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viscose rayon

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the most common manufactured fibre

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viscose rayon

  1. 1. Viscose Rayon
  2. 2. Rayons According to FTC (Federal trade commission): A manufactured fiber composed of regenerated cellulose in which substituent have replaced not more than 15 % of hydrogen of hydroxyl groups
  3. 3. Viscose Rayon  Rayon is the oldest commercial manmade fiber.  The process of making viscose was discovered by C.F.Cross and E.J.Bevan in 1891  It is now manufactured abundantly as its raw material is cellulose and is available in large quantities in timber and vegetable matter
  4. 4. Viscose Rayon  The viscose method is relatively inexpensive and of particular significance in the production of nonwoven fabrics.  It is not synthetic.  Its properties are more similar to cotton and flax rather than polyester and nylon.  Viscose Rayon has silk like aesthetic and good feel.  The name viscose was derived from the word viscous, which mean liquid state of spinning solution.
  5. 5. Manufacturing of viscose rayon  Preparation of wood pulp  Steeping and pressing  Recovery of Caustic soda  Shredding  Aging  Churning (Xanthation or Sulphidising)  Mixing  Ripening  Spinning
  6. 6. Preparation of Wooden pulp  Soft wood trees are used  Wood is chipped into pieces about 0.9’’ X 0.5’’ X 0.25’’  Chips are treated with Calcium bi sulphite Ca(HSO3)2 for 8 -12 hours  Chips are cooked with steam under pressure for 14 hours to convert into pulp form  Pulp is washed with water to remove Calcium bi sulphite  Pulp is bleached with sodium hypo chlorite (NaOCl) solution  Pulp is converted into paper board
  7. 7. Steeping and pressing  The cellulose pulp sheets are steeped in 17.5 % NaOH solution for 1-4 hours  It is then pressed to remove excess solution  This process is called “ steeping”  Cellulose is swollen and liquid turn brown  Excess of alkali is pressed out  This process is known as “ pressing”  Moist soda cellulose mass is obtained
  8. 8. Recovery of caustic soda  Moist soda cellulose is allowed to diffuse through parchment membranes to obtain pure caustic soda  Recovery of caustic soda is important for economic purpose  Used Caustic soda is concentrated and mixed with fresh caustic soda to
  9. 9. Empirical formulae of cellulose = (C6H10O5)n Steeping: (C6H10O5)n + NaOH = [C6H9O4-ONa]n (Soda cellulose) Xanthation: [C6H9O4-ONa]n + nCS2 → [C6H9O4- OCS2Na]n
  10. 10. Shredding  The shredding machine consists of drum inside which high speed revolving blades with serrated edges are installed  Moist soda sheets are shredded and converted into fine crumbs
  11. 11. Shredding Machine
  12. 12. Ageing  Carried out in stirring vessel  Very important for properties of fabric  Polymeric chains of cellulose are degraded in the presence of atmospheric oxygen at temp 20-25 degree centigrade  Completed in 1-2 days
  13. 13. Churning  Stainless steel air-tight rotating drum  It can rotate at about 2 rpm  Soda cellulose crumbs contain about 30% cellulose  10% CS2 solution is added to soda cellulose crumbs  Soda cellulose and CS2 are churned together to form deep orange gelatinous mass of sodium cellulose xanthate  Churning is completed after 3 hours  After completion of churning, sodium cellulose xanthate is discharged
  14. 14. Mixing and blending  Dilute NaOH soln is added in sodium cellulose xanthate and mixing is carried out for 4-5 hours  A clear viscous liquid is obtained which is known as viscose  Viscose contains 6.5 % NaOH and 7.5 % of cellulose  Different viscose solutions obtained from different mixers are blended together along with TiO2 to balance inequalities and to obtain
  15. 15.  Uniform homogeneous mixture produces better quality of Rayon  It is filtered to remove any un dissolved particles  Air bubbles are removed
  16. 16. Ripening  It is very important part of manufacturing process  The uniform homogenous viscous solution is stored in stainless steel vessel at 10-18 ◦C for 4-5 days for ripening  During ripening, first of all the viscosity of solution falls down and then again reaches to its original viscosity
  17. 17.  When original viscosity reaches, this is the proper time to spin the solution and solution is immediately spun
  18. 18. Spinning  A ripened viscose solution is forced to a centrifugal pump by compressed air, which delivers it to filtering media and then glass tubing which carries a spinneret jet  The centrifugal pump delivers the viscose solution constantly and regularly  The spinneret is submerged in acid bath  Viscose solution comes out into acid bath after passing through “spinneret” solidifies into filaments owing to regeneration of cellulose  Temp. of acid bath = 40~55 ⁰C
  19. 19. Longitudinal view
  20. 20. Cross sectional view
  21. 21. Properties of viscose rayon: Tensile strength: The tensile strength of normal viscose rayon is 30000 – 46000 lbs per square inch. Elongation: Normally it will elongate 17-25 % of its original length before breaking.
  22. 22. Elastic properties: At 2% extension it has elastic recovery of 60% Specific gravity: 1.50 to 1.52 Effect of moisture: It has moisture regain of 13%.
  23. 23. Effect of heat: It begins to lose strength at 150 degree centigrade and decomposes at 205 degree centigrade. Effect of sunlight: It can withstand exposure to sunlight without discoloration.
  24. 24. Chemical properties: It can be attacked by oxidizing agents like hydrogen peroxide. Effect of Acids: Can be attacked by hot dilute acids and cold concentrated acids. Effect of alkali: It has high resistance to dilute alkali and can be attacked by strong alkalis.
  25. 25. Resistance to insects: Resistance to insects is good but can be attacked by silver fish. Microorganisms: Resistance to mildews is much better than cotton.
  26. 26. Major uses of Rayon:  Apparel: Accessories, dresses, jackets, sport shirts, sportswear, suits, ties, work clothes etc.  Home Furnishings: Bedspreads, blankets, curtains, sheets, tablecloths.

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