Researchers from the College of Texas at Dallas (UT Dallas) have launched a contemporary method to 3D printing polymer foams that may obtain a broader vary of mechanical properties and enlargement capabilities.
Having used catalyst-free dynamic covalent chemistry (DCC), their technique embeds dynamic phosphodiester bonds inside polymers containing foaming agent microspheres. These bonds can alternate throughout thermal foaming, permitting the supplies to increase extra successfully with out sacrificing structural integrity.
Printed in RSC Utilized Polymers, this analysis was co-led by chemistry doctoral college students Ariel Tolfree, and Rebecca Johnson below the supervision of Dr. Ron Smaldone, Affiliate Professor of chemistry and biochemistry within the Faculty of Pure Sciences and Arithmetic and who can be the corresponding creator of the research.
“That is most likely the longest challenge I’ve ever completed,” mentioned Johnson, who plans to finish her PhD in chemistry in Could. “From begin to end, it was somewhat over two years. Plenty of it was attempting to get the polymer formulation appropriate to be suitable with the 3D printer.”
Overcoming structural limitations with dynamic bonding
Polymer foams are valued for his or her light-weight construction, insulation, and mechanical properties, however balancing pore measurement, density, and energy stays difficult. Typical strategies utilizing fuel injection usually face trade-offs. Furthermore, larger crosslinking density enhances toughness however limits enlargement, whereas bigger pores scale back density and mechanical energy.
The researchers addressed this concern utilizing DCC, which permits bonds to rearrange below particular situations. In contrast to standard polymers with fastened bonds, these adaptable networks improve efficiency and recyclability. Subsequently, they targeted on phosphodiester bonds for his or her chemical stability and skill to alternate at temperatures as little as 50°C with out dangerous or expensive catalysts.
Foaming microspheres have been embedded inside a polymer matrix containing various concentrations of dynamic and non-dynamic crosslinkers. When these printed components have been heated at 165°C for quarter-hour, the foaming course of started. Because the thermoplastic shell of the microspheres softened, the liquid hydrocarbon inside vaporized and expanded. Cooling then hardened the shells, forming a closed-cell foam.
“We’re definitely not the one ones attempting to do that,” Smaldone mentioned. “The novelty is utilizing dynamic chemistry to print actually nice foam materials. The subsequent query to handle might be, how will we tune the properties and use this new sort of data to suit a wide range of totally different wants?”
Comparative testing and recyclability outcomes
In testing, researchers in contrast non-dynamic tetraethylene glycol diacrylate (TEGDA) crosslinkers with dynamic Bis[2-(methacryloyloxy)ethyl] Phosphate (DPE) crosslinkers and located that dynamic crosslinkers persistently achieved higher enlargement. The foaming course of concerned direct phosphodiester exchanges, rearrangements forming triester and monoester merchandise, and interactions with ester teams, mechanisms that enhanced community reorganization and enlargement.
To make sure the bond exchanges have been working as supposed, researchers used Fourier rework infrared spectroscopy (FTIR), which confirmed dynamic bond alternate by means of transesterification and condensation mechanisms. Differential scanning calorimetry (DSC) confirmed larger crosslinker content material raised glass transition temperatures, indicating improved community uniformity.
When put to the check, unfoamed dynamic polymers demonstrated larger compressive strengths, starting from 180 to 216 MPa, in comparison with the 130 to 150 MPa recorded for non-dynamic polymers. After foaming, the dynamic polymers demonstrated higher power dissipation and compressive energy than non-dynamic foams with comparable enlargement.
There’s extra. The staff additionally examined the foams’ recyclability by compressing unfoamed cylinders to 70% of their peak and permitting them to get better earlier than foaming. Dynamic phosphodiester polymers retained their mechanical properties higher than non-dynamic TEGDA foams, indicating efficient harm restore by means of bond rearrangement and condensation reactions.
Finally, the research means that dynamic phosphodiester bonds present a promising path to reaching larger foam enlargement, improved mechanical energy, and power dissipation with out the necessity for catalysts. It’s a technique that might prolong the lifespan of 3D printed foams and open up broader functions for these supplies.
3D printing with foam
Away from UT Dallas, contributions in foam 3D printing additionally got here from Nano Dimension-acquired Desktop Metallic, which launched FreeFoam, a 3D printable photopolymer resin developed by its subsidiary Adaptive3D.
Launched at Foam Expo North America in June 2022, FreeFoam allows customizable foam components to increase as much as seven occasions their unique measurement when heated between 160 – 170°C. Accessible on the ETEC Xtreme 8K DLP 3D printer, it permits for decreased waste, enhanced design flexibility, and improved transport effectivity throughout sectors like automotive, furnishings, footwear, and healthcare.
Elsewhere, UC San Diego’s Division of NanoEngineering researchers developed an expandable foaming resin suitable with SLA 3D printers. Designed for heat-induced enlargement post-UV-curing, the resin enabled the creation of components as much as 4000% bigger than the printer’s construct quantity.
The research aimed to beat geometric limitations in manufacturing, with potential functions in aerospace, structure, power, and biomedicine. Testing concerned heating 3D printed HEMA resin fashions at 200°C for as much as ten minutes, reaching important enlargement and suggesting makes use of in light-weight parts like aerofoils and buoyancy aids.
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Featured picture exhibits tiny dog-shaped items of sturdy, light-weight 3D printed foam. Picture by way of UT Dallas.
