Vat Photopolymerization-Based Multi-Material 3D Printing of Overhangs with Highly Removable and Recyclable Thiol-ene Photopolymer Supports

Vat photopolymerization (VPP) based 3D Printing technology boasts the capability to print 3D structure with remarkable precision and rapidity. In the fabrication of complex structures beyond traditional capabilities, extensive additional support structures are often essential for creating overhanging and free-hanging features. Yet, these internal supports pose challenges as they are not directly removable, necessitating time-consuming manual removal and potentially causing unintended damage and surface imperfections. While specific materials like NaOH-soluble substances and wax have been employed for creating removable supports, these solutions are limited to specific printable materials and often result in considerable waste during the removal process. The current predicament lies in the fact that traditional vat photopolymerization 3D printing of overhangs employs a photocurable liquid resin, which forms a permanently crosslinked polymer. This invariably leads to disposal of body and especially support structure after its usage due to the material’s non-recyclable nature.<br/><br/>To counter these drawbacks, this study leverages the properties of crosslinked thiol-ene photopolymer, such as polybutadiene and polyisoprene, which are renowned for their robust structures and excellent thermomechanical characteristics. The innovation lies in utilizing liquid polydiene elastomer as a building block in VPP-based 3D printing, a technique yet to be thoroughly explored. The research focuses on creating a chemically recyclable crosslinked polydiene elastomeric liquid resin, capable of undergoing photoinitiated thiol-ene click reactions with commercially available materials, apt for VPP-based 3D printing. The approach involves using liquid polysulfides with photoreactive thiol end groups and dynamic disulfide bonds, which react with polydienes’ carbon-carbon double bonds (ene groups) through photo-crosslinking. The internal disulfide bonds in the resulting crosslinked polydiene elastomers allow for base-catalyzed thiol-disulfide exchange reactions, leading to the decrosslinking or degradation into photoreactive thiol oligomers. Combining conventional permanently crosslinked resin with developed recyclable resin allows for the printing of complex multi-material structures. Subsequent processing to recycle thiol-ene photopolymers can yield intricate overhangs, such as microfluidic channels, spinning tops, and interlocked da Vinci drones. In addition, the impact of surface to volume ratio and crosslinking rate under grayscale projection on the recycling rate is extensively investigated. The optimized porous support structures exhibit properties that are highly removable and recyclable. By demonstrating this scalable method, the study opens up new avenues for fabricating overhangs with easily removable and highly recyclable elastomeric resins via VPP, maintaining material properties across multiple recycling. This development not only offers a superior alternative to current casting/molding manufacturing methods for elastomeric materials but also paves the way for more sustainable and environmentally friendly practices in 3D printing technologies.