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 circular economy model offers great opportunities to companies, as it not only allows them to capture additional value from their products and materials, but also reduce the fluctuations of price-related risks and material supply. These risks are present in all kind of businesses not based on the circular economy. The circular economy also enables economic growth without the need for more resources. This is because each unit has a higher value as a result of recycling and reuse of products and materials after use. Following this circular economics framework, the Polytechnic University of Madrid (Universidad Politécnica de Madrid, UPM) has adopted strategies aimed at improving the circularity of products. In particular, this article provides the result of obtaining recycled PLA filament from waste originating from university 3D FFF (fused filament fabrication) printers and waste generated by “Coronamakers” in the production of visors and parts for PPEs (Personal Protective Equipment) during the lockdown period of COVID-19 in Spain. This filament is used in the production of 3D printed parts that university students use in their classes, so the circular loop is closed. The obtained score of Material Circularity Indicator (MCI) of this material has been calculated, indicating its high level of circularity.

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.

Corrugated cardboard has waved cores with small flutes that prevent the use of detailed numerical models of whole structures. Many homogenization methods in the literature overcome this drawback by defining equivalent homogeneous plates with the same mechanical behaviour at a macro-mechanical scale. However, few homogenization works have considered complete structures, focusing mainly on beams or plates. For the first time, this study explores the application of homogenization approaches to larger structures as an aid in their design process. We also considered triple-wall boards rather than single- and double-wall configurations commonly addressed in the literature. To this end, we adapted the homogenization methods proposed by Talbi and Duong to analyze thin-walled stools made of triple-wall corrugated cardboard. Using a progressive design process, we performed an efficient stool design by removing material zones with lower stresses, with 35% less material, 35% lower vertical deflections, and 66% lower stresses than the initial design. Unlike other corrugated cardboard stools, this design comprises just one folded piece instead of three, thus saving storage space. These results demonstrate the utility of homogenization techniques as an aid in the design process of whole structures made of corrugated cardboard. Further research will consider buckling analysis.

A traditional use of bioenergy is the main source of residential energy in developing countries, essentially using firewood to cook, boil water or heating affecting people in developing countries. Improved cook stoves are more efficient and less polluting, and there is a need to evaluate different design options to facilitate their adoption. There are different types of very economical improved cookstoves with high combustion efficiency. In Mexico, multiple projects about cook stoves have been carried out, the root of this study being one of them: the Patsari cook stoves. The goal of this project was to modify previous stove designs to align with local people’s habits and traditions. This study shows the importance of including the participation of users in the design of the portable model of Patsari cook stoves, applying the Design Thinking methodology. Many designs or design changes have been carried out on cook stoves by different researchers, but users often do not adapt to them. This article, through a field study, shows the importance of integrating theoretical analyses along with user experiences to facilitate the adoption of improved cook stoves and ensure their success.