Recycled Thermoplastics for 3D Printing Filament Production: A Review of Circular Economy Drivers, Material Behavior, and Current Research Gaps

The article focuses on the potential of recycled materials for the production of 3D printing filaments.. The individual parts are focused on defines the relationship between circular economy/3D printing technology, and the key motivations for the use of recyclates in the context of sustainability. Core of the article describes different types of recycled polymers, with emphasis on the number of recycling cycles and the associated changes in material properties. It also includes a discussion of degradation processes resulting from repeated thermal loading, i.e., mechanical recycling. Simultaneously, individual recyclates are comparatively evaluated in terms of mechanical properties, rheological characteristics (particularly the melt flow index), and their processability in 3D printing. Furthermore, key challenges are identified, and perspective directions for future research in this field are outlined.