Impact of contamination on yarn and fabric quality

y R.Senthil Kumar.

Contamination has vital role in deciding the quality of cotton apart from essential properties such as length, strength, fineness. Contamination of raw cotton can take place at every step i.e. from the farm picking to the ginning stage. Contamination, even if it is a single foreign fibre, can lead to the downgrading of yarn, fabric or garments or even the total rejection of an entire batch and can cause irreparable harm to the relationship between growers, ginners, merchants, spinner and textile and clothing mills. An International Textile Manufacturers Federation (ITMF) reported that claims due to contamination amounted to between 1.4 – 3.2% of total sales of 100% cotton and cotton blended yarns. The main aim of this paper is to give a perspective about the contaminants and its types, causes, effects, statistics of contaminants, preventive measures to eliminate contaminants and contamination cleaning methods.

Contamination

Mixing of foreign material /matter with main product at any stage of collection, production, handling, storage, processing in the yarn manufacturing process is termed as contamination. ITMF classifies contaminants as shown in the fig.1.

Contamination level in cotton

The perceived degree of contamination has steadily increased from 1989 to 2007. The cotton from India and Pakistan shows high contamination level due to poor work practices right from picking to finishing stage.(Table 1)

A further breakdown of contaminants as shown in Table.2  reveals that the major source of contamination in all bales continues to be organic matter such as leaves, feathers, paper, leather, etc., which has steadily increased.

The next most prevalent contaminant is fabric and string fragments made from cotton, woven plastic, plastic film and jute/hessian, followed by sand and dust. The incidence of oily substances/chemicals and inorganic matter such as rust and metal has remained fairly consistent.

Causes of  contamination in picking and ginning process

Most of the contamination arises from impurities being incorporated into the bale as a result of human interaction during harvesting, ginning and baling as shown in figure 2. Some of the reasons behind high contamination level in cotton are given as:

Fig.2: Contaminants collected during ginning process.

• Hand picking method.
• Reuse of fertilizer bags.
• Lack of infrastructure and awareness.
• Improper maintenance work methods.
• Iron tap for bale packing.
• Labels.

Effects of contamination

• Contamination causes the cotton to become sticky, which creates obstruction in rollers.
• It causes wastage of fabrics due to defects in dyeing.
• Even after cleaning leftover embedded pieces of contamination in yarn affect its quality and value.
• Contaminants such as stones, metal pieces, etc… causes disturbance to material flow especially in spinning preparatory process which affects production as well as quality of the process.
• Metal pieces tend to cause fire hazard which leads to severe machine and material loss.
• Fabric appearance produced with contaminated yarn will be poor and prone to rejection. (fig.3).
• Dyeing affinity of contamination is different from dyeing affinity of fabric which leads to uneven fabric coloration. (Fig.3).

Fig 3: Polypropylene contaminants in Knitted fabric.

Measures to reduce contamination

• Introduction of standardized picking storage and marketing of raw cotton.
• Dissemination of awareness through mass media to the targeted segment.
• Cloth bags instead of jute and fabric bags must be provided by farmers and ginning factory owners to pickers.
• Cotton should be stored on clean and proper floors.
• Metal body open trolleys should be used for quick transportation of cotton from field to factories.
• Sheds and platforms should be built properly in the market.
• Bags should be opened by unsewing instead of cutting twine in to small pieces.
• Bags should not be beaten. Instead it should be beating should be done separately and obtained cotton should be cleaned properly to be added in heap.
• Conveyers can greatly facilitate the flow of bales.
• Plastic strips are used for strapping bales to avoid contamination by rust.
• Bale packing should be graded and awareness programs should be incorporated to improve bale packing.

Contamination cleaning methods

1. Hand picking method:

A small number of spinning mills are able to manually check and remove contamination from every bale of cotton, before it is repacked and released for processing in the mill.

This manual sorting as shown in fig.4 is either done directly from the bale or the bale is first opened using a bale opener with a spiked lattice to open the cotton prior to manual sorting.

Fig.4: Hand Picking Method.

Spinning mills situated in countries where labour costs are comparatively low employ large numbers of people to patrol the bale lay down and remove contamination from bales before cotton is fed into the blow room line by the bale opener as shown in fig.5.

Fig.5: Patrolling in the bale lay down.

2. Blow room equipped with contamination detection and ejecting units

Although manual intervention is helpful even low labour cost spinning mills have come to realize that it is not always sufficient as generally only the bigger contaminants are removed. The blowroom these days are equipped with systems for detection, separation and measurement of foreign material as shown in fig.6.

Fig.6 Contamination clearer attached in Blow room line.

These systems detect contaminants using acoustic, optical and colour sensors that monitor the material as it flows (is processed) through the machinery. When a sensor is activated by a contaminant it is measured (registered) and, depending upon the system, mechanically removed via an alternate material flow outlet. These systems are normally installed at the beginning of the blow room line before the   final cleaning stage.

3. Contamination detect & removal at winding machinery

Equipping winding machines with yarn clearers that detect and remove foreign matter from the yarn before it is wound onto packages and delivered to the knitter or weaver. The types of contamination and the efficiency of removal depend on the sensors employed in these systems, with modern clearers able to detect the finest defects not visible by the human eye.

Fig .7: Contamination clearer in yarn stage in winding.

4. Installation of Ultraviolet (UV) lights in the packing and inspection section

Installing ultraviolet lights in the packing and inspection departments to detect chemical/oily substances and foreign fibres such as polyester and other synthetic man-made fibres and defective packages are   rejected manually.

Fig .8: Contamination clearer in yarn stage in winding.

Conclusion

Fiber contamination is a serious and expensive problem for the mills. Contaminants can end up in finished yarn and fabric products. These tainted yarns and fabrics become “seconds.” The study found that the harvesting and bale preparatory operations are the major contributors to contaminants found in modules and the challenge for the industry is to raise the awareness of the causes and effects of contamination.

References

1. Contamination and its significance to the Australian cotton industry-CSIRO report.
2. Contamination issues in cotton - Agrocel Jan 2008 OE regional conference.
3. Contamination of cotton falling, says survey  - G. Gurumurthy, The Hindu-Business line, DEC2005.

About Author: R.Senthil Kumar is a senior lecturer at Deptt. of Textile Technology at Kumaraguru College of Technology based in Coimbatore, Tamilnadu, India.The author can be contacted at sen29iit@yahoo.co.in.