Effect of Silane Grafting of PET Foam and Areca Fiber on Hot Water Aged Vinyl Ester Composite

This study investigates the development and performance evaluation of sustainable composites using recycled PET foam core, areca fiber, and pectin-modified vinyl ester resin. The surface of the PET core and areca fiber was modified with 3-aminopropyltrimethoxysilane to enhance fiber–matrix bonding. The composites were fabricated using a hand layup method, and mechanical, thermal conductivity, and flammability properties were evaluated under untreated and silane-treated conditions, including aging treatments with hot water at 50 °C and cold water at 20 °C. The results demonstrate that the silane-treated composites exhibit significantly better performance than untreated specimens across all tests due to improved fiber–matrix adhesion. Specifically, specimens O1 and O2, composed of 60 vol% PET foam core, 20–30 vol% areca fiber, and 3 vol% pectin filler, show superior properties. O1 shows increases in tensile strength from 34.24 to 40.66 MPa, flexural strength from 64.73 to 76.51 MPa, and interlaminar shear strength from 7.65 to 10 MPa. O2 similarly shows an increase in tensile strength from 37.45 to 43.87 MPa, flexural strength from 70.62 to 84.74 MPa, and interlaminar shear strength from 9.18 to 11.53 MPa. These enhancements are attributed to the combined effect of pectin filler and silane treatment, which improves fiber–matrix interactions and load transfer capabilities. Thermal conductivity also shows notable improvements with silane treatment, enhancing the heat transfer properties of the composites due to better interfacial bonding. The SEM analysis further confirms these findings, showing enhanced fiber–matrix bonding with fewer voids and gaps, even after aging, indicating that silane treatment improves the durability and mechanical integrity of the composites. This makes the silane-treated composites, particularly O1 and O2, suitable for structural, automotive, and marine applications requiring high strength, durability, and thermal stability.