Innovative coating made from dynamic polymer networks improves repair processes for lightweight components
Researchers at the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM have for the first time developed a plastic patch that can significantly speed up and simplify previously time-consuming repair processes on damaged lightweight aircraft co.
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.
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Use in aviation: longer service life through resource- and energy-efficient repair of lightweight structures
The new material is characterised by its high mechanical strength and thermal stability, making it particularly suitable for mobility applications such as automotive and rail vehicle construction as well as in aviation. It can be moulded and has self-healing properties. At the end of its life, it can be recycled, as the polymer network can be dissolved and both the fibres and the polymer system can be reused. “Conventional duromers cannot be subsequently moulded and are not recyclable. Our benzoxazine-based vitrimers, on the other hand, combine all of these properties. The convertible material covers many aspects of the sustainable use of plastics in terms of the circular economy,” emphasises the researcher. “Through repair and reuse, it extends the service life of lightweight constructions and helps to reduce the amount of new raw materials used.” Another advantage is that it can be combined with other materials and is therefore also suitable for integration into metallic structures such as steel.
Use in orthopaedics: patient-specific, subsequent moulding and adaptation of prostheses and orthoses
The flexibility of the benzoxazine-based Vitrimers opens up potential applications in various sectors – even outside the mobility industry: in orthopaedics, the thermoformable plastic can be used to create customisable orthoses and prostheses in the future. At present, a great deal of manufacturing effort is required to produce custom-fit lightweight aids, as conventional fibre composite materials only allow for a limited amount of post-processing after the resin has hardened. “Prostheses are customised for patients. However, the aids do not always fit. Minimal fitting inaccuracies or physiological changes mean that the prosthesis or orthosis causes pain for the patient and counteracts the therapy. Until now, new prostheses have had to be produced, which can take up to several months due to the demand and the time-consuming manual work involved in orthopaedics,” explains Dr Koschek.
By using thermoformable materials, it would be possible to avoid having to manufacture a new medical aid. In the CFKadapt project, researchers at the Fraunhofer IFAM, together with REHA-OT Lüneburg Melchior und Fittkau GmbH, E.F.M. GmbH and the Leibniz Institute of Polymer Research Dresden (IPF), have developed a new, highly adaptable fibre-plastic composite material based on dynamic polymer networks. The main difference to commercial matrix systems for orthopaedic aids made of fibre composites is the possibility of post-processing and modelling the new material at the corresponding pressure or support points for dynamic adaptation to the patient and their changing needs over the course of therapy. The trick: the new polymer-fibre composite mix can be heated locally and individually adapted. “The advantages lie in the great freedom of design and layout as well as in the significant reduction of rejects during production and a longer service life of the aids, as they can be continuously adapted during therapy. For those affected, one thing counts above all – getting a custom-fit orthopaedic aid as soon as possible,” summarises Koschek. The standardised production of components with subsequent customisation also results in cost benefits and an efficient manufacturing process in the long term.Source: Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM)
Source: Fraunhofer-Institut für Fertigungstechnik und Angewandte Materialforschung (IFAM)
