Technology for Wood and Natural Fiber-Based Materials

Research Project

ReRoBalsa – Recycling of rotor blades in order to recover balsa wood/foam for the production of insulation materials

Wind turbines are producing increasing quantities of sustainable electricity. The recycling of the rotor blades, however, is very complicated and expensive, due to the highly stable shell made from glass fiber-reinforced composite plastic. Rotor blades have therefore usually been burned up until now. This, however, is also problematic, as the fiber-reinforced plastics clump together during combustion and can thereby block and damage conventional waste incineration plants. Furthermore, valuable raw materials are lost in vast quantities during combustion. The main objective of this research project is therefore the development of an innovative recycling technology for the recovery of balsa wood and plastic foam from the rotor blades. In addition, we

are developing innovative recycling technologies for these recyclates, in order to utilize them in the production of new, improved insulation and building materials.

© Fraunhofer WKI | Peter Meinlschmidt
Each of the 53.3m-long rotor blades has a total surface area of approx. 300m². The entire balsa wood area of 180m² yields a volume of approx. 3.6m³ of balsa wood. In addition, there is also the inner bridge, with an area of approx. 80m² and a thickness of 30mm, which yields an additional volume of 2.4m³ of balsa wood
© Fraunhofer WKI | Peter Meinlschmidt
Newly produced 75m-long rotor blade with an area of approx. 500m² and a volume of 10m³ of balsa wood
Picture of balsa-wood pieces from a rotor blade.
© Fraunhofer WKI | Manuela Lingnau
Balsa-wood pieces from a rotor blade.

The necessary recycling steps for the recovery and material recycling of used balsa wood or foam from end-of-life rotor blades are the on-site dismantling into transportable pieces, a rough dissection into a practicable size for processing units, and the separation of the filler material from the fiber-reinforced plastic. The latest state of technology is essentially determined by the method developed by the company CompoCycle. The rotor blade is thereby cut transversely on site by means of a diamond-studded wire saw, loaded, and transported to a stationary processing plant. Through a multistage system, the material mix is chopped to produce pieces with a size of max. 50mm then crushed and mixed, for dust-binding purposes, with a second moist material flow (often rejects from the paper industry). The subsequent recycling is carried out through incineration in a cement plant, whereby the calorific value of the plastic (50 percent of the matrix) is used and the components contained in the ash serve as a material substitute in cement production.

The novelty of our solution approach is the fact that as early on as the dismantling of the rotor blade on site, the valuable areas with the filler material are severed and can be fed into a separate processing and high-quality recycling procedure. We thereby consider all the necessary processing steps for the reclamation and material recycling of used balsa wood and foam from a holistic perspective. A recovery of the severed fiber-containing areas via material/energetic recovery in the cement plant can be ensured through industrial partners. The industrial plant for the crushing of GRP waste typically incorporates a two-stage crushing process. In the first stage, the material is coarsely crushed in a primary crusher, and in the second stage, it is finely crushed in a cross-flow grinder or impact reactor, into which moist waste materials from the paper industry are added (for dust-binding purposes). Metals are separated via a magnetic separator and a downstream eddy current separator following the fine grinding. A separation of the incorporated filler materials does not currently take place.

The material recycling of used (end-of-life) balsa wood to create building materials and raw materials generally takes the course through the production of wood chips and fibers, which serve as a basis for adhesive- or cement-bonded particle board. In our research project, we want to investigate and test the utilization of the secondary balsa wood and plastic foam extracted from the rotor blades by means of specific applications. The following materials are intended to be produced from the recycled end-grain balsa and foam blocks:


  • Wood-fiber insulation (with various adhesives and additives)[1]
  • Wood foam (without adhesives)[2]
  • Composite materials and insulation panels (via intermediate stage of the compound)



[1] E. Mörath: “Die Holzfaserplatte”, Holzforschung 1950, Issue 1, P. 14-25

[2] J. Scholtyssek, “Geschäumtes Holz: eine nachhaltige Alternative zu konventionellen Dämm- und Verpackungsmaterialien”, NMN Material Kompass, Edition 02/2013, P. 11

Project partners

Affiliated partners:

  • Fraunhofer WKI (Project coordinator)
  • Technische Hochschule Nürnberg (Nuremberg Tech) – Research Group PuR
  • Kovalex GmbH (SME)
  • BINOS GmbH (SME)

Associated partners:

  • Sachverständigenbüro Otto Lutz (expert consultant) (SME)
  • Mau und Mittelmann GmbH (SME)
  • Airex AG | 3A Composites Core Materials, Schweiz
  • rub Berlin – Gesellschaft für Recycling, Umwelt und Biotechnologie mbH (association for recycling, the environment and biotechnology) (SME)


Funding body:
German Federal Ministry of Education and Research (BMBF) within the framework of the funding guideline “KMU-innovativ: Ressourceneffizienz und Klimaschutz” (SME innovative: Resource efficiency and climate protection)


Project management:
Projektträger Jülich (PTJ)


1.8.2017 to 31.6.2019