3D printing PLA wastes were recovered from a well-known reference grade and from different sources. The recovered wastes were subjected to an energic washing step and then reprocessed into films by melt-extrusion, followed by compression molding to simulate the industrial processing conditions. The obtained materials were characterized and the optical, structural, thermal and crystallization behavior are reported. The mechanical recycling process leads to an increase of the crystallinity and a decrease of the intrinsic viscosity of the formulations, particularly in the sample based on blends of different 3D-PLA wastes. Moreover, the obtained films were disintegrated under composting conditions in less than one month and it was observed that recycled materials degrade somewhat faster than the starting 3D-PLA filament, as a consequence of the presence of shorter polymer chains. Finally, to increase the molecular weight of the recycled materials, the 3D-PLA wastes were submitted to a solid-state polymerization process at 110, 120, and 130 °C, observing that the recycled 3D-wastes materials based on a well-known reference grade experiences an improvement of the intrinsic viscosity, while that coming from different sources showed no significant changes. Thus, the results show that 3D printing PLA products provides an ideal environment for the implementation of distributed recycling program, in which wastes coming from well-known PLA grades can successfully be processed in films with good overall performance.

The importance of 3D printing is growing rapidly. A recent example of this increasing importance involves the fight against the Covid-19 pandemic, in which 3D printing has helped to overcome the shortage of critical supplies. However, 3D printing generates large amounts of plastic waste that could pose an environmental problem, thus making it necessary to find methods for the correct management of such wastes. The combination of additive manufacturing and distributed mechanical recycling can contribute to the development of a more circular economy. The main goals of this work were to characterize the poly(lactic acid) (PLA) wastes generated in 3D printing processes and evaluate the effect of their heterogeneity on the technical feasibility of mechanical recycling. Two PLA 3D printing wastes were used: waste coming from a well-known PLA grade, and a mixture of PLA 3D printing residues coming from an association of coronamakers in Madrid. Recycled material obtained from the waste of a well-known PLA grade shows good properties, similar to those for non-used material. However, the recycled material obtained from mixed PLA waste shows lower viscosity values, higher crystallization ability and less transparency. These results highlight that special attention should be paid to the sorting and characterization of the 3D wastes, to obtain recycled materials with good properties.