Dynamic Mechanical and Tensile Behavior of Epoxy Composites Reinforced with B4C- and Gd2O3-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 \(^{\circ }\text {C}\), and the highest glass transition temperature of 116.8 \(^{\circ }\text {C}\). 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.