Interphase-mediated toughening of poly-(lactic acid) by hierarchical carbon nanotube and carbon fiber reinforcement

Polylactic acid composites reinforced with carbon nanotubes (CNTs) and carbon fibers (CFs) were investigated to assess their morphological and mechanical properties. Nanocomposites (0–1 wt% CNT) and hybrid composites (30 wt% CF with 0–1 wt% CNT) were analyzed using small-angle neutron scattering, X-ray diffraction, differential scanning calorimetry, and mechanical testing. The CNT-only composites showed CNT aggregation, while hybrid composites exhibited improved CNT dispersion and extended structures due to CF-assisted distribution. Both reinforcements increased the rigid amorphous phase and reduced crystallinity, suggesting refined crystalline structures. X-ray diffraction revealed enhanced lateral crystallite growth, particularly in CF-containing systems, indicating the crystal nucleating behavior of the reinforcing materials. Mechanical testing demonstrated significant improvements in tensile strength, elongation at break, and toughness in hybrid composites, with optimal performance at 0.25–1 wt% CNT. These results highlight a synergistic effect between CNTs and CFs, enhancing both dispersion and composite performance.