<![CDATA[This study reports the development and multi-response optimisation of poly(vinyl chloride) (PVC) hybrid composites reinforced with coconut fibre and corncob ash for sustainable, low-load applications. Nine hybrid formulations, combining 3-10 wt.% coconut fibre and 3-10 wt.% corncob ash with a balance of PVC, were fabricated by compression moulding and evaluated for tensile strength, hardness, flexural strength and water absorption; the constituent materials and composites were further characterised by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). FTIR confirmed a hydrophobic, carbon-chlorine-rich PVC backbone, a hydroxyl-rich lignocellulosic coconut fibre and a siliceous corncob ash, indicating a physically compatible but chemically dissimilar hybrid system. SEM micrographs linked dense, well-wetted microstructures to superior hardness and flexural performance, whereas fibre pull-out cavities and heterogeneous interfaces corresponded with reduced tensile strength and higher water uptake, while XRD confirmed persistent, quartz-dominated crystalline phases that intensified with ash loading. Reinforcement reduced tensile strength from 55.46 MPa (control) to between 19.27 and 36.89 MPa, but increased hardness (up to 34.54 HV, +76.2%) and flexural strength (up to 41.79 MPa, +216.1%) relative to neat PVC, while water absorption rose from 0.60% to a maximum of 1.90%. A mixture-design, desirability-function optimisation that simultaneously maximised flexural strength and hardness while minimising water absorption identified a global optimum of 88.40 wt.% PVC, 5.95 wt.% coconut fibre and 5.66 wt.% corncob ash, predicting 32.14 MPa flexural strength, 29.11 HV hardness and 1.36% water absorption (composite desirability = 0.560). Benchmarked against recent PVC- and polymer-based natural-filler composites, this balanced formulation is proposed for non-load-bearing interior cladding, demonstrating a scientifically defensible route for valorising agricultural residues within sustainable PVC composite design]]>
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