Viscose Rayon

Viscose is a man made, natural polymer, cellulosic or regenerated cellulose filament or staple fiber. According to U.S. Federal Trade Commission “Rayon is a manufactured fiber composed of regenerated cellulose in which substituent’s have replaced not more than 15% of the hydrogen’s of the hydroxyl groups”.
Types of Regenerated cellulose fiber: Regenerated cellulose fibers are three types. They are:
  1. Viscose.
  2. Cuprammonium/ Cupro.
  3. Polynosic/Modal.
Chemical reaction for viscose rayon production: Regeneration reaction:
  1. The cellulose is treated with 17.5% solution of NaOH which converts into soda-cellulose.
Cell-OH+ NaOH → Cell-OHa+ H2O
 Cellulose                    Soad-cellulose
  1. The soda cellulose reacts with carbon disulphide to form sodium cellulose xanthate.
Cell-ONa+ CS2 → Cell-O-CS-SNa
  1. Then it is dissolved in a dilute solution of caustic soda. It is extruded into H2SO4 which regenerates the cellulose. Now in the form of long filaments.
Cell-O-CS-SNa+ H2SO4 → Cell-OH+ Na2SO4
                                                Regenerated cellulose
Flow chart of viscose rayon:
Cellulose pulp
Steeped in warm caustic soda for an hour
Pressed to remove excess solution
Powdery Crumbs
Aged for up to a day (formation of soda cellulose)
Mixed with carbon disulphide (formation of sodium cellulose xanthade)
Mix into a dilute caustic soda solution (to give a viscose solution)
Ripening for up to a day (Regenerated cellulose)
Physical properties of Viscose Rayon:
  1. Moisture absorption: Viscose rayon absorbs moisture more than cotton. Viscose rayon moisture content 13% at 65% relative humidity.
  2. Tensile strength: Less tensile strength than cotton in wet condition.
  3. Elasticity: Less elasticity than cotton, about 2-3% less.
  4. Abrasion resistance: Low.
  5. Flammability: Like as cotton.
  6. Melting temp: Do not decompose at 176ºC to 204ºC.
Chemical properties of viscose rayon:
  1. Effect of acid: Acid like H2SO4 or HCl, break down the macromolecules of viscose and produce hydro-cellulose. Dilute acid for short time do not attack.
  2. Effect of alkali: Concentrated alkali causes swelling and reduces strength. But week alkali does not damage.
  3. Effect of bleaching: Viscose can withstand both oxidizing and reducing bleaches.
  4. Biological agent: mildew, bacteria etc affect the color, strength and luster of rayon.
  5. Dye affinity: Better affinity for dyes than cotton.
  6. Flammability: Burns rapidly.
End uses of viscose rayon:
  1. It is used in making umbrella cloths and protective cloths.
  2. It is used as sewing embroidery threads.
  3. Viscose + cotton, this blend is used for reducing cost.
  4. Viscose + polyester, this blend is used for comfort strength and absorbency.
  5. Uses in curtains, cushions, beach and sports wear.
  6. Fire fabrics and evening gowns.

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