Synthetic fibres are often used for the production of textiles, as they offer several advantages for both, the manufacturer and the consumer. For example, synthetic fibres are usually stronger and more durable than natural fibres. However, synthetic fibre textiles often become electrostatically charged, which is related to a lack of water absorption, and they can promote sweaty odour when wearing (Callewaert et al. 2014, AEM).

A synthetic fibre is usually spun from a liquid or viscous mass through spinnerets, creating thin fibres. This offers many advantages, because by changing the spinneret, customised fibres can be produced, such as hollow fibres, 4-channel fibres and many more. In addition, the spinning mass can be modified and already provided with finishes, such as flame retardants, or with a dye, which can save the time for subsequent application or dyeing. However, dyeing via the spinning mass is not often chosen, as with this method, the finished applied colour can no longer be determined.

Finished synthetic fibres, such as polyester yarn, can only be dyed very poorly compared to natural fibres. In an aqueous bath, the dye does not penetrate the fibres and anchor itself stably, as is the case with cotton, for example, and thus such a conventional dyeing process would result in poor wash fastness.

So how can it be that polyester in particular is known for its rather good wash fastness properties?

The secret is so-called organochlorine carriers, auxiliary agents such as chlorobenzenes and chlorotoluenes. They help to introduce the dye into the synthetic fibres and stabilise it there. The fibres swell when the carriers are used, and the dye can penetrate the fibre. As a result, the dye is introduced into the synthetic fibres in a stable and washfast way with the help of the carriers.

Of course, these auxiliaries can and must be washed out again, because they are often carcinogenic, toxic and/or toxic to aquatic life. When the carriers are washed out, the swollen fibre becomes thinner again. But since residues of the carriers can still remain in the fibres, it makes sense to test for chlorobenzenes and chlorotoluenes, especially in polyester samples.

Legislation directly restricts the presence of some chlorobenzenes and chlorotoluenes in textiles. For example, according to Regulation 1907/2006 (REACH) Annex XVII, entry 49, trichlorobenzene is not allowed in finished products, but its use in manufacturing/finishing is. It is common practice in the industry to test all chlorobenzenes and chlorotoluenes in textiles and to restrict them together, regardless of how much chlorine is contained and where in the textile the substances are located.

We carry out the test according to DIN 54232. In this process, the chlorobenzenes and chlorotoluenes are extracted with dichloromethane in an ultrasonic bath and then the concentration in the extract is determined by GC-MS analysis. The concentration is then extrapolated from the analysed sample to the respective test piece.