Effect of kenaf and oil palm fibers on the mechanical, physical and morphological properties of the bio-epoxy hybrid composites

Despite the growing use of bio-composites, the challenge of achieving optimal mechanical and water-resistance properties in natural fiber hybrids remains underexplored. This study investigates the mechanical, physical and morphological properties of novel innovative bio-epoxy composites reinforced with hybrid kenaf and oil palm fibers. Five bio composites, pure kenaf (K), pure oil palm (O) and hybrids 7K3O, 5K5O and 3K7O, were fabricated and evaluated. Each consisted of 50 wt% fibers with varying kenaf-to-oil palm ratios and 50 wt% epoxy resin. Mechanical and physical properties of bio-composites analysed. Fracture morphology was examined via scanning electron microscopy (SEM). Results showed that increasing kenaf content improved tensile strength and stiffness, with the 7K3O composite achieving the highest tensile strength (37.66 MPa) and modulus (5.50 GPa) due to strong interfacial bonding and high cellulose content. In contrast, impact strength and resistance were highest in the kenaf-composite (K), reaching 6977.8 J/m² and 71 J/m respectively, suggesting superior energy transfer despite brittle failure. Among hybrids, 7K3O demonstrated competitive impact performance, while 3K7O (4801.8 J/m², 49.4 J/m) underperformed, likely due to voids and poor fiber-matrix bonding. The 5K5O hybrid showed the highest water absorption (14.78 %) and swelling (16.36 %), reflecting inefficient fiber packing and interfacial voids. Conversely, the 7K3O hybrid, despite having the highest void content (7.50 %), exhibited the lowest swelling (9.32 %), indicating better void isolation and matrix encapsulation. SEM analysis corroborated these findings, showing fiber breakage in kenaf-rich bio composites and fiber pull-out in oil palm rich ones, with hybrids displaying mixed failure modes. These findings affirm the synergistic potential of fiber hybridization. The 5K5O and 7K3O hybrids demonstrate balanced mechanical behaviour, making them suitable for multifunctional uses such as automotive components and sustainable construction materials. The 7K3O hybrid composite exhibited the highest tensile strength of 37.66 MPa, along with a good balance of stiffness and ductility and reduced water absorption (10.9 %), outperforming the single fiber composites (12.7 % for oil palm-only composite).