The Effects of Fiber Treatment on Tensile, Compressive, and Impact Strength of Sisal‐Polyester Composite Laminates

ABSTRACT

Natural fiber‐reinforced polymer composites have attracted considerable attention as sustainable alternatives to synthetic fiber composites because of their low cost, biodegradability, and favorable mechanical properties. This study investigates the influence of alkali (NaOH) and silane surface treatments on the mechanical performance of sisal fiber‐reinforced polyester composites. The hand lay‐up method was used to fabricate laminated composites, and ASTM‐compliant tensile, compressive, and impact tests were conducted. The silane treatment raised the tensile strength by 12.3% to 129.6 MPa, while the alkali‐treated composites showed the maximum tensile strength of 135.1 MPa, a 17.1% increase over the untreated composites. Similarly, compressive strength increased by 27.5% for the alkali‐treated composites (110.3 MPa) and by 20.9% for the silane‐treated composites (104.6 MPa). Impact strength also increased by 11.3% for alkali‐treated composites (from 150.64 kJ/m ² to 167.73 kJ/m ² ) and by 6.8% for silane‐treated composites. Alkali treatment enhances fiber surface roughness and mechanical interlocking by removing hemicellulose, lignin, and other surface impurities, whereas silane treatment improves fiber–matrix adhesion through chemical coupling. The improved mechanical performance results from this technique. A one‐way analysis of variance (ANOVA) and Tukey's Honestly Significant Difference (HSD) test revealed significant increases in mechanical parameters (p < 0.001).