Читать книгу Sustainable Practices in the Textile Industry - Группа авторов - Страница 14

In the present scenario people are more inclined to be nature-friendly, health conscious and become aware about the environment. The meticulous environmental standards are being imposed by many countries in response to the toxic and allergic reactions associated with synthetic dyes. It has created a revolution in research and development in eco-friendly and non-toxic colorant. Environmental considerations are now becoming vital factors during the selection of consumer goods including textile as well as in cosmetic, pharmaceutical and food industry all over the world. Coloring agent or dyes play an important role in all these industries during manufacturing and other production process. Both qualitative and quantitative research investigations have been undertaken all over the world on safe coloring substance. Natural dyes are widely used in following application (Figure 1.1):

Figure 1.1 Schematic representation of applications of natural dyes.

a. Textile Coloration

Coloring of textile material is called dyeing. Dyeing is a process to enhance the beauty of fiber or fabric by coloring them. The coloring compounds can be synthetic or natural and capable of being fixed to fabric defined as dye. India is a diverse country of region and culture. Dyeing practices varied immensely due to availability of local dye-yielding plants and minerals, the natural sources. Until year 1856, these natural sources were used in coloring but with the discovery of chemical dyes, the use of natural dyes decreased. The side effects of the continuous use of chemical dyes gradually began toappear as health problems and skin diseases that resulted by wearing synthetic dyed fabric for decades. Hazardous chemicals were used in the manufacture of dyes in large scale for rapid growth of textile industries. All those synthetic, hazardous chemicals disposed of in nature after dye preparation, coloring and printing, which ultimately created various pollution problems in the environment. Keeping this situation in mind, many experiments are being done by scientists and researchers for the development of new sources and techniques of natural colors, so that it can be adopted by textile industries on a large scale. There is an increasing awareness among humans about their health and nature, due to which the demand for eco-friendly clothes is also increasing. Natural clothes can be obtained at a higher price from some small scale industries and handlooms, but they are not able to meet the demand of all people. In the past few years, many research works related to natural dye have been done. In this chapter, an attempt has been made to exhibit how natural dyes are used on clothes and their significance for human health and nature.

b. Food Coloration

Human appetizer and choice of food are influenced by color. Food colors are used in processed food, drinks and condiments. They are often added to maintain and improve the appearance of the food. The addition of saffron, turmeric and other spices are reported from ancient times. Commercially available colors are made of chemicals that can be harmful to human and environment. Therefore, natural food colors are in demand again. Most commonly used natural food dyes are saffron, turmeric, annatto, beetroot and carrot etc.

c. pH Indicator

pH is measure of relative amount of free hydrogen and hydroxyl ions in water. The range of pH is in between 0 and 14, where 7 is considered neutral. pH greater than 7 indicates the base, whereas pH less than 7 indicates acidity. A pH indicator is a compound that changes color in solution over a narrow range of pH value. Small amount of indicator compound is sufficient to produce a visible color change. There are many colors of indicators in nature thus, influenced by change in pH range. Some of the natural dyes show color changes with variation of pH. Red cabbage dye is very good example of natural pH indicator [1].

d. Histology Staining

Study of the microanatomy of cells, tissue and organs is called histology. Observations of cells are performed with the help of a microscope. Staining is the technique to highlight and differentiate the structure of tissue. Stain and dyes are applied in staining on tissue and cells. Dyes also can be used to color cells, tissue, organelles as well as microorganism such as bacteria and fungi [2]. Saffron, a natural dye extracted from Saffron crocus was the first stain in histology used by Antonie van Leeuwenhoek, the father of microbiology [3]. Hematoxylin stain is a naturally occurring dye found in Logwood tree widely used in histological study. Researchers also found Punica granatum, Curcuma longa, Syzygium cumini and Sorghum bicolor effective in staining [4–7].

e. Cosmetics and Pharmaceutical

Cosmetic products are used to clear, improve or change the complexion, skin, hair and nails. Colors or dyes are the most important ingredient in production of cosmetics. Henna is traditionally used for coloring hands and hair. Saffron and turmeric also examples of natural dyes utilized in cosmetics. In pharmaceutical field colors of medicine are used to differentiate the dosage. Imparting color to drugs helps in their distinctive appearance. The colorant employed in pharmaceuticals is considered safe such as beet root, paprika and annatto.

f. Dye-Sensitized Solar Cells

Dye-sensitized solar cell is third generation photovoltaic (solar) cell that converts any visible light into electrical energy. It is low-cost solar cell belonging to the group of thin film solar cells. Performances of dye sensitized solar cells are mainly based on dye used as a sensitizer [8]. Godibo et al., attempted the preparation of Dye Sensitized Solar Cells using flowers of Amaranthus caudatus, Bougainvillea spectabilis, Delonix regia, Nerium oleander, Spathodea companulata and a mixture of the extracts [9].

In addition to the above mentioned applications, there is a growing interest for using natural dyes to dye leather, stain wood, pulp, some plastics [10–14]. This chapter intends to discuss the application of natural dyes in textile.