The Cotton Fibre
Cotton is arguably the most versatile textile fibre available and its wide range of end-uses testifies to this belief. Uses range from footwear to floor coverings, industrial to medical, engineering to household and the full range of apparel.
Ginning, bale-making and transportation
After harvesting, the `seed cotton' is passed through a gin to separate the fibres from the seeds. Ginning is usually carried out in the country of origin and, where possible, close to the growing locality. The raw cotton is then compressed into bales weighing 200kg / 500lbs each, or more, and transported to a spinning mill.
Opening and Cleaning
A spinning mill employs a number of processes to convert the fibres into yarn or thread. These processes contrive to clean the fibres, straighten and align them, and then bind them together as a strand by means of twist.
The processes which contribute to achieve this are, firstly, opening and cleaning during which the large agglomerations of ginned cotton fibre are reduced in size to small tufts. This aids in releasing from the cotton much of the extraneous matter, which may be of cellulosic or mineral origin. Commonly, 2.5% to 9.0% of the bale weight may consist of impurities, depending on the grade of cotton. These impurities are removed by a combination of mechanical and pneumatic methods.
Simultaneously, blending may take place during which batches of fibres from a number of similar types of bale are mixed together. Blending serves to minimise the effect on the raw material of slight variations between the bales; this commonly occurs with natural fibres such as cotton.
It is now necessary to separate the fibres from each other and to remove as much as possible of the remaining impurities. This is achieved by passing the fibres between closely spaced surfaces clothed with opposing sharp wire teeth in a process known as carding. The fibres are assembled into a loose strand (sliver or tow) at the conclusion of this stage.
Next, the fibrous tows or slivers are drawn by passing them between a series of pairs of rollers having progressively increasing circumferential velocity. During drawing, the fibres are made to slide past each other in a controlled way such that the inter-fibre friction straightens them. This aligns the fibres approximately parallel to each other and causes them to overlap, randomly, along the length of the strand to preserve its coherence.
An optional process may be employed at this stage, which is designed to comb out the shorter, less valuable, fibres from the material. While the combing process adds cost to the overall process sequence, it adds value to the eventual yarns in yielding improved strength and smoothness which reflects in enhanced fabric properties.
View the Preparatory processes collection to find out more >