Powder binders used for the manufacturing of wind turbine rotor blades. Part 2. Investigation of binder effects on the mechanical performance of glass fiber reinforced polymers

The automated manufacturing of wind turbine rotor blades needs binder systems which meet the requirements for online processing, show good preforming properties and do not affect the mechanical performance of the glass fiber reinforced polymer (GFRP) composites. In this study, especially the binder effect on the mechanical performance of corresponding glass fiber reinforced polymer is focused on. Three commercially available thermoplastic binders of different chemical composition and solubility in a rotor blade proven epoxy resin are used: Grilon MS (strongly soluble), D 2433E (partially soluble) and K140 (non-soluble). After manufacturing the binder-modified glass fiber reinforced polymer plates by the vacuum-assisted resin infusion technique, their mechanical performance is investigated with respect to binder solubility and concentration (1-3 wt.%). The mechanical characterization is based on tensile and compression tests - both longitudinal (0 degrees) and transversal (90 degrees) - as well as shearing tests (+/- 45 degrees). It is found that the glass fiber reinforced polymer strength and stiffness is strongly controlled by binder solubility and content. In the case of limited binder solubility and insolubility (D 2433E and K140), the performance of the composites reduces significantly as binder content increases. In contrast, stiffness and strength are not affected by the soluble binder Grilon MS, regardless of its content. These glass fiber reinforced polymer results strongly correspond with the results obtained for binder modified resin plates in a previous study. This correlation highlights the fact that binder ability for the preforming process might be classified by a simple pre-test for solubility and mechanical properties using the modified resin instead of applying the costly and time-intensive manufacturing steps of glass fiber reinforced polymer plates.