Dyeing of Cotton / Polyester Blended Knit Fabric with Reactive / Disperse Dyes Using Jet Dyeing

Dyeing of Cotton / Polyester Blended Knit Fabric with Reactive / Disperse Dyes Using Jet Dyeing Machine 
Raihan Shobhan Rana
B.Sc in Textile Engineering,
Textile Engineer,
How Are You Textile Industry Ltd
Email: ranatex1@gmail.com


Pretreatment:
Generally, cotton fiber is slightly cream color & polyester fiber is almost white. Thus grey fabric (CVC/TC) need to be bleach to remove natural color of cotton and get an optimum degree of whitening. Hydrogen peroxide will bleach the cotton fiber. Scouring agent is used to remove oil, wax and any other impurities of cotton fiber. This also used as surface active agent which works between fabric-liquor interface & reduce the surface tension of liquor. Emulsify oil removing agent is used to remove knitting oil & as well as wetting agent. Combined scouring and bleaching is done to save time, utilities & chemical. 
 
Recipe:
  • Hydrogen peroxide (H2O2) 35% = 5 g/L
  • Scouring Agent (Surfactants) = 3 g/L
  • Emulsify Oil Removing Agent/Wetting Agent = 0.5 g/L
  • Temperature = 98°C
  • Time = 30 min
  • M: L = 1:10
Fabric for Example: 80:20 CVC French Terry [30s/Cotton + 75D/36F polyester + 12/s (80:20) CVC] 
 
Procedure:
  1. Add all substrate at room temperature and raise the temperature to 98°C@3°c/min.
  2. Run the bath for 30min at 98°C.
  3. After 30min drop the temperature around 40°C (to avoid crease) and drain off the liquor.
  4. Rinse twice with hot (around 60°C) & cold water. Wash off very properly to remove residual peroxide remain in the fiber.
  5. Neutralize with acetic acid = 0.5 g/L at room temperature for 10min. (M: L=1:10)
Note: Even without peroxide killer, the overall dyeing is very stable though it is recommended to kill the very residual peroxide in the fabric.
Process curve (Combined scouring and bleaching)
Fig: Process curve (Combined scouring and bleaching)
Condition of fabric after scouring and bleaching
Fig: Condition of fabric after scouring and bleaching
Two bath Two Stages Dyeing

Stage 1: Polyester part dyeing with Disperse Dyes (High Temp, High Pressure)
The polyester part should be dyed at first because of high temperature dyeing and reduction clearing process. Otherwise, Sodium Hydro Sulfite, which used in reduction clearing will remove the colorants from cotton. The amount of leveling agent & dispersing agent should be consider depending on the percentage of polyester i.e. less percent of polyester need less amount of dispersing & leveling agent. For 80:20cvc only dispersing agent is enough for even dyeing. 
 
Recipe:
  • Disperse Yellow 4GSL = 0.035%
  • Disperse Yellow Brown XFN = 0.09%
  • Dianix Blue Ace = 0.013%
  • Acetic Acid = 0.2 g/L (pH=4.4-4.6)
  • Dispersing Agent = 0.5 g/L
  • Bath softener = 3g/L
  • Anionic softener = 3 g/L
  • Temperature = 130°C
  • Time = 35min
  • M: L= 1:10
Procedure:
  1. Add all auxiliaries & dyes at room temperature & run machine about 15min. Meanwhile check the pH of liquor & make sure the range of pH is 4.4 to 4.6. If need add extra acetic acid to acquire the given pH range.
  2. Set the bath at 130°C@3°C / min and run for 35min at 130°C temperature.
  3. Lower down the bath temperature to 80°C@3°C/min and cut two samples from two different piece of fabric. If shade is ok, then go for reduction clearing.
Carbonizing:
To check the shade of polyester part of the fabric, cotton part should be removed by means of carbonizing with sulfuric acid (generally).
  • Add 50ml acid with 50ml water very slowly & carefully and stir. (Approximate size of each sample should be 10square cm)
  • Drop the samples in the solution and stir until removal of cotton part.
  • Wash with soap properly.
  • Neutralize with ammonia and wash again.
Reduction Clearing:
Reduction clearing is necessary to remove all unfixed dyes from the fabric surface & get optimum color fastness properties. Reduction clearing should be carried on with the dye liquor present in the dye bath.
 
Recipe:
  • Sodium hydro sulfite = 2g/L
  • Caustic Soda = 2g/L
  • Temperature = 80°C
  • Time = 20min
  • M: L= 1:10
Procedure:
  1. First add caustic soda at 80°C & run for 5min.
  2. Add Sodium Hydro Sulfite & set the bath at 80°C
  3. Run 20min at 80°C
  4. Gradually lower down the bath to 40°C (to avoid crease) & Drain off the liquor & rinse with cold water successively.
  5. Neutralize with acetic acid = 0.5 g/L at room temperature for 10min. (M: L=1:10) 
Fabric state before and after carbonizing and dyeing
Fig: Fabric state before and after carbonizing and dyeing
Polyester part dyeing with disperse dyes
Fig: Process curve (Polyester part dyeing with disperse dyes)
Stage 2: Cotton part dyeing with reactive dyes
Partial dye solution and Soda are added to dye bath to avoid uneven dyeing for 80:20/ 60:40 CVC. But for fabric with less cotton say 80:20/60:40 T/C, dye solution and soda could add in short time without dosing. For T/C fabric i.e. less percent of cotton, leveling agent is not necessary at all. The amount of salt and soda varies according to color percentage as per vendor recommendation. 
 
Recipe:
  • Reactive Yellow 3RS= 0.55
  • Reactive Red 3BS= 0.055
  • Reactive Blue BRF= 0.035
  • Glauber’s Salt (Na2SO4) = 50 g/L [As per vendor recommendation]
  • Soda (Na3PO4) = 3.0 g/L [As per vendor recommendation]
  • Leveling Agent= 1.0 g/L
  • Bath softener for cotton= 3g/L
  • Anionic softener = 3 g/L
  • Temperature = 60°C
  • Time = 40min [As per vendor recommendation]
  • M: L= 1:10
Procedure:
  1. At room temperature add leveling agent, softener & 1/10 of total dye solution for 30min.
  2. At room temperature add 3/10 of total dye solution for 30min.
  3. At room temperature add 6/10 of total dye solution for 30min.
  4. At room temperature add salt for 30min & raise the temperature to 60°C @1°C/min.
  5. At 60°C add 1/10 of total soda for 30min.
  6. At 60°C add 3/10 of total soda for 30min.
  7. At 60°C add 6/10 of total soda for 30min.
  8. Run the bath for 40min at 60°C. (according to color percentage & vendor recommendation)
  9. Lower down the bath to 40°C@3°C/min and drain off the liquor.
  10. Rinse twice with hot (around 50-60°C) & cold water.(To remove salt & soda)
  11. Soap Wash (Optional)
  12. Treat with Acetic Acid =0.2g/L (To neutralize alkalis), Bath softener =5g/L, Anionic softener = 5 g/L, Smoothing Agent = 5g/L at 50°C for 20min. (For smooth & softer hand feel properties).
Cotton part dyeing curve
Fig: Process curve (Cotton part dyeing)
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