We are living in a throwaway society; this is also true for clothes. When we think of the personal protective equipment for work safety such as mechanically robust and fire resistant clothes, it makes sense that they also have an expiration date. But that does not mean that also the ingredients have lost their functionality. Usually, these compounds have been produced with considerable energy effort, thus, it reasonable to find an efficient recycling method.

Flame retardant compounds are a “must-have” in personal protection equipments. A common ingredient in this context are so-called aramid staple fibres. They are characterized by high robustness and heat resistance up to 400 °C. A second important constituent are flame-retardant viscose fibres that incorporate a flame retardant pigment. They guarantee for a good wearing comfort and at the same time impart a cooling effect, when exposed to great heat. When these protective garments are disposed of after some time, the ingredients do not necessarily loose these characteristics and value. For this reason, researchers are looking for possibilities to recover the synthetic fibre fraction and flame retardant pigment.

The problem of recycling protective suits

So far, conventional recycling methods for fire resistant textiles have not been successful. When considering the synthetic fibre share, a critical parameter is the fibre staple length. Conventional recycling methods rely on mechanical technologies, which do not guarantee this and cause random material mixes. They were thus found to be unsuitable for the treatment of such complex textile structures.

Enzymatic decomposing

On the contrary, enzymatic approaches promise to work in milder conditions. The idea was to apply enzyme mixtures for the hydrolytic degradation of the cellulosic part, in order to achieve a selective and environment-friendly technology for the depolymerization of viscose fibres, which are mostly cellulose-based as well. The produced monomers, mostly sugars, can then be used for the production of other valuable compounds such as biofuels. In parallel, the flame retardant compound is released successively into the reaction solution, and can be re-utilized for the production of new fire-resistant viscose fibres. Applying this approach then also makes it possible for the first time to recycle the aramid fibre in high quality and free of contaminants.

The researchers of this project are eager to bring this technology on an industrial level now. Pilot experiments are already in progress.