Interlaminar Fracture Behavior of Polypropylene Fiber/Glass Fiber Hybrid Composites

Polymeric fibers were added to glass fiber-vinyl ester composites as an interlayer to improve fracture toughness. The polymeric fibers were expected to absorb and dissipate energy upon impact. Furthermore, the interlayer was thought to allow larger plastic deformation zone and affect failure mechanism and crack propagation. Commercial small diameter (~1 µm) polypropylene (PP) fibers were selected as the interlayer and commercial vinyl ester (VE) resins were used as matrix materials. The observed poor interface of PP and VE matrix drove us to improve the interfacial properties by adding functional groups on the fiber surface. Surface modification was conducted by applying silane-grafting at the surface of PP fibers after oxygen plasma treatment to create stable functional groups at the fiber surface. Untreated PP fibers or silane-modified PP fibers were used as an interlayer in the glass fiber-vinyl ester composites. Composites were fabricated via vacuum assisted resin transfer molding technique. Interlaminar fracture toughness in mode I and mode II, as well as short-beam strength, will be studied to evaluate the interlayer toughening, using glass fiber-VE composites as control. Volume fraction of each component and thickness of each layer for all composites will be measured to provide supplemental information for data analysis. Interfacial morphologies at the fracture surface will be investigated to analyze the micromechanical behavior.