A novel biological core material from Agave sisalana flower stalks for bio-based composite sandwich panels

Among plant-grown lignocellulose-based core materials, balsa wood remains unique for its combination of low density and high mechanical properties, making it the predominant natural alternative to petrochemical rigid foams in sandwich panels for low-density and structural applications. The flower stalk of Agave sisalana P. exhibits a rigid, foam-like cellular structure in its core, with densities lower than those of conventional balsa wood (57-84 kg/m3). Given the growing demand for sustainable and circular material solutions, this work introduces this underutilised by-product of the sisal fibre production as a novel bio-based core material. This study presents a multi-scale characterisation using SEM and μCT to establish a relationship between cellular architecture and performance. This is supplemented by mechanical tests and analyses that assess structural, property, and sustainability performance indicators. The compressive properties demonstrate highly anisotropic behaviour. Flexural testing of the composite sandwich panels demonstrates that the agave core material has competitive strength (57.9 ± 4.3 MPa) and effective stiffness (94.35 ± 5.8 Nm2), offering a sustainable alternative to balsa and petrochemical rigid foams such as PU, XPS, or rPET. Overall, the novel core material exhibits a lower performance-related environmental impact than balsa. Its lower density and comparable mechanical performance make it a promising sustainable core material for mass-efficient applications.