This commentary discusses
current capabilities of vat photopolymerization,
an additive manufacturing (AM) technique also known as VP, with recent
advances in the literature, current challenges/limitations, and future
outlook in novel materials design. Current trends and recent research
advances are broadly discussed covering a spectrum of material classes
such as performance, medicine, energy, and active materials in parallel
to their importance in diverse technologies. Current challenges and
limitations of VP are also discussed in terms of material properties,
photodegradation, and material toxicity with directions in future
material design to overcome these challenges. This commentary paper
is intended to be of broad interest to both chemists and engineers
actively involved in the AM field, in terms of future material design
and processing for further development of VP-based AM technology.
Vat
photopolymerization (VP) additive manufacturing fabricates
intricate geometries with excellent resolution; however, high molecular
weight polymers are not amenable to VP due to concomitant high solution
and melt viscosities. Thus, a challenging paradox arises between printability
and mechanical performance. This report describes concurrent photopolymer
and VP system design to navigate this paradox with the unprecedented
use of polymeric colloids (latexes) that effectively decouple the
dependency of viscosity on molecular weight. Photocrosslinking of
a continuous-phase scaffold, which surrounds the latex particles,
combined with in situ computer-vision print parameter optimization,
which compensates for light scattering, enables high-resolution VP
of high molecular weight polymer latexes as particle-embedded green
bodies. Thermal post-processing promotes coalescence of the dispersed
particles throughout the scaffold, forming a semi-interpenetrating
polymer network without loss in part resolution. Printing a styrene-butadiene
rubber latex, a previously inaccessible elastomer composition for
VP, exemplified this approach and yielded printed elastomers with
precise geometry and tensile extensibilities exceeding 500%.
Unparalleled temporal and spatial control of colloidal chemical processes introduces immense potential for the manufacturing, modification, and manipulation of latex particles.
Vat
photopolymerization (VP) is a high-throughput additive manufacturing
modality that also offers exceptional feature resolution and surface
finish; however, the process is constrained by a limited selection
of processable photocurable resins. Low resin viscosity (<10 Pa·s)
is one of the most stringent process-induced constraints on resin
processability, which in turn limits the mechanical performance of
printed resin systems. Recently, the authors created a VP-processable
photosensitive latex resin, where compartmentalization of the high
molecular weight polymer chains into discrete particles resulted in
the decoupling of viscosity from molecular weight. However, the monomers
used to form the hydrogel green body resulted in decreased ultimate
material properties due to the high cross-link density. Herein, we
report a novel scaffold that allows for facile UV-based AM and simultaneously
enhances the final part’s material properties. This is achieved
with a chemically labile acetal-containing cross-linker in conjunction
with N-vinylpyrrolidone, which forms a glassy polymer after photocuring.
Subsequent reactive extraction cleaves the cross-links and liberates
the glassy polymer, which provides mechanical reinforcement of the
geometrically complex VP-printed elastomer. With only a 0.1 wt % loading
of photoinitiator, G′/G′′
crossover times of less than 1 s and green body plateau moduli nearing
105 Pa are obtained. In addition, removal of the hydrophilic
and thermally labile scaffold results in decreased water uptake and
increased thermal stability of the final printed part. Ultimate strain
and stress values of over 650% and 8.5 MPa, respectively, are achieved,
setting a new benchmark for styrene–butadiene VP elastomers.
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