Study Unit 6: Manufactured cellulosic: Rayon Flashcards
History
The first manufactured fibres were made in an attempt to reproduce the production of silk by a silkworm. In 1883 J W Swan from England, and in 1885 Count Hilaire Chardonnet from France patented synthetically made fibres. Chardonnet exhibited and sold his fibres at the Paris Exhibition of 1889 under the name of Chardonnet silk. In 1891 two English scientists, Cross and Bevan, discovered the viscose process of making rayon. In 1910 the first American rayon plant, the American Viscose Company, was opened.
The cuprammonium process of manufacturing rayon was introduced in Germany in 1891. In 1975 the United States of America stopped its production of cuprammonium rayon, although it is still produced in Italy, Japan and Germany. Most of the rayon used today is viscose rayon, and for that reason the other types will not be discussed in detail.
In 1989, Curtaulds introduced a new process of manufacturing rayon, a solvent–spun method. The product is called lyocell (See study unit 13), and it was the first new manufactured fibre developed in many years.
Fibre production
Rayon is made from cellulose that is obtained from wood pulp and cotton linters. The wood pulp and cotton linters are processed, and pure cellulose is extruded and formed into sheets. The sheets are steeped in caustic soda (sodium hydroxide (NaOH)) and then shredded and aged. Carbon disulphide is added to convert the cellulose into a form which is soluble in caustic soda, in the case of viscose rayon, or a solution of ammonia, copper sulphate and caustic soda, in the case of cuprammonium rayon. This forms a viscous (thick and sticky) honey-coloured liquid (this is why it is called viscose), which is then forced through a spinneret (wet spinning). The fibres coagulate in an acid bath. High-wet-modulus rayon is manufactured by making certain changes to the process. The fibre retains its microfibrilar structure and has a higher degree of polymerisation compared to regular rayon. This means that its performance is more similar to cotton than that of regular rayon.
Fibre properties
Rayon’s use is largely dictated by its aesthetic qualities rather than its durability. The lustre of the fibre can range from dull to bright. Rayon is soft and comfortable to wear next to the skin. The fibres burn easily.
Physical structure
As with most other manufactured fibres, the length and diameter of rayon can be controlled. Diameters can vary, for example, from 12 to 1000 micrometres. Manufactured fibres are white, cream or beige, unless pigment dyed during manufacture.
Properties relating to durability
1. Abrasion resistance
Abrasion resistance is low.
- Strength
The tenacity of rayon varies from 13–22 cN/tex. High-wet-modulus rayon can have a tenacity of about 44 cN/tex. Both fibres lose strength when wet; regular rayon losing about half of its strength. The tenacity of the different fibres is given so that you can compare different fibres. It is not necessary to remember the exact figures but you should be able to say whether a fibre is stronger or weaker than another.
- Flexibility
Rayon has poor flexibility.
- Elongation
Rayon has a low elongation (15% elongation at break).
Properties relating to comfort
1. Moisture absorption
Rayon is more absorbent than cotton and linen, and only wool and silk exceeds it. Rayon has a moisture regain of between 12–14%. Rayon accepts colours easily and can be dyed or printed with beautiful colours.
- Heat conductivity
Rayon is a good conductor of heat and therefore cool to wear.
Properties relating to appearance retention
1. Resiliency
Rayon has little resiliency and needs special finishes to prevent creasing and wrinkling.
2. Dimensional stability
Rayon shows some relaxation shrinkage in the first wash. It shrinks more than cotton, and the fabric must be pre-shrunk before a garment is cut out.
- Elasticity
Rayon has little elasticity (80% at 2% stretch); the lowest of any fibre. The fabric stretches easily without returning to its original size and shape which is a problem for home sewers, who may find that the fabric ‘grows’ if handled too much. High-wet-modulus rayon has better elastic recovery.
Properties relating to care
1. Effect of alkalis
Concentrated solutions of alkali will cause rayon to disintegrate, but weak alkalis do not damage it.
- Effect of acids
Hot diluted acids and cold concentrated acids will cause rayon to disintegrate.
