Empa demonstrates recyclable flame-retardant aircraft composite

At Empa in Switzerland, solvent and heat have been used to pull apart a material built like a sandwich: an aramid honeycomb core, woven glass or carbon-fiber layers, and epoxy holding it together. The structure is used in applications such as aircraft and train cabin floors, and the researchers say their new flame-retardant epoxy system can be softened, reshaped and separated—offering a possible route beyond incineration or landfill.

The challenge sits in the binder. Cured conventional epoxy normally cannot be melted and reshaped, and it is difficult to chemically separate from the fibers and honeycomb. Empa’s composite uses a phosphorus-containing additive that changes the resin’s behavior: under specific conditions, the cured epoxy can soften and be reshaped, enabling what is known as thermomechanical recycling.

The team and industrial partner Elantas, part of ALTANA, then demonstrated a second step. Using an appropriate solvent and some heat, they separated the composite into its individual components, including the aramid honeycomb and woven fiber layers. That matters because aramid honeycomb and carbon fiber are relatively expensive; recovering them could bring both environmental and economic benefits. Empa says the epoxy itself may also be recovered from the solution, but that work is still ahead.

The reported performance is close to the conventional material: the resulting composite retains nearly the same mechanical properties while complying with relevant fire-safety requirements, according to researcher Sabyasachi Gaan. That combination is particularly important inside aircraft, where materials must meet stringent fire rules while adding as little weight as possible. Gaan noted that making a material flame-retardant can alter its other properties.

Concretely, if the process scales successfully, manufacturers of aircraft and train interiors could have a way to recover valuable layers instead of sending the whole composite to incineration or landfill. The project, supported by Innosuisse, has demonstrated the technology’s potential at industrial-application level; scaling both production and recycling is the next step, and researchers are also investigating uses in energy and construction.