Composites Strengthen Wind Turbine Blades

Biobased polyurethane materials and a new process from Bayer MaterialScience may help strengthen blades and decrease the weight of root rings in wind turbines while reducing volatile organic compounds (VOCs) in composites.

The traditional resin infusion process for forming large, high-strength components such as wind turbine parts uses vinyl ester, unsaturated polyester, and epoxy. These materials have limited strength and give off VOCs. Increasing blade sizes make limited strength a problem. The gravity-induced bending loads on blades increase dynamic stress, so materials that reduce blade mass while retaining blade strength are needed.

Bayer MaterialScience has developed the Baydur family of polyurethane systems for producing large polyurethane composites by vacuum infusion with increased stiffness and fatigue endurance. The composites are lighter, tougher, and stronger than their counterparts.

"Polyurethane has usually been associated with fast processing, such as reaction injection molding, not resin infusion, where gel times can be an hour or two," Dr. Usama Younes, Bayer's principal scientist, said in a press release. The Baydur resins possess low viscosity and long-gelling properties.

Compared with epoxy- and vinyl ester-based composites, the Baydur polyurethane system has a faster infusion time and superior tensile fatigue, interlaminar fracture toughness, and fatigue crack growth. "The infusion rate is about two times faster than epoxy," Younes told us in an email. "Tensile fatigue is about 10 times better than epoxy, and fracture toughness is about two times higher than epoxy. The Baydur sustainable raw material is a soy-based polyether polyol." Polyurethane also gives off fewer VOCs.