German scientists have developed a concept that reduces the amount of flame retardants in carpet yarns—while maintaining the same high level of flame retardancy. The structure of the textile product is optimised for material recycling.
- The research has been carried out by scientists at the German Institutes of Textile and Fiber Research (Deutsche Institute für Textil- und Faserforschung - DITF) and the Institut für Bodensysteme (TFI).
The context: Textile-based carpets with flame retardants reduce the risk of fire. Such carpets are used in large quantities in commercial buildings.
- However, it is difficult to recycle these materials because the carpets consist of several interconnected layers and the established flame retardants are usually ecologically problematic.
The research: The newly designed carpet yarn is made of flame-retardant polyamide 6 (PA6) and will be fully recyclable. The PA6 has been equipped with intrinsic flame retardancy.
- This means that the flame-retardant chemical, in this case a phosphorus compound, is not applied to the surface of the fibres, but is chemically bound to the molecular structure of the PA6. As a result, the flame retardant is permanent and cannot be washed out or emitted into the environment.
- The concept of intrinsic flame retardancy is not new. It was developed at the DITF around ten years ago, but has since been optimised.
- The polyamides used in the current research project have been precisely adjusted in terms of their viscosity and phosphorus content. As a result, the two requirements for spinnability and high flame retardancy, which are difficult to reconcile, were fully met.
The material: The new material is spun into fibres on a bicomponent spinning machine at the DITF pilot plant. This way, so-called bicomponent fibres are produced, which have a core of conventional polyamide and a sheath of PA6 with a highly concentrated flame retardant.
- The core and sheath components of the fibres complement each other perfectly: the fibre core ensures good technical spinnability and sufficient strength of the fibres. The sheath, on the other hand, contains the flame retardant exactly where temperature and flames attack: on the surface of the fibre.
- The phosphorus content of about 0.2% by weight is precisely adjusted so that the fibre sheath is not flammable. As a side effect, the yarn is cheaper to produce because the expensive flame retardant is only added to part of the fibre volume.
Towards recycling: The second aspect of the research project deals with the production and recyclability of the carpet.
- Using the polymers and bico-yarns produced at the DITF, the project partner TFI is developing the carpet with a top layer of flame-retardant modified multifilament yarn and the textile backing.
- The backing coating is designed to allow thermal separation of the backing from the flame-retardant top layer. Hot melt adhesives are used for this purpose and their flammability is also taken into account. The TFI determines the flammability of the textile products. The separability of the top layer and the backing is verified in laboratory tests.
