Page 39 - Curriculum Visions Dynamic Book

(Right) Cellulose is from processed wood chips.
Rayon fibre
Cellulose is so useful because it
belongs to a large family of related
chemicals called alcohols. This
means that it is possible to make a
variety of related, but subtly different, material easily from the same basic unit. However, cellulose chains
are normally strongly held together by special bonds called hydrogen bonds. These bonds mean that cellulose cannot melt (it chars when heated) or be dissolved in common solvents.
Rayon is the most common form of artificial
fibre made from dissolved cellulose (see page 12 for a representation of a rayon polymer chain). The process by which the cellulose is dissolved is called the viscose process, so much rayon is known as viscose.
To make viscose, cellulose fibre is put in a bath
of caustic soda (sodium hydroxide). This produces a reaction that creates a substance called soda cellulose. The soda cellulose is squeezed to remove excess caustic soda solution, and then the soda cellulose is shredded to increase its surface area and improve the rate of chemical reaction. The soda cellulose is then allowed to stand in air. The reaction of soda cellulose with oxygen in the air is called aging.
At an appropriate moment the aged soda cellulose is put in a vat and reacted with carbon disulphide gas to form substances called xanthate ester compounds. These compounds are again dissolved in caustic soda solution, and that is when the cellulose chains pull apart, and the cellulose goes into solution.
Because the cellulose xanthate solution is very sticky, or viscous like syrup, the product was named viscose.
(Left and above) Rayon is used as a substitute for cotton in clothing and in scatter rugs.
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