Low-Temperature Assembling Strategy of a Nacre-Inspired Lamellar Configuration to Upcycling Biaxially Oriented Polypropylene Film Waste.

The efficient recycling and utilization of plastic waste have become a hot topic of global concern, but conventional mechanical recycling not only deteriorates the performance of recycled plastic but also loses the intrinsic structure and properties of the original product. Herein, an upcycling strategy of a biaxially oriented polypropylene (BOPP) film was proposed by duplicating the lamellar configuration established in nature nacre. Especially the suspension of PP wax was deposited on the surface of the BOPP film by spray-coating, followed by layer-by-layer assembling and hot-pressing at 160 °C above the melting temperature of PP wax but below the initial melting temperature of the BOPP film. In this case, PP wax not only functioned as a binder to enable strong interfacial adhesion between the BOPP films via interfacial diffusion but also acted as a soft phase to insert between the rigid BOPP films, constructing a soft-hard alternatively aligned configuration similar to brick-and-mortar architecture in nature nacre. As a result, the mechanical properties of the lamellar sample markedly outperformed those of the conventional mechanically recycling sample, evidenced by 113 and 1141% increases in tensile strength and impact strength, respectively. This simple and effective method provides a new strategy for efficient upcycling of oriented packaging films, which is important to realize the sustainable recycling of plastic waste.