Introduction

Fabric dyeing usually requires three basic dyes in a mixture to achieve the desired hue and shade. Dyes with similar reactive groups and same exhaustion properties will be said to be compatible with each other and are ideal for use in such mixtures. Selecting compatible dyes is a part of ensuring an optimum dyeing recipe which will most efficiently utilize the dye, produce optimal dyeing results and will reduce the number of chemicals that enter the wastewater.[1] This research has been taken to describe the parameters like M:L, temperature, time, costing, scouring, bleaching, enzyme treatment, recipe, dyes, auxiliaries and two types of process etc. Reactive dye has high affinity for knit fabric because of its very good fastness properties.

General structure of reactive dye: D-B-Y-X Where,

D= Chromophore of dye part
B= Bridge (such as, -NH-, -NR- group
Y= Reactive group bearing parts
X= Reactive atom or group

The reactions are as follows:

(i) Substitution reaction

(a) In case of cellulose fibers:

D-R-Cl + cell-OH  NaoH   D-R-O-cell+NaCl+H2O

(b) In case of protein fibers:

D-R-CI+ NH2- Protein D-R-NH-P+NaCI+ H2O

(ii) Addition reaction

(a) In case of cellulose fibers:

D-F-CH=CH2 + HO-cel  D-F-CH2-CH2-O-cell

(b) In case of protein fibers:

D-F-CH= CH2 + NH2- Protein    D-F- CH2-CH2-NH-Protein

Chemical and dyes

The author some of the following chemicals.

1. Sandoclean PCLF- Detergent.
2. Ck- wetting agent.
3. Sirrix 2UD- Sequestering agent.
4. Centafoam SC- Anti-foaming agent.
5. H2O2- Hydrogen Per-oxide.
6. Na2CO3/NaOH.
7. Caustic soda flax.
8. Imacol C2G- Anti-creasing agent.
9. SOF- Stabilizer.
10. Centalizer ASB - Per-oxide Killer.
11. Strong acid.
12. Bio-Polish 80L- Enzyme.
13. Drimazin E2R - Leveling agent.
14. Salt & Soda.
15. Sandoper Sp- Soaping agent.
16. Sandofix EC- Fixing agent.
17. Softener- Alkamine CWS.

Dyes: Color: Pink

• Dri. Yellow K2R=0.0012%
• Dri. Red K8B=0.0097%
• 20/5 600C.
• Salt: Soda: 20:5;
• Temperature: 600C.
• Shade %: 0.0109%.

Process parameters

The required knit fabric was dyed in Winch dyeing machine from Fongs National Engineering. Dyeing parameters plays a vital role during dyeing. Temperature, Liquor ratio, Salt and Soda concentration, fabric weight, etc is very important stipulations during dyeing process.

1. Machine weight:750 kg (250kg/nozzle)
2. Fabric weight: 600 kg (80%)
3. Fabric type: 1*1 Rib
4. M:L: 1:8; 1:7;
5. Dyeing process: Migration; Isothermal.
6. Color: Pink.
7. Scouring temperature: 980C
8. Bleaching temperature: 800C
9. Scouring acid temperature: 600C
10. Enzyme temperature: 550C to 700C
11. Leveling temperature: 600C
12. Dyeing temperature: Varying due to process
13. Salt : Soda : 20:5
14. Softener.

Process study

Exhaustion & Fixation study

The  dye-bath  exhaustion  and  fixation was studied  by  known  methods by collecting  the samples  of exhausted  liquor  at  various intervals  and  studying  the   absorbancy  by diluting  the  exhausted   liquor  up  to  various  folds. [2]

Solubility

Due  to  the  presence  of  the  OH  and  NH  functional  group  in  the  dye  molecule,  a  dissociation  resulted  in  a  higher  solubility  during  the  dyeing  process  at  low liquor  ratio. Also,  the  presence  of  the  sulfonic  chromophores  (two to  three)  and  the  novel  sulphatoethyl  sulphone  groups  promoted  the  solubility  of  the  new bifunctional (MCT/SES) dyes. [2]

pH value of dye bath

The  pH  of  dye bath  during  exhaust  dyeing  method  was  widely  taken  into  consideration, where, we  first  used  the  neutral  pH  and  gradually  increased  the alkalis  by  dosing  the Na2CO3/NaOH  to  a  pH  of  11.5  to  differentiate  the  probable exhaustion  in  both  cases. Both SES  and  MCT  groups  functioned  as  the  reactive  sites. However,  we  recommend  a  dyeing  process  for  this  type  of  dye  exhaust  dyeing  method  set  at  60°C  with  a  control  dye bath  pH.[2]

Color measurements

The  (%R)  percent  reflectance  of  the  dyed  material  was  measured  at  different  wavelengths  in  the  visible  region  (400- 700 nm)  using  a  ACS-600 color  control  system. [2]

Shade evaluation

The  hue  over  the  knitted  cotton  fabric  as  checked  by  matching  it  with  standard shade  cards. The   shade appeared at a somewhat higher wavelength of  the  dye. [2]

