Pineapple leaf fiber (PaLF) is one of the promising natural fibers expected to be used as an alternative material to glass fiber. Ensuring interfacial adhesion between the matrix and fibers is critical for using natural fibers as reinforcements in composite materials. In this study, using thermoplastic bio-based polyamide resin as the matrix, the effect of the treatment time with sodium hydroxide solution on the fiber/matrix interfacial shear strength and fiber tensile strength were investigated. Alkaline treatment removed lignin and other minor components from the fiber surface, resulting in a reduction in fiber diameter. When the alkaline treatment was performed for 15 min, higher fiber/matrix interfacial shear strength was obtained. In contrast, although the interfacial shear strength decreased with treatments for 30 and 60 minutes, the tensile strength tended to improve. These results indicate that controlling the alkali treatment time is necessary to optimize both the fiber/matrix interfacial adhesion and fiber tensile strength.
