الأصباغ العضوية: مقدمة في اللون

• Organic Dyes

مقدمة (Introduction)

• For a substance to be a dye, it must meet certain conditions.
• It must have a specific and stable color.
• It must be able to dye the fabric directly or indirectly.
• It must be colorfast when applied to the fabric, meaning it shouldn't fade easily.
• It should be resistant to the effects of water.
• It should exhibit some resistance to diluted acids and alkalis, especially the latter, due to the alkaline nature of washing soda.
• Many natural dyes have been known since ancient times, obtained from animal and plant sources.
• Today's dyes are mostly synthetic, prepared from aromatic organic compounds whose primary source is Coal Tar.

Colour اللون

• When white light falls on a substance, the light is either reflected entirely or absorbed entirely.
• If reflected, the substance appears white; if absorbed, it appears black.
• If specific wavelengths of light are absorbed, the remaining wavelengths are reflected, giving the substance the color of the reflected light.
• If one wavelength is absorbed, the substance has the complementary color of the absorbed wavelength.

Chromophores

• If a substance absorbs all visible light except for one wavelength, which it reflects, then the substance will appear the color of the reflected wavelength.
• The substance appears blue because it absorbs the yellow part of the spectrum, or because it absorbs the entire visible spectrum except for blue.
• Color typically appears in an organic compound when the compound contains "unsaturated groups."
• A more accurate term than "unsaturated groups" is "groups with multiple bonds," referred to as Chromophores.

auxochromes

• Color enhancers can be acidic (phenolic) or alkaline, with -OH, -NH2, NHR ,NR2 being the most common groups.

Batho - Chromic Groups & Hypso-chromic Groups

• Groups that deepen the color are known as bathochromic groups.
• Groups that lighten the color and inversely affect the perceived color are called hypsochromic groups.
• Making the color "deeper" (in color chemistry) means changing the color as follows: yellow → orange → red → purple → violet → blue → green → black.
• Since the visible color is complementary to the absorbed wavelength, bathochromic groups shift the maximum absorption towards the red end, lowering the frequency of the absorbed light.
• Conversely, hypsochromic groups shift the maximum absorption towards the violet end, increasing the frequency of the absorbed light.

تسمية ومصطلحات الأصبغة (Nomenclature of Dyes)

• Many dyes have multiple names given by manufacturers.
• Each dye has names (or a trade name) and a color index indicated by letters.
• G or Y stands for yellow
• O for orange
• R or B for red
• Sometimes the letter is repeated, and the number indicates the intensity and strength of the color.
• Methyl Violet 6B is a very dark violet color (close to blue).
• The D in Alizarin Blue D indicates that the dye directly colors cotton.
• The S in Fuchsin S indicates the dye is acidic.
• The letter F is occasionally used to indicate that the dye is fast (colorfast).
• Every dye is identified by a unique color index number listed in the Society of Dyers and Colorists directory.

تصنيف الأصبغة (Classification of Dyes)

• Dyes are classified according to their chemical composition and structure, or according to how they are used on fabrics.
• The former is more for chemists.
• The latter is more for dyers interested in how a dye interacts with a fabric.
• Chemical classifications:
  • Nitro dyes
  • Nitroso dyes
  • Azo dyes
  • Diphenylmethane dyes
  • Triphenylmethane dyes
  • Xanthene dyes
  • Diphenylamine dyes
  • Heterocyclic dyes
  • Vat dyes
  • Anthraquinone dyes
  • Sulfur dyes
  • Phthalocyanine dyes

تصنيف الأصبغة حسب الاستعمال (Classification According to Application)

Acid Dyes

• Acid dyes are sodium salts of sulfonic acids and nitrophenols.
• They dye animal fabrics directly but not plant fabrics.
• They are widely used on silk and wool.

Basic Dyes

• Basic dyes are colored salts of bases (alkalis) with hydrochloric acid or zinc chloride.
• These dyes directly color animal tissues and also plant tissues that have their color fixed using tannic acid.
• They are often used on cotton and silk.

