Impact-modified polyamide 11/carbon nanotubes 3D printing and potential enhancement of toughness in fiber reinforced polymers

Fused filament fabrication (FFF) of semi-crystalline polymers, such as polyamide 11 (PA11), is challenging due to significant shrinkage that occurs during cooling. This issue can be mitigated by blending the polymer with chemically compatible additives, which alter its rheological, thermal, and mechanical properties, thereby improving processability. In this study, we demonstrate the successful FFF printability of PA11 filaments modified with an ethylene–acrylic acid copolymer grafted with maleic anhydride (EAA-g-MAH) as an impact modifier. Carbon nanotubes (CNTs) were incorporated to compensate for the loss in terms of stiffness caused by the addition of EAA-g-MAH compound. Bulk compositions were prepared via melt compounding and compression molding and characterized, revealing that the addition of 20 wt% EAA-g-MAH increased the specific impact energy of PA11 by 282%. Two optimized impact-modified PA11 formulations—with and without CNTs—were subsequently extruded into filaments and, for the first time, successfully 3D printed through FFF. Mechanical testing demonstrated substantial improvements in ductility for the 3D-printed specimens, with increases of up to 56% for unfilled PA11 and 105% for CNT-reinforced PA11, relative to their bulk counterparts. This work opens new possibilities for directly printing tough polymers onto reinforcing fibers to create self-healing composites. Additionally, strong interfacial adhesion was achieved between glass fibers and the printed CNT-reinforced PA11, suggesting a potential increase in interlaminar toughness in fiber reinforced polymers (FRPs). These multifunctional materials processable via FFF represent a promising step toward the development of smart, self-healing structural composites.