Hierarchical aerospace epoxy composites of carbon fiber and hyperbranched filler: toughening behavior from nanocomposites to composites

In this work the effect of a glassy hyperbranched polymer (G_HBP), characterized by a Tg higher than room temperature (-77 degrees C), on the mechanical properties of a patented epoxy resin was investigated. To define an optimized filler concentration, three different G_HBP contents were prepared by a solvent-free technique and improvements of fracture toughness compared to the neat matrix (Delta KC - 16 % and Delta GC - 39 %) and to the corresponding laboratory solvent-based procedure. The solvent-free procedure and the found optimal filler content were considered to manufactured long carbon fiber composite samples of both neat and G_HBP loaded matrix later tested and compared in terms of tensile and flexural properties, as well as fracture toughness performance. Mode I and II interlaminar fracture toughness tests were carried out, revealing remarkable increase of both onset and propagation (Delta GIConset - 29 % and Delta GICprop - 53 %) and preserving the GIIC value (Delta GIIC-+ 6 %). Validation tests in compression after impact were also performed and analyzed.