Textile Dyeing Chemicals and Auxiliaries | Yarn and Fabric Dyeing Assistance

Posted by Firoz Kabir on Tuesday, September 23, 2014 2

Dyeing of textile materials such as fiber, yarn, fabric or garments is a process of imparting color to these material through different dyeing processes and procedures in machines with the help of different dyestuffs and dyeing assistance. Different types of dyeing assistants are described as below which are most important.

 

Anti-creasing Agent:
For anti-creasing treatment a suitable polymer precurson is used which either reacts with hydroxyl groups in the cellulose to form cross links between adjacent polymer chain or it polymerises in the amorphous regions of the fiber. Cross links between adjacent polymer chain considerably limit the movement of the cellulose molecules so that creasing is more difficult.
The types of chemicals used for crease resistant for cotton are condensation products of the urea-formaldehyde. 

This are
a)    Urea / Formaldehyde(U/F)
      e.g.  Dimethylol urea.
b)    Melamine / Formaldehyde
e.g. Trimethylol Melamine
c)    Dimethylol ethylene urea (DMEU)
d)    Dimethylol-4,5-Dihudroxyethylene urea(DMDHEU)
 

Sequestering agent:
A sequestering or chelating agent is a complex forming auxiliary chemical with metals such as Iron, Copper, Nickel, Zinc & Magnesium that are present in water and affects the textile processing in many way. Certain organic compounds are capable of forming coordinate bonds with metals through two or more atoms of the organic compound; Such organic compounds are called chelating agents.

EDTA (CO2CH2)2NCH2CH2N(CH2CO2)2 is a common hex dentate chelating agent. Chlorophyll is a chelate that consists of a magnesium ion. Part of hemoglobin in blood is an iron chelate. Chelating agents are important in textile dyeing. Water softening and enzyme deactivation and as bactericides. Chelating agent eliminates water hardness & heavy metals Such as iron and copper which can affect the scouring process.

Some sequestering agents are -  
•    Tetra sodium pyrophosphate (TSPP)
•    Tripoly sodium phosphate (TSP)
•    Ethylene diamine tetra acetic acid (EDTA)
•    Nitrilo triacetic acid (NTA)
•    Ethylene diamine tetra (methylene phosphonic acid) [EDTMP]
 

Wetting agent (Surfactants):
The word “Surfactants” is coined from the expression “Surface active agent”. As the phrase implies, a surfactant molecule possesses surface activity, a property associated with the chemical structure of the molecule. A few primary functions of auxiliaries are: 

•  To prepare the material perfectly for coloration or to enhance whiteness of white goods.
• To improve sorption characteristics of the colorants by acceleration, retardation, blocking or migration.
• To stabilize colorant in the application media by improving solubility, dispersion, emulsification, preventing or promoting oxidation or reduction, etc.
• To improve fastness of dyes.

Classification Wetting agent:
The surfactants used as textile auxiliaries can be divided into four major groups, depending on the type and distribution of the polar forces as shown in table –

CLASS    HYDROPHOBIC    HYDROPHILIC
Anionic    Weakly negative    Strongly positive
Cationic    Weakly positive    Strongly negative
Nonionic    Unchanged    Unchanged
Amphotaric    Both positive & negative    Both positive & negative

Salt:
For level dyeing of cotton fiber with reactive dye we need two types of force in the dye bath. These are:-
•    Force of attraction: - Which should be developed between the dye molecule and fiber.
•    Force of repulsion: - Which should be developed between the dye molecule and water.

But when the fiber is in water it become (-)ve charged and the dye in water is also (-) vely charged. So following condition arise.  

Mechanism of salt in textile dyeing
 

OBA(Optical Brightening Agent):
The OBA possesses the property of fluorescence which means that they can absorb shorter wave-length light and re-emit it at longer wave-lengths. It absorbs invisible ultra-violet rays and re-emits them within the visible spectrum. So substance contain OBA can emit more than the total amount of daylight that falls on it, giving an intensity brilliant white.
For cotton fiber anionic OBA is used.
 

Enzyme:
Enzymes are high molecular weight protein biocatalyst that is very specific in their action. Enzymes are named after the compound they break down, for example, Amylase breaks down amylose and amylopectin. Maltase breaks down maltase and cellulose breaks down cellulose.

Enzyme consists of three-dimensional proteins that are composed of polypeptide chains. However, the mechanism of hydrolysis of cellulosic material is complicated. The enzymes have a specific three dimensional shape and have a true active center in the form of fissures, holes, pockets, cavities or hollows. These are adsorbed onto the surface of some substrate in lock and key fashion. At the active side of the enzyme, hydrolysis of he substrate is accelerated. The product of decomposition of the substrate is formed and the enzyme is released to be reabsorbed onto a different location on the substrate. The process continues until the enzyme is deactivated by conditions in the processing bath.
Others dyeing auxiliaries are-

 Detergent: It is mainly used for cleaning grey fabric.

Anti-foaming Agent: It is used to protect foam during dyeing.

Stabilizer: It is used for removing iron of water. It also increase the activity of  H2O2.

Oil remover: It is used to remove oil or oil type substance.

Caustic soda or NaOH: It is used to clean the fabric. It is the main chemical of scouring process. When it is used in Dye bath, then it is used to fix up the Dye molecule in the fabric surface.
 

Hydrogen Peroxide (H2O2): It is used as a Bleaching agent. It is used to remove the natural colour of grey fabric. It makes the fabric more white . Other name of it Brightening agent. It is also used to remove waste of detergent, caustic & fabric.

Peroxide killer: It is used to remove the action of  H2O2. Enzyme base H2O2 killer is used in DELTA.

Acetic Acid: In scouring bath Acetic Acid is used for pH    controlling . After treatment, it is used for neutralizing, Because  before using Acid, soda must be used. For this reason, to neutralize  that chamber Acid must be used.

Leveling: It is used for level or even dyeing .

Gluber salt (Na2SO4.10H2O): It acts as carrier. It bears dye molecule into fiber      surface. In other word, It reaches the dye   molecule     into fiber surface     properly but not fix up. In this treatment, at about     20% dye fixation is     completed.

Soda ash: It is used to attach the dye molecule into fabric surface. It is also used  to fix up the dye molecule into the fabric surface. After soaping, if carrier is used then colour must be removed (this operation is performed when     more dark shade will appear but needed light colour).

Soaping:  It is used to clean the fabric.

Softener: It is used for soft. It makes the dyed fabric more soft or     smoothness. It increase the smoothness of dyed fabric.

Fixing agent: It is used to fix up the extra colour.