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Abstract
This study explores the development and characterization of sustainable polymer composites reinforced with coconut shell powder (CSP), an agricultural by-product, incorporated into a recycled polypropylene (rPP) matrix. The composites were fabricated via homogeneous blending using a twin-screw extruder followed by injection molding, with CSP loadings of 2%, 5%, 8%, 10%, 12.5%, 15%, 18%, and 20% by weight. The mechanical and physical properties, including tensile strength, Izod impact strength, hardness, and density, were systematically evaluated to determine the reinforcing effect of CSP as a natural filler within the recycled matrix. The results revealed a significant improvement in mechanical performance up to 15 wt.% CSP, where the tensile strength reached 25.60 MPa, yield strength increased to 20.99 MPa, and the elastic modulus nearly doubled to 1213.72 MPa compared to neat rPP. The impact strength improved to 5.98 kJ/m², Shore-D hardness increased from 68 to 71, and density rose from 0.890 g/cm³ to 0.930 g/cm³. Beyond this threshold, excessive filler loading led to particle agglomeration and reduced matrix cohesion. These findings indicate that CSP–rPP composites offer a promising balance between strength, stiffness, and weight, making them suitable for non-structural and semi-structural applications in marine auxiliary machinery systems, such as pump housings, valve components, insulation covers, and pipe supports, where corrosion resistance and low density are critical. Furthermore, the utilization of recycled and bio-based constituents contributes to sustainable shipbuilding practices, aligning with green ship design principles and international maritime environmental standards. This work highlights the potential of agricultural waste valorization in producing eco-efficient materials tailored for marine engineering applications.
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