Thermoplastic foam: the gospel of "weight loss" for offshore wind turbines

Wind power generation has gradually become huge with offshore wind turbines, and transportation, assembly, disassembly and handling of such huge rotor blades have become a major problem for operators. The highly durable thermoplastic foam and composite materials developed by Fraunhofer's researchers and industry experts not only reduce the weight of the blade but also make it recyclable. Due to its special properties, the new material is also suitable for other lightweight components in the automobile and other industries. Their first product will be presented at the 2016 Düsseldorf International Plastics and Rubber Fair from October 19th to 26th.

wind power

Legend: Rotor blade made of thermoplastic sandwich material.

Nowadays, there is an unabated trend for offshore wind farms to become larger. In order to maximize energy production, the length of the rotor blades of the wind turbine is 80 meters, and the diameter of the rotor exceeds 160 meters. Since the length of the blade is limited by its weight, it is necessary to develop high-strength lightweight system materials. The low weight not only makes the wind turbine easy to assemble and disassemble, but also improves the stability at sea. In the European Union's WALiD (Highly Cost-Effective, Advanced Design of Lightweight Wind Blades) project, scientists at the Fraunhofer Institute of Chemical Technology (ICT) in Pfinztal worked closely with ten industrial and research teams on lightweight rotor blades the design of. They hope to reduce the weight of the blade by improving the design and materials, thereby increasing its service life.

Thermoplastics are replacing thermoset materials

At present, the rotor blades of wind turbines are mainly hand-made thermosetting resin systems. However, because the system materials are difficult to melt, it is difficult to recover materials. The best case is to recycle granular thermoset plastic waste and use it as a filler for some simple applications. Florian Rapp, project coordinator of FraunhoferICT, said: "In the WALiD project, we are pursuing a new blade design. We are realizing the conversion of material categories and using thermoplastic rotor blades for the first time. The meltability of thermoplastics helps We use automated production equipment for effective processing." Their goal is to separate glass and carbon fiber to achieve the reuse of thermoplastic matrix materials.

The project team used a sandwich material made of thermoplastic foam and fiber-reinforced plastic to manufacture the outer shell of the rotor blade and certain parts of the internal support structure. Generally, the area where the rotor blade bears the greatest load uses carbon fiber reinforced thermoplastics, and the less stressed portion uses glass fiber reinforced plastics. As for the core of the sandwich, Rapp and his team are developing thermoplastic foam and connecting it with a cover layer made of fiber-reinforced thermoplastic. This combination improves the mechanical strength, efficiency, durability and life of the rotor blade. Rapp's words: "We are breaking new ground with thermoplastic foam."

New uses for lightweight construction materials

The performance of ICT's thermoplastic foam is superior to that of the existing material system, which enables it to have new applications in the automotive, aviation, and marine industries. For example, the goggles and seats of the vehicle are made of foam, but the structure that bears the load cannot be made of foam. The foam currently on the market has some problems. For example, due to the poor thermal stability of the foam, no foam insulation is installed near the engine. Rapp said: "In contrast, our fusible plastic foams are thermally stable and are suitable for use as insulating materials to be placed close to the engine. They have good high temperature resistance. Among them, expanded polystyrene foam (EPS) and Polypropylene foam (EPP) is a good example. The enhanced mechanical properties also make them useful for door modules or as a strengthening element for sandwich composites. "They can be processed quickly and save materials.

Another advantage is that thermoplastic foams such as cork are easier to obtain than renewable sandwich core materials. These new materials are made in the institute’s foam extrusion workshop. Rapp’s explanation of the process is: “After the plastic particles are melted, the foaming agent is mixed into the polymer melt to foam the material. Next, these foamed, stable particles and semi-finished products can be molded and cut on demand.” In the field of foamed polymers, the ICT foam technology research team covers the entire thermoplastic foam production chain from material development and the manufacture of extruded foam particles and semi-finished products to the completion of process media and components.

At the Düsseldorf International Plastics and Rubber Expo held from October 19th to 26th, 2016, researchers will showcase micro wind turbines made of new foam and composite materials. Participants can see the exhibits (Exhibit No. SC01) in the Fraunhofer booth in Hall 7.