Interlaminar toughening of resin transfer molded laminates by electrospun polycaprolactone structures: Effect of the interleave morphology

Today, fiber reinforced polymer composites are a standard material in applications where a high stiffness and strength are required at minimal weight. Although fiber reinforced polymer composites show many advantages compared to other materials, delamination between reinforcing plies remains a major problem limiting further breakthrough. Previous work has shown that electrospun nanofibers can significantly improve the interlaminar fracture toughness of fiber reinforced composites thus preventing delaminations. In the present paper, the effect of the morphology of the toughening polymer is analyzed by incorporating different polycaprolactone structures in the interlaminar regions. Both Mode I and Mode II interlaminar facture toughness of composites containing five different electrospun morphologies - nanofibers, microfibers, microspheres, dense films, and PCL spray coated glass fibers - were evaluated. Analyzing the fracture behavior of the PCL toughened laminates ensures a better insight in the micromechanical fracture mechanisms behind the observed interlaminar fracture toughness and results in guidelines on the optimal interleave morphology. The results clearly demonstrate the distribution of PCL in the interlayer has a large effect on the crack path of the delamination and the resulting interlaminar fracture toughness. In order to improve the interlaminar fracture toughness in both Mode I as well as Mode II without adverse effects, porous PCL structures such as PCL nanofibers, microfibers, and microspheres are much more suitable than non-porous structures such as PCL films or spray-coated glass fibers. Among the porous structures, the nanofibers had an overall better performance with an increase in Mode I and Mode II interlaminar fracture toughness of about 60% and 80% respectively.