New Epoxy Composite Lets Aircraft Cabin Panels Be Taken Apart and Recycled

Researchers at the Swiss Federal Laboratories for Materials Science and Technology (Empa), working with the specialty-chemicals company Elantas, have developed an epoxy-based composite that can be taken apart for recycling at the end of its life — something conventional epoxy composites cannot do.

Aircraft and train interiors, including cabin flooring, often use a "sandwich" composite: a lightweight honeycomb core made from aramid, the heat-resistant polymer family that includes Kevlar, sandwiched between woven layers of glass or carbon fiber and bound together with epoxy resin. "Bringing all these properties together under one roof is a challenge," said Sabyasachi Gaan, a researcher at Empa's Advanced Fibers laboratory. "When you make a material flame-retardant, you always end up altering its other properties as well." Epoxy is a thermoset plastic that becomes a permanently cross-linked network once cured, giving it strength and heat resistance, but this also means the fibers and honeycomb inside usually cannot be recovered; such composites are typically incinerated or sent to landfill at the end of their service life.

Empa's solution is a phosphorus-containing additive mixed into the epoxy before it cures, creating a network with dynamic bonds that can undergo bond-exchange reactions under the right heat and processing conditions, allowing the cured material to be softened and reshaped later. In the new project with Elantas, researchers used heat and a solvent to break down an entire aerospace-style sandwich composite, successfully separating it into its aramid honeycomb and woven reinforcing fibers.

The phosphorus additive also makes the material flame-retardant, which matters because aircraft cabin materials must meet strict fire-safety rules. In earlier Empa experiments, a formulation with 2.5% phosphorus reduced peak heat-release rate by 75% and total smoke production by 72.5% compared with a reference material in cone-calorimeter testing, while concentrations above 5% phosphorus were needed for effective recycling. The composite developed with Elantas meets required fire-safety regulations while keeping nearly the same mechanical properties as conventional epoxy-based material, according to Empa.

The team has not yet recovered the epoxy resin itself from the process, but says that step should also be possible and plans to pursue it in future work.