Supramolecular topological adhesion boosts delamination resistance in carbon fiber reinforced polymers

In this study, we introduce supramolecular topological adhesion as an innovative and effective methodology to enhance interlaminar fracture toughness in carbon fiber reinforced polymers (CFRPs). We achieved remarkable improvements in delamination resistance by physically entangling phenoxy resins within an epoxy matrix and introducing sacrificial H-bond interactions via ODIN (1-(7-Oxo-7,8-Dihydro-1,8-Naphthyridin-2-yl)urea) units. The ODIN units form sextuple H-bonding dimers in the cured epoxy matrix among plies, experimentally quantified via UV-Vis spectroscopy, whose detachment hinders crack propagation. The viability of this approach was tested using various phenoxy resins with different molecular weights and with different levels of ODIN functionalization. Single lap shear (SLS) tests demonstrated a notable increase in adhesion strength, sorting out PKHB-ODIN 13% as the best candidate as interlaminar adherent. Delamination resistance was determined through double cantilever beam (DCB) and end-notched flexure (ENF) tests, showing up to 120% and 80% increases in Mode I and Mode II fracture toughness, respectively. The limited DCB and ENF test increments observed for control adherent PKHB-PU 23% functionalized with phenylurea (PU) groups, demonstrates that the strength of topological H-bonding is pivotal to boost delamination resistance. The results indicate that this method holds great potential for improving the durability of CFRP composites, especially in applications requiring high resistance to delamination.