Properties of hybrid fiber- and filler-reinforced epoxy/polyurethane matrices

In this study, six epoxy (E)-based glass fiber (GF)/bamboo fiber (BF) composites were fabricated with a constant fiber fraction of 30% and a matrix fraction of 70%, wherein the epoxy matrix was systematically modified using polyurethane (PU), waste rubber (WR), and aluminum–silicon (Al–Si) fillers. The composites (B1–B6) were prepared via the hand layup process and tested as per American society for testing and materials (ASTM) standards. Compositionally, the epoxy content ranged from 44% to 47%, PU from 22% to 23%, and hardener from 4.3% to 4.7%, with selective incorporation of WR (∼3.3–3.6%) or Al–Si (∼3.3%). Performance evaluation revealed distinct property tailoring: B1, with ∼46.7% epoxy, showed the lowest water uptake (0.21%) and the highest flexural and interlaminar shear strength (ILSS) due to its rigid, cross-linked epoxy network and strong fiber adhesion; B2 (45% epoxy, 22.7% PU) exhibited the most prominent viscoelastic response in Dynamic mechanical analysis (DMA), with maximum storage modulus and clear loss modulus/damping peaks at Tg = 75–85 °C, indicating an excellent stiffness–damping balance; and B3, containing ∼3.55% WR, achieved the highest tensile strength (37.69 MPa) via crack-blunting mechanisms typical of rubber-modified epoxies. By contrast, Al-Si filled composites (B5, B6) absorbed more moisture and displayed reduced bending and shear properties, attributed to interfacial flaws and void-induced weakening. Overall, these findings highlight how epoxy matrices can be micro-engineered through the combination of rigid networks, elastomeric tougheners, and polymeric additives to unlock customized performance behaviors suited for structural panels, automotive interior parts, vibration-damping components, protective casings, building reinforcement elements, and environmentally resilient lightweight laminates.