Mechanical Performance Retention of CNT-­ Modified Sisal Biocomposites Under Hygrothermal-­ Saline Aging

This study investigates the influence of carbon nanotubes (CNTs) on the moisture absorption kinetics and mechanical deg- radation of discontinuous random fiber (DRF) biocomposites under accelerated hygrothermal–saline (HTS) aging. CNTs are dispersed into an epoxy matrix via shear mixing at concentrations of 0.25, 0.5, and 1 wt% to fabricate compression-­ molded sisal-reinforced composites with a 30% fiber volume fraction. The research evaluates how nanofiller incorporation modulates the interfacial integrity and residual mechanical properties of the biocomposites following HTS exposure. Mechanical characteriza- tion, including tensile, flexural, impact, and short-­ beam shear (SBS) tests, is conducted on samples in three distinct conditions: before aging (UNAGED), immediately following aging (WET), and after a one-­ week recovery period via air-­ drying (DRY). CNTs incorporation significantly mitigated moisture diffusion, yielding a 58% reduction in water absorption after 3 weeks of HTS ex- posure compared to the neat biocomposite. In the UNAGED state, the optimized CNTs-­ reinforced composites exhibit strength increases of 21% (tensile), 13% (flexural), 34% (impact), and 26% (SBS). These improvements are even more pronounced in DRY samples, where gains reach 85%, 51%, 19%, and 73%, respectively. The optimal CNTs concentration is found to be sensitive to the specific mechanical loading mode and aging exposure. Together with an economic sustainability study, the outcomes clarify the mechanical interplay of CNTs, fibers, and matrix under HTS environment exposure history, highlighting the improvements in life-­ span extension obtained and the annexed economic investment required, serving as design guidelines for the application of biocomposites to industrial components.