Notes on Reactive Dye

Last updated on August 13th, 2023 at 01:12 am

Reactive dyes are special coloring agents that textile industries use for dyeing fibre, yarn, fabrics, and garments. These dyes are popular in the textile industry because they make colors that fix well and don’t fade quickly. Unlike other dyes that fix on the fabric’s surface, reactive dyes combine with the fabric’s molecules through a chemical reaction. It makes the colors they create stay firm even after you wash them many times.

Stripping Process of Reactive Dyed Fabric

Stripping

Stripping becomes necessary when uneven dyeing occurs. By stripping azo groups (- N = N -) of the dye is removed. There are two methods of stripping such as:

Partial stripping method.
Full stripping method.

Partial Stripping Method

Partial stripping is obtained by treating the dyed fabric with dilute acetic acid or formic acid. The recommended concentration is between 5 to 10 ml glacial acid or 2.5 – 10 parts of formic acid (85%) per 1000 parts of water.
Recipe:

Glacial acetic acid:	5 – 10 gm/L
Time:	20 – 30 mins.
Temperature:	85ᵒC – 90ᵒC

Full Stripping

For complete stripping, the goods are firstly treated with Sodium hydrosulphite (Na₂S₂O₄) at boil. Then washed off and bleached at ordinary atmospheric temperature in liquor containing 1 part per 100 of commercial sodium hypochlorite.

Recipe:

Na₂S₂O₄:	5 gm/L
Na₂CO₃:	2 gm/L
Boiling:	20 – 30 mins.
Time:	20 – 30 mins.
Temperature:	Boiling

Functions of Different Chemicals used in Reactive Dye

Salt

Salt acts as an electrolytic material. It helps to absorb the dye particle.

Soda Ash

Soda Ash acts as an alkali medium and it also acts as a fixing agent.

Urea

It will give deeper shade in dyeing bath. A few amount of urea will give light shade. To soluble the dye stuff properly urea is used.

Sodium Alginate

It is a thickening agent. It is collected from sea – weeds. It helps to bind the dye materials in their position. It will also act as a fixing agent

Why Soaping is Necessary After Dyeing

We use different types of dyes in the dye bath. Maximum cases dye stuffs are sedimented on the bottom of the dye bath and deposited on the textile material we use soaping method to increase the brightness and to remove the floated color we use soaping process.

Salt & soda ash used in Reactive Dye for Shades

Shade	Salt (g/l)	Soda Ash (g/l)
Light Shade	37	12
Medium Shade	60	15
Dark Shade	80	20

Application of Reactive Dyes on Cotton Goods

Now a day reactive dyes are popularly used for cotton goods. Generally 4 types of cotton goods are used to dye with the reactive dye:

Loose fiber form.
Yarn form.
Knit goods
Woven fabric.

Jigger dyeing m/c (Woven fabric), Winch dyeing m/c (Knitted fabric) and Jet dyeing m/c (Knitted + Woven)

Test Method of Reactive Dye

Recipe

H₂SO₄:	1 cc/litre of water
Na₂S₂O₄:	2 cc/litre of water
M : L	1:20
Temperature:	Up to boiling
Time:	30 mins.

When a sample of reactive dyed fabric is treated in a test tube containing H₂SO₄ of 1 cc per 1 litre water, it results bleaching of reactive color from the dyed fabrics. It is one of the identification tests of reactive color.

The reactive color remains fixed on the textile material though it is treated or boiled with pyridine or chloroform. On the other hand, textile material dyed with direct, azoic etc. dye stuffs and treated with above chemicals then color will come out easily. It is one of the identification tests of reactive color.

The second one is one of the most efficient test methods of reactive dye.

Classification of Reactive Dye with Example

On the basis of reactive group: Two types;

Halogen added group (Cl₂, F₂, Br₂,I₂), Example: Pyrimidine.
Vinyl added group (– CH = CH₂) (– D – SO₂ – NH – CH = CH₂) [– CH = CH₂……….Reactive group], Example: Levafix.

