Thermoplastic foam could make wind turbine blades lighter

Fraunhofer researchers work with industry experts to develop long-lasting thermoplastic foams and composite materials that can make blades lighter and easier to recycle.

Fraunhofer researchers work with industry experts to develop long-lasting thermoplastic foams and composites that can make blades lighter. Due to the special properties of the new materials, they are also suitable for use in other lightweight structures, such as in the automotive sector. The first mock-ups will be on display at the K 2016 trade fair in Düsseldorf from October 19th to 26th.

The trend toward ever larger offshore wind farms continues unabated. Wind turbines have rotor blades up to 80 meters long and rotor diameters exceeding 160 meters, designed to maximize energy production. Since the length of the blade is limited by its weight, lightweight systems with high material strength had to be developed. 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 for Wind Blades at Low Use Cost) project, scientists from the Fraunhofer Institute for Chemical Technology ICT in Pfinztal are working with ten industries and The research partners work closely together on the lightweight design of the rotor blades. They hope to reduce the weight of the blades and thereby increase their service life by improving the design and materials used.

These days, wind turbine rotor blades are mainly hand-made from thermoset resin bodies. However, these materials are not allowed to be melted and are not suitable for recycling. Granular thermoset plastic waste can be recycled as filler in simple applications at most. “In the WALiD project we are pursuing a completely new blade design. We are switching material categories and using thermoplastics in rotor blades for the first time,” says Florian Rapp, project coordinator at Fraunhofer ICT.

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

Project partners are using a sandwich material made of thermoplastic foam and fiber-reinforced plastic for the outer shell of the rotor blades as well as the internal support structure. Typically, carbon fiber reinforced thermoplastics are used in the areas of the rotor blade that bear the greatest loads, while fiberglass is used to consolidate smaller stress areas.

For sandwich panels, Rapp and his team are developing thermoplastic foam covered with a bonding layer made of fiber-reinforced thermoplastic. This combination improves the mechanical strength, efficiency, durability and life of the rotor blades. “We are breaking new ground with thermoplastic foam!” says Rapp.

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

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