You may have noticed that some cotton yarns are described as combed, mercerised and gassed. But what does it mean?
When cotton is harvested, it first needs to be cleaned to remove dirt and seeds. It is then carded, which separates the fibers and makes them all line up in the same direction. The cotton is divided into hanks of raw cotton which can then be spun into yarn. Combing is an additional process, whereby after carding, the fibres are brushed with very fine brushes to pull out all remaining impurities plus any short cotton fibers. This means that up to another 15% of volume of the original raw cotton is removed. You are left with long, straight and evenly aligned fibers which are then spun into yarn.
Mercerisation is a chemical treatment for cellulosic material such as cotton fibres for yarns. The yarn is dipped in a sodium hydroxide bath, followed by an acid bath. This treatment causes the fibres to plump up before it relaxes and straightens once again. It strengthens the fibre and gives it a lustrous, shiny appearance. Mercerized yarn also accepts dyes more easily and holds the color longer. It is stronger than non-mercerized thread and resists mildew. The same process is also sometimes used for linen and hemp yarns. The process was invented by John Mercer in 1844.
Gassed Cotton Yarns
Gassed yarn is mercerized cotton yarn that has been exposed very rapidly to a hot gas flame. This process removes any fuzz or excess lint on the thread. This results in a brighter and smoother appearance.