Improved sustainable sandwich panels based on bottle caps core

A sandwich panel based on upcycled bottle caps core and sustainable components is investigated to contribute to advances in lightweight and environmentally friendly structural solutions. Ecological alternatives to the panel skin and adhesive, such as a recycled PET-bottle foil and a castor oil bio-polyurethane, respectively, are tested and compared to commercial components (aluminium skin and epoxy polymer). Bottle caps are characterised using a small punch test specially developed to obtain the properties of the bottle caps. Additionally, low-cost reinforcement (Portland cement) is added to adhesives to enhance the mechanical behaviour of the panel. The sustainable panels achieve enhanced efficiency compared to aluminium-based panels for core shear strength and stiffness, besides having similar specific flexural properties compared to those of epoxy-based PET panels. Despite their higher strength and stiffness, epoxy polymer-based panels show visible adhesive peeling off to bottle caps core and aluminium skin. In contrast, the biopolymer exhibits larger deformation and debonding of both substrates, indicating a progressive and ductile failure. The satisfactory efficiency of sustainable panels confirms the promising reuse of recycled bottle caps in structural applications.