VISCOSE NEEDS CARE IN PRETREATMENT

-Due to alkali & temperature sentivity of Viscose Rayon; special pretreatment technogies arerequired.

-Peroxide/Soda pretreatment is no longer enough for high whiteness requirements 

Much has been written about Viscose/Rayon and the special processing conditions that are required to generate new and novel aesthetic character on fabrics produced from this fiber.  Due to its nice drape and bright colors, consumption of this fiber is increasing tremendousl However, very little has been written about the fundemental dyeing behaviour of viscose and how it contrasts with native mature fibre-cotton Generally viscose is produced from cotton and cellulose rest. Cellulose is reacted with sodium hydoxide solution to produce alkaline cellulose, following the pre-maturation process (degradation of cellulose molecule to smaller units) using carbon disulphide, is converted xanthogate – into syrup form. This syrup form is processed thru nozzles to produce viscose filament and carbon disulphide is recirculated. In poor quality viscose productions, CS2 traces remain in the fiber and may create unlevelling problem during reactive dyeing.

Other drawbacks of of viscose fiber concerning the dye masters.

-         Low wet tensile strength,

-         Sensitive to creasing,

-         High uptake dyes,

-         Poor migration of dyes..

Eksoy, as a major chemical and dye supplier for viscose dyers   , advises following hints for trouble free dyeing of viscose and its spandex blends.

1.            Higher liquor ratio, 1:10 – 1:12

2.            Efficient lubricating agent.

EXOLUBE NC, is oil – ester based effective lubricating and levelling agent. Recomm amount

         EXOLUBE NC                       1g/lt

3.      Oxidative bleaching to eliminate reductive sulphur before dyeing.

Conventional method of viscose bleaching was Peroxide / Soda / 95⁰C / 45 min. Viscose and Spandex is damaged, weakend and sometimes pin-holed at this severe processing condination.

Eksoy developed VISCO-COLOR®   to treat viscose at mild temp. range low pH.

               VISCO-COLOR®                 3 %

               E-WET SVS                       0,5 %

               EXOLUBE NC                    0,5-1,0 %

               Temp.                               60-70⁰C

Time                                 45 min.

Fabric is hot washed and passed to dyeing.

Below , Viscolor & clasical peroxide&soda method is compare on same viscose&spandex fabric.

4.      High grade full-bleaching cannot be reached by conventional Peroxide & Soda  at 95⁰C . At low pH, Peroxide can not be activated fully.   

Eksoy designed VISCOBLEACH® to overcome this disadventage to approach high degree whiteness index. 

               VISCOBLEACH®                 3g %

               Peroxide, %50                     7 %

               E-WET SVS                         0,5 %

               EXOLUBE NC                      0,5–1,0 %

               Temp.                                 95⁰C

Time                                   60-75 min.

Below,Viscobleach & clasical Peroxide&Soda method is compared .After bleachingBoth fabric samples are treated with 0.5% OPTIC CO (OBA)

DYEING

5.      Instead of sodium chloride, sodium sulphate is preferred.

6.      Amount of sulphate is 30 per cent reduced with respect to catalog values, given for cotton dyeing.

7.      Due to poor migration property, either 70⁰C isothermal or 80/60⁰C S cooling system preferred.

Conclusion

If Viscose and Viscose/Lycra blended fabrics treated with VISCO-COLOR® or VISCOBLEACH/Peroxide  at low temp. and pH, even poorest quality of brands can be dyed as trouble–free and spandex fibers are not damaged.