Interlaminar fracture toughness of carbon fiber/epoxy–polyimine laminates with dynamic imine bonds

Interlaminar delamination limits the damage tolerance of carbon-fiber laminates and remains challenging to quantify and mitigate using conventional thermoset matrices. Here, the Mode I and Mode II interlaminar fracture behavior of carbon-fiber/epoxy-polyimine laminates containing dynamic imine bonds was investigated using double-cantilever beam and end-notched flexure tests, with cohesive-zone simulations employed to assist interpretation. The polyimine used in this study is chemically distinct from polyimide, as it is based on reversible imine (C = N) bonds rather than permanent imide linkages. The laminates exhibit interlaminar fracture toughness values of 2.39 kJ/m²in Mode I and 6.03 kJ/m²in Mode II. The simulations show good agreement with the measured load-displacement responses and support the interpretation that the dynamic interface delays delamination growth. As an additional demonstration, partial property recovery is observed after hot-press treatment, indicating potential for maintainable laminate structures. Overall, the results provide experimental evidence and supporting modeling for improving delamination resistance in epoxy-based carbon-fiber laminates via dynamic imine bonding.