Viscose Rayon Fibre is often referred to as semi-synthetic fibre. It is produced from naturally originated cellulose in the laboratory conditions. That is why it is also called regenerated cellulose fibre. The chemical reactions that are involved in the manufacture of viscose are as follows:
Viscose rayon manufacturing:
The cellulose is treated with a 17.5% solution of caustic soda (NaOH) which converts it into soda cellulose.
The reaction between the soda cellulose and the carbon disulphide may be represented:
Each glucose residue in the cellulose polymer chain must be thought of as reacting in the following way:
The reaction takes place on the hydroxyl group (OH-) in position 2 in the glucose residues in the cellulose polymer. When the sodium cellulose xanthate is dissolved in weak caustic soda to form the viscose solution known as “VISCOSE” the xanthate radicals probably combine loosely with the molecules of caustic soda.
When the viscose solution is first made, it is very thick. On standing, it becomes thinner and then, later, more viscose again. This process is known as “Ripening”.
Now, Sodium Cellulose xanthate is spun into a coagulating bath of sulphuric acid, H2SO4 which completes the conversion of the Sodium Cellulose xanthate to cellulose.
This complete the series of chemical reactions by which viscose is made. Essentially they consist of the following stages:
1. Wood cellulose and concentrated caustic soda react to form soda cellulose.
2. The soda cellulose reacts with carbon disulphide to form sodium cellulose xanthate.
3. The sodium cellulose xanthate is dissolved in dilute caustic soda to give a viscose solution.
4. The solution is ripened.
5. It is extruded into sulphuric acid which regenerates the cellulose, now in the form of long filaments (Viscose Rayon).
- MAN-MADE FIBRES
- R. W. MONCRIEFF
Lecturer, Department of Textile Engineering, Primeasia University; Bangladesh