Hybrid bamboo-banana-cotton sandwich composites for lightweight roofing: Mechanical, thermal and microstructural analyses

The growing demand for sustainable and energy-efficient building materials has led to increased interest in natural fiber-reinforced composites as alternatives to conventional synthetic materials. This study explores the fabrication and characterization of bamboo-banana-cotton hybrid sandwich composites for sustainable roofing applications. The composites were fabricated using the compression molding technique, with a total fiber content of 35 wt% incorporated into epoxy resin (65 wt%). Bamboo woven sheets (20 wt%) were utilized as the skin layers, while banana and cotton fibers (15 wt%), in varying proportions, formed the core layer. Their mechanical properties (flexural, impact, and hardness) and thermal properties (conductivity, thermogravimetric analysis, and stability), as well as their microstructure, chemical composition, and water absorption are then examined. It is found that the composite containing 20 wt% bamboo, 11.25 wt% cotton, and 3.75 wt% banana exhibits superior flexural modulus (2.87 GPa), flexural strength (124.61 MPa), impact strength (29.12 kJ/m 2 ), and thermal stability, along with a minimum water absorption rate. SEM micrographs reveal effective fiber–matrix interfaces—with bamboo skins and cotton/banana core fibers tightly embedded, minimal voids, and clearly delineated sandwich layers—while FTIR spectra display the broad O–H band at ∼3400 cm −1 , C–H stretches at ∼2900 cm −1 , C O vibrations at 1735 cm −1 , aromatic C C peaks at 1510 cm −1 , and C–O–C/C–O–H bands near 1050 cm −1 , confirming the characteristic functional groups and successful integration of the natural fibers within the crosslinked epoxy matrix. The findings highlight that these composites offer excellent mechanical and thermal insulation properties, making them lightweight, eco-friendly, and cost-effective solutions for energy-efficient roofing applications.