Multi-scale "core-sheath" structure of electrospun veils to enhance the interlaminar fracture toughness and in-plane properties of CF/poly(phthalazinone ether ketone) laminates

Carbon fiber reinforced polymer laminates' weak interlaminar properties limit application in high load-bearing structural components. Interleaving electrospun polymer veils or nanofillers between layers has been shown to improve laminate interlaminar fracture toughness (ILFT). In this work, we constructed a "core-sheath" reinforced veil based on a bionic principle inspired by the "tree-root system" by combining ZnO nanowires with electrospun nanofibres to achieve uniform nanocomponent distribution and directional modulation. The effect of "core" structures with different thermal properties and "sheath" structures with different dimensions on the mode I and mode II interlaminar fracture toughness were investigated. It was found that mode I and mode II ILFTs impose different requirements on the interlaminar reinforcement structure due to the different loading modes. The intact nanofiber morphology and longer ZnO nanowires are more advantageous for mode I ILFT. Mode II ILFT, however, is more dependent on the adhesion of the reinforcing veil to the matrix. Mode I and mode II ILFTs values increased by up to 75.6% and 118%, respectively, when enhanced with suitable reinforcement veils.