Effect of NaOH Concentration, Fiber Length, Fiber Loading, and Filler Loading on the Mechanical Properties of Banana Fiber‐Reinforced Polyester Composites

The growing demand for eco‐friendly, lightweight, and high‐performance materials has driven the development of natural fiber‐reinforced polymer composites for use in construction, manufacturing, and automotive applications. However, identifying the optimal fabrication parameters for these composites remains a significant challenge. In this study, polyester‐based composites were fabricated using a simple hand lay‐up method, reinforced with banana fibers and nano alumina (Al 2 O 3 ) powder. Banana fibers of random orientation were used in three lengths (10 mm, 15 mm, and 20 mm) and treated with NaOH solutions at concentrations of 0%, 2.5%, and 5%. A total of nine composite samples were produced by varying the weight percentages of banana fiber (10%, 15%, and 20%) and nano alumina (2 wt%, 4 wt%, and 6 wt%). Gray relational analysis (GRA) was employed to optimize the influence of fiber length, NaOH treatment, fiber content, and filler content on mechanical properties. The optimized composite achieved a tensile strength of 61.7 MPa, a flexural strength of 108.47 MPa, and an impact strength of 19 J at 15 wt% fiber content, 2 wt% nano alumina, 15 mm fiber length, and 5% alkali treatment. The maximum hardness value of 164 HV was recorded for a composite with 20 mm untreated fiber, 15 wt% fiber loading, and 4 wt% nano alumina. The lowest water absorption rate (2.97%) was observed with 10 wt% fiber loading, 6 wt% nano alumina, 20 mm fiber length, and 5% NaOH treatment. These findings contribute to the development of sustainable composite materials, with potential applications in the automotive and aerospace industries.