Recyclable Epoxy Composite Combines Fire Safety With Lightweight Performance
Aircraft and passenger trains rely on composite materials that combine low weight, mechanical strength and high fire resistance. However, many of these composites contain thermoset epoxy resins, which cannot normally be melted or dissolved after curing. As a result, they often end up in landfill or are incinerated. Researchers at Empa, working with speciality chemicals company Elantas, have now developed a flame-retardant epoxy system that enables the composite’s components to be recovered for reuse.
A Recyclable Composite Sandwich
The material targets interior applications in aircraft and trains, including passenger cabin flooring. It consists of a lightweight aramid honeycomb core covered on both sides with layers of woven glass or carbon fibres. Epoxy resin binds these components together to form a strong, rigid sandwich structure.
Conventional epoxy creates a permanent bond that makes separating the different material layers difficult. Empa’s Advanced Fibers laboratory addressed this issue by developing a phosphorus-containing additive for the resin. Besides providing flame-retardant properties, the molecule changes the epoxy network so that the cured material can be softened and reshaped under specific conditions. This allows thermomechanical recycling, which is generally not possible with conventional epoxy.
Recovering High-Value Fibres And Cores
Within the Innosuisse-supported project, the researchers and Elantas investigated the complete separation of the composite. Using a suitable solvent and moderate heat, they could dismantle the sandwich structure and recover the aramid honeycomb and woven fibre layers.
This recovery route is particularly relevant because aramid honeycombs and carbon fibres are relatively expensive and energy-intensive to manufacture. Retaining their material value could reduce waste and improve the economic case for recycling lightweight transport components. According to Empa, recovering the epoxy resin itself from the resulting solution should also be technically possible, although this will require further research.
Tests indicate that the new composite meets relevant fire-safety requirements while approaching the mechanical performance of conventional epoxy systems. It therefore offers a possible route towards combining fire protection, structural performance and improved end-of-life options in one material system.
From Transport To Construction
The next stage will focus on scaling both production and recycling processes for industrial use. Empa is also investigating applications beyond aircraft and trains, including components for the energy and construction sectors.
For designers and engineers, the development highlights how resin chemistry can influence the circularity of an entire composite structure. Designing the binder for controlled separation could make it easier to recover valuable reinforcement fibres and lightweight cores rather than treating the complete component as waste.
Source & photos: Empa