Waste-derived sustainable coir composites for thermal insulation applications with enhanced mechanical properties

Upcycling waste materials is a key step towards a circular bioeconomy by reducing the reliance on virgin resources, maximizing resources efficiency and minimizing environmental impact. Sustainable materials aim to establish a circular bioeconomy to maximize resources efficiency and promote positive social and environmental impacts. This research investigates the development of eco-friendly thermal insulating sustainable composite using waste coir fibers and waste polypropylene. To enhance fiber-matrix adhesion and improve composite properties, coir fibers underwent alkaline treatment. Compression molding was employed to fabricate coir-fiber reinforced composite sheets with varying coir fiber loadings (30%, 35%, and 40%). The resulting composites exhibited enhanced thermal insulation properties, characterized by reduced thermal conductivity up to 0.10 W/m.K, moderate specific heat capacity up to 1.8844 J/g°.C and lower thermal diffusivity up to 5.28 × 10^{− 8} m²/s, as fiber loading was increased. Moreover, the mechanical properties of tensile strength, tensile modulus, Charpy impact strength and drop weight impact strength were improved by 20%, 74%, 146% and 109%, respectively when coir fiber loading was increased from 30% to 40%. Higher mechanical properties and lower thermal properties demonstrate the potential of coir-fiber reinforced composite as a sustainable and high-performance thermal insulation material for domestic applications, contributing to waste upcycling, resource efficiency and environmental sustainability.