Foam makes lightweight blades for wind turbines

Fraunhofer's researchers work with industry experts to develop durable thermoplastic foams and composites that make blades lighter and easier to recycle.

Foam makes lightweight blades for wind turbines

Fraunhofer's researchers work with industry experts to develop durable thermoplastic foams and composites that make blades lighter. Due to the special properties of new materials, they are also suitable for other lightweight structures, such as the automotive sector. The first physical models will be on display at K 2016 in Düsseldorf from October 19th to 26th.

The trend of increasing offshore wind farms is increasing. Wind turbine rotor blades are up to 80 meters in length and rotor diameters over 160 meters to maximize energy production. Since the length of the blade is limited by its weight, it is necessary to develop a lightweight system with high material strength. The lower weight makes the wind turbine easier to assemble and disassemble and also improves its stability at sea.

In the EU's WALiD (Advanced Lightweight Design with Low Cost of Wind Blades), ICT scientists at the Fraunhofer Institute of Chemical Technology in Pfinztal are working closely with ten industry and research partners to design lightweight rotor blades. They hope to reduce the weight of the blades by improving the design and materials used, thereby increasing their service life.

Recently, rotor blades of wind turbines have been primarily manufactured by thermoset resin bodies. However, these materials are not allowed to melt and are not suitable for recycling. Granular thermoset plastic waste can be recycled as a filler in simple applications. “In the WALiD project, we are pursuing a new blade design. We are converting the category of materials and using thermoplastics for the first time in rotor blades,” said Florian Rapp, project coordinator at Fraunhofer ICT.

These are meltable plastics that can be processed efficiently in automated production facilities. The researchers' goal was to separate the glass fibers from the carbon fibers and reuse the thermoplastic matrix material.

The project partner uses a sandwich material made of thermoplastic foam and fiber reinforced plastic as the outer casing of the rotor blade and the internal support structure. Typically, carbon fiber reinforced thermoplastics are used to withstand the maximum load of the rotor blade area, while glass fibers are used to consolidate smaller stress areas.

For sandwich panels, Rapp and his team are developing thermoplastic foams that are covered with a bonding layer made of fiber reinforced thermoplastic. This combination improves the mechanical strength, efficiency, durability and longevity of the rotor blades. “We opened up new horizons with thermoplastic foam!” Rapp said.

ICT foams offer better performance than existing material systems, enabling new applications – for example in the automotive, aerospace and shipping industries. For example, in vehicles, manufacturers have used foam in sun visors and seats, but not for load-bearing structures. Current foams also have some limitations, such as stability to temperature, so they cannot be used for insulators near the engine.