Pengaruh Konsentrasi NaOH dan Durasi Alkalisasi terhadap Sifat Mekanik Komposit PLA/Serat Rami Berorientasi Searah

Abstract

This study examines the effect of NaOH alkalization concentration (5%, 10%, and 15%) and immersion duration (2, 3, and 4 hours) on the tensile and flexural properties of unidirectional long ramie fiber-reinforced polylactic acid (PLA) composites, fabricated by hot pressing at 140°C for 15 minutes with a fiber-to-matrix mass ratio of 40:60. Tensile and flexural testing were carried out using a Universal Testing Machine (Hung Ta HT-2402), and the resulting data were analyzed with descriptive statistics and two-way ANOVA. Alkalization enhanced the mechanical properties of the composite by removing lignin, hemicellulose, and surface impurities, which improved interfacial adhesion between the ramie fibers and the PLA matrix. Tensile strength reached its highest value of 137.88 ± 12.48 MPa at 5% NaOH for 4 hours, with 5% and 10% NaOH consistently producing tensile strengths in the range of 132–138 MPa across all durations, while 15% NaOH was markedly lower (99–108 MPa) at every duration tested. The highest tensile modulus, 2.87 ± 0.22 GPa, was obtained at 10% NaOH for 2 hours, and the highest yield stress, 1.51 ± 0.75 MPa, at 15% NaOH for 4 hours. For flexural properties, the highest flexural strength (91.66 ± 27.20 MPa) occurred at 5% NaOH for 2 hours, while the highest flexural modulus (10.30 ± 4.43 GPa) was recorded at 15% NaOH for 2 hours, with 15% NaOH consistently yielding the highest flexural modulus across all durations tested. Two-way ANOVA showed that alkalization duration significantly affected all five mechanical parameters tested (tensile strength, tensile modulus, yield stress, flexural strength, and flexural modulus). NaOH concentration was a significant factor for tensile strength, yield stress, and flexural strength, but had no significant effect on tensile modulus or flexural modulus. The concentration–duration interaction was significant only for tensile strength and yield stress. These results indicate that the optimal alkalization condition differs depending on the mechanical property of interest, and that excessive NaOH concentration degrades tensile-related properties through cellulose structure damage, even as it continues to enhance flexural stiffness