Reengineering structural properties of recycled semi-crystalline polymers

Most of the plastic materials produced to date are not biodegradable and, therefore, their discards that escape waste-management will persist in the environment for centuries and are already causing ecological disruption. These challenges motivate the concept of a circular economy in which polymers can be recycled multiple times and maintain their valuable structural material properties. Therefore, understanding the deterioration of polymers’ mechanical properties in each step of a recycling process is of high priority to guide the design of polymeric materials, their manufacturing processes, and their recycling processes. In this work, we investigate the effect of repeated recycling on the static mechanical properties of a semi-crystalline polymer (PLA). With the objective of uncovering the degradation mechanisms induced by repeated recycling, the mechanical properties of multiple-times recycled semi-crystalline PLA in injection molding and fused filament fabrication (FFF) additive manufacturing processes are analyzed. Basic microstructural observations are carried out on as-received and recycled semi-crystalline polymers to observe initial defects/voids and how the material morphology changes with recycling. Furthermore, we investigate the potential of pretreating the recycled material to promote in situ crystallization during additive manufacturing to improve the structural properties.