Effect of hygrothermal exposure on the mechanical characteristics of hybrid glass fiber/palmyra-palm-leaf-stalk-reinforced polyester composites

The growing demand for sustainable materials has increased interest in eco-friendly hybrid composites with enhanced mechanical and durability performance. The present study investigates the effect of hygrothermal aging on the mechanical and thermal behavior of palmyra palm leaf stalk/polyester composites with and without chopped strand mat glass fiber reinforcement. The composites were fabricated using the hand lay-up method and exposed to 40 °C and 90% relative humidity for 4 weeks to evaluate their environmental durability. Mechanical performance was assessed through tensile and flexural tests, while thermal, chemical, and morphological changes were analyzed using thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The results showed that hygrothermal aging progressively reduced the behavior of both composite systems. The tensile strength of the unreinforced composite decreased by 38.67%, whereas the chopped strand mat-reinforced composite showed a lower reduction of 35.30% after 4 weeks of aging. Similarly, the flexural strength decreased by 31.50% in the unreinforced composite and by 30.87% in the reinforced composite, indicating slightly better flexural retention in the hybrid structure. Thermal analysis revealed a 39.54% reduction in residual weight for the unreinforced composite, while the reinforced composite exhibited only a 15.52% reduction, confirming improved thermal stability. Fourier transform infrared spectroscopy and scanning electron microscopy analyses indicated that the incorporation of chopped strand mat glass fiber outer layers reduced moisture-induced degradation by improving interfacial protection and delaying structural damage. Overall, the hybrid composites exhibited better resistance to hygrothermal aging, demonstrating their potential for lightweight structural applications requiring enhanced environmental durability.