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HOW IT'S MADE - From bottle to blade

News International-French

1 Oct 2020

With an industrial heritage going back to 1835, Gurit has an extensive track record in advanced composites, gained over the last 30 years in various market sectors. Today, the company specializes in advanced composite solutions for the wind turbine blade industry as well as lightweighting solutions for industries such as marine, rail, aerospace and many more.

HOW IT'S MADE - From bottle to blade

HOW IT'S MADE - From bottle to blade

Wind energy is a fast-growing segment and one of the largest markets for composite materials. One of the key aspects making the wind energy sector so successful is the scalability of the technology, especially in terms of blade size. In recent years, enormous developments were undertaken in the field of wind turbine construction. The largest turbines are approaching the height of the Eiffel tower as blades are getting longer and rotor diameters now reach the 200 meter mark. This is not only impressive from a constructional point of view, but it also has a significant impact on performance.

These larger turbines are able to capture and transform more energy during their lifetime, ultimately resulting in a substantial cost reduction for the energy produced – the so called levelized cost of energy. As cost parity with fossil fuel-based energy generation has now been reached, wind is one of the largest sources of clean, renewable power. Further developments in the sector include the increasing utilization of the offshore wind potential, leading to further increases in blade length. Offshore wind installations have the benefit of relying on a more stable wind source and the sector is forecasted to grow significantly in the coming years.

Why sustainability is so important in the composites Wind Energy sector ?
Emiliano Frulloni, Chief Technological Officer, Gurit, answers:

Emiliano Frulloni, Chief Technological Officer, Gurit

"Wind turbines have been a sustainable source of clean energy for the last decades. Advancement in technology have made wind energy a competitive alternative to fossil fuel based power generation. Renewable wind energy will be decisive to combat climate change. To even further improve sustainability we have to  look at all aspects of the value chain."


Core material development
From a composite material point of view, this rapid development, especially in terms of blade construction, is forcing the supply chain to mature in an equally fast pace to offer solutions at competitive prices in order to support a low levelized cost of energy for wind power globally.

Advanced composites in a typical wind turbine blade

Advanced composites in a typical wind turbine blade

The design of turbines relies on a few key elements. The requirements for these elements are extremely high in terms of mechanical properties as well as their ability to withstand rough climate conditions for a prolonged amount of time. Among others, buckling is an important failure criterion applied when designing a turbine blade and the structural design is largely driven with rigidity and resistance in mind. During this process, much focus is put on the blade core since this is a key contributor to attain the required stiffness.

Balsa wood – a naturally-grown core solution
Historically, end grain balsa is one of the materials that was first adopted as a core in wind turbines and is still widely used. This material is produced by gluing lumber along the direction of the fibres, which creates a resilient block. The block is then sliced perpendicular to the fibre direction, creating core panels that are utilized in the blade structure. In addition to being environmentally friendly, balsa wood is an exceptional core material due to its extraordinary strength and stiffness.

However, it takes approximately four years for a balsa tree to grow to the point where the wood can be cut and material production can start. The lag induced by its natural growth cycle as well as its exposure to different climate conditions and other circumstances that could further prolong the production time is a challenge, particularly for the dynamic wind energy industry.

Is Gurit will develop (or has developed) other solutions for a 100% recyclable composite wind turbine blade ?
Emiliano Frulloni, Chief Technological Officer, Gurit, answers:

Emiliano Frulloni, Chief Technological Officer, Gurit
"Our Kerdyn PET structural core is the area where Gurit have made the most advancement, by replacing non-recyclable thermoset materials with a recyclable thermoplastic material that is to a great portion produced with recycled PET bottles. While the industry still faces huge challenges in achieving cradle-to-cradle recyclability, we believe the use of recyclable thermoplastics is a huge step into the right direction. We are ready to collaborate with our customer to bring this technology even further."

How it's made: Recycled PET as a synthetic core material
Given the importance of the core in blade construction, several synthetic cores have been considered over the years. A modern answer for a scalable synthetic core technology came with the adoption of thermoplastic extruded foam. In this respect, PET is the polymer that offers the greatest benefits in terms of the balance of thermal resistance (to withstand the blade production process), mechanical performance (delivering the necessary stiffness and strength) and cost.

A greener core material produced from recycled PET! Gurit vertical integration of the recycling technology

A greener core material produced from recycled PET! Gurit vertical integration of the recycling technology

Moreover, PET offers a well-developed and resilient supply chain for recycled material, further improving the environmental credentials of a material and a production technology that already ensures great efficiency, allowing  for any production waste to be recycled into fresh foam core material.

Recycled PET is a viable raw material for thermoplastic foam extrusion but, in order to obtain stable foam, the material’s viscosity needs to be significantly modified and a reactive extrusion process used. Therefore, the extruder is more than a process aid to introduce a physical blowing agent. It also becomes a chemical reactor where the molten PET reacts with a modifier to change the polymer’s behaviour and significantly improve its ability to maintain a fine low-density foam status when cooling down.

Thermoplastic foam extrusion process

Thermoplastic foam extrusion process

Since post-consumer PET is widely recycled, there is an opportunity to utilize an already well-organized supply chain. Gurit recently invested in the vertical integration of the recycling technology, from the recycle stream (bottle and industrial) to the PET foam, with the aim of leveraging this supply chain and giving a second life to PET waste. The recycled PET is then processed into foam in a very energy efficient process with minimal waste. In the subsequent kitting process, PET structural foam is cut to fit the size and requirements of wind turbine blades. This cutting process generates waste, which would have to be disposed of. However, by co-locating extruders next to the kitting operations, this waste material can now be directly recycled in the adjacent extruder. This reduces overall costs while minimizing waste and transportation emissions. Gurit has started to implement such a co-location strategy to the benefit of its customers.

A sustainable offering
Both balsa and recycled PET are strong contributors to the wind energy sector’s target to reduce its environmental footprint even further and minimize waste without compromising on mechanical properties or resin uptake performance – at a competitive cost.

Gurit’s sustainable core materials offering for the Wind industry

Gurit’s sustainable core materials offering for the Wind industry

However, despite these innovations and advancements, challenges remain, for example the recyclability of advanced composite materials at the end of their life cycle. The scope of this challenge is such that only a broader industrial collaboration is likely to be successful in solving it.

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