Substantivity

The  dyes  showed  medium-to-good substantivity  which  can  be  detected  by   the exhaustion  and  fixation  study. This  can  be  due  also  to  the  presence  of  the  two  pioneer  groups  as  the  reactive  sites  involved  in  the  dye  substrate. The  substantivity  of  the  hydrolyzed  byproduct  can  be  readily  detected  from  the amount  of  unfixed  dye  and  can  easily  be  removed  after  three  or  four  washes  at  different  temperatures. [2]

Experimental  Procedure

Knit fabric dyeing procedure  consists  of  five  steps; scouring, bleaching, enzyme treatment, dyeing and softener treatment.  These  five  steps  are  necessary  for  completing  the  whole  dyeing  process.  Fongs  dyeing  machine is used for this experiment and  subsequent steps are given as under.

Scouring

In this experiment, 1*1  rib  fabric  of  weight 600 kg  (Grey  fabric) is used, with NOF, 2UD, PCLF, FFC and Caustic chemical  used for scouring  process. The  required  amount  of  chemical  used  for  this  process  are as follows:

1. NOF: 0.5 g/l
2. 2UD:   0.5 g/l
3. PCLF :  0.6 g/l
4. 2UD:  0.3 g/l
5. FFC:  .05 g/l
6.  Caustic:  2.5 g/l
7. Process  temperature:  700C.

Both the processes given as above are satisfactory, but first  process  is  preferable  because  in  this  process,  fabrics  are  better cleaned  and  absorbency  power  will  be  increased. The first process also removes  the  natural  impurities,  dirt  or  grease  from  cloth  more efficiently.

Bleaching

Normally scouring and bleaching is done simultaneously in the dyeing machine. Bleaching creates a permanent whiteness in the fabric which is helpful for dyeing knit fabrics. Acid and peroxide killer are added in the bath for this light color dyeing. Strong acid is more beneficial than Acetic acid because strong acid controls the PH values more strictly. The chemicals used for this process:

1. H2O2: 4.0 g/l
2. Centalizer ASB (Per-oxide destroyer): 0.6 g/l
3. Stabilizer SOF: 0.25 g/l
4. Strong acid: 0.6 g/l

Enzyme treatment

Enzyme removes the hairiness from the fabric surface which is helpful for fabric dyeing. Normally enzyme percentage varies from 0.9-1.0 and following two processes are applied. The using chemicals for this process are as follows:

1. Bio-Polish 80L : 0.9 % (on the weight of the fabric)
2. Acetic acid: 0.6 g/l.
3. PH: 4.5 – 5.5

First process consists of two steps. At temperature 550C, 0.6% enzyme concentration is used in the machine, with a runtime of 30 minutes. The fabric sample is then take for hairiness checking, and then 0.3% enzyme is added with a running time of 20 minutes, with another fabric sample to check the hairiness. In order to ensure better fabric performance the temperature is increased upto 700C, with further 10 minutes runtime in the bath.

The second process entails a single step, at bath temperature of 550C, with 0.9% enzyme ratio, with running time of one hour. The first process is comparatively better, because in this process hairiness of fibers is smoothly removed which is helpful for the next dyeing process.

Method analysis

For this experiment, two methods are being used, one is migration process and another is isothermal process.

Process curve (Migration)

In migration process, color (300C), salt (600C), then runtime 30 minutes at 800C, soda (600C), then again temperature rises up to 800C, to be completed in the dye bath.

Process curve (Isothermal)

At first the dye bath is prepared by adding chemicals and auxiliaries, with temperature raised to 600C. The dyestuff are added slowly into a bath over a period of 20 mins. After the addition of dyestuff, the required amount of salt is added in two portions or in some case slowly over the duration of 20 mins. Afterwards the soda ash is added to the bath in two portions or over a period of 20 mins.

Softener

After matching the shade, the CWS softener is added and for pink color dyeing.

Results and discussion

In isothermal process dyeing process has been completed at 600C (for light color dyeing). In migration process, dyeing is being completed at 600C-800C-600C process. In migration process, the value added time remains 90 mins, whereas at isothermal process this time remains 60 mins that’s why total time saving of 30 mins is observed for one batch. Fixation and exhaustion has been completed at same temperature during isothermal process for light color dyeing. In migration process, Fixation and exhaustion has been completed at various temperatures, so that chemical and dyes consumption and energy expenditure also increases the cost of production. Therefore, it can be concluded from this experiment that for light color dyeing, isothermal process is much better alternative to migration dyeing process.

References
[1] Razia Sultana and M. Zulhash Uddin “Compatibility Testing of Reactive dyes”Journal of Mechanical Engineering, Vol. Me38, Dec. 2007. transaction of the Mech. Eng. Div., The Institution of Engineers, Bangladesh.
[2] M.M. Dalal, K.R. Desai “Dyeing effects of Bi-functional Reactive Dyes on Knitted Cotton Fabrics”.