Researchers at the Fraunhofer Institute for Chemical Technology are partnering with industry to develop durable thermoplastic foams to make wind turbine rotor blades lighter and recyclable.

Wind turbines with rotor blades of up to 80 meters in length and rotor diameters of over 160 meters, designed to maximize energy yields, are increasingly common. Since blade length is limited by weight, it is essential to develop lightweight systems with high material strength. The lower weight also makes the wind turbines easier to assemble and disassemble and improves their stability at sea.

Rotor blades made of thermoplastic sandwich materials. Image credit: ©Fraunhofer ICT. "We’re switching the material class and using thermoplastics in rotor blades for the first time," says Florian Rapp, Fraunhofer's project coordinator on the European Union’s Wind Blade Using Cost-Effective Advanced Lightweight Design project. "These are meltable plastics that we can process efficiently in automated production facilities. [The] goal is to separate the glass and carbon fibers and to reuse the thermoplastic matrix material."

For the outer shell of the rotor blade, as well as for segments of the inner supporting structure, the project partners are opting for sandwich materials made from thermoplastic foams and fiber-reinforced plastics. Carbon fiber-reinforced thermoplastics are generally being used for the areas of the rotor blade that bear the greatest load, while glass fibers reinforce the less-stressed areas. For the core, Rapp and his team are developing thermoplastic foams that are bonded with cover layers made of fiber-reinforced thermoplastics in sandwich design.

According to Fraunhofer, the foams provide better properties than existing material systems (typically thermosetting resin systems) that may enable applications beyond wind energy—for instance, in the automotive, aviation and shipping industries. Vehicle manufacturers have been using foam materials in visors and seating, for example, but not for load-bearing structures. The current foams also have limitations with regard to temperature stability that restricts them from being installed as insulation near the engine.

“Our meltable plastic foams, by contrast, are temperature stable and therefore suitable as insulation material in areas close to the engine," says Rapp. "They can permanently withstand higher temperatures than, for example, expanded polystyrene foam or expanded polypropylene. Their enhanced mechanical properties also make them conceivable for use in door modules or as stiffening elements in the sandwich composite.”

An additional advantage, according to Fraunhofer, is that thermoplastic foams are more readily available than renewable sandwich core materials such as balsa wood.