End-of-life of wind turbine blades – Value chain, recycling and composite materials

Recycling of fibre reinforced thermoset composites, and of wind turbine blades has been studied for many years, but industrial scale recycling solutions are not available in all countries. As an increasing number of wind turbines are reaching end-of-life, more solutions and recycling facilities will be needed.

This PhD thesis investigates the reasons for this situation from three perspectives: the value chain, the recycling process and the composite materials. First, recycling of blades is analyzed from a broad perspective, defining the concept of end-of-life value chain, and detailing the important parameters that will influence the existence of recycling solutions. This analysis lists a number of challenges, which need to be overcome in order to enable recycling. Then, the thesis looks at the recycling process and the materials perspective. Here, recycled materials from blades in the form of shredded composites and recycled glass fibres are analyzed, and their reuse as reinforcement in new polymer composites is investigated. Finally, based on learnings from the challenges observed, the thesis also looks at future materials for wind turbine blades. The possibility to use sustainable material alternatives and replace glass fibre reinforced thermoset composites is investigated. The potential of self-reinforced composites made of the biopolymer PLA is investigated.

The results in the thesis show that the challenges related to recycling of wind turbine blades are not only related to the nature of the materials used in blades or the existence of a recycling process. Aspects such as tracing end-of-life wind turbine blades, predicting future blade waste amount, retrieving blade information (materials content, geometries, etc.), and communication between the main stakeholders of the end-of-life value chain are also important. One of the main findings from this thesis is the definition of the end-of-life value chain of wind turbine blades. This value chain is described by a succession of decisions and processes performed by stakeholders with different interests. As recycling is taking place at the end of this value chain, it is highly affected by decisions taken upstream. Understanding the decision mechanisms and the interaction between the stakeholders in the value chain is crucial to enable the recycling of wind turbine blades. The thesis recommend the establishment of a holistic approach to the end-of-life of wind turbine blades. This approach is defined as a coordination of the stakeholders, decisions and processes throughout the value chain. The results on the material level show that the recycling of glass fibre reinforced thermoset composites and the use of recycled materials obtained from them, as reinforcement in new polymer composites has limited potential. The studied shredded composites are shown to be made of short randomly oriented glass fibres, and with poor adhesion to the new polymer. The studied recycled glass fibres are shown to be characterized with low stress and strain at failure. The quality of the materials recovered is a challenge when the application targeted is the reinforcement of new polymer composites. However, other applications for recycled blade materials exist, and the thesis list a number of investigations that could support their implementation. Finally, the results obtained for biobased self-reinforced composites made of PLA show that their mechanical properties are significantly lower than those of glass fibre reinforced thermoset composites. This represents the main barrier when considering these types of materials for wind turbine blades.

The outcome of this PhD thesis contributes to a greater understanding of how sustainable recycling solutions for wind turbine blades can be implemented. It is shown that a clear definition of the end-of-life value chain for wind turbine blades is essential in this process. The knowledge produced in the thesis on the recycling of composite materials provides an important contribution to the development of solutions to reuse recycled materials from blades.