Mechano-electric conversion of biaxially oriented polypropylene films from plastics-packaging waste sources

Abstract

Biaxially oriented polypropylene (BOPP) is a widely used packaging polymer with excellent dielectric and mechanical properties and large-scale availability. In this study, we demonstrate that post-consumer waste BOPP films, collected after their intended use without any reprocessing, can directly serve as functional materials for energy harvesting and sensing. Using three designed experimental modes: static contact under defined pre-pressure, dynamic contact–separation, and non-contact arrangement, it is possible to disentangle the roles of triboelectric charging, electrostatic induction, and strain-gradient-induced polarization. Notably, the static-contact mode produced significant voltage signals (up to ±15 V) without macroscopic separation of electrodes, highlighting a practical route for applications where large-scale motion is undesirable. Comparative analysis with re-melted BOPP, isotactic polypropylene, and amorphous polypropylene revealed similar triboelectric charge densities. Long-term cycling tests (1000 compression cycles) confirmed excellent durability, supported by tensile testing and surface roughness analysis. The results demonstrate that the common packaging BOPP film exhibits the electromechanic response under pressure-driven excitation, making it a promising candidate for low-cost energy harvesting and sensing applications.