Characterization of Mechanical, Viscoelastic, Thermal Properties of Epoxy/Mariscus ligularis Fiber Composites

Environmental concerns drive the demand for sustainable alternatives to synthetic materials, as high synthetic usage leads to waste and toxic emissions, while natural fibers offer biodegradability, low cost, and lightness. In this study, Mariscus ligularis fiber, developed into bidirectional mats with orientations of ±45°, ±60°, and 0°/90° (A, B, and C), was reinforced with epoxy resin LY556 and hardener HY951. Nine composite laminates with 20, 30, and 40% fiber weight fractions were fabricated using hand lay-up techniques. The mechanical, viscoelastic, thermal, heat distortion temperature (HDT), Vicat softening temperature (VST), and water absorption properties were characterized according to ASTM standards. The mechanical characterization reveals that the 0°/90° laminate with 40% fiber (C40) exhibited the best tensile strength (22.97 MPa) and flexural strength (45.31 MPa). The ±60° laminate with 40% fiber (B40) had the highest impact strength (8 J) and hardness (93.25). The viscoelastic studies indicated that the C40 composite exhibited the most elevated storage modulus (Eʹ) and loss modulus (Eʺ), and the highest glass transition temperature (T_g), signifying strong interfacial bonding and effective stress transfer. The thermal stability of the composites is up to 270 °C. C40 had an HDT of 60.2 °C, a VST of 75.3 °C, and a minimal water absorption of 4.5% after 24 h. The microstructural study confirmed favorable fiber-matrix adhesion and structural properties, making these composites suitable for automotive interior panels and lightweight applications.