Investigation of the effect of SiO2 and melamine cyanurate fillers loading on the physical, mechanical, vibration, and flammability behaviors of hybrid waste mesocarp fiber/denim fabric epoxy composites

The transition to a green economy is motivating industries to replace non-renewable materials with sustainable alternatives derived from agricultural and industrial waste. Therefore, this study aims to evaluate palm-oil mesocarp fiber (MF) and denim textile waste as reinforcing constituents for hybrid fiber-reinforced polymer composites (FRPC) to address performance limitations of natural-fiber composites in structural and safety-sensitive applications. Two separate sets of hybrid composites were fabricated: one modified with silicon dioxide (SiO 2 , 1–3 wt%) and another modified with melamine cyanurate (MCA, 5–15 wt%). The characterization process included physical, mechanical (tensile, flexural, and buckling tests), vibration (natural frequency and damping ratio), and flammability (vertical and horizontal burning) tests. The experimental results showed that hybridization with denim improved load transfer, flexural or tensile response, and damping capacity. SiO 2 loading also increased density, stiffness, and strength but reduced ductility and damping, which are associated with matrix stiffening and particle agglomeration at higher filler loadings. Among the MCA-filled composites, 5 wt% MCA provided the highest tensile strength, while 10 wt% MCA resulted in the highest tensile modulus. The 15 wt% MCA formulation exhibited the greatest reduction in water absorption and the highest flame-retardant performance. The observations indicated that SiO 2 -filled composites were more effective in enhancing stiffness-related properties, whereas MCA-filled composites provided greater improvements in moisture resistance and flame-retardant behavior. These findings highlight the importance of selecting appropriate filler types and loading levels according to the intended structural application.