The disposal of plastic wastes in the environment has been an urgent issue due to pollution of the soil and the sea. The incorporation of polymeric residues into innovative and sustainable structural composites can be considered a promising recycling route. This work investigates the use of disposed polyethylene (PE) caps from drinking water bottles as a sustainable honeycomb core with circular cell geometry. A full factorial design was conducted to identify the effect of bottle caps orientation (single and alternated directions), polymeric adhesive (epoxy and polymer), and aluminium roughness (smooth and rough surface) on the mechanical properties of sandwich panels. The use of epoxy polymer contributes significantly to enhance panel strength and stiffness.Smooth aluminium skins lead to increased panel strength, suggesting a limited effect of roughness increase to enhance aluminium and skin bonding. Finally, single directed caps in the core achieve better mechanical performance than alternated caps. The results evidence the feasibility of alternative uses for bottle caps into structural and sustainable applications. 1.

This work describes aluminium skin sandwich panels made of recycled polyethylene (PE) bottle caps as a sustainable honeycomb core. A full factorial design is carried out to identify the effects of the orientation of the caps (single and alternated caps), skin roughness (smooth and rough substrate) and the type of adhesive (epoxy or polyester polymer) on the mechanical properties of the panels. Numerical analysis is performed to better assess the failure mechanisms involved. Sandwich panels made with epoxy adhesive, smooth aluminium skin and single oriented caps obtain greater mechanical properties at failure compared to the alternative levels of the factorial design. Increased results are observed for core shear stress (0.38 MPa), facing stress (56.75 MPa), core shear modulus (16.70 MPa), and flexural modulus (1437.47 MPa). This performance reveals an alternative recycling route for used PE bottle caps in structural and sustainable applications.