, they may also require mordant as an additional chemical to improve the dye and pigment materials' fastness over textile fibers and other materials, such as plastic and various polymers. Organic dyes and pigments are derived from plants or extracted chemically. Natural dyes and pigments, unlike paint, man-made, or synthetic dyes or pigments, do not build up on the fiber's surface but are absorbed into the pores [1]. Due to its aesthetic and social appeal, color has always fascinated scientists and humanity throughout history. Dyes and pigments have been essential commodities throughout history. Dye is used to producing nearly all commercial products, and there are currently over 9,000 different colorants with over 50,000 other trade names. Until the 1850s, almost all dyes were derived from natural sources, most of which came from plants, trees, and a few insects. Dyed fabrics discovered in Egyptian tombs provide compelling evidence that dyeing methods date over 4,000 years. Alizarin is a red dye made from the roots of Rubia tinctorium, a madder plant. The blue dye indigo, obtained in Europe from the leaves of the dyerswoad herb Isatis tinctoria and in Asia from the Indigofera tinctoria, is the oldest known dye [2].

Mauve, the first commercially successful synthetic dye, was discovered by chance in 1856 by British chemist William H. Perkin, who recognized and exploited its commercial significance immediately. The introduction of mauve in 1857 signaled the end of natural dyes' dominance on global markets. Mauve only lasted about seven years on the market, but its popularity sparked research that led to better dyes [3]. Dyes must have possessed the following properties:

• Color
• Water solubility to a certain degree. Although there are certain water-insoluble dyes like vat dyes, sulphur dyes and disperse dye.
• Ability to be absorbed and retain by fiber (substantively), or to be chemically combined with it (reactivity).
• Ability to withstand washing, dry cleaning and exposure to light [1].

The continuous wet processing of textiles, which comprises mainly of continuous pre-treatments and continuous dyeing, is essential, particularly in those fields of application where large quantities of material, uniform quality and low cost are demanded. Continuous dyeing first came to the fore with DuPont's pad-steam method to produce military uniforms with vat dyes and was later adopted for different dyes. Continuous dyeing has seen a lot of changes since then in the form of better dyeing routes that provide good reproducibility from lab to bulk and bulk, such as the newly developed E-control process. It has also seen innovations in specialized dyestuffs explicitly aimed at the continuous dyeing operation, such as Novacron C series of reactive dyes by Huntsman Ltd., which provide all the properties desired by the continuous dyer. This chapter deals with detailed studies on the classification of textile dyes and pigments. The data mainly concerned the type of the dyes based on their sources, chemical structure, and applications. This chapter also discusses the application using advanced technology, such as ultrasonic cavitation, electrochemical dyeing, plasma technology, supercritical CO2 dyeing, etc.

1.2 Classification of Dyes

The classification of dyes can be accomplished in a variety of ways. Each dye class is distinct, with its chemistry, structure, and chemical bonding type. Dyes and pigments in these categories have a high dye/pigment substantivity, which means they react quickly with substrates and textile materials. Some dyes have moderate to poor dye/pigment substantivity because they do not form strong bonds held together by physical forces during the dyeing/ pigmentation process. Some of the major classifications of dyes and pigments are:

1. Classification depending on the source of materials
2. Classification depending on the nature of their respective chromophores.
3. Classification depending on methods of application

1.2.1 Classification Based on the Source of Material

This classification is made based on the source of the dyes and pigments. They are classified into two categories

1. Natural dyes
2. Synthetic/man-made dyes and pigments

1.2.1.1 Natural Dyes

Natural dyes are made with natural materials. The majority are derived from plants and can be found in roots, wood, barks, berries, lichens, leaves, flowers, nuts, and seeds. Insects, shellfish, and mineral compounds are among the sources of others. Plants, animals, and minerals are the three primary sources of natural dyes. Around 4000 years ago, Egyptians used Indigo dyes made from the stems and leaves of a specific plant. Alizarin dyes are made from the roots of the madder plant. Trees are used to extract logwood dyes, which are then used to dye silk and cotton fabrics black [4]. Cochineal dye was extracted from a type of insect called Coccus Cacti. The dye was taken after the female insects were killed. These dyes were used to give red and orange hues to silk and wool fabrics. Tyrian purple dye was made from shellfish. Natural minerals produce a variety of dyes that can be used in various applications [5-10].

1.2.1.2 Synthetic/Man-Made Dyes and Pigments

Inorganic molecules are used to make synthetic dyes/pigments. Synthetic dyes are used in almost all of the colors we see. Synthetic dyes are widely used. This is because they are less expensive to manufacture, brighter, more color fastness, and easier to apply to fabric. In 1856, coal tar was used to create the first synthetic dyes. Later, many dye compounds were developed from coal tar, and their color beauty and color fastness are constantly being improved. The following are the details:

1.2.1.2.1 Direct Dye

This class of water-soluble anionic dyes has a reasonably high affinity for cellulose fibers, particularly under favorable dyeing conditions (2-10 g/l electrolyte in dye bath). Thus, initially dissolved in the dye bath, a large part of the dye has exhausted the fiber when equilibrium is achieved. However, as this involves equilibrium, the dye/fiber bond is fully reversible and the wet fastness properties are therefore poor. Direct dyes and "post-coppering" dyes, another form of direct dyes, belong to this group. After-treatment of post-coppering dyes with copper salts reduces the tendency to de-sorption of the dye absorbed by the fiber (creation of a metal complex) and improves their wet fastness slightly. Direct dyes can be used on both animal and vegetable fabrics, but they are most commonly used on cotton and are referred to as direct cotton dyes. These colorant materials are mostly amines and phenols and are water-soluble. Because a small amount of salt is added to the dyeing solution when using direct dyes, they are also known as salt dyes. The dye colors often have only fair light fastness, poor washing fastness and are not very bright.

1.2.1.2.2 Basic Dyes

The first coal-tar dye was referred to as a "basic dye/pigments." Salts of organic color bases are used to make basic dyes. It was created to create a variety of vibrant silk and wool shades. Basic colorant materials, also known as cationic dyes, are used in cotton, linen, acetate, nylon, polyester, and acrylics with a mordant, Tannic acid. This dye produces a lovely color, but it is not resistant to sunlight, washing, or perspiration.

1.2.1.2.3 Acid (Anionic) Dyes

The sodium or calcium salts of organic acid make acid dyes/pigments. They are mainly used on wool and silk. Acid dyes/pigments are inexpensive and lightfast, but they take long to wash out. If alkali soap is used, the color will change.

1.2.1.2.4 Chrome or Mordant Dyes

In the chromic dyes/pigment process, sodium or potassium dichromate mordant is added to the dyeing bath. The mordant, as well as the dyes, will penetrate the fabric. These are used for both dyeing wool and printing cotton. These are fast or resistant to light, washing, and sweat.

1.2.1.2.5 Azo-Developed Dyes

Unlike vat and sulphur dyes, characterized by a...