Question

Explain the reactions involved in the preparation of viscose rayon.

Answer 1

1. Viscose rayon is a semisynthetic fibre which is regenerated cellulose.
2. Cellulose in the form of wood pulp is transformed into viscose rayon. Cellulose is a linear polymer of glucose units and has the molecular formula [(C₆H₁₀O₅)_n]. A modified representation of the molecular formula of cellulose is Cell-OH.
3. Method of preparation:
   a. Cellulose in the form of wood pulp is treated with concentrated NaOH solution to get fluffy alkali cellulose.
   b. It is then converted to xanthate by treating with carbon disulphide.
   c. On mixing with dilute NaOH, it gives viscose solution which is extruded through spinnerets of the spinning machine into the acid bath when regenerated cellulose fibres precipitate.
4. Reactions involved in the preparation of viscose rayon:
   \[\ce{\underset{\text{(Cellulose pulp wood)}}{Cell - OH + NaOH} -> \underset{\text{(Akali cellulose)}}{Cell - O- Na+} + H2O}\]
   \[\begin{array}{cc}
   \ce{Cell - O- Na+ + CS2 ->Cell - O - C - S- Na+}\\
   \phantom{............................}||\\
   \phantom{............................}\ce{\underset{\text{(Cellulose xanthate)}}{S}}
   \end{array}\]
   \[\begin{array}{cc}
   \ce{Cell - O - C - S- Na+ + H2O -> Cell - O - C - SH + NaOH}\\
   \phantom{..}||\phantom{..................................}||\phantom{.....}\\
   \phantom{..}\ce{S}\phantom{..................................}\ce{S}\phantom{.....}
   \end{array}\]
   \[\begin{array}{cc}
   \ce{Cell - O - C - SH + H2O -> \underset{\text{(Viscose rayon) (Regenerated cellulose filaments)}}{Cell - OH + CS2}}\\
   ||\phantom{.........................................}\\
   \ce{S}\phantom{.........................................}
   \end{array}\]