dyespigments (1).docx

Publish in

Documents

13 views

Please download to get full document.

View again

of 18
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Share
Description
Chapter 2 Dyes and Pigments: Their Structure and Properties Abstract 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, phar- maceutical, 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 fluore
Tags
Transcript
  Chapter 2   Dyes and Pigments: Their Structure and Properties    Abstract 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, phar-maceutical, 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 fl uorescent particulate organic or inorganic fi nely 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. Keywords Dye Pigment Colorant Chromophore Auxochrome Color    2.1 Introduction   A color additive is a substance capable of imparting its color to a given substrate, such as paint, paper or cotton, in which it is present. Dyes and pigments are the most important colorants used to add a color or to change the color of something. A dye must be soluble in the application medium, usually water, at some points during the coloration process. It will also usually exhibit some substantivity for the material being dyed and be absorbed from the aqueous solution. On the other hand, pigments are the colorants composed of particles that are insoluble in the appli-cation medium (Broadbent 2001). Dyes and pigments as colorants are widely used in the textile,  pharmaceutical, food, cosmetics, plastics, paint, ink, photographic and paper industries. It is estimated that over 10,000 different dyes and pigments are used industrially and over 7 ×  10 5  tons of synthetic dyes are annually produced worldwide (Zollinger  1999; Chequer et al. 2013). The terms, dye , dyestuff  , pigment , © The Author(s) 2016   13   A. G ü rses et al., Dyes and Pigments , SpringerBriefs in Green Chemistry for Sustainability, DOI 10.1007/978-3-319-33892-7_2    14   2 Dyes and Pigments: Their Structure and Properties   color  ,  colorant , and  paint are often wrongly used interchangeably. This chapter    focused on the properties of dyes and pigments, chemical and structural consid-erations, the relationship between light and color. 2.2   Dyes and Pigments  Paint is de fi ned as any liquid, lique fi able, or mastic composition designed for application to a substrate in a thin layer which is converted to an opaque solid fi lm after application. Paint is used for protection, decoration, or identi fi cation, or to serve some functional purpose such as the fi lling or concealing of surface irregu-larities, the modi fi cation of light and heat, etc (Kirk-Othmer  1998a). Both pigments and dyes are used to provide color to all sorts of substances and have been important to humans since the dawn of history. The difference between the two is that dyes are soluble in the substrate and thus disperse at a molecular level, while pigments are insoluble and are dispersed as particles. Dyes provide  brighter color than conventional pigments, but they are less light stable and less  permanent (Rothon 2012). Pigments are colored, colorless, or fl uorescent particulate organic or inorganic fi nely divided solids which are usually insoluble in, and essentially chemically   unaffected by, the vehicle or medium in which they are incorporated. They alter appearance either by selective absorption and/or scattering of light. Organic and inorganic pigment powders are fi nely divided crystalline solids that are essentially insoluble in application media such as ink or paint (Kirk-Othmer  1998b). Dyes, on the other hand, are colored substances which are soluble or go into solution during the application process and impart color by selective absorption of light. In contrast to dyes, whose coloristic properties are almost exclusively de fi ned by their chemical structure, the properties of pigments also depend on the  physical characteristics of its particles (Kirk-Othmer  1998b). Ever since pre-historic time, man has been fascinated to color the objects of daily use employing inorganic salts or natural pigments of vegetable, animal, and mineral srcins. These coloring substances, known as dyes, are the chemical compounds used for coloring fabrics, leather, plastic, paper, food items, cosmetics, etc., and to produce inks and artistic colors. Dyes are of two types, i.e. synthetic and natural. Synthetic dyes are based on petroleum compound, whereas natural dyes are obtained from plant, animal, and mineral matters (Singh and Bharati 2014). Colorants are normally understood to include both pigments and dyestuff. Pigments refer mainly to inorganic salts and oxides, such as iron and chromium oxides, which are usually dispersed in crystal or powder form in an application medium. The color  properties of the dispersion depend on the particle size and form of the pigment. Pigment colorants tend to be the highly durable, heat stable, solvent resistant, lightfast, and migration fast. On the other