Comparative mechanical performance of halloysite and graphene modified unidirectional GFRP laminates

Abstract In this study, the effects of graphene and halloysite fillers on the mechanical properties of GFRPC were experimentally investigated. A reference composite unfilled was produced; in addition, six different composites were prepared containing graphene and halloysite at 0.5, 1, 1.5 wt.%. All samples were prepared according to ASTM standards and subjected to tensile and compressive tests in the directions parallel to the fibers (0°) and perpendicular to the fibers (90°), as well as bending tests. In tensile tests, both filler types increased strength in the 0° direction but decreased ductility values. In the 90° direction, graphene filler decreased strength, while 1.5 % halloysite filler provided a limited increase in tensile strength. In compressive tests, both filler types showed improvements, especially in the 90° direction; graphene filler provided the highest increase in strength. In the 0° direction, graphene increased compressive strength, while halloysite addition significantly improved deformation capacity. In bending tests, fillers generally reduced strength; however, graphene filler increased deformation capability, exhibiting more elastic behavior. SEM analyses showed that graphene has a leaf-like and sometimes agglomerated morphology, while halloysite has a tube-like structure and is more homogeneously distributed within the matrix. The findings reveal that the type, ratio, and loading direction of the filler significantly affect the composite performance.