10/03/2006 - Chances of cleaning contamination (2 of 6)

2. Colourless or white contamination

 

It is correct that most of the impurities are darker than raw cotton.

There are, however, exceptions. Materials which are white or come close to the colour of raw cotton cannot be recognized by conventional optical methods. The problem with these impurities is the fact that they will possibly disturb the later fabric appearance in the form of light stripes. If these light stripes are investigated it can be seen that they consist of synthetic material. These materials stand out for the fact that they hardly absorb dyes.

The question now is - which synthetics is it about? Not all materials are equally dangerous. The critical point is their appearance and not their molecular structure. Foil pieces seem to be less problematic. They may be fragmented by the opening machines but they will not defibrillate. Most of them will be eliminated during the opening process.

 

Picture 2: Coloured and white contamination

 

 

 Picture 3: Foil pieces and fabric woven from polypropylene tapes

 

Dangerous are synthetic materials in the form of tapes or fabrics woven from such tapes. Such materials are frequently used for packing materials such as bags or strings. In most cases they will consist of polypropylene. If parts of these materials contaminate raw cotton they will be torn to fibre bundles or single fibres during the opening process. Then they will show the same behaviour as other textile fibres and pass through the whole production until they are integrated into the yarn. Polypropylene occurs sometimes as coloured material but quite often as transparent, whitish material. Since this contamination cannot be detected by conventional optical means, a lot a research has been undertaken to find a suitable principle for its detection.

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