Effect of Alkali Treatment on the Structure, Mechanical Behavior and Damage Response of Areca Leaf Sheath Fiber Reinforced Epoxy Composites

Areca leaf sheath fiber (ALSF) was investigated as a sustainable reinforcement for epoxy composites, focusing on the effects of sodium hydroxide (NaOH) treatment on structural, mechanical, and thermomechanical properties. ALSF was treated with 0, 3, 5, 7, and 10% NaOH, and composites were fabricated using 200 mL of epoxy resin through compression molding at 50 bar and room temperature for 24 h. FTIR and XRD were used to examine chemical modifications and crystalline characteristics, respectively. Tensile, flexural, impact, hardness, and dynamic mechanical properties were evaluated to determine the influence of alkali treatment. Among the investigated concentrations, 5% NaOH provided the best overall performance. Tensile strength increased from 18.2 to 26.4 MPa, while flexural strength improved from 31.5 to 42.6 MPa. Impact strength increased from 6.3 to 9.8 kJ/m2, and Shore D hardness rose from 62 to 72. Higher NaOH concentrations reduced performance, suggesting excessive fiber modification and structural degradation. XRD and dynamic mechanical analysis supported treatment-dependent changes in crystallinity and glass-transition behavior. SEM revealed fiber fragmentation, irregular fracture regions, possible fiber pull-out, and matrix cracking. These findings demonstrate that controlled alkali treatment, particularly at 5% NaOH, enhances the mechanical and thermomechanical performance of ALSF/epoxy composites.