الأصبغة المباشرة (Direct Dyes/Substantive dyes)

• Direct dyes do not require a mordant.
• They dye animal and plant fabrics (fibers).

الأصبغة المرسخة (Mordant Dyes) adjective dyes

• Mordant dyes don't directly dye plant and animal fibers, they require a mordant.
• If the dye is acidic, the mordant must be basic, and vice versa.
• For acidic dyes, the mordants are metallic hydroxides; for basic dyes, the mordant is usually tannic acid.
• Tannic acid is a mixture of organic tanning substances found in oak and tea leaves.

أصبغة الحوض (Vat Dyes)

• These dyes are insoluble in water, but they are reduced by sodium hyposulfite in an alkaline solution (dithionate) into soluble compounds that can be oxidized back into a dye.
• These reduced compounds are often white or colorless and called leuco compounds.
• They dye both animal and plant tissues directly.
• Vat dyes are often used on cotton fabrics.

نظرية الصباغة (Theory of Dyeing)

• The theory of dyeing depends on the nature of both the fabric and dye.
• Fabric fibers are divided into three groups: plant, animal, and synthetic/composite.
• Plant fibers: cellulosic fibers such as cotton, linen, hemp, and jute.
• Animal fibers: protein fibers such as wool, silk, and leather.
• Synthetic and composite fibers: such as rayon (cellulose model) and nylon (protein model).

أصبغة النيترو (Nitro Dyes)

• Nitro dyes contain a nitro group as a chromophore and a hydroxyl group as an auxochrome.
• The simplest nitro dye is picric acid used to dye silk a shiny yellow.
• The color is not stable.
  • Martius yellow
    • 2,4-Dinitronaphthalen-1-ol
    • Also called Yellow Manchester.
    • Used as a sodium, calcium, or ammonium salt, but it is unstable and easily sublimates from the fabric.
  • Naphthol yellow S
    • Disodium 5,7-dinitro-8-oxidonaphthalene-2-sulfonate
    • Used as an acidic dye for silk and wool.
  • Lithol Fast Yellow GG
    • A pigment used as a non-toxic alternative to chrome yellow (lead chromate).

أصبغة النيتروزو (Nitroso Dyes)

• In nitroso dyes, the chromophore is a nitroso group, and the auxochrome is a hydroxyl group.
• Often used in the form of mordant green iron dyes in dyeing and printing.
  • Gambine R, 2-Nitroso-1-naphthol
  • Gambine Y, 1-Nitroso-2-naphthol

:أصبغه آزو (Azo Dyes)

• The chromophore in azo dyes is the azo group (-N=N-), with the well-known auxochromes being -OH,-NH2, and NR2.
• Azo dyes, from an operational standpoint, are classified as basic, acidic, direct, fast, and mordant dyes.

:أولا أصبغة آزو القاعدية (Basic Azo Dyes)

- Chrysoidine G
    - An orange dye that is employed on cotton with a tannin mordant.

:ثانيا أصبغة آزو الحمضية(Acid Azo Dyes)

• The following group of dyes contains a sulfonic acid group.
  • Methyl Orange
    • Sodium 4-{[4-(dimethylamino)phenyl]diazenyl}benzene-1-sulfonate
    • Dyes in inconsistent color gradients and appears as a pH indicator or indicator, where the color is orange in a pH less than and red in a pH more than.
  • Orange I
  • Orange II
  • Fast Red AV
  • Ponceau 2 R
  • Crystal ponceau 6R
    • Used as a food dye.
  • Naphthal Blue Black B
    • One of the most widely used acidic black dyes.

ثالثا أصبغة آزو المباشرة (direct Azo - dyes)

- Congo Red
    - When in an alkaline state becomes red in color and when in a sodium salt state helps dye cotton giving it a red color.
    - It was the first synthetic structural dye able to help dye fabrics such as cotton.
    - Is directly affected by acids altering its color ranging from a red to a dark blue when influenced by non-organic acids.