Rapid Open‐Air Digital Light 3D Printing of Thermoplastic Polymer

Abstract

printing is, however, limited by various factors, with printing speed and material versatility being the most decisive. From the standpoint of printing speed, layerwise printing by digital light processing (DLP) offers significant inherent advantage over point-wise printing by most other methods such as fused deposition modeling (FDM) and stereolithography (SLA). [20] Further innovations on DLP such as continuous building in the z-dimension allow achieving a printing speed far exceeding any other methods. [21][22][23] Recent attempt on direct forming 3D object in a volumetric fashion forgoes even the layer-wise printing, but the technique has yet to evolve into the mainstream. [24,25] Generally, DLP employs light curable liquid resins. Upon digital light exposure, the resin cross-links and forms a thermoset polymer that ensures its separation from the surrounding liquid precursors. This rapid liquid-solid separation is the key enabling characteristic for DLP. Although cross-linking ensures such, the resulting thermoset polymers cannot be reprocessed. This prohibits its broader utility in situations that require further processing of the printed materials. In principle, this limitation can be overcome if the DLP processing can be extended to reprocessable thermoplastic polymers. Although light curable thermoplastic polymers are known, meeting the unique DLP requirement for rapid separation between the liquid monomer and the un-crosslinked polymer is not straightforward because of their intrinsic good miscibility. Hereafter, we describe our successful attempt in DLP printing of a thermoplastic polymer and lay out key enabling factors for such a process. We further illustrate that the water dissolvable nature of the resulting polymer is advantageous in making various multifunctional 3D structures. We find that the oxygen naturally present in ambient air can inhibit the light curing process. This effect can be utilized to achieve rapid open-air printing without the complex interfacial engineering typically required for fast DLP printing methods. [21][22][23] We hypothesize that two key factors should be carefully considered for DLP printing of thermoplastic polymers (Figure 1a). Herein, two concurrent and competing processes occur: 1) the polymerization and 2) the diffusion/dissolution of the polymer into the surrounding uncured liquid monomer. Rapid liquidsolid separation is possible only if the first process dominates 3D printing has witnessed a new era in which highly complexed customized products become reality. Realizing its ultimate potential requires simultaneous attainment of both printing speed and product versatility. Among various printing techniques, digital light processing (DLP) stands out in its high speed but is limited to intractable light curable thermosets. Thermoplastic polymers, despite their reprocessibility that allows more options for further manipulation, are restricted to intrinsically slow printing methods such as fused deposition modeling. Extending DLP to thermoplastics is highly desirabl...

Microfluidic Synthesis of Iron Oxide Nanoparticles

“…A major advantage to this technique is the ability to create complicated channel geometries [ 37 , 38 ]. The main disadvantages of this technique are that it can be inaccurate due to the polymer shrinking upon cooling, and the available polymers that can be used are mostly thermoplastics [ 56 , 57 ]; however, some thermosets can be 3D printed [ 58 ]. Some other disadvantages of 3D printing are limited printing resolution and limited build sizes.…”

Photopatternable Electrolytes for Conducting Polymer Actuators

“…The capability to cure thiol-ene photopolymers in the openair is also favorable as the curing process in open vat stereolithography setups occurs in the presence of ambient air. 3D printing of thermoplastic polymer in open-air at high speed is achieved with a thiol-incorporated printing formulation [148]. A thiol-ene free radical photopolymer developed for 3D printing system is shown in Figure 3.4 [149].…”

Circular 3D Printing: Reprintable Polymers for Digital Light Processing Printing

“…In particular, based on the rapid light-curing process of liquid resins, digital light processing (DLP) 3D printing shows the advantages in creating complex 3D objects with high-resolution geometry and high printing efficiency [8][9][10][11][12][13][14][15] . During DLP printing process, the rapid liquid-solid transition under light irradiation always requires dual-functional or multi-functional monomers, which cause 3D items to be constructed by thermosets cross-linked by covalent bonds 13,[16][17][18][19] . Thermosets show better durability and mechanical properties than uncross-linked thermoplastics, however, their infusible and insoluble features make them hard to be reprocessed or recycled, and will be inevitably discarded as waste at the end of their life cycle [20][21][22][23][24] .…”

“…To address the above-mentioned problems, thermoplastics and dynamically crosslinked thermosets have been successfully developed for DLP printing 19,25,26 . The obtained 3D objects can be reprocessed via heating or solution processing, however, they cannot convert into liquid resins for reprinting by the same DLP, failing to recover the high-resolution geometry of original 3D objects.…”

“…reported DLP printing of ACMO, they pointed out that the obtained thermoplastics cannot be reprinted using the same DLP method 19 . However, we find that poly(ACMO) can dissolve in ACMO completely at a temperature above its T g and a recycled resin can be obtained for reprinting.…”