Textile dyeing | methods description and environmental impact

Textile dyeing

Textile dyeing is the process where dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired colorfastness and other properties. It is generally done in a special solution containing dyes and particular chemical material. Pigment molecules are fixed to the fiber by binding as a factor controlling absorption, expansion, or temperature and time. The bond between the dye molecule and fiber can be strong or weak, depending on the dye used.

Textile dyeing methods description

Textile dyeing can be described as a process where a textile fiber absorbs the dye molecule from its solution so that the dyed material retains the dye and prevents it from returning to the color from which it was absorbed. Dyeing processes that occur in aqueous water solutions are always a distribution process between two stages, such as dye solution and solid layer, and they are based on the physicochemical interactions between the dye and layer molecules. These processes can lead to chemical reactions between dye molecules and layers, for example, in the case of Vat, reactive, and chrome dyes. In the case of dispersion dyes, the second solid phase involved in the process is the dye scattered particles. These particles dissolve in water and thus transporting the dye to a solid occurs similarly to water-soluble dyes. In contrast to these two cases, the dyeing layer with the pigment is based on the mechanical anchor of the pigment particles on the surface.

The dyeing process in water solutions can be divided into four stages:

i. Convectional diffusion of the dye into the dyebath during which the individual dye molecules move towards the fiber in the liquid phase. This is a relatively fast process that can be accelerated by the relative motion of the dye solution and the fiber.

ii. Absorption of dye on the fiber surface where the dye molecule goes from the liquid phase (dye solution) to the solid phase (fiber). Here the surface of the fiber is understood not only as of the visible surface on the outside of the fiber, which is defined by the fiber diameter and length of the fiber but also as the surface of the hole that can penetrate deep inside the fiber. This stage largely determines the color uniformity of the end-use product.

iii. Molecular spread of dye from the surface of the fiber to the interior of the fiber. This is a slow process whose rate can be increased by increasing the temperature of the dye solution. High temperatures also help increase fiber swelling.

iv. Dye molecule fixation on fiber molecules by forming bonds between dye and fiber molecules. The stability of the bond depends on the type of bond that is formed.

Water quality of textile dyeing methods

Water quality is extremely important for textile dyeing, and it must meet the requirements listed below. Water purification is usually required to avoid unpleasant dyeing defects such as unevenness, dye precipitation, shade dullness, stiff handles, or chalking. Yarn or fabric preparation and pre-treatment also have a significant effect on dyeing quality. For example, poor scouring and bleaching can lead to serious unevenness in dyeing, and uniform rotation of a yarn package can lead to color differences in package dyeing. As a result, adequate and uniform preparation and pretreatment can make dyeing standards more controllable and predictable. Therefore, control of the dyeing process is important in achieving high-quality products and increasing dyeing production efficiency.

Item                                                    Requirement

Color:                                                 Colorless

pH:                                                      6.5–7.5

Total hardness (as CaCO3):       50 mg/L (for general use) and 17.5 mg/L (for dyestuff dissolution)

Iron:                                                     0.1 mg/L

Manganese:                                        0.1 mg/L

Transparency:                                     30 cm

Textile dyeing methods

These are different textile dyeing methods, such as below-

a.    Fiber dyeing

b.    Yarn dyeing

c.    Fabric dyeing and

d.    Garments dyeing

a. Fiber dyeing

Fiber dyeing is a method where textile is dyed in fiber form. It is mainly done on wool and man-made fiber. It is a special process of dyeing. Although, fabric stage dyeing is overall known. But the fancy item is dyed in this form.

b. Yarn dyeing

The dyeing method where the yarn is dyed in package or hank form is called yarn dyeing. There are many forms of yarn dyeing. Normal forms are the package form and the hanks form. Cotton yarns are dyed in package form, and acrylic or wool yarn is dyed in hank form. In the filament industry, polyester or polyamide yarns are generally dyed in package form, while viscose rayon yarns are partly dyed in hank form.

c. Fabric dyeing

The dyeing process where woven or knitted fabric is dyed in continuing by machine in fabric form is called fabric dyeing. In other words, dyeing in textiles is a process in which color is transferred to a finished textile or textile material to add permanent and long-lasting color. Fabric dyeing may be done by hand or by machine. In woven fabric dyeing, fabric passes through a dye bath liquor and gets optimum shade. In knitted fabric dyeing, the fabric dyeing process is carried out in a vessel by dossing chemicals step by step.

d. Garments dyeing

Garments dyeing is a process where a complete body is dyed in a machine or by hand. This process mainly is done in denim or woven garments. Sometimes knitted garments also dyeing in garments form. Today it has become popular due to cost-saving and fashion trends. Also, it is capable to react much closer to actual market demand if the apparel is post dyed which reduces lead time and increases forecasting accuracy.

Textile dyeing environmental impact

In a textile dyeing process, many chemicals, and dyes must be applied. The protection of dyed products, especially in the case of chemicals or dyes used, becomes an important issue. There are many product safety regulations in the EU, China, Japan, Australia, USA, Canada, etc. It deals with the registration, evaluation, approval, and limitation of chemicals. Dyeing companies have a legal obligation to comply with these rules when choosing chemicals and dyes. Substances of very high concern (SVHC), the list of substances listed in the American Apparel and Footwear Association's (AAFA) Restricted Materials List, and limited or limited chemicals and restrictions should be considered. Standards listed in the global textile market such as Oeko-Tex Standard 100, etc., play an important role in testing hazardous materials for the decision to be made when buying textiles.

Eco-friendly and low-carbon emission production for dyeing production is another important aspect of the textile industry. All kinds of new dyeing equipment, dyes and chemicals, and technology related to the minimization process, have been brought to market to increase production efficiency and reduce carbon emissions by reducing water and energy costs. We should keep a close eye on the development of new chemicals, machinery, and technology, which could bring about changes in the dyeing and control of the printing process.

Conclusion

Modern fashion depends a lot on dyeing. Color diversity, manipulation, and increase attraction all depend on the dyeing. Color variations cannot be brought without dyeing. So the importance of dyeing in textiles is immense.