Alkali Treatment and Concentration Effects on Epoxy/Agel Fiber Composite Mechanical Properties for Marine Engineering Use

Abstract

The development of polymeric composite materials in shipbuilding has increased tremendously. To improve the sustainability of ship hulls, natural fibers have gained increasing attention as an alternative reinforcement material in polymer composites due to their renewability, low cost, and favorable specific mechanical properties. One of the natural resources that can be used as fiber reinforcement is agel leaf fibers (ALF). ALF is harvested from Corypha gebanga plant that is available throughout Indonesia. However, the inherent hydrophilicity and presence of non-cellulosic constituents on natural fiber surfaces often result in poor interfacial bonding with hydrophobic polymer matrices, limiting composite performance. This study investigated the effect of NaOH concentration and alkali treatment duration on the tensile properties of agel fiber-reinforced epoxy composites. Agel fibers were treated with NaOH solutions at concentrations of 1%, 2%, 3%, 4%, and 5%, with immersion durations of 1, 2, 3, and 4 hours, then rinsed with distilled water until reaching a neutral pH (7.5–8.5). The treated fibers were used as reinforcement in epoxy matrix composites fabricated using a self-made resin transfer equipment. Tensile testing was conducted at a loading speed of 5 mm/min to evaluate tensile strength and elongation at break for each treatment combination. Results showed that both NaOH concentration and treatment duration influenced mechanical performance in different manner. The mechanical properties of composites improved with longer duration. However, the effect of alkali concentration is more complex. The strength and stiffness behaves inversely with ductility. So the optimum parameter of ALF’s alkalization should be decided carefully depending on the priority of the mechanical characteristics required in the application. Based on the dataset obtained from the experiment, it is suggested that alkali treatment in 1% NaOH for 4 hours, yields a good balance of tensile strength, modulus of elasticity, and maximum elongation among all combinations.