Upcycling Postconsumer Polypropylene/Aluminum Multilayer Packaging Waste into Functional Additives with Improved UV Protection

Polymers, particularly in laminated packaging, play a crucial role in preserving product quality and shelf life in the food and cosmetic industries. However, the widespread use of multilayer packaging, which consists of polyolefins and aluminum, poses significant recycling challenges. This study investigates the mechanical recycling of postconsumer multilayer packaging through cleaning and size reduction to obtain micron-sized aluminum-containing particles, which are used as additives. These particles are compounded with neat polypropylene in a twin-screw extruder and subsequently employed as feedstock for injection molding. This additive has dual functionality, serving as both a metallic pigment and an ultraviolet (UV) protective additive for injection-molded PP parts. The mechanical properties of the recycled composite, including tensile strength, elastic modulus, and ductility, were quantitatively comparable to those of neat PP, with an elastic modulus of approximately 1.9 GPa and a maximum tensile stress close to 38 MPa for particle contents between 15 and 25 wt %. These properties remained essentially unchanged with respect to neat PP, indicating no major loss in structural integrity. Fracture tests revealed that composites containing recycled particles behaved in a more ductile manner than neat PP, exhibiting larger deformation capability. An increase in fracture toughness of PP was observed when recycled particles were incorporated into PP (from 40.5 N·mm–1 to ∼50 N·mm–1) with no significant differences among composites with varying particle content. UV degradation tests showed that recycled aluminum particles provide moderate resistance to oxidation, delaying carbonyl group formation. This study confirms the feasibility of transforming postconsumer multilayer packaging waste into sustainable composite materials, supporting circular economy initiatives.