counter easy hitFabric dyeing process with Reactive Dye -3 (Last part)

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Fabric dyeing process with Reactive Dye -3 (Last part)

Fabric dyeing/coloration process with ” Reactive Dye “

Criteria of cellulose for attaching Reactive dye:

Chemical structure of cellulose molecule:

Glucose unit
  • Each glucose unit contains one primary hydroxyl group (-CH2OH) and two secondary hydroxyl groups (-CHOH)
  • Primary hydroxyl group (-CH2OH) at C6 position is more reactive than the secondary hydroxyl groups at Cand Cposition
  • C2 Hydroxyl group is supposed to be acidic than C3  hydroxyl group under suitable alkaline condition and more reactive.
  • The hemiacetal group at C1 position is the more active while the additional hydroxyl group of C4 position is least reactive.
  • The reaction between reactive group and cellulose takes place predominantly with primary hydroxyl group
  • In case of monochlorotriazinyl dyes , the reaction ratio of -CH2OH & -CHOH is 15:!
  • In case of dichlorotriazinyl dyes, the reaction Ration of -CH2OH & -CHOH 3:1 to 7:1
  • Secondary hydroxyl group is the least reactive while primary one is the most reactive

Process applied for dyeing

Dyeing can be carried out by

1) Batch dyeing processes

2) Continuous dyeing process

Batch dyeing processes keeping in mind the following points:

  • The pH of the dye bath
  • The temperature of the dyeing
  • The concentration of the electrolyte
  • The time of dyeing
  • The liquor ratio

Continuous dyeing processes:

Reaction of dye with the fibrein the presence of water and alkali in a short time at elevated temperature takes place.

The rate is further increased if the pH is high.

This is the basis of continuous dyeing process to be possibly used with reactive dyes

Depending on the reactivity of the dye two processes are possible single padding and double padding

Differen methods of reactive dye application:

1) Pad-batch method

Pad batch processes are of two types-

  1. a) Pad (alkali) batch (Cold) process.
  2. b) Pad (alkali) Batch (Warm or hot) process.

2) Pad dry method

3) Pad steam method

1)Pad-batch method:

  1. a) Pad (alkali)- batch (cold) process.

Steps:

1) The fabric is first padded in a padding mangle with reactive dye in presence of an alkali

2) The padded fabric is rolled in a batch and the batches are wrapped by polyethylene sheets and stored in wet condition for 1-24 hours at 200-300oC in a room.

3) During the storage period, the rolls may be kept slowly rotating to prevent seepage of the dye liquor.

4)After storing time is finished fabric is washed in a rope washing machine to remove the unfixed dye from fabric surface

  1. b) Pad batch (hot) process:

Steps:

1) The fabric is first padded in a padding mangle with reactive dye in presence of an alkali

2) The fabric is then passed in between infrared heater to preheat the padded fabric to 500 to 900oC

3) The fabric is then batched on a large diameter roller in a hot chamber. The batching is done under controlled conditions of temperature and humidity for a sufficient time to ensure diffusion and fixatin of the dye in the fibre.During this period the batch is kept slowly rotating to avoid the seepage of dye liquor.

4) The cloth is then washed in a rope washing machine to remove the unfixed dyes.

Pad dry method:

Steps:

1) Fabric is first padded in a padder with reactive dye in presence of an alkali

2) Padded fabric is then passed through a squeezing roller into a dryer. As a dyer cylinder, stenterete may be used. During drying due to higher temperature fixation of dye in fibre increases and at the same time water is removed by evaporation

3) After drying fabric is washed in a washing machine to remove unfixed dye

3)Pad steam method:

Steps:

1) Fabric is firs padded in a padder with the dye

2) It is then passed through between two squeezing roller in a dryer. Drying should be done slowly, otherwise precipitation of dye due to quick removal of water may take place leading to lower color value

3) After coming out from dryer fabric is padded in a padder containing salt and alkali. Due to salt exhaustion of dye takes place and due to alkali fixation occurs.

4) Fabric then passed through a steamer where it is kept for 15-19 second. Due to high temperature here fixation rate increases.

5) In this step fabric is washed in a washing machine to remove the unfixed dye

How much reactive dyes are fixed

  • Mono reactive dye- Dye fixation is 75% and dye hydrolysis is 25%
  • CIBACRON DYES-Pad batch 90-99%
  • Pad dry-pad steam 85-95%
  • Pad thermofix 82-92%
  • Pad humidity fix 82-92%
  • Pad steam 70-90%

How important is affinity factor

If the reactive dye chosen has low/medium affinity, it will show the following:

1) Good penetration and levelling

2) Excellent wash off and wet fastness properties

3) Low risk of tailing

Cotton dyeing with Reactive Dyes

Cotton fabric after pre-treatments e.gdesizing, scouring & bleaching can be dyed using the following recipe:

Reactive dyes—————————–x%

Sequestering agent——————— 0.5 G/L

Wetting agent—————————- 0.1- 0.5 G/L

Anti creasing agent——————— 0.5-2. G/L

Salt—————————————— 10-80 G/L

Soda—————————————– 2-20 G/L

Temperature—————————— 60-80 degree

Dyeing time——————————–60 minute

When the cotton fabric dyeing is complete, the dye liquor is drain off. The fabric is washed with hot water at 40 degree & then with cold water.Again wash the dyed fabric with 1-3 G/L soap or detergent at 60 degree-80 degree for  at least 10 minutes. Then drain off washing liquor. Again wash the dyed fabric with hat water & then with cold water. Finally, the dyed fabrics is taken out from the machine, hydroextuchtthe fabric and dry the fabric passing through any other drying machine.

Stripping:

Stripping becomes necessary when uneven dyeing occurs. By stripping azo groups(-N=N-) from the dye is removed

  1. i) Partioal stripping method:

Partial stripping is obtained by treating the dyed with dilute acetic acid or formic acid . The recommendes is between 2-5 gm/L acetic acid or formic acid.

Recipe:

Acetic acid= 2-5 gm/L

M:L ration =1:10

Temperature= 70-100C

Time= Until the desired shade is obtained

ii) Full stripping:

For complete stripping , the goods are treated with Na2S2O2 & NaOH at boil

Recipe

Hydrose = 2-4 gm/L

NaOH= 4 gm/L

M:L ratio = 1:10

Temperature=90-100o

Time = 30 minute

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To read the first,second part click below:

Fabric dyeing/coloration process with “Reactive Dye” -1

Fabric dyeing/coloration process with Reactive Dye -2

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