Dynamic Mechanical and Tensile Behavior of Epoxy Composites Reinforced with BC- and GdO-Modified Electrospun Nylon 6.6 Nanofiber Mats

Abstract

Epoxy resins are widely used in structural and functional composite components; however, their inherently brittle fracture behavior and temperature-dependent stiffness degradation limit their reliability under combined mechanical and thermomechanical loading. In this study, L160 epoxy composites were reinforced with electrospun nylon 6.6 (N6.6) nanofiber mats modified with B4C, Gd2O3, or hybrid B4C/Gd2O3 nanoparticles, thereby introducing ceramic functionality through the nanofiber interleaf rather than by direct nanoparticle dispersion into the resin. Five systems were examined: neat epoxy (Epoxy), epoxy with neat N6.6 mats (Epoxy/N6.6), and epoxy with B4C-modified, Gd2O3-modified, or hybrid-modified N6.6 mats (Epoxy/N6.6/B4C, Epoxy/N6.6/Gd2O3, and Epoxy/N6.6/B4C-Gd2O3, respectively). The mats were incorporated by a layer-by-layer hand lay-up route to obtain 16-layer composite plates, and the resulting systems were evaluated by SEM, TEM, XRD, EDX, FTIR, TGA, tensile testing, fracture-surface analysis, and dynamic mechanical analysis. Neat N6.6 mats increased the tensile strength of epoxy from 71.24 to 75.73 MPa, whereas B4C-modified mats produced the highest tensile strength of 88.65 MPa, corresponding to a 24.45% improvement. The hybrid B4C/Gd2O3-modified system exhibited the highest approximate onset temperature of the principal mass-loss stage, 390 degrees C , and the highest glass transition temperature of 116.8 degrees C . Fractographic observations showed brittle fracture in epoxy-rich regions and fiber pull-out, fiber breakage, interfacial debonding, and crack bridging in nanofiber-rich regions. Within the tested formulations, B4C modification gave the highest tensile strength, whereas the hybrid-modified system gave the highest reported approximate onset temperature of the principal mass-loss stage and tan-delta peak temperature. Residual voids and incomplete wetting were observed in some laminates and are considered when interpreting the results.