Dye Fiber Interaction/ Anchoring system

Dye fiber interaction system can be divided into

1. Nonionic system

2. Ionic system

3. Reactive system

4. Hydrogen bond system

5. Other interactions

1. Nonionic system: PET, acrylic, polyamide etc.

2. Ionic system

   • Fiber which possess charged group:

Anionic and cationic: Acrylic fiber (contain negatively charged sulfonic or –COOH group) and basic dyes

Wool, Silk, Nylons (contain charged –NH4+ groups) & acid dye

• Fiber which contain no charged groups

Anionic and Anionic: Cellulose is dyed with direct & vat dyes both of which carry negative charges. The dye is absorbed by virtue of its attraction to the fiber & in doing so it is accompanied by other ions of electrolytes e.g. Na+ & Cl-.

3. Reactive system: cellulose, wool and reactive dye

4. Hydrogen bond system

5. Other interactions: Van der Waals force

Role of fiber functional groups in dye fiber interaction systems

• Cotton: ionic system and covalent bond forces and H-bond

Cotton fiber has –OH groups, which is highly electronegative and is capable of hydrogen bonding. It is also capable of reacting with reactive groups of reactive dyes and form covalent bonds.

• Protein: ionic system

Wool fiber has –COOH and –NH2 groups which are capable of ionizing and at certain pH are positively or negatively charged. So it can be dyed with basic and acid dyes.

• Polyester:

contains –COOH, -OH as functional groups but don’t undergo ionisation, so it is not possible to dye them with ionic dyes. So nonionic system and hydrophobic interaction and Van der waals force exist.

• PAN: ionic and nonionic system

Contains –OSO3H, can be dyed with cationic/basic dyes

• Rayon: Ionic system

Contains –OH groups, -COOCH3 groups

Forces in dyeing systems

1. Electrostatic force

2. Hydrogen Bond

3. Covalent bond

4. Van der Waals force

5. Physical force

6. Hydrophobic interactions/Entropy factors

• Electrostatic force:

The forces have a range about 100A°.

Electrostatic force formed when the dye particle and fiber surfaces are oppositely charged. Such force exists in the dyeing of wool, silk, polyamides with anionic dyes (or fibers containing anion with cationic dyes). The polymers of these fibers contain amino and carboxyl groups depending on pH value in water, these groups are either neutral (-COOH, -NH₂), cationic (-NH₃⁺) or anion (-COO^-).

• Hydrogen Bond:

When hydrogen atoms are united with strongly electronegative group element, the latter by attracting the electron of the hydrogen atom, gives to it a positive bias. This positively charged hydrogen atom may form bond with groups containing unshared pale of electrons. They are of short range 1A° to 5A° (0.1 to 0.5nm)

R^-δ------H^+δ … …. … …ö= C O---^1.5-1.9Aº-----H …^1Aº…… ö

Hydrogen bonds are formed because of extra attraction between such atoms. It is a weak type of bond. This bond may be intermolecular or intramolecular.

• Covalent bond

The covalent bond between carbon atom in most organic compound is very stable. They are of short range 1A° to 5A° (0.1nm to 0.5nm). Covalent bonds are formed when dyes react chemically with fibers. All reactive dyes form covalent bonds so fastness properties of such dyes are generally good.

• Van der Waals force

Van der waals forces are only effective for sorption of dyes to fiber molecules if the distance between the dye and fiber is very small. These are weak forces and depend on atoms being at certain relative position.

• Physical force

It is found that although –OH, -NH₂, -N=N- and –CO groups might be responsible for attachment by hydrogen bonds to the fiber but this explanation is to a great extent discounted because the coordinating power of these groups is satisfied by chelation within dye molecules which is due to nonpolar or physical force.

• Hydrophobic interactions/Entropy factors:

It is found that increasing the no of aromatic rings or unbranched aliphatic chain makes a much greater increase in affinity than does the introduction of potential bond forming groups. This is assumed that the hydrophobic part of unbranched aliphatic chain dissolved in water because of ice-like structure of the water molecules in the immediate vicinity of hydrophobic molecules, which is of completely entropy factors