Direct Pellet Material Extrusion of PLA-Collagen Composites: A Circular Approach to Leather Waste Valorization

The adoption of pellet-based additive manufacturing technologies represents a promising avenue for the valorisation of industrial waste materials. This study presents an experimental investigation of the printability of a composite material consisting of a PLA (polylactic acid) matrix filled with collagen fibres derived from solid residues of leather tanning processes, as part of a broader effort aimed at valorising leather waste. The composite material, after drying and homogenization, was directly fed into a 3D printer equipped with a pellet extruder system. To evaluate the printability of the material, specimens with different geometries (such as cylinders, cubes, and dog-bone shapes) were fabricated. Optical microscopy was employed to examine the dimensional conformity of the printed parts in comparison with their CAD models, as well as to identify surface defects or irregularities in layer deposition. The results demonstrated good compatibility of the material with the pellet extrusion process, showing acceptable dimensional tolerances and a satisfactory level of repeatability across different geometries. Moreover, the presence of collagen did not significantly affect the flow consistency or interlayer adhesion, making the material suitable for non-structural applications in prototyping and sustainable product design. This work supports the viability of direct pellet extrusion as a key enabling technology for the recycling and reuse of biomaterials derived from industrial waste, promoting a circular economy approach. The findings highlight the potential of pellet-based 3D printing not only in reducing material waste but also in expanding the range of usable bio-based and upcycled materials in additive manufacturing.