On the basis of reactivity: Three types;

High reactivity. Ex. Procion – E. {Medium alkali (NaHCO₃) used}.
Moderate reactivity. Ex. Livafix – E. {Medium alkali (Na₂CO₃) used}
Low reactivity. Ex. Premazine: {Strong alkali (NaOH) used}.

On the basis of use: Two types;

Cold brand reactive dyes (High reactivity): 40ᵒC – 50ᵒC
Hot brand reactive dyes (Low reactivity): 90ᵒC – 95ᵒC

Use of Hot brand is maximum in our country, Cold brand is used for batik, tie dye etc.

Reactive Dyeing Methods

Batch dyeing method (Discontinuous method):

Hot brand Dye.
Cold brand Dye.

Continuous method:

Pad system method.
Pad thermo fixation method.

Semi – continuous method:

Pad roll method
Pad – jigger method.

Description of Cold Brand Dyeing with Reactive Dye

Recipe

Dye stuff:	3% (According to the wt of mlts)
Soda Ash:	15 gm/L
H₂O:	10 times
Temperature:	40ᵒC
Salt:	60 gm/L
Time:	1 Hour

Dyeing Scheme

Working Procedure

At first solubilize the dye stuff with a little amount of cold water. Take required water to the dye bath. Dye liquor and salt is given to the dye bath and stirred thoroughly. Then the textile material is taken to the dye bath and dyed for 20 – 30 mins. After dyeing the material is rinsed with cold water. Then treated with 20% soap and 1% soda solution in a bath for 30 minutes, then the material is washed and dried.

Cotton Dyeing with Reactive Dyes (Hot Brand)

Recipe

Dye stuff:	1 – 3% (According to the wt of mtls)
Salt:	30 – 60 gm/L
Soda Ash (Na₂CO₃):	15gm/L
Water:	20 times
Temperature:	90ᵒC – 100ᵒC
Time:	1.5 – 2 Hour

Working Procedure

When soda ash is used as fixing agent the temperature should not be below 80ᵒC. In case of Turquoise blue the temperature should be raised to 90ᵒC – 95ᵒC while fixing. After dyeing, the material lifted from the bath, squeezed, rinsed well in water, soaped at boiling temperature for 30 minutes, then rinse and dried.

Shade	Salt Addition
Light Shade	40 – 50 gm/L
Medium Shade	60 – 75 gm/L
Dark Shade	80 – 100 gm/L

Notes:

Salt is used for sustainly of color on fiber.
Soda Ash is used only for permanency of color.

Pad – Steam method of Reactive Dye

Recipe (For medium shade)

Dye stuff:	10 – 20 gm/L
Soda Ash:	5 – 10 gm/L
Common salt:	60 – 80 gm/L
Urea:	150 gm/L
Sodium Alginate:	Little amount

Sequence of Operation

Working Procedure

In this method fabric is dyed in large scale. Two bowls are used here. In the first, Padding is done on the fabric with urea & dye solution at 60ᵒC – 80ᵒC temperature. Urea is used to dissolve the dye stuff and to penetrate into the fabric. Na – Alginate is used as a migration inhibitor (বাধা দান কারি). Then the fabric is passed through the drying chamber & again padding is done with NaOH at 60ᵒC temperature. Then steaming is done at 100ᵒC – 102ᵒC for 30 – 60 seconds. Then after rinsing & soaping, fabric is washed & dried.

Pad Thermo – Fixation Method of Reactive Dye

Recipe

Dye stuff:	2% (According to the wt of mtl)
Soda Ash:	1%
Salt:	8%
Urea:	15%
Sodium Alginate:	Little amount

Working Procedure

In this method padding bath continuously dye, alkali, salt, urea and Na – Alginate liquor. Padding is done in the bath at room temperature. Then fabric is passed through drying chamber. Then thermo – fixation is done at 160ᵒC for 5 minutes. Finally rinsing, soaping and again rinsing is done. This method is suitable for moderate reactive dye.

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