Zebra project: three questions to Jean-Paul Moulin, Material Science Director at Arkema

JEC Composites Magazine: What stage has the Zebra project reached?   

Jean-Paul Moulin: The Zebra project has just demonstrated that it is possible to manufacture fully recyclable wind turbine blades in a closed loop. We’re talking about a closed loop because, by using chemical recycling through thermolysis, we can recover the resin and the glass fibre, which can then be reintegrated into new wind turbines.    

Our project addresses the wind energy market in its entirety. It covers all types of wind turbine blades, including very large offshore blades.    

Zebra is first and foremost an R&D programme. We first demonstrated through sample tests that it was possible to manufacture recyclable blades, and then manufactured 62 and 77 metre blades. These blades are built using Arkema’s Elium resin and Owens Corning’s Ultrablade fabrics. One of the two blades includes a major structural element made from recycled Elium resin. They have the required aerodynamic and mechanical properties.   

We are now going to manufacture wind turbine blades to get them approved. This is quite a long process, which can take 2 or 3 years. It involves manufacturing blades, fitting them to a turbine and then validating their operation under real conditions. The manufacturing processes must be representative of industrial production. The use of Elium resin requires a few adaptations to the resin supply and the infusion zones, but the process remains very similar to traditional processes.   

Why are there two types of recycling involved in the treatment of blades?   

J.-P. M.: Two main types of recycling are used in this project: mechanical recycling, which is feasible in the short term for production scrap, and chemical recycling by thermolysis, which will enable larger volumes to be processed at the end of the life of wind turbine blades. The composite parts of wind turbine nacelles may also be concerned. Mechanically recycled parts can be converted into compounds that can be used in other applications or to manufacture parts or reinforcements that can be used again in the composition of wind turbines. This is known as downcycling, because the fibres cut during compounding no longer have the same performance. Elium is a thermoplastic that can be used in other applications when mechanically recycled.   

Chemical recycling allows us to recover the resin and the fibreglass, so that both can be reintegrated into new wind turbines. This is known as upcycling. When the resin is heated to between 300 and 400 degrees, it breaks down into its original monomer, methyl methacrylate (MMA), making it possible to produce a new resin for making blades. This recycling method was first tested on laboratory samples and then on real blade parts, achieving a yield of 75%, which is already excellent for a composite. It has also been made possible by the development of a Bostik adhesive compatible with blade assembly.  But we are already working on several ways that will enable us to achieve a yield of over 90%, which is the one that can be achieved with resin alone.   

What are the ecological and economic advantages of the solution proposed by Zebra?   

J.-P. M.: The ecological benefits lie first and foremost in the fact that wind turbines are a way of producing the low-carbon electricity needed for the ecological transition. There are also manufacturing benefits. Thermoplastic resin, easier to recycle at the end of the product’s life, enables us to work at lower temperatures than those required by current thermosetting resins, resulting in lower energy consumption.  Recycling at lower temperatures and without solvents is also more economical than existing solutions for these same thermosets. It allows us to recover clean reinforcements and reusable monomers without altering their properties. Owens Corning thus recovers glass fibres that it can remelt and reintegrate into its Sustaina product range.   

The life of a wind turbine is theoretically around thirty years, so the business model that will result from the Zebra project has yet to be put in place – we’re only at the beginning of the circularity loop.