The demand for high-efficiency, low-energy consumption materials, with high durability and stability, has led to the rapid increase of the demand and prices of Rare Earth Elements (REE). The REE monopoly of some countries has held the shift of humanity towards sustainability and renewable energy sources back. The isolation, recovery, and recycle of REE from waste electric and electronic equipment (WEEE) constitute the disengagement strategy and can lead to significant economic benefits, via sustainability. The introduction of critical raw materials (RM), derived from WEEE, as additives to filaments used for the synthesis of composite materials, employed by Additive Manufacturing (AM) applications, has tremendous potential for the performance and the commercialization of the final products by adding unique characteristics, such as antibacterial properties, enhanced mechanical and magnetic properties, and thermal and electrical conductivity. The low cost of the recycled RM, the small numbers of process stages, and the inception of a zero-waste paradigm, present its upscalability, with a realistic view to its industrial employment. Although there are many articles in literature that have reviewed WEEE recycle, a comprehensive review on the conditions, parameters, procedure flow charts, and novel properties of the final composite materials with regards to every RM is missing.

Glass was introduced as an additive to filaments used for the manufacturing of composite materials, employed by Additive Manufacturing applications. Glass accounts for a large waste electric and electronic equipment (WEEE) percentage, and its recovery and recycling can lead to the production of sustainable composite materials. In this work, poly(lactic acid) (PLA)/commercially available silicon oxide composite filaments were manufactured and their structural, thermal, rheological, and mechanical properties were assessed. Scanning Electron Microscopy confirmed the 1:2 ratio of silicon: oxygen, along with the relatively low adhesion between the filler and the matrix. Differential Scanning Calorimetry presented steady glass transition and melting temperatures of composites, whereas a crystallization temperature of 10% wt. and a crystallinity of 15% wt. composite slightly increased. Rheological analysis showcased that the viscosity of the composite filaments decreased compared to PLA (10–100 compared to 300–400 Pa·s), with a more shear-thinning behavior. Dynamic mechanical analysis exhibited increased elastic, flexural moduli, and flexural strength of composites (up to 16, 23, and 11%, respectively), whereas tensile strength and elongation decreased. The affordability of raw materials (with the future introduction of recycled ones) and the minimal processing steps can lead to the potential scaling up of the study.

Polyhydroxyalkanoate (PHA) is a biopolymer that can be 3D printed using the material extrusion method. Nevertheless, their mechanical properties are inferior to those of petroleum-derived polymers, which restricts their broader application. Herein, nanobiocomposites comprising naturally sourced PHA and cellulose nanocrystals (CNC) as fillers were successfully synthesized. These nanobiocomposites were prepared with filler concentrations ranging from 0.5 to 2.5% by weight, in increments of 0.5 wt %. Filaments were produced from binary PHA/CNC mixtures and subsequently employed for 3D printing of the respective nanobiocomposite samples. They were subjected to mechanical, rheological, thermal, and structural analyses using analytical techniques and the respective standards. The integration of CNC into the pure PHA polymer matrix has been reported to enhance PHA's mechanical properties of PHA, with an increase in flexural strength by 23.3%, flexural modulus by 20.8%, and Young's modulus by 47.3%, although there was a reduction in impact strength and microhardness. Morphological characterization confirmed the homogeneous dispersion of CNC, whereas the thermal and rheological properties remained almost unchanged. The porosity and geometric accuracy of the 3D-printed samples, evaluated using micro-CT, were improved by incorporating CNC into the PHA matrix. The 0.5 wt % CNC concentration was the optimum one, improving mechanical and quality metrics. These findings highlight the potential of PHA/CNC nanocomposites as innovative high-performance biodegradable materials for 3D printing for biomedical, packaging, and structural engineering applications. Such nanobiocomposites can contribute to reducing the environmental impact of petroleum polymers through a cost-effective additive manufacturing method.