Effect of basalt and kenaf fiber hybridization on the physical, mechanical, and thermal properties of polymer composites

Abstract Fiber-reinforced polymer composites are important for sustainable structural materials, but balancing mechanical strength and thermal stability remains challenging, especially with natural and hybrid fibers. This study addresses the gap by examining basalt (B) and kenaf (K) fiber hybrid composites with different stacking sequences. The objective was to assess how fiber arrangement affects physical, mechanical properties, thermal stability, and microstructure in polyester composites. Six configurations (B/B/B, B/K/B, B/K/K, K/B/K, K/K/B, and K/K/K) were fabricated using hand lay-up and compression molding. Results show that B/B/B has the highest tensile strength (85 MPa), lowest void content (2.6 %), and minimal water absorption, indicating strong fiber–matrix bonding. The K/K/K composite exhibited the lowest tensile strength (42 MPa), highest void content (5.5 %), and greatest water uptake, reflecting poor bonding. Thermal analysis revealed degradation between 120 and 220 °C, with basalt-rich composites having lower thermal stability than kenaf-rich ones. SEM images confirmed strong adhesion in basalt-rich composites and fiber pull-out with matrix cracks in kenaf-rich laminates. These findings highlight that basalt fibers enhance mechanical properties while kenaf fibers improve thermal resistance, guiding the design of hybrid composites for applications requiring a balance of strength and thermal stability.