“Study Unit 6: Manufactured cellulosic: Acetate VS Triacetate Flashcards
History
Cellulose acetate was developed in England during the First World War by the Dreyfus brothers. It was developed to be used as a lacquer on the wings of aircrafts. After the war, in 1918, they developed the technique for spinning the substance into “artificial silk” fibres. Commercial production of acetate fibres started in 1921 in England and in 1924 in the United States of America. Although triacetate fibres were developed along with regular acetate, triacetate manufacture had to be delayed until 1952 when satisfactory and safe solvents became available. In 1954 the Celanese Corporation of America began with the large-scale commercial production of Arnel®, a triacetate fibre. The production of Arnel® was stopped in 1986.
Fibre production
Manufacturing processes
The raw materials for the manufacturing of acetate are cellulose, acetic acid and acetic anhydride, with sulphuric acid as a catalyst. After the cellulose has been ripened, washed and dried, the acetate flakes are dissolved in acetone. The spinning solution then formed is forced through a spinneret into a chamber of warm air where the acetone evaporates and the acetate fibres coagulate (dry spinning).
Triacetate follows very much the same process except that the acetate solution is not allowed to ripen. After washing and drying, the acetate flakes are dissolved in dichloromethane and then dry spun into a warm-air chamber.
Finishing processes
Acetate and triacetate fibres differ from all the fibres discussed thus far in that they are thermoplastic. This means that they can be softened by the application of heat and placed or pressed into a particular shape. Consequently, they can be permanently embossed or pleated. This also means that they must be ironed at lower temperatures.
Fibre properties
Acetate has a high lustre and pleasant hand. Its aesthetic properties are more important than its durability and ease of care. Most dry-cleaning solvents have no effect on acetate and triacetate. But acetone (found in nail-polish remover) will destroy acetate and other solvents will destroy triacetate.
Physical structure
Acetate has and keeps a good white colour, which is one of its advantages over silk.
Properties relating to durability
1. Abrasion resistance
Acetate has poor abrasion resistance.
- Strength
Acetate is a weak fibre having a tenacity of 10–13.2 cN/tex when dry and 7–9 cN/tex when wet. Other weak fibres have some compensating property, such as good elastic recovery in wool and spandex, but acetate does not.
Triacetate is also weak with a tenacity of 10.3–11 cN/tex when dry and 6–7 cN/tex when wet.
- Flexibility
Acetate is not a very flexible fibre.
- Elongation
Acetate has an elongation at break of 25%.
Properties relating to comfort
1. Moisture absorption
Acetate has a moisture regain of 6–7 % and is subject to static build up.
Triacetate is less absorbent.
The low water absorption means that the fabric is uncomfortable to wear in warm, humid weather, although it dries quickly.
- Heat conductivity
Heat conductivity is moderate. Although acetate and triacetate are poor conductors of heat and warm to wear, it is possible to make garments suitable for summer wear by using very fine yarns and sheer fabric construction.
Properties relating to appearance retention
1. Resiliency
Acetate fabrics are not very resilient. They wrinkle as they are worn and may develop wrinkles during washing which are hard to remove.
Triacetate is the most resilient of the cellulosic fibres.
- Dimensional stability
Dimensional stability is moderate; the fibres are weaker when wet and much heat make them shrink.
- Elasticity
Elastic recovery is low (58% at 4% stretch) but is better than that of the rayon.
Properties relating to care
1. Effect of alkalis
- Effect of acids
- Effect of sunlight
- Biological properties
Alkalis have little effect on acetate.
