Mechanical and Morphological Characterization of Agricultural Waste-Reinforced Recycled HDPE Composites for Offshore Cage Frames

Abstract

This study presents the fabrication and properties of eco-friendly composite materials using recycled high-density polyethylene (rHDPE) as the matrix, reinforced with agricultural by-products, including wood powder, coconut fiber, and rice-husk-derived nano-silica (SiO₂). Nano-SiO₂ with a size range of 10–20 nm was successfully extracted from rice husk ash. The composites were prepared via thermal melting and compression molding at 180°C and 5 tons of pressure. Structural and morphological properties were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Mechanical tests revealed that the addition of 2 wt% nano-SiO₂ significantly improved the tensile strength (640.88 MPa) and elastic modulus (1141.48 MPa) compared to those of pure rHDPE, 402.16 and 953.07 MPa, respectively. While increasing the content of wood powder or coconut fiber generally decreased tensile strength, these fillers modified flexural and water absorption properties. The significantly improved tensile and elastic properties confirm that structural requirements for marine aquaculture systems. By utilizing agricultural waste and recycled plastics, this material serves as a potential low-cost substitute for expensive virgin HDPE, drastically reducing the capital investment for offshore cage frame fabrication. These findings support the transition towards sustainable, bio-based engineering solutions for the regional mariculture industry.