“No flying machine will ever fly from New York to Paris,” aviation pioneer Orville Wright once said. What even the visionary Wright brothers considered impossible is now a reality—thanks, in part, to new materials that make modern aircraft and engines possible in the first place. In the more than 100 years since the Wrights’ first flight attempts, aviation has not only become more powerful but, fortunately, also significantly safer. The materials used in aircraft construction must meet the strictest safety requirements, including fire safety standards. At the same time, they must be lightweight and mechanically robust—and, increasingly, recyclable as well.

“Bringing all these properties together under one roof is a challenge,” explains Empa researcher Sabyasachi Gaan from the “Advanced Fibers” laboratory. “For example, when you make a material flame-retardant, you always end up altering its other properties as well.” Gaan and his team, together with their industry partner Elantas—part of the German specialty chemicals group ALTANA—took on this challenge in a project supported by Innosuisse. Their focus was on a specific composite material used in the interior construction of airplanes and trains, such as for the floor of the passenger cabin.

In the Innosuisse project, however, the partners pursued a different goal: the complete recycling of the composite material. With the right solvent and a little heat, the “sandwich” can be broken down again into its individual components: the honeycomb structure and the woven fibers. Aramid honeycombs in particular—but also carbon fibers—are relatively expensive. Recycling them is therefore also economically attractive. “In principle, it’s also possible to recover the epoxy resin itself from the solution. We plan to tackle that in future projects,” says Gaan.

The recyclable epoxy resin was developed at Empa. Working with Elantas, the researchers have now explored its potential for industrial application for the first time. “Our material complies with fire safety regulations and achieves nearly the same beneficial mechanical properties as conventional epoxy,” says Gaan. “But for the first time, it allows for the complete recycling of the composite material.”

The project partners are satisfied with how the project is progressing. The next step is to further scale up production and recycling. “For the aerospace industry, it is crucial to combine fire protection, lightweight construction, and recyclability. This epoxy composite system demonstrates that this is now possible for the first time,” says Fiorenzo Lenzi, Head of the Aerospace/Ballistic Product Line at Elantas.

At the same time, Sabyasachi Gaan and his team are already conducting research into further applications for the recyclable, flame-retardant plastic, such as in the energy sector and the construction industry. The scientist emphasizes that the fact a material has come this far is also thanks to basic research. “Before we can work on the applications, we need to have a very good understanding of the material’s properties.” The Wright brothers would likely agree with him. For, as Wilbur Wright wrote in a letter to engineer Octave Chanute in 1900, “It is possible to fly without engines, but not without knowledge and skill.”