Stacking sequence effects on banana–pineapple hybrid epoxy composites

Natural-fiber epoxy laminates are increasingly used as sustainable alternatives to synthetic composites, yet how the through-thickness stacking sequence of hybrid plies governs their coupled thermal and mechanical response is not well established. This study fabricated four hand-lay-up/compression-moulded laminates at a constant 50 wt% total fibre loading, banana-only (Bf), pineapple-leaf-only (Pf), and two hybrids differing in both ply order and per-fibre loading (Bf/Pf: 30 wt% banana outer, 20 wt% pineapple; Pf/Bf: 20 wt% banana, 30 wt% pineapple outer), and characterised them by DSC, TGA, tensile, flexural, Izod impact, interlaminar shear, Shore-D hardness, density and SEM testing. The Bf/Pf laminate showed the highest glass transition response (344.38 °C DSC peak) among the four configurations, exceeding the pineapple-only laminate (323.79 °C), while pineapple-rich laminates also showed the highest TGA decomposition onset temperatures relative to the banana-only laminate (507 °C). The Pf/Bf laminate, with pineapple plies at the outer surfaces, gave the best mechanical performance: tensile strength 49.50 MPa (+ 27% over Bf/Pf), flexural strength 187.98 MPa (+18%), impact strength 45.50 kJ m⁻² and interlaminar shear strength 19.24 MPa, corroborated by SEM evidence of improved fibre–matrix adhesion and fewer interfacial voids. Because ply position and fibre-composition were varied together between the two hybrids, the relative contribution of stacking sequence alone is discussed as a design-level (not strictly isolated) effect, and composition-matched follow-up testing is identified as the next step to fully decouple the two variables. Overall, outer-ply placement of the higher-modulus pineapple fibre is identified as the primary lever for mechanical performance, whereas banana–pineapple co-lamination favours thermal stability, indicating a thermal–mechanical trade-off that can guide material selection for structural, automotive interior and packaging applications where either property is prioritised.

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