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Reactive infusible thermoplastics have the potential to be advantageous for wind turbine blade composites because they are recyclable at end of life, can have reduced manufacturing costs, enable thermal joining and have similar, and in some cases better, structural properties than traditional thermoset epoxy composites. However, these materials are new to the wind industry and there is risk to investing in a material that has not been validated at a blade scale. Industry cannot adopt a new material such as this without large-scale validation and demonstration of system-level advantages in cost and/or performance. This paper presents structural characterization of a 13-m thermoplastic composite wind turbine blade compared to an identical geometry thermoset epoxy blade. The results of this comparison showed that the flatwise structural static performance and the fatigue performance of the two blades were similar, but the thermoplastic composite blade had increased damping compared to the epoxy blade, which may result in reduced operational loads.

Two-part, in-situ reactive thermoplastic resin systems for composite wind turbine blades have the potential to lower the blade cost by decreasing cycle times, capital costs of both tooling and equipment, and energy consumption during manufacturing, and enabling recycling at the end of the blade life. This paper describes a techno-economic model used to estimate the cost of a thermoplastic wind turbine blade relative to a baseline thermoset epoxy blade. It was shown that a 61.5-m thermoplastic blade costs 4.7% less than an equivalent epoxy blade. Even though the thermoplastic resin is currently more expensive than epoxy, this cost reduction is primarily driven by the decreased capital costs, faster cycle times, and reduced energy requirements and labor costs. Although thermoplastic technology for resin infusion of wind turbine blades is relatively new, these results suggest that it is economically and technically feasible and warrants further research.

Reactive thermoplastics are advantageous for wind turbine blades because they are recyclable at end of life, have reduced manufacturing costs, and enable thermal joining and shaping. However, there are challenges with manufacturing wind components from these new materials. This work outlines the development of manufacturing processes for a thick glass fiber–reinforced acrylic thermoplastic resin wind turbine blade spar cap, with consideration given to effects of the exothermic curing reaction on thick composite parts. Comparative elastic properties of these infusible thermoplastic materials with epoxy thermoset materials, as well as thermoplastic coupon components, are also included. Based on the results of this study it is concluded that the thermoplastic resin system is a viable candidate for the manufacturing of wind turbine blades using vacuum-assisted resin transfer molding. Significant gains in energy savings are realized avoiding heated molds, ability for recycling, and providing an opportunity for utilizing thermal welding.

A biaxial resonant test method was utilized to simultaneously fatigue test a wind turbine blade in the flap and edge (lead-lag) direction. Biaxial resonant blade fatigue testing is an accelerated life test method utilizing oscillating masses on the blade; each mass is independently oscillated at the respective flap and edge blade resonant frequency. The flap and edge resonant frequency were not controlled, nor were they constant for this demonstrated test method. This biaxial resonant test method presented surmountable challenges in test setup simulation, control and data processing. Biaxial resonant testing has the potential to complete test projects faster than single-axis testing. The load modulation during a biaxial resonant test may necessitate periodic load application above targets or higher applied test cycles.

Blade testing is required to meet wind turbine design standards, reduce machine cost, and reduce the technical and financial risk of deploying mass-produced wind turbine models. NREL?s National Wind Technology Center (NWTC) in Colorado is the only blade test facility in the U.S. capable of performing full-scale static and fatigue testing of multi-megawatt-scale wind turbine blades. Rapid growth in wind turbine size over the past two decades has outstripped the size capacity of the NWTC blade test facility leaving the U.S. wind industry without a suitable means of testing blades for large land-based and offshore turbines. This CRADA will develop and commercialize testing technologies and test equipment, including scaling up, value engineering, and testing of equipment to be used at blade testing facilities in the U.S. and around the world.

Currently, wind turbine blades are manufactured from a combination of glass and/or carbon fiber composite materials with a thermoset resin such as epoxy, which requires energy-intensive and expensive heating processes to cure. Newly developed in-situ polymerizing thermoplastic resin systems for composite wind turbine blades polymerize at room temperature, eliminating the heating process and significantly reducing the blade manufacturing cycle time and embodied energy, which in turn reduces costs. Thermoplastic materials can also be thermally welded, eliminating the need for adhesive bonds between blade components and increasing the overall strength and reliability of the blades. As well, thermoplastic materials enable end-oflife blade recycling by reheating and decomposing the materials, which is a limitation of existing blade technology. This paper presents a manufacturing demonstration for a 9-m-long thermoplastic composite wind turbine blade. This blade was constructed in the Composites Manufacturing Education and Technology facility at the National Wind Technology Center at the National Renewable Energy Laboratory (NREL) using a vacuumassisted resin transfer molding process. Johns Manville fiberglass and an Arkema thermoplastic resin called Elium were used. Additional materials included Armacellrecycled polyethylene terephthalate foam from Creative Foam and low-cost carbonfiber pultruded spar caps (manufactured in collaboration with NREL, Oak Ridge National Laboratory, Huntsman, Strongwell, and Chomarat). This paper highlights the development of the thermoplastic resin formulations, including an additive designed to control the peak exothermic temperatures. Infusion and cure times of less than 3 hours are also demonstrated, highlighting the efficiency and energy savings associated with manufacturing thermoplastic composite blades.