Effect of sustainable fibers’ length on mechanical, acoustic, and physical properties of composite materials

With growing environmental concerns and the need for ecofriendly materials, sustainable natural fibers have gained significant attention as viable alternatives to synthetic reinforcements in composite manufacturing. This study investigates the influence of fiber length - specifically sisal, kenaf, and banana fibers - on the mechanical, thermal, acoustic and physical properties of composite materials. Using compression moulding technique, nine composite samples were fabricated with fiber lengths of 1.5 cm, 6 cm, and 10 cm. These were systematically evaluated for tensile strength, flexural rigidity, shore hardness, thermal conductivity, Ultraviolet (UV) protection, acoustic properties, water absorption and dimensional stability. The findings indicate that increasing fiber length generally enhances mechanical strength and thermal insulation, while shorter fibers are more effective at reflecting sound, revealing a trade-off between structural reinforcement and acoustic behaviour. Among the tested fibers, 10 cm sisal fibers yielded the highest tensile strength (463.7 kgf) and shore hardness (75), whereas banana fibers outperformed others in UV shielding (UPF = 2148.8), thermal insulation, and sound waves reflection. These results underscore the importance of optimizing fiber type and fiber length to achieve a balanced integration of safety, comfort, and environmental sustainability in helmet design.