Wind Blades of a Different Stripe

Launched in September 2020, the ZEBRA (Zero wastE Blade ReseArch) project is led by French research center IRT Jules Verne, with partners that include resin manufacturer Arkema, R&D center CANOE, wind farm operator Engie SA, blade manufacturer LM Wind Power, glass fiber producer Owens Corning and recycling expert SUEZ. ZEBRA’s goal is to demonstrate, at full scale, the technical, economic and environmental advantages of fully recyclable thermoplastic wind turbine blades.

Nicolas Valloir, business manager at Arkema, spoke with Composites Manufacturing magazine about the project.

CM: What’s the background of the ZEBRA project?

Valloir: It goes back about five years ago, to when IACMI started working with the National Renewable Energy Laboratory (NREL) and with industry partners on a project that focused on finding a solution for end-of-life wind blades. Arkema became involved because we had developed Elium^®, the first liquid thermoplastic resin designed for manufacturing composite parts with mechanical properties similar to thermosets. The NREL team produced a 9-meter blade and then a 13-meter blade, and we learned a lot about making wind blades with this resin.

The French National Research Agency was really interested in the work that was done, and in September 2020 it created the ZEBRA project to take this research further. They assembled multiple partners along the value chain and funded this program so we could go from manufacturing a blade all the way through to the recycling of the blade.

CM: How is the ZEBRA project different from IACMI’s work?

Valloir: The work at IACMI was on small blades, but here we are talking about blades that are 62 meters plus. We also needed to fine tune a resin with a longer filing time, so we changed the formulation. The blade manufacturer we’re working with already had its own setup, so we’ve had to adapt some things to work with that.

CM: Thermoset composites have been the material of choice for wind blades for many years. Why move to thermoplastics?

Valloir: The industry adopted thermosets at the beginning because of the way you can process them. The resin is in a liquid form, so you can wet out the fiber. It’s faster and cheaper.

We’ve had some thermoplastic wind blades in the past, but the resin was still in solid form, so you had to process it at high temperature, and it’s impossible to inject with continuous fibers.

Elium changes the paradigm because it is the first liquid thermoplastic resin. We can make it work like a thermoset resin. So you get all the advantages of thermosets in terms of processing, but at the same time, as a thermoplastic, it’s thermoformable and recyclable. That means we can infuse parts, we can do pultrusion and we can do filament winding like we do with a thermoset. But the material is still a thermoplastic.

The mechanical properties of the thermoplastic blades are very similar to the epoxy thermoset blades. In fact, the first results show that we could possibly be 5% better, which could potentially increase the life cycle of the blade. But we still have to correlate that with more iterations, so at the moment we can’t really say if we are better or worse than the current solutions.

CM: What’s the main value proposition for thermoplastic wind blades?

Valloir: On performance we’re about the same, and in terms of the price of resin we’re in the same ballpark as epoxy. We are seeing a reduction in curing time for thermoplastic wind blades, so you’re going to save in the manufacturing process.

But the key driver for thermoplastics is recyclability. In Europe and here in the United States, we have more and more demand every day for sustainable materials. The fact that we can recycle thermoplastics is why I hope this industry will adopt them in the future.

CM: What will the recycling process for thermoplastic wind blades look like?

Valloir: First, we’re not talking about recyclability 10 or 20 years in the future. We’re talking about recycling today because thermoplastic construction scrap manufacturing waste is recyclable. When you trim the blade, or have a bad pass, you have production scrap that can be recycled, which can be up to 10% of the material used.

For this we use a mechanical way of recycling, where you take all these production scraps, grind them up and then inject them like a plastic to make a different product. For one customer we’ve made a table that’s very much like casting resin from these scraps. You could also manufacture products like cell phone cases.

In this type of recycling, the performance is different from the original material, because you’re downcycling. But if you have a cell phone case made out of thermoplastic wind blade scraps, you’re going to increase its mechanical performance by nearly 20% in some cases.

Today people pay to bury this scrap, but with this solution they will add value and they can get the material for free. It’s not very complicated, and it doesn’t take a large capital investment.

CM: What about recycling when the wind blades reach end of life?

Valloir: We would do that recycling with a chemical treatment. You’re going to recover more than 90% of the monomer and all the fiber. You’re going to be able to use that resin again and again, and you’re going to get exactly the same properties as the virgin resin.

We did some life cycle analyses, and with thermoplastic blades made with Elium you can save the carbon consumption of manufacturing by recycling.

This process already works on an industrial level. It’s just a question of scale. To be able to justify the capital investment to recycle this, you’re going to need a big amount of material to keep the plant working.

CM: Can wind blade manufacturers use the same equipment for producing thermoplastic wind blades that they’re using for thermoset blades?

Valloir: They wouldn’t have to change their setups, although they would have to make some adjustments. The equipment to dispense the resins will be different, and the way that Elium polymerizes makes it a shorter process. They’d also need a special mold release. But it would not take huge capital investment to switch from a thermoset blade to a thermoplastic one.

CM: Are there differences in the other materials used for thermoplastic blades?

Valloir: We can work with all the glass fibers on the market. The type of glass fiber really depends on the blade design.

If you don’t have good sizing with this material, then you can have a problem with compaction and delamination. But as long as we use good sizing, there isn’t a problem.

The adhesive used to bond the two shells of the wind blades together was challenging. The requirements for the wind blade are pretty high – they last 20, 30, 40 years – so we had to find a formulation that could make it through all the tests that have to be done for certification. We worked with our sister company, Bostik, and came up with a formulation last August that is specially developed to work with Elium and that can fulfill all the requirements.

CM: What blades has ZEBRA produced so far?

Valloir: We manufactured our first 62-meter blade at the beginning of 2022, and we’re going to do another one at the beginning of this year, using some carbon fiber reinforced thermoplastic parts inside the blade.

There’s a mechanical load in the interior of the blade that has to be sustained, and the type of fiber is a key factor. So they are currently using carbon fiber parts [with epoxy resin] there. But if you want to recycle the entire blade – and that is the idea – you have to make the entire blade with thermoplastics, not only the shells but also the interior parts. So that is challenging.

Another step in the project is going to be to increase the size of the blades to 100 to 120 meters in the future. Because the thermoplastic resin is very similar to an epoxy, we don’t see why we wouldn’t be able to do that.

CM: Are there any thermoplastic blades in use in a wind turbine today?

Valloir: Right now the first blade is still under mechanical evaluation. We have to go through a lot of tests to certify the blade, and the blade manufacturer will have to certify the design with the Elium resin. So it’s going to take a few more months until we can commercially fly the first thermoplastic blade, but we hope that’s within three years.

CM: How do you anticipate the market will react once thermoplastic wind blades can be manufactured at a large scale?

Valloir: It’s up to us as consumers to push really hard for this new technology. If consumers push for more recyclable materials, then I think the market adoption will be pretty quick because we will be changing the paradigm. We also have governments passing legislation on adopting more sustainable materials.

I really expect that we will see the industry change pretty quickly and choose more materials.

Mary Lou Jay is a freelance writer based in Timonium, Md. Email comments to mljay@comcast.net.