Hydrothermal aging, diffusion behavior and mechanical properties of nano-silica doped natural fiber composites

Abstract In this study, the effects of nano-silica additive on the water absorption behavior, hydrothermal aging performance, and mechanical properties of hemp fiber-reinforced/epoxy polymer composites were experimentally investigated. Samples were aged in tap water at 30 °C for 800 h. Water absorption was measured experimentally and theoretically. The mechanical behaviors of the samples were evaluated under dry, wet, and re-dry conditions. The water absorption results showed that nano-silica additive affected the maximum weight change rates of the composites. While the maximum water absorption in the pure sample was measured as 37.464 %, this value decreased to 30.377 % and 29.758 % in the samples with 0.5 % and 1.5 % additive, respectively. Tensile test results showed that the highest strength in the dry condition was obtained in the sample with 1.5 % additive, reaching 73.23 MPa. Although tensile strength temporarily increased in wet conditions, all samples lost strength after re-drying. Flexural test results exhibited a more sensitive behavior to aging effects. Although the flexural strength decreased in the wet condition, partial recovery was observed after re-drying. For the 1.5 wt.% nano-silica composite, hydrothermal aging reduced the flexural strength from 84.36 MPa to 58.43 MPa, whereas re-drying restored the strength to 81.11 MPa, indicating partial recovery of the moisture-induced damage. Scanning electron microscope (SEM) analyses of fractured surfaces revealed that water related degradation at the fiber-matrix interface and damage mechanisms dependent on the nano-silica additive ratio were consistent with the mechanical results.