Development and Characterization of Functionally Graded Sisal/Glass Fiber-Reinforced Polymer Composites

Structural applications require materials that provide an optimal balance of strength, durability, and sustainability. This study develops functionally graded sisal/glass fiber-reinforced polymer composites and evaluates their tensile, compressive, and flexural properties, as well as their water absorption behavior. First, an experimental approach was adopted in which sisal fibers were treated with a 6% sodium hydroxide (NaOH) solution to improve fiber–matrix adhesion. The composites were fabricated using the hand lay-up method with varying sisal fiber ratios. Mechanical testing showed that the composites achieved a tensile strength of 146 MPa for the rectangular specimens and 199.5 MPa for the composite bars. The highest compressive strength (120 MPa) and flexural strength (326 MPa) were observed at 20% sisal fiber content. In addition, finite element analysis (FEA) results showed maximum tensile and compressive strengths of 181.24 MPa and 147.57 MPa, respectively, and were in reasonable agreement with the experimental results. Moreover, water absorption studies showed a direct correlation between fiber content and moisture uptake, with values of 1.40% (10% sisal), 2.55% (20%), and 3.85% (30%). The results indicate that functionally graded sisal/glass fiber-reinforced composites exhibit superior mechanical properties compared with conventional composites. The graded structure enhances design flexibility, optimizing material performance for structural applications. These findings highlight the potential of functionally graded composites as a sustainable alternative that addresses the limitations of traditional materials while promoting more efficient and environmentally friendly engineering solutions.