Effect of surface-modified makana fiber and Selenicereus undatus nanocellulose on the mechanical performance of vinyl ester composites under different service temperature conditions

This study investigates the development of makana fiber-reinforced vinyl ester composites incorporated with crystalline nanocellulose derived from dragon fruit ( Selenicereus undatus ) to enhance mechanical performance and long-term durability. Composites were fabricated with 40 vol.% makana fiber and varying nanocellulose contents (0, 1, 3, and 5 vol.%), designated as VC0, VC1, VC2, and VC3. The incorporation of nanocellulose significantly improved tensile, flexural, impact, hardness, and interlaminar shear properties, with the VC2 composite (3 vol.%) exhibiting optimal performance, achieving a flexural strength of 187 MPa and impact energy of 4.98 J. These enhancements are attributed to improved interfacial adhesion and effective stress transfer between the matrix, fiber, and nanocellulose. However, a slight decline in properties at 5 vol.% was observed due to nanocellulose agglomeration. Fatigue and creep analyses demonstrated reduced crack propagation and lower time-dependent deformation, indicating enhanced durability under cyclic and sustained loading. Scanning electron microscopy revealed good nanocellulose dispersion, strong fiber–matrix interaction, and energy-absorbing mechanisms such as fiber pull-out. Overall, the results highlight the importance of optimizing nanocellulose content to achieve a balance between strength, toughness, and long-term stability, supporting the suitability of these composites for advanced engineering applications.