Hierarchical Fracture Toughening of Epoxy by MWCNT ‐Doped Electrospun Polysulfone Interlayers Under Notched Tensile Loading

Epoxy‐based nanocomposite laminates reinforced with electrospun polysulfone (PSU) nanofiber interlayers, with and without multi‐walled carbon nanotubes (MWCNTs), were fabricated and evaluated under notched tensile loading. The study was structured around a systematic design matrix consisting of 13 material groups: neat epoxy and PSU nanofiber interlayer systems produced with 0, 1, 2, and 3 wt% MWCNT at 5, 10, and 15 interlayer counts, with five specimens prepared for each group. Fracture performance was compared using an apparent critical stress‐intensity factor, , calculated for a finite‐width single‐edge‐notched strip under uniform tension. Both interlayer number and MWCNT content affected . The highest value was obtained for the 15‐layer laminate containing 1 wt% MWCNT, which reached MPa m 1/2 and showed a 96% improvement over neat epoxy. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations linked the fracture‐resistance trend to a structure–mechanism–property relationship involving nanotube dispersion, interlayer‐mediated crack tortuosity, crack bridging, and interfacial wetting/debonding. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) showed higher residual mass for the reinforced laminates and an increase in glass‐transition temperature with MWCNT addition.