Viscose Dyeing Process: Fiber, Yarn and Fabric Form

Last Updated on 17/06/2021

Viscose Fabric:
Viscose is created from a combination of natural and man-made components, specially made from regenerated wood cellulose, and it can be made into the more common form of rayon used for many types of textile products, including clothing. It is the most commercially important regenerated cellulosic fiber. Viscose is based on natural cellulose and it is pressed through spinnerets and is coagulated in a bath of sulphuric acid. Viscose has a silky appearance and feel, and has the ability to breathe in a manner similar to cotton. Viscose fabrics have been modified to improve the attraction for metal oxides such as aluminium, zinc, or titanium in order to impart antimicrobial activity against two types of microorganisms. Nanosafe textile using the extracts of yellow papaya peel has been developed by extracellular synthesis of highly stable silver nanoparticles. Viscose fabric is used for different textile and nonwoven applications. In this article I will discuss different methods of viscose dyeing.

Viscose Dyeing Process:

Viscose fabric is not a common fabric like as cotton. The hand feelings of this fabric are same as silk and soft. So dyeing process of viscose fabric slightly difference from cotton or others fabric. Viscose fibers exhibit highest expansion in wet state, which also leads to the so-called “wet stiffness” of viscose fabrics. As a result of the high water uptake, a substantial decrease in wet tensile strength is observed with viscose fibers. Viscose can be dyed with three form; loose fiber dyeing, hank dyeing and fabric dyeing. Dyeing of viscose in hank form cabinet hank dyeing machines are used, which convert hank to cone and sell in the market. Viscose dope dyeing is also popular which is done by pigments. Dope dyeing means that the colorants are added to the viscose before the spinning process takes place. In this article I will discuss about exhaust dyeing of viscose loose fiber and viscose fabric dyeing process flow chart.

Exhaust Dyeing of Viscose Loose Fiber:
Nowdays the dyestuff technology has advanced and viscose fiber is being dyed using vat dyes, reactive dyes and sulphur dyes. The types of dyes are selected as per the end-use. Viscose fiber is dyed in HTHP dyeing machines. The material/liquor ratio in the dyeing machine should be maintained between 1/7 and 1/10. If water is hard, it is better to add EDTA. For example, in a 500-kg-capacity dyeing machine, the loading will be 550 kg (maximum).

Viscose is a semi-synthetic fiber. It is a purified form of cellulose and hence unlike cotton scouring is not required directly start dyeing. Before dyeing, water should be checked. The soft water should have a total dissolved solid between 100 and 200 ppm. Water hardness <50 ppm. pH should be neutral (7). To avoid uneven dyeing of viscose fiber, it should be opened properly with hand and manually loaded (no stamping machine should be used). Loading density should be uniform to avoid channelling and uneven dyeing.

Following are the steps for dyeing viscose loose fiber:

Setting of dyebath: use sequestering agent/dyebath conditioner and Tata salt and run for 15 min.
Dissolve HE dyes outside and filter and add half quantity through addition tank 3. Run for 10 min at 50°C.
Then add half quantity of dyes at 60°C and run for 5 min.
At 60°C add Tata salt (as per depth of shade) in three to four installments through stock tank.
Raise the temperature to 85°C at 1°C/min and run for 30 min.
Then cool to 70°C and add soda ash (as per depth of shade) in two installments and run for 30 min at 85°C.
Cool to 60°C and drain.
Washing with plain water and drain.
Hot wash at 95°C and drain.
Then acid wash and drain.
Soaping at 95°C and drain.
Hotwash at 95°C and drain.
Cold wash with plain water.
Dye fixing at 40°C with acetic acid and drain.
Washing with plain water.
Finish with cationic softener / antistatic finish at 50°C and drain.

Total time required for the process varies from 6 to 7 hr per batch. The dyed fiber goes to hydroextraction. Wet fiber opener is avoided as chance of fiber damage is there. Then it goes to steam dryer/RF dryer. The fiber is dried and goes to spinning with 12–13% moisture. In shades like royal blue, turquoise blue and any bright shades Glauber’s salt should be used. A suitable levelling agent would ensure greater uniformity. In many dyehouses, bifunctional reactive dyes are used to dye viscose fiber at 60°C and better levelling.

Viscose Fabric Dyeing:
Actually viscose dyeing process is same as cotton spandex fabric. Viscose needs reactive dyes, just like cotton does. Process sequence of viscose fabric dyeing is given below.

Process Flow Chart of Viscose Fabric Dyeing:

Water filling in dyeing machine
↓
Fabric loading
↓
Hot Wash, 80^oC, 10 min
↓
Drain
↓
Water filling
↓
Chemical Auxilaries
↓
pH check (6.5-7.5)
↓
Reactive dye (dosing 30 min) (Run 15 min, Temp 50^oC)
↓
Salt dosing 2 step, 60^oC (Run 15+15 min)
↓
Soda 60 min dosing (Run 60 min)
↓
Shade check
↓
Cooling
↓
Drain
↓
Acetic Acid (Neutralization)
↓
Drain
↓
Soaping
↓
Drain
↓
Hot Wash (2 or 3 times)
↓
Cool wash
↓
Shade check
↓
Fabric unload

Actually dyeing performance depends on proper procedure and qualified dyes, chemicals and auxiliaries. Viscose fabric has a luster property; also it stays bright and colorful throughout the life of the products made with it. So, if to work with various kind of bold and colorfast fabric then you can choose viscose.

References:

Textile dyeing by N. N. Mahapatra
Physico-chemical Aspects of Textile Coloration by Stephen M. Burkinshaw
Textile Chemistry by Thomas Bechtold, Tung Pham

You may also like:

Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.