Direct Ink Writing of Recycled Composites with Complex Shapes: Process Parameters and Ink Optimization

Within the complex framework of additive manufacturing, direct ink writing (DIW) processes significantly contribute to extending the range of 3D‐printable materials (i.e., thermosetting resins, ceramics, hydrogels). Thanks to this technology, viscous inks are easily extruded for the creation of 3D structures. Nevertheless, the quick recovery of the solid‐like behavior after extrusion remains one of the most crucial open issues for 3D‐printable inks. The main goal herein is to improve the printability of a UV‐curable thermosetting composite ink reinforced with mechanically recycled glass fiber composites by modifying its rheological behavior. The overall process is optimized, leading to the definition of the optimal extrusion parameters for these types of materials. Furthermore, the retraction mode is successfully developed for the DIW of recycled composites. Additional features are achieved, thanks to the aforementioned improvements, such as 3D complex shapes, assembled pieces, and/or moving built‐in mechanisms, increasing the number of new potential applications of recycled glass fiber‐reinforced polymers. Thanks to the addition of a rheological modifier, the solid‐like behavior of a UV‐curable thermosetting composite ink reinforced with mechanically recycled glass fibers is quickly recovered after extrusion. Accordingly, a rheological model for direct ink writing is defined. Moreover, the process is optimized, including the possibility to use the retraction mode for the production of more complex 3D objects.