Powder binders used for the manufacturing of wind turbine rotor blades. part 1. Characterization of resin-binder interaction and preform properties

Glass fibre reinforced plastics (GFRP) are the predominant materials used for wind turbine ro-tor blades. To manufacture blades in a vacuum-assisted resin infusion process (VARI), a binder is needed for fibre fixation and preform stability. Moreover, solubility and mechanical compatibility of the binder and the epoxy resin matrix are important parameters for processa-bility and the mechanical properties of the composite. The present study therefore character-ised and evaluated five chemically different binders with regard to their solubility in a rotor-blade-proven epoxy resin using microscopy, viscometry and differential scanning calorimetry (DSC). The solubility tests enabled a binder-classification into critically soluble (KE-60, Epikote 05390), strongly soluble (Grilon MS), partially soluble (D 2433E), and non-soluble (K-140) binder types. In subsequent mechanical and thermo-mechanical testing of resin-binder plates, the strongly soluble binder Grilon MS showed the best performance, followed by the non-soluble binder K-140 and the partially soluble binder D 2433E. These results suggest that binders developing no interfaces within the resin should be preferred. Furthermore, interply adhesion for these three binders was investigated in a peeling test using fibre preforms. It was found that differences in peel strength might be controlled predominantly by different kinds of binder layer formations, but also to some extent by the different binder-fibre interaction (binder and fibre sizing correlation). Best performance was shown by D 2433E, followed by Grilon MS and K-140. All in all, the soluble binder Grilon MS exhibited the best results in mechanical testing of resin-binder plates and is therefore expected to also show the best mechanical performance in GFRP laminates.