Synergetic improvement of interlaminar fracture energy in carbon fiber/epoxy composites with nylon nanofiber/polycaprolactone blend interleaves

Carbon fiber/epoxy (CF/EP) composites are highly utilized materials for many applications in aeronautical and aerospace structures because of their superior specific mechanical properties. However, delamination between adjacent plies remains a major problem owing to the inherent brittleness of epoxy matrix. In the present work, PA66 nanofiber/PCL blend films were used as interleaves to increase the interlaminar fracture energy of CF/EP composites. PA66 nanofibers maintained their one-dimensional structure during epoxy curing, while PCL first melted and then mostly phase-separated from epoxy. It was found that modes I and II fracture energies of the laminates interleaved with PA66 nanofiber/PCL blend films were increased significantly by 110% and 101%, respectively, demonstrating a synergistic effect. At the same time, the flexural strength and flexural modulus of the CF/EP laminates were unchanged. DMA tests confirmed better interfacial adhesion between PA66 nanofibres and epoxy when PCL was added. Blend interleaves with nanofibres embedded in a polymer matrix with a low melting point provide a new route to synergetic enhancement of the delamination fracture energies of CF/EP laminates.