The thermoformable and recyclable repair patch is pressed onto the damaged area and achieves its final strength in just 30 minutes. Thanks to its versatility, the innovative fibre-reinforced plastic can be used in a wide range of industries, from aviation to orthopaedics. The repair of fibre composite lightweight components, for example in wings, fuselage sections, tail surfaces and doors of aircraft, is time-consuming and cost-intensive and requires several work steps. The damaged area is usually restored using a complex wet lamination process or by applying fibre-reinforced plastics (FRP) or aluminium structures, known as doublers, to the surface.

However, these variants take a long time to cure and require additional adhesives. Researchers at the Fraunhofer IFAM have now developed a repair patch made of dynamic polymer networks – experts also call them vitrimers – that shortens the previously lengthy, time-consuming repair process to 30 minutes. The special feature of the new material, which is based on benzoxazines – a new class of duromeric polymers: The polymerised plastic does not melt and does not otherwise behave like a classic resin system in the wet lamination process. Due to the dynamic cross-linking processes of the polymer, the material can be heated locally. When heated, the cured patch moulds itself to the area to be repaired. At room temperature, the polymer has duromeric properties, resulting in a non-tacky and storage-stable patch. This saves energy as the patch can be stored at room temperature without cooling, thus reducing storage costs.

The patch is applied to the lightweight component to be repaired by means of pressure and thermally induced exchange reactions, enabling rapid repair with final strength being achieved within 30 minutes. There is no need to handle reactive hazardous substances, as is necessary with conventional resin systems. The vitrimeric properties enable residue-free removal of the patch if required. “With our adhesive-free, storage-stable fibre-reinforced patch, direct repair of damaged composite materials and hybrid structures is possible. Thanks to the vitrimeric nature of the polymer, the patch behaves like a conventional thermoset composite during storage, but can be easily and cleanly joined by simple heating without the need for additional adhesives,” explains Dr Katharina Koschek, Head of the Adhesive Bonding and Polymeric Materials division at Fraunhofer IFAM in Bremen.