hand, they also tend to be hard to process and have  poor color brilliance and strength. Dyes (also called dyestuff) are conventionally understood to refer to organic molecules dissolved, as molecular     2.2 Dyes and Pigments   15   COLORANTS   Organic   Inorganic   (16%)   (84%)   Dyes   Pigments   Pigments   (75%)   (25%)   (5:95)   Fig. 2.1 Share of colorants from organic and inorganic classes. Reproduced from Zollinger,   Copyright 2003, with permission from Wiley  chromophores, in the application medium. Examples are azo dyes, coumarin dyes, and perylene dyes (Zhang 2010). Figure 2.1 presents total production amount (weight %) of different classes of colorants (Zollinger  2003; Chakraborty 2010). The global market production of organic colorants in 2010 is forecast to be 2.1 million metric tons valued at 14.4  billion dollars and projected to grow at an annual rate of 3  – 4 %. The market for inorganic colorants is roughly 5 times larger (Barden 2010). The color imparted by dyestuff to the resulting solution depends on the elec-tronic properties of the chromophore molecule. Dyestuff colorants tend to have excellent brilliance and color strength, and are typically easy to process, but also have poor durability, poor heat and solvent stability, and high migration. Because of the contrasting properties of both types of colorants, much work has been done trying to improve the attributes of each class of colorant. Nanocolorants were regarded as a new class of colorants that could get out of dilemma between dye-stuffs and organic pigments. In nature, nanocolorants are a class of nanocomposites that recombine dye acted as an essential ingredient and suitable  polymeric matrix, and its performance target is to integrate excellent chromatic  properties and good processibility of dyestuffs and good durability of organic  pigments. Nanocolorants are new kind of colorants that can combine the advantages of both pigments and dyes, and will be promisingly applied to  photoelectric high-tech fi elds (Zhang 2010).  Dyes can generally be described as colored substances that have af  fi nity to the substrates to which they are being applied (Pereira and Alves 2012). Dyes are soluble and/or go through an application process which, at least temporarily, destroys any crystal structure by absorption, solution, and mechanical retention, or  by ionic or covalent chemical bonds (Nwokonkwo 2013). Color Pigment Manufacturers Association (CPMA) has de fi ned pigments as colored, black, white  16   2 Dyes and Pigments: Their Structure and Properties  or fl uorescent particulate organic or inorganic solids which usually are insoluble in, and essentially physically and chemically unaffected by, the vehicle or substrate in which they are incorporated. They alter appearance by selective absorption and/or by scattering of light (Merchak  2012). The key distinction is that dyes are soluble in water and/or an organic solvent, while pigments are insoluble in both types of liquid media. Dyes are used to color substrates to which they have af  fi nity. Pigments can be used to color any  polymeric substrate but by a mechanism quite different from that of dyes, in that surface only coloration is involved unless the pigment is mixed with the polymer  before fi  ber or molded article formation (IARC 2010). The most important differentiation of colorant is that colorant is either dyes or  pigment. These terms are often used indiscriminately, in particular, pigments are quite often considered to be a group of dyes. Ideal pigments are characterized by  being practically insoluble in the media in which they are applied. Pigment  particles have to be attached to substrates by additional compounds, for example  by a polymer in paint, in a plastic or in a melt. Dyes, on the other hand, are applied to various substrates (textile materials, leather, paper and hair) from a liquid in which they are completely, or at least partly, soluble. In contrast to pigments, dyes must possess a speci fi c af  fi nity to the substrate for which they are used (Zollinger 2003). Some properties of malachite green and pigment green which are important col-orants and they are used as coloring agents for different materials were  presented in Table 2.1.  Table 2.1 Some properties of malachite green and pigment green 36   Malachite green   Pigment green 36 (phthalocyanine   (basic green 4)   green YS)   CAS No   569-64-2   14302-13-7   Chemical   Br    Cl   structure   Cl   Br    Cl   Cl   N   H 3 C   CH 3   N   N   Cl   +   Cl - N   N   N  Cu   Cl   Cl   CH 3   CH 3   N   Br    N   N   N   Br    Cl   Cl   Br    Br    Cl   Class   Triarylmethanes   Phthalocyanines   Chemical   C 23 H 25  N 2 Cl   C 32 Br  6 Cl 10 CuN 8   Formula   Solubility   Very soluble in water    Insoluble in water    Physical form   Green crystals   Yellowish green powder   
Related Search

Previous Document

Marvin Feldman

Next Document

apstate-u092017